How to balance the new 1345T quick release props...

[Joe R]

Joe,
As result of your investigation and summation as presented on this prop balancer, I was curious if you had presented your findings to the seller, and if there was any response offered by EJH in that regard.

I have order this balancer for its ease of use over the laser pointer method, but now from what you've mentioned I may need to return the balancer if it doesn't work as advertised, or I too find that further disassembly of the motor hub assembly is required to perform a proper prop balancing.

Btw, wouldn't it be in your best interest to simply return the balancer under the Amazon satisfaction policy rather than selling to another for less than half the cost you had paid for balancer & shipping costs. : )

Hi Skynet,

Yeah, I contacted EJH but haven't heard anything back yet. I have a feeling they will continue selling those balancing adapters for those who don't care if everything is really balanced right or not.

I removed the hubs from the motors (one for each direction, so you have to remove two hubs) but when I spooled the motors up without the hubs on they were definitely out of balance, that's how I found out for sure the locking tabs on those hubs are part of the balance of the motors too. I suspected that would be the case at first glance, then confirmed it by testing it out while using an official machine shop vibration meter (not the app), the meter showed a lot of X, Y axis movement (sideways vibrations) but hardly any Z axis movement (Vertical).
A small part of those locking tabs add weight to the center part of the prop, so, IMHO, there's just no way to truly balance them without using the laser method.
As mentioned before, the motors, hubs and props all work together as one system.
I really wish I had been able to balance them without using the laser method cause it does take time and patience but it just doesn't work that great using traditional balancing methods.

If the locking tabs would lock-in at a 90° angle to the longitudinal (length of the chord) axis of the prop, you could probably just balance it to the point where it rests perfectly horizontal when but the locking tabs lock-in at about a 45° angle. I thought about not locking them in all the way but that throws it off from where they set when in use on the motors.

The main reason I started using the laser method with my S800 and S1000 is to use the prop to perfectly balance the motors at the same time. I've found that the motors aren't balanced exactly true either. The motors not being as balanced as possible cause premature bearing wear as well so it just made better sense to balance everything by laser.
If the motors weren't perfectly balanced, you could use any prop on any motor (not considering the counter rotation thing) but since they aren't, I mark the props so they go back on the motor it was balanced on.
Another issue for me, is the vibrations imposed on the electronics and other parts of the Inspire (and others). I've found that the IMU and other sensors work better, longer and are more reliable if they aren't subjected to those vibrations from the props "and" motors. Remember, the only part really dampened from vibrations is the gimbal, everything else feels that vibration!

A short story about my S800 when I first got it:
I couldn't get the thing to sit still in a stable hover even though it was locked onto 12 or so satellites and the GPS receiver was offset for magnetic north in our area (it didn't have the toilet bowl effect thing going on), it just wouldn't stay put even in calm wind. It wouldn't drift off far but it was trying to hit that GPS positioning wall with the gain set in the medium range. It was trying to drift to the left and the IMU was definitely level and held firmly in place by a strap and a thin piece of foam tape as prescribed. I tested the outputs of the IMU and ESCs with my Oscilloscope and found it to be operating normal in all axis. I kept calling DJI and asking around until I finally decided to check for vibrations. Alas, that was the culprit. I laser balanced every prop and motor and it immediately flew the way it was supposed to. The gimbal even behaved much better (I kept having to try different durometer values on the damper balls). After the balance was completed, I was able to go back to the original damper balls for the gimbal.

I performed a rather risky test one day after the balancing part was finished. I strapped the whole MR to the workbench and set the legs on a piece of high density foam rubber, then I spooled all of the motors up at once. After putting on a face shield and protective welding leather, I reached down from under table level to put my hands on the arms near the center hub just to see if it felt smooth and I couldn't feel any vibrations whatsoever. ;-) I DO NOT recommend that anyone try that, looking back on it, I shouldn't have done it either. I should have used a long, thin fiberglass rod to test for vibrations.

As mentioned earlier, I know this is a lot of trouble but in reality, once you've set everything up, it only takes about an hour to an hour and a half to balance all 8 props (including the 4 spare props).
Then, when the props wear down and get too sloppy and need to be replaced, it's not that bad to do again since the initial setup has already been done.

Only speaking for myself here, I tested the vibrations on the Inspire frame before the laser balance thing, then tested it afterwards (with my machine shop vibration meter) and there was a major reduction in vibration to the frame and all of the electronics.

I can't help but believe (after all of my tests and seeing the results) that minimizing the vibrations at the frame level wouldn't make the on-board sensors such as the IMU and other sensors much more reliable in-flight.
I had a few highly erratic readings on the IMU sensors with the Inspire in a stable hover in perfectly calm wind before the balance job. Now they are all very stable a hover and in-flight. I only flew it a couple of times before balancing the props and motors.
They claim the motors are perfectly balanced and some or most may very well be but mine were not.
Maybe I'm being too picky but I feel that if it's as in-tune as possible, it has to be more reliable and last longer.
That's the way I am with my machine tools in my shop (always have been), some of them are nearly 30 years old now and are still working almost as good as new!! To me, it does really pay off in the long run!!

Sorry, I got a little carried away here, I don't usually do that.

Yes, I could return that balancer to Amazon but it hadn't crossed my mind. You're right, I should return it and I will, so, thank you for mentioning that!!!

Keep me posted and if there's anyway I can help, please let me know.

PS, I balanced a friend's Inspire yesterday and I decided to make a CD mirror with slots on the top and bottom so I could feed velcro through the slots and just strap it onto the motor/ESC housings. It's much easier to do that part now. My local hobby shop sends people to me for repairs and to have special project parts made (like for camera mounts or replacement parts that are hard to find on old or homebuilt planes, helis and MRs). I have a CAD program with a CNC milling machine and they like to have carbon fiber parts made for them sometimes. They just bring me the measurements with a rough drawing, then I make a 3D model in the software, then send it to the milling machine to be milled out. I don't charge much of anything but I really enjoy helping them out from time to time. They are a great bunch of people!! I have a feeling you all are a great bunch of people as well!!

I hope all of this has helped!!

Joe

 

[unyks]

BTW EJH is also in this forum, saw him recently in this THREAD, Username is EJ Harris

Chris

 

[Joe R]

BTW EJH is also in this forum, saw him recently in this THREAD, Username is EJ Harris

Chris

Cool!
Thank you for that!

I'll pop over and give him a heads up on this thread.
Maybe he'll chime in on this one so we can get his thoughts on the matter.

Thanks again!

Joe

PS, I just sent EJ an invitation to have a look at what we're discussing over here.

 

[Skynet1]

Thanks Joe,

I certainly agree, proper balancing would provide for a much more stable platform, but more importantly less stress on the motors and other various electronics used to maintain control and overall stable operation of the model itself.
I would like to have seen your interpretation of the motor mounted mirror fabrication used in your laser balancing procedure.
I can't say I completely understood the two jack rabbits in the YouTube laser balancing video offered earlier in this post who demonstrated a technique they use, but that's probably just me. : )

I like you was hoping to balance the props using the more traditional static balancing method.

Winding up the motors with props attached and model secured to a fixed surface is something I would have rather avoided personally.
However, I do want a model with minimal vibration when hovering, and flying at substantial speeds.

 

[Terry Lowe]

I'm new here and my name is

Joe

Hi Joe,
I'm sure that a lot of readers are thinking "awwwwe, I don't want to do all that to balance a prop"

I set mine up with a piece of DVD using two sided tape and discovered that I couldn't hold my hand held laser still enough to read results. I ended up using close hanger wire, duct tape and a few zip ties (I'm from the south) to mount my laser

I secured my inspire1 pro to the table and then cranked it up with only one prop and shot the laser. Two of my props looked ok to me, but on my third one, my laser dot looked like a "C". I was expecting a vertical line like the video. Does the direction of the line created by the vibration correlate with the type of balance problem I have? Can I tie down the bird so securely that I could dampen the vibration and I'd just think it was ok? Could the C shaped line be because the bird was not secure enough and was wobbling?

In the past, I would sand my phantom 2 props when I rod balanced them. Is there an easy way to tell which end of the prop is heavy/light? (Just apply a little tape on one side and see if the vibration worsens or improves?)

Thanks for taking your time to post what you know about this.

 

[EJ Harris]

Hi Skynet,

Yeah, I contacted EJH but haven't heard anything back yet. I have a feeling they will continue selling those balancing adapters for those who don't care if everything is really balanced right or not.

I removed the hubs from the motors (one for each direction, so you have to remove two hubs) but when I spooled the motors up without the hubs on they were definitely out of balance, that's how I found out for sure the locking tabs on those hubs are part of the balance of the motors too. I suspected that would be the case at first glance, then confirmed it by testing it out while using an official machine shop vibration meter (not the app), the meter showed a lot of X, Y axis movement (sideways vibrations) but hardly any Z axis movement (Vertical).
A small part of those locking tabs add weight to the center part of the prop, so, IMHO, there's just no way to truly balance them without using the laser method.
As mentioned before, the motors, hubs and props all work together as one system.
I really wish I had been able to balance them without using the laser method cause it does take time and patience but it just doesn't work that great using traditional balancing methods.

If the locking tabs would lock-in at a 90° angle to the longitudinal (length of the chord) axis of the prop, you could probably just balance it to the point where it rests perfectly horizontal when but the locking tabs lock-in at about a 45° angle. I thought about not locking them in all the way but that throws it off from where they set when in use on the motors.

The main reason I started using the laser method with my S800 and S1000 is to use the prop to perfectly balance the motors at the same time. I've found that the motors aren't balanced exactly true either. The motors not being as balanced as possible cause premature bearing wear as well so it just made better sense to balance everything by laser.
If the motors weren't perfectly balanced, you could use any prop on any motor (not considering the counter rotation thing) but since they aren't, I mark the props so they go back on the motor it was balanced on.
Another issue for me, is the vibrations imposed on the electronics and other parts of the Inspire (and others). I've found that the IMU and other sensors work better, longer and are more reliable if they aren't subjected to those vibrations from the props "and" motors. Remember, the only part really dampened from vibrations is the gimbal, everything else feels that vibration!

A short story about my S800 when I first got it:
I couldn't get the thing to sit still in a stable hover even though it was locked onto 12 or so satellites and the GPS receiver was offset for magnetic north in our area (it didn't have the toilet bowl effect thing going on), it just wouldn't stay put even in calm wind. It wouldn't drift off far but it was trying to hit that GPS positioning wall with the gain set in the medium range. It was trying to drift to the left and the IMU was definitely level and held firmly in place by a strap and a thin piece of foam tape as prescribed. I tested the outputs of the IMU and ESCs with my Oscilloscope and found it to be operating normal in all axis. I kept calling DJI and asking around until I finally decided to check for vibrations. Alas, that was the culprit. I laser balanced every prop and motor and it immediately flew the way it was supposed to. The gimbal even behaved much better (I kept having to try different durometer values on the damper balls). After the balance was completed, I was able to go back to the original damper balls for the gimbal.

I performed a rather risky test one day after the balancing part was finished. I strapped the whole MR to the workbench and set the legs on a piece of high density foam rubber, then I spooled all of the motors up at once. After putting on a face shield and protective welding leather, I reached down from under table level to put my hands on the arms near the center hub just to see if it felt smooth and I couldn't feel any vibrations whatsoever. ;-) I DO NOT recommend that anyone try that, looking back on it, I shouldn't have done it either. I should have used a long, thin fiberglass rod to test for vibrations.

As mentioned earlier, I know this is a lot of trouble but in reality, once you've set everything up, it only takes about an hour to an hour and a half to balance all 8 props (including the 4 spare props).
Then, when the props wear down and get too sloppy and need to be replaced, it's not that bad to do again since the initial setup has already been done.

Only speaking for myself here, I tested the vibrations on the Inspire frame before the laser balance thing, then tested it afterwards (with my machine shop vibration meter) and there was a major reduction in vibration to the frame and all of the electronics.

I can't help but believe (after all of my tests and seeing the results) that minimizing the vibrations at the frame level wouldn't make the on-board sensors such as the IMU and other sensors much more reliable in-flight.
I had a few highly erratic readings on the IMU sensors with the Inspire in a stable hover in perfectly calm wind before the balance job. Now they are all very stable a hover and in-flight. I only flew it a couple of times before balancing the props and motors.
They claim the motors are perfectly balanced and some or most may very well be but mine were not.
Maybe I'm being too picky but I feel that if it's as in-tune as possible, it has to be more reliable and last longer.
That's the way I am with my machine tools in my shop (always have been), some of them are nearly 30 years old now and are still working almost as good as new!! To me, it does really pay off in the long run!!

Sorry, I got a little carried away here, I don't usually do that.

Yes, I could return that balancer to Amazon but it hadn't crossed my mind. You're right, I should return it and I will, so, thank you for mentioning that!!!

Keep me posted and if there's anyway I can help, please let me know.

PS, I balanced a friend's Inspire yesterday and I decided to make a CD mirror with slots on the top and bottom so I could feed velcro through the slots and just strap it onto the motor/ESC housings. It's much easier to do that part now. My local hobby shop sends people to me for repairs and to have special project parts made (like for camera mounts or replacement parts that are hard to find on old or homebuilt planes, helis and MRs). I have a CAD program with a CNC milling machine and they like to have carbon fiber parts made for them sometimes. They just bring me the measurements with a rough drawing, then I make a 3D model in the software, then send it to the milling machine to be milled out. I don't charge much of anything but I really enjoy helping them out from time to time. They are a great bunch of people!! I have a feeling you all are a great bunch of people as well!!

I hope all of this has helped!!

Joe

Cool!
Thank you for that!

I'll pop over and give him a heads up on this thread.
Maybe he'll chime in on this one so we can get his thoughts on the matter.

Thanks again!

Joe

PS, I just sent EJ an invitation to have a look at what we're discussing over here.

 

[EJ Harris]

Hey Joe,

Just got your invite on to this post. No argument from me as far as balancing whether it be turbins, blowers or props at full operating speed, aka elastic balancing.

I use high speed balancing in the development & testing of my balancers to ensure that my rods performance are accurately balancing props.

Due to the internal shape of this prop, I thought it best to design a balancer that would work in conjunction with a locking hub. After the testing I did, I concluded the results were satisfactory for dynamic balancing.

Please note the tip needs to be securely pressed into the hub to hold the front dead nut center .

Regret to hear your not satisfied with this product. Feel free to return and gladly refund.

Thanks EJ

 

[Joe R]

Hi Joe,
I'm sure that a lot of readers are thinking "awwwwe, I don't want to do all that to balance a prop"

I set mine up with a piece of DVD using two sided tape and discovered that I couldn't hold my hand held laser still enough to read results. I ended up using close hanger wire, duct tape and a few zip ties (I'm from the south) to mount my laser

I secured my inspire1 pro to the table and then cranked it up with only one prop and shot the laser. Two of my props looked ok to me, but on my third one, my laser dot looked like a "C". I was expecting a vertical line like the video. Does the direction of the line created by the vibration correlate with the type of balance problem I have? Can I tie down the bird so securely that I could dampen the vibration and I'd just think it was ok? Could the C shaped line be because the bird was not secure enough and was wobbling?

In the past, I would sand my phantom 2 props when I rod balanced them. Is there an easy way to tell which end of the prop is heavy/light? (Just apply a little tape on one side and see if the vibration worsens or improves?)

Thanks for taking your time to post what you know about this.

I'm so sorry, I left out an important part of this procedure! :-(
I use a piece of high density foam about 2 inches thick under the legs to keep the vibration from transmitting to the workbench.
I also only tighten the strap that is fastened to the cleats on the workbench to the point where it just presses into the foam. I also use straps with closed clasps to prevent the strap from breaking free from the cleats. This vital step allows the arm to raise up off of the workbench while still being in contact with the foam pad and be more "Free" to "Float" so to speak. It's probably not a bad idea to wrap the strap with foam at the point where it lays across the arm to further isolate the vibration from the strap and workbench. I think I would zip tie or tape the foam on to prevent it from coming loose and flying into the prop. I haven't done that but it just crossed my mind that it may come a little closer to simulating the Inspire while in flight.

The "C" shaped line that it produces is most likely an indication that there is a significant amount of lateral (sideways) movement/vibration, this is usually caused by the motor housing not being balanced along the side of the prop rather than inline with the prop. It causes movement in both the X and Y axis rather than just one axis. I've had this problem before on my S1000. It turns out that I had to add weight to the inside of the motor housing, I had to take the motor apart to add a heat resistant compound in between the magnets (I went to an electric motor company that rebuilds electric motors for advice and for the proper compound to use for balancing and that is the way they do it as well), I would try isolating the Inspire from the workbench with the high density foam first and try it again, if it still produces the "C" shaped line, I would ask DJI to replace the motor rather than modifying the balance of the motor housing yourself (especially if it's still under warranty!). Note: I was able to use a balancing jig on the housing after it was removed so I could balance it with small magnets. After it was balanced, I weighed the magnets and used the same amount of compound that matched the weight of the magnets, then I applied the compound in between the magnets. It usually requires about 24 hours or more to fully cure. It's always best to add just a little more than you need, then cut some away as it begins to cure or use a dremel tool after it cures to very carefully grind some away until it's perfectly balanced.
After it cures, it should be checked for balance one last time before re-installing the housing.
You really have to feel completely confident with what you're doing to balance the housing!! A bad job here could cause you to lock up a motor in flight as a result of the compound coming loose. I always use alcohol to clean the housing to make sure there is no oil, dirt or grease where I want to apply the compound. Make sure to use a compound made especially for electric motor balancing!!! I can't stress that enough!!!
If you've ever taken one apart, you'll usually notice some type of red or green color compound between the magnetics somewhere. This is exactly how the factory does it (as opposed to cutting weight away from the heavy side).

Check out this Link to a compound made for electric motor balancing

As for some way of holding the laser, I ordered a bench clamp made for holding circuit boards off of Amazon for $27, it works great and is right at the height I needed. I use it for soldering work as well though.

Link to PanaVise

You can still sand the bottom of the prop as normal if you'd rather not use the tape.

Figuring out which side needs the weight almost has to be done by trial unless you do a static balance first but that's even more trouble and time consuming since you have to remove two hubs to do a static balance test. It's a give and take thing I guess.

I can do a video of the whole process on the Inspire but it may be a few days before I have the time.to do that.

I hope this helps to clarify some issues (especially the "C" shaped line on the wall). BTW, that type of vibration is particularly hard on the electronics as well as the frame itself. It probably won't show up as major problems until it gets a little age and use on it but if you're anything like me, I want this thing to be as reliable as possible and last as long as possible!

I will try my best to do a video as soon as I can.

Sincerely,

Joe

 

[Joe R]

Hey Joe,

Just got your invite on to this post. No argument from me as far as balancing whether it be turbins, blowers or props at full operating speed, aka elastic balancing.

I use high speed balancing in the development & testing of my balancers to ensure that my rods performance are accurately balancing props.

Due to the internal shape of this prop, I thought it best to design a balancer that would work in conjunction with a locking hub. After the testing I did, I concluded the results were satisfactory for dynamic balancing.

Please note the tip needs to be securely pressed into the hub to hold the front dead nut center .

Regret to hear your not satisfied with this product. Feel free to return and gladly refund.

Thanks EJ

Thank you so much, EJ for chiming in!! And, I'm glad to meet you!

Don't get me wrong, EJ, I "DO" feel that your design is a good one in all regards. After all, what could you have done to make it any easier than you did for static balancing? Nothing in my opinion, unless I come with an idea for ya to make it better!

In many if not most cases, doing a static balance alone with your balancing tool could produce satisfactory results. However, in cases like Terry Lowe where the motor housing is out of balance in the wrong place, nothing short of balancing the housing or replacing the motor will cure his problem. If he had not done the elastic test, he'd most likely never have known he had that problem to begin with, and, at some point he would likely have a premature failure of that motor or some other part on the Inspire.
I could easily suggest using your static balancing tool for the initial balancing, then use the elastic procedure to confirm the results or to at least to identify any "Other" balancing issues that may be there.
Either way, I recommend doing an elastic balance as at least a way to be certain everything is in good harmonic balance. I'm sure you are very familiar with resonant frequencies and the aftermath it can cause. Like the Tacoma Narrows Bridge, once a mechanical device reaches a certain level of harmonic imbalance and vibration, it can literally destroy itself or in this case, render sensitive electronics useless if it's bad enough.

One of the motors on my Inspire Pro produced a very slight arch shape on the wall with the laser but after using an X, Y and Z axis balancing and centering sensor, I determined that the imbalance wasn't severe enough to warrant further balancing of the motor housing but I will retest it every once in awhile to make sure it's not wearing the bearings out too quickly.

From my own personal point of view, if I'm going to do an elastic balance test, I may as well go ahead and do the initial "and" final balancing with the elastic method but that's just me. Not everyone here feels comfortable doing an elastic test.
I'm sure many Inspire owners will just use the static method using your tool given the fact that the elastic method is time consuming and rather complex (even slightly dangerous if you're not careful!!).

Just to clarify, It's not that I'm not satisfied with your product at all, it's the method used with this crazy complex motor, hub and prop configuration that has me concerned.

To be perfectly honest, I wish DJI had of designed a hub and prop system that could be balanced using conventional methods. For example, what if they had just machined a hole perfectly in the center of the prop that would allow a standard balancing tool to be used? Or, what if they had designed the prop so the locking mechanism would have rested in the locked position at a 90° angle from the longitudinal axis of the prop, that way your tool could be used to an even greater degree of accuracy than it already is!

With every new complex design comes the opportunity for people like yourself to design a tool that will help users/owners to fine tune the results of that design. Also, new complex designs seem to always come with a whole new set of complex problems. All we can do is use our knowledge and experience to try our best to adapt and overcome those problems.

In my mind, DJI (as well as other companies and even other industries) seem to place the majority of their focus on the technology but somehow slack off when it comes to the small things like making sure the motors and props are perfectly balanced and balanced with each other before installing them! In my opinion, it all boils down to the lack of quality control on what seems minor to them but major to us at some point during the life of the product we paid for.

Just thinking here, but, what if you could come up with a "Kit" made specifically for the Inspire that nearly anyone could use to perform an elastic balance? It could include the self adhesive monocote strips with numbers that would indicate the weight, it could include what's needed to do the sanding if they prefer to sand rather than add weight. It could also include the cleats, a special made strap, the foam and maybe even a board with padding on the bottom already made with the cleats and one that can be clamped to a kitchen table (made so it wouldn't scar the table) in case they don't have a workbench. You could include the laser and a special stand for it along with a special made polycarbonate mirror that just straps on. The possibilities are endless!!! Pilots are serious about these Inspires and want to make sure they function as perfect as possible on all levels. I know I do. And, if I didn't already have what I need or the experience to gather what I need? I would buy that kit for my expensive Inspire!!! No doubt in my mind.

The "MAIN" reason I posted this procedure is because I couldn't help but notice the frustration people were having with balancing the props. I also wanted to make people aware that the hub is part of the balance of the motor and not just the prop. I just wanted to give Inspire owners the "TOOLS" (figuratively) they need to get the very best and most out of their investments as possible short of offering a kit myself.
I don't intend to offer a kit at all, I just don't have the time cause I have my hands in too many projects as it is but I am taking the time to do this for other Inspire owners.

Hey!! Here's another idea for ya, EJ! How about making a ring with weights on it that would snuggly fit over the top of the prop center that would simulate the balance of the motor housing with the hub attached? That would insure that it's balanced! The only issue left would be if the motor housing itself is out of balance like Terry Lowe's.
This would be a way to make your tool perfect!!

Please keep in mind that I'm just trying to help everyone I can, including you!!

Give it some thought, EJ, I'm sure it's worth looking into offering a kit to do elastic balancing or making a weighted ring as just mentioned (or both).

I tend to go into great detail about everything I do. I've been in business for 35 years and never once advertised. I don't even have a business card.
I've been doing photography and videography for more than 20 years. It started out as a hobby until people kept asking me to do weddings, then promotional stuff for local businesses and industries that I work for, now I'm part of a documentary group that is in full force on environmental issues. I better not get into any of that stuff. It's too deep into politics and I might get kicked off of here.
The point is, I just enjoy helping people and enjoy doing things as close to right as I possibly can. That's what has kept people coming to me rather than me going out looking for work, at least that's what my customers and friends tell me. Enough about that part, eh!!

My interest in photography led me to doing videos and stills while flying my full scale Cessna 172 (had my license since 1987). That led me to an interest in RC helicopters, then multirotors for aerial filming work. Now I'm waiting on my exemption for part 333 to come through, should be any day now (keeping my fingers crossed here). I don't have any violations so there shouldn't be any problem there.
Ok, now I'm ranting.

Oh, almost forgot. I had never used the term elastic balancing till now. I've always referred to it as Dynamic Balancing. Thanks for the term.

Best wishes and best regards,

Joe

 

[EJ Harris]

Thank you so much, EJ for chiming in!! And, I'm glad to meet you!

Don't get me wrong, EJ, I "DO" feel that your design is a good one in all regards. After all, what could you have done to make it any easier than you did for static balancing? Nothing in my opinion, unless I come with an idea for ya to make it better!

In many if not most cases, doing a static balance alone with your balancing tool could produce satisfactory results. However, in cases like Terry Lowe where the motor housing is out of balance in the wrong place, nothing short of balancing the housing or replacing the motor will cure his problem. If he had not done the elastic test, he'd most likely never have known he had that problem to begin with, and, at some point he would likely have a premature failure of that motor or some other part on the Inspire.
I could easily suggest using your static balancing tool for the initial balancing, then use the elastic procedure to confirm the results or to at least to identify any "Other" balancing issues that may be there.
Either way, I recommend doing an elastic balance as at least a way to be certain everything is in good harmonic balance. I'm sure you are very familiar with resonant frequencies and the aftermath it can cause. Like the Tacoma Narrows Bridge, once a mechanical device reaches a certain level of harmonic imbalance and vibration, it can literally destroy itself or in this case, render sensitive electronics useless if it's bad enough.

One of the motors on my Inspire Pro produced a very slight arch shape on the wall with the laser but after using an X, Y and Z axis balancing and centering sensor, I determined that the imbalance wasn't severe enough to warrant further balancing of the motor housing but I will retest it every once in awhile to make sure it's not wearing the bearings out too quickly.

From my own personal point of view, if I'm going to do an elastic balance test, I may as well go ahead and do the initial "and" final balancing with the elastic method but that's just me. Not everyone here feels comfortable doing an elastic test.
I'm sure many Inspire owners will just use the static method using your tool given the fact that the elastic method is time consuming and rather complex (even slightly dangerous if you're not careful!!).

Just to clarify, It's not that I'm not satisfied with your product at all, it's the method used with this crazy complex motor, hub and prop configuration that has me concerned.

To be perfectly honest, I wish DJI had of designed a hub and prop system that could be balanced using conventional methods. For example, what if they had just machined a hole perfectly in the center of the prop that would allow a standard balancing tool to be used? Or, what if they had designed the prop so the locking mechanism would have rested in the locked position at a 90° angle from the longitudinal axis of the prop, that way your tool could be used to an even greater degree of accuracy than it already is!

With every new complex design comes the opportunity for people like yourself to design a tool that will help users/owners to fine tune the results of that design. Also, new complex designs seem to always come with a whole new set of complex problems. All we can do is use our knowledge and experience to try our best to adapt and overcome those problems.

In my mind, DJI (as well as other companies and even other industries) seem to place the majority of their focus on the technology but somehow slack off when it comes to the small things like making sure the motors and props are perfectly balanced and balanced with each other before installing them! In my opinion, it all boils down to the lack of quality control on what seems minor to them but major to us at some point during the life of the product we paid for.

Just thinking here, but, what if you could come up with a "Kit" made specifically for the Inspire that nearly anyone could use to perform an elastic balance? It could include the self adhesive monocote strips with numbers that would indicate the weight, it could include what's needed to do the sanding if they prefer to sand rather than add weight. It could also include the cleats, a special made strap, the foam and maybe even a board with padding on the bottom already made with the cleats and one that can be clamped to a kitchen table (made so it wouldn't scar the table) in case they don't have a workbench. You could include the laser and a special stand for it along with a special made polycarbonate mirror that just straps on. The possibilities are endless!!! Pilots are serious about these Inspires and want to make sure they function as perfect as possible on all levels. I know I do. And, if I didn't already have what I need or the experience to gather what I need? I would buy that kit for my expensive Inspire!!! No doubt in my mind.

The "MAIN" reason I posted this procedure is because I couldn't help but notice the frustration people were having with balancing the props. I also wanted to make people aware that the hub is part of the balance of the motor and not just the prop. I just wanted to give Inspire owners the "TOOLS" (figuratively) they need to get the very best and most out of their investments as possible short of offering a kit myself.
I don't intend to offer a kit at all, I just don't have the time cause I have my hands in too many projects as it is but I am taking the time to do this for other Inspire owners.

Hey!! Here's another idea for ya, EJ! How about making a ring with weights on it that would snuggly fit over the top of the prop center that would simulate the balance of the motor housing with the hub attached? That would insure that it's balanced! The only issue left would be if the motor housing itself is out of balance like Terry Lowe's.
This would be a way to make your tool perfect!!

Please keep in mind that I'm just trying to help everyone I can, including you!!

Give it some thought, EJ, I'm sure it's worth looking into offering a kit to do elastic balancing or making a weighted ring as just mentioned (or both).

I tend to go into great detail about everything I do. I've been in business for 35 years and never once advertised. I don't even have a business card.
I've been doing photography and videography for more than 20 years. It started out as a hobby until people kept asking me to do weddings, then promotional stuff for local businesses and industries that I work for, now I'm part of a documentary group that is in full force on environmental issues. I better not get into any of that stuff. It's too deep into politics and I might get kicked off of here.
The point is, I just enjoy helping people and enjoy doing things as close to right as I possibly can. That's what has kept people coming to me rather than me going out looking for work, at least that's what my customers and friends tell me. Enough about that part, eh!!

My interest in photography led me to doing videos and stills while flying my full scale Cessna 172 (had my license since 1987). That led me to an interest in RC helicopters, then multirotors for aerial filming work. Now I'm waiting on my exemption for part 333 to come through, should be any day now (keeping my fingers crossed here). I don't have any violations so there shouldn't be any problem there.
Ok, now I'm ranting.

Oh, almost forgot. I had never used the term elastic balancing till now. I've always referred to it as Dynamic Balancing. Thanks for the term.

Best wishes and best regards,

Joe

Joe,
You've got some great ideas. I got started making prop balancers by a request from fellow flyers. I enjoy helping other pilots & get the greatest satisfaction when they tell me how much better their bird flies with balanced props. I must admit I'm not a big fan of this 1345T prop lock design but is seems work just fine . I would love to chat on the phone with you sometime. I bet we could solve some the world's greates problems . LOL
EJ

 

[Joe R]

Joe,
You've got some great ideas. I got started making prop balancers by a request from fellow flyers. I enjoy helping other pilots & get the greatest satisfaction when they tell me how much better their bird flies with balanced props. I must admit I'm not a big fan of this 1345T prop lock design but is seems work just fine . I would love to chat on the phone with you sometime. I bet we could solve some the world's greates problems . LOL
EJ

Sounds great, EJ!

I'll send you my cell phone number in a PM and we can chat away. We may not be able to solve the world's problems but maybe together we can solve our own little world problems eh?!

I'm sitting here at my computer writing an article for a documentary and doing some line by line budget stuff for the next segment. Otherwise I'd likely be in my shop.
It's nice to have a mix of things to do to keep life interesting

Thanks, EJ!!

Joe

 

[SteveT1]

I'm so sorry, I left out an important part of this procedure! :-(
I use a piece of high density foam about 2 inches thick under the legs to keep the vibration from transmitting to the workbench.
I also only tighten the strap that is fastened to the cleats on the workbench to the point where it just presses into the foam. I also use straps with closed clasps to prevent the strap from breaking free from the cleats. This vital step allows the arm to raise up off of the workbench while still being in contact with the foam pad and be more "Free" to "Float" so to speak. It's probably not a bad idea to wrap the strap with foam at the point where it lays across the arm to further isolate the vibration from the strap and workbench. I think I would zip tie or tape the foam on to prevent it from coming loose and flying into the prop. I haven't done that but it just crossed my mind that it may come a little closer to simulating the Inspire while in flight.

The "C" shaped line that it produces is most likely an indication that there is a significant amount of lateral (sideways) movement/vibration, this is usually caused by the motor housing not being balanced along the side of the prop rather than inline with the prop. It causes movement in both the X and Y axis rather than just one axis. I've had this problem before on my S1000. It turns out that I had to add weight to the inside of the motor housing, I had to take the motor apart to add a heat resistant compound in between the magnets (I went to an electric motor company that rebuilds electric motors for advice and for the proper compound to use for balancing and that is the way they do it as well), I would try isolating the Inspire from the workbench with the high density foam first and try it again, if it still produces the "C" shaped line, I would ask DJI to replace the motor rather than modifying the balance of the motor housing yourself (especially if it's still under warranty!). Note: I was able to use a balancing jig on the housing after it was removed so I could balance it with small magnets. After it was balanced, I weighed the magnets and used the same amount of compound that matched the weight of the magnets, then I applied the compound in between the magnets. It usually requires about 24 hours or more to fully cure. It's always best to add just a little more than you need, then cut some away as it begins to cure or use a dremel tool after it cures to very carefully grind some away until it's perfectly balanced.
After it cures, it should be checked for balance one last time before re-installing the housing.
You really have to feel completely confident with what you're doing to balance the housing!! A bad job here could cause you to lock up a motor in flight as a result of the compound coming loose. I always use alcohol to clean the housing to make sure there is no oil, dirt or grease where I want to apply the compound. Make sure to use a compound made especially for electric motor balancing!!! I can't stress that enough!!!
If you've ever taken one apart, you'll usually notice some type of red or green color compound between the magnetics somewhere. This is exactly how the factory does it (as opposed to cutting weight away from the heavy side).

Check out this Link to a compound made for electric motor balancing

As for some way of holding the laser, I ordered a bench clamp made for holding circuit boards off of Amazon for $27, it works great and is right at the height I needed. I use it for soldering work as well though.

Link to PanaVise

You can still sand the bottom of the prop as normal if you'd rather not use the tape.

Figuring out which side needs the weight almost has to be done by trial unless you do a static balance first but that's even more trouble and time consuming since you have to remove two hubs to do a static balance test. It's a give and take thing I guess.

I can do a video of the whole process on the Inspire but it may be a few days before I have the time.to do that.

I hope this helps to clarify some issues (especially the "C" shaped line on the wall). BTW, that type of vibration is particularly hard on the electronics as well as the frame itself. It probably won't show up as major problems until it gets a little age and use on it but if you're anything like me, I want this thing to be as reliable as possible and last as long as possible!

I will try my best to do a video as soon as I can.

Sincerely,

Joe

Joe ,
Great description, where are/would you put the strap? I am trying to figure where to put the strap, on the arm? Close to the center? Strap in 4 places, one on each side, near the motor?

Thanks for any help
steve

 

[Joe R]

Joe ,
Great description, where are/would you put the strap? I am trying to figure where to put the strap, on the arm? Close to the center? Strap in 4 places, one on each side, near the motor?

Thanks for any help
steve

Hi Steve,

Put one strap on the housing just behind the motor with the prop on it, then put another strap on the arm that is diagonally across from it just to hold the Inspire down to keep it from tipping or sliding. All that's needed are two straps (Use good straps that won't come loose). Don't forget to use some foam between the feet of each leg and the workbench or table, then strap it down to the point where the feet (legs) are pushing into the foam about 3/4 of an inch if you are using a 2 inch thick piece of foam.
The foam pieces shouldn't be any larger than about 3 inches square because you don't want to take a chance on the foam being pulled up into the prop. Oh, and put a piece of foam under each foot (4 pieces of foam).
I don't like to put the strap in the middle of the horizontal arm because it may slide on the table.
One in diagonal corners will prevent any movement of the Inspire. Make sure the other pieces of foam are nice and snug too so they don't come loose either, if they aren't, strap it down a little tighter.
I use a very high density foam but if you use a low density foam, you may have to push the leg into the foam farther.
Run the motor up while in the atti mode. Don't use GPS mode cause if it has enough satellites, it will try to run the motors at different speeds and overwork the sensors in the IMU.

Just please be careful not to get your hands close to the prop that's spinning, make sure to do the CSC shutdown and wait for the motors to stop before making any adjustments to the prop (to add weight or do any sanding). Again, don't use electrical tape, it won't stick good enough!

I hope this helps to ease your concerns.

I'll keep a close eye on this thread to answer any questions as quickly as possible.

If you would, please come back and post your results so we can use it as a database. If we all work together, we should get this thing licked.

I think EJ and I can come up with something to make it easier and still be very acceptable.

I did notice a while ago how they counterbalanced the motor housings and even found the fine balancing compound. The fine balancing compound is dark blue and just under the top of the motor housing in the little vent openings (on the Pro model but should be the same for the V2 model). If you take a flashlight and look up under the top of the motor housing through the vent holes, you'll see the compound in two or three of the vent holes (depending on how much they had to use). At least if this compound comes loose, it'll just get slung out. The downside is, it should be inside the motor next to the magnets so it can't come loose.

Take your time till you feel comfortable with what you're doing, never be in a hurry with this procedure!

Sincerely,

Joe

 

[Terry Lowe]

I'm so sorry, I left out an important part of this procedure! :-(
...
Joe

Thanks for the informative reply! I'll set very thing up this weekend when I am not pressed for time and let you know here how it turned out.

Maybe that C shape was artifact as I really did have things a bit haphazardly rigged just to see if I understood the concept.

 

[Joe R]

Thanks for the informative reply! I'll set very thing up this weekend when I am not pressed for time and let you know here how it turned out.

Maybe that C shape was artifact as I really did have things a bit haphazardly rigged just to see if I understood the concept.

Hi Terry,

That sounds good.
It would be good to start getting some feedback to build a database.

The "C" shaped line shouldn't be there even on a simple or haphazard setup. If it turns out that you can't get rid of the "C" shape or even if you get it down to an arch shape, it will still mean that the motor housing is out of balance on the side that's 90° from the length of the prop.

I discovered a while ago that the fine balancing compound is dark blue and just under the top of the motor housing in the little vent openings. If you take a flashlight and look up under the top of the motor housing through the vent holes, you'll see the compound in two or three of them (depending on how much they used to do the fine balancing).
It could be that one or two of those little blue blobs of balancing compound has come loose and were slung out of the motor. The way it's in there, if it did come loose, it would just be gone, leaving you with an unbalanced motor housing. It's really not the best way to fine balance a motor. It is much harder to balance it on the inside in between the magnets so I guess this was a time saver for them but it leaves us with a "Weak Point" I'm really disappointed with this new finding. I didn't look there before because every outrunner I've ever seen was balanced on the inside.
I was looking to see how the main counterbalancing was done when I saw the compound.

BTW, the main counterbalancing is in the top of the motor as well but that part was done right.
Take a small screwdriver and gently stick it straight into a vent hole till it stops (horizontally).
Put a mark on the screwdriver and move it to different vent holes and you'll find that the holes are different depths (by a fair amount too!).
This is the way they done the main counterbalancing on the housing.
A small part of the balancing is still on the tabs that go in the notches on the sides of the props though.

Now I need to figure out a way to keep those little blue blobs of balancing compound from coming loose and flying out!!
That balancing compound isn't stuck to the top very well either since the top is polished aluminum. It wasn't even roughened up or ground before they stuck the compound on there.
I'm almost willing to bet that one of those come out of your motor, Terry.

Have a good close look, please? You may be able to see where the compound used to be at one time. If you do, that's the problem for sure.

All it takes is for the motor to sling a really tiny rock or something hard through the vent and hit that blob and it's gone!
I've seen where tiny rocks get picked up from sandy soil or even grassy areas with loose dirt in it. I have literally found particles like that inside of motors when I was replacing the motor bearings in some of my electric sport helicopters.
Even taking off from pavement (which is the worst really) is bad, there are lots of tiny rocks lying on pavement.

I finally got to where I always carry a heavy mat with me with flat steel bars to lay around the edges of the mat so I don't pick up anything from the ground anymore. That stuff isn't good for the camera either.

Still, there's an issue with where they placed those compound blobs even without dust or very tiny rocks (the size of grains of sand)!

Maybe there's a way to put some type of coating on it. I'll have to some some serious research on that one! I need to find a coating that will take the heat and not degrade over time and come apart.
Either that or open up the motors and rebalance them with the compound on the inside like it should be.

I just now tested the compound for hardness and it is hard but it's brittle, which is not good!!

Argh!

Keep me posted on the compound thing please!!

Thanks,

Joe

 

[Joe R]

Hi all,

I need to share something that I learned this morning. I'm still learning some of this too. These are different from the S800, S900 and S1000 multirotors. The difference is the legs, since they have that spring action that acts as a shock absorber for landing, it allows the copter to move back and forth.

My goal was to try to duplicate the "C" shaped line that Terry told us about.

What I did was put a piece of duct tape on one of the props to purposely make it out of balance, then spool it up and watch the laser dot on the wall, it did produce a vertical line on the wall until I added even more weight, then it started producing that "C" shaped line. It was vibrating the copter back and forth very fast which was exactly what produced the "C" shaped line. I then added weight to the side of the motor and it really started moving back and forth, almost to the point where the line was horizontal.

I also watched the gimbal plate and camera and it was shaking too.

Then I tried it with the prop off but still with the added weight on the motor housing and it produced more of a straight horizontal line, it wasn't as bad as it was with the prop on but it was still there.

Try running the motor without the prop to see if there are any horizontal lines at all (or at least short arch shaped line) (still using the laser), if it does, then the motor housing is out of balance.

I've attached some photos of the motor to this message.
The first one shows the direction of airflow through the motor. I tested it with a candle to tee which way the flame was moving. It's the same as with many other outrunner motors I've used.
The second one shows the Blue Balancing Compound I was referring to earlier. If that compound is missing, there should be a discolored area where it used to be.
The third photo shows the depth from the outer part of the motor housing to the internal counterweight on the side that's 90° to the locking tabs.
The fourth photo shows the depth from the outer part of the motor housing to the counterweight that is inline with the locking tabs (the locking tabs are shown in the locked position). The difference in measurements were slightly over 3mm.

Note 1: I found one spot on one of my motors where the compound used to be but it was very small and didn't seem to affect the balance. It could be that they removed it at the factory, maybe they put in in the wrong place and needed to remove it?

Note 2: If they put the compound in place when the compound wasn't fresh (partially cured), it wouldn't have stuck to the housing as good as it should have. I'm just guessing here. I don't have a clue what their method is when installing the compound.

Note 3: I imagine (still guessing) that they used the dynamic method to balance these motors (spinning). I also imagine that they use something similar to what tire shops use to dynamically balance tires at tire shops. Basically, a computer will tell them where to put the weight and even how much. They do so many of these so quickly I can't imagine them doing it manually with a static balancer.

Note 4: After seeing how the air flows through the motor, it's apparent that if small particles of sand or dirt gets drawn into the motor, it will flow straight up into the coil windings and hit the blue compound in a way that will act like a sandblaster. I can see that compound getting "Sandblasted" down in size over time since it's brittle. In the air toward evening, small bugs and insects get suck into these motors as well.
I've even had to take a motor apart to clean out all of the insect guts when the motor started losing power.

Not related to Inspires but I have a Raptor 90 nitro (Upgraded the engine to an OS 105 HZR, what a powerhouse!) It's a 3D helicopter that actually sucked a beetle into the venturi of the carburetor one evening and literally choked off the air from the engine causing it to come to an idle while in an inverted low altitude backwards hurricane maneuver. Fortunately it went down in tall, thick, growing hay that prevented it from extensive damage. Only cost me for a new set of blades and a new tail boom. I got lucky. I installed a screen over the carb to keep that from happening again. Sorry, I couldn't help it, I still love flying with no gps or self level stuff, just raw stick and rudder flying! For those who aren't familiar with these, this thing has a five foot diameter rotor disc. See the attached photo below if interested. This story does let you know that the hazards of insects and other material can get into the motors and cause damage.
With the way the Inspire stops a motor if it's obstructed, a hard shelled bug could stop a motor in flight. it would be extremely rare but it could happen. Most bugs or insects would just get chewed up and spit out by the motor but ya never know. The best thing is to avoid flying when the bugs are thick in the air, if possible.

I need to find out what's the best kind of compound to use if the motor housing is out of balance. If it's still under warranty, I'd get them to fix it. If not, it can be done by adding tape to different spots on the housing until it's balanced, then use the compound as they did at the factory to re-balance it.
I'll try to make a video of how to do that for those who own an Inspire that is out of warranty and want to balance it yourself.
The other option is to order a new motor if you're not comfortable with balancing it yourself.

Another thing to keep in mind is that it could be another motor (other than the one you're testing at the moment) that's causing the vibration.

The measurements I took is concrete proof that the motor housing is indeed balanced to counteract the weight of locking tabs on the hub.

Summation:

* Test for vibrations with the props off first.

* While testing the motors with the props off, touch the arm as close to each motor as you can without touching the motor itself. You will easily be able to tell which motor is vibrating. I just tried it with weight added to one motor housing and it was very obvious which one it was just by touching the arm near that motor.

* Once you're satisfied that the motor housings are indeed balanced, then proceed with testing the balance of each prop (one at a time).

* Use the foam rubber under the feet, I just tried it without the foam rubber and it really makes a difference. The copter really does need to be isolated from the table to get good results.

I hope this helps!! I know that this morning's tests have helped me to better understand how it works, how it's designed and what to do if it's not right (except for knowing what type of compound to use......yet)

Click in the thumbnails to see the full size photo (I'm sure you already know that but I did have some ask one time to upload a bigger photo )

If you don't feel comfortable and confident about doing this, DON'T do it!
Please don't wear any loose clothing including loose shirt tails on button up shirts, they can get pulled into the prop if you are too close!
The force of air movement from these props are literally enough to blow a heavy screwdriver across the table so please BE CAREFULL!!


Wishing all your flights are great ones!

Joe

 

[SteveT1]

Hi Steve,

Put one strap on the housing just behind the motor with the prop on it, then put another strap on the arm that is diagonally across from it just to hold the Inspire down to keep it from tipping or sliding. All that's needed are two straps (Use good straps that won't come loose). Don't forget to use some foam between the feet of each leg and the workbench or table, then strap it down to the point where the feet (legs) are pushing into the foam about 3/4 of an inch if you are using a 2 inch thick piece of foam.
The foam pieces shouldn't be any larger than about 3 inches square because you don't want to take a chance on the foam being pulled up into the prop. Oh, and put a piece of foam under each foot (4 pieces of foam).
I don't like to put the strap in the middle of the horizontal arm because it may slide on the table.
One in diagonal corners will prevent any movement of the Inspire. Make sure the other pieces of foam are nice and snug too so they don't come loose either, if they aren't, strap it down a little tighter.
I use a very high density foam but if you use a low density foam, you may have to push the leg into the foam farther.
Run the motor up while in the atti mode. Don't use GPS mode cause if it has enough satellites, it will try to run the motors at different speeds and overwork the sensors in the IMU.

Just please be careful not to get your hands close to the prop that's spinning, make sure to do the CSC shutdown and wait for the motors to stop before making any adjustments to the prop (to add weight or do any sanding). Again, don't use electrical tape, it won't stick good enough!

I hope this helps to ease your concerns.

I'll keep a close eye on this thread to answer any questions as quickly as possible.

If you would, please come back and post your results so we can use it as a database. If we all work together, we should get this thing licked.

I think EJ and I can come up with something to make it easier and still be very acceptable.

I did notice a while ago how they counterbalanced the motor housings and even found the fine balancing compound. The fine balancing compound is dark blue and just under the top of the motor housing in the little vent openings (on the Pro model but should be the same for the V2 model). If you take a flashlight and look up under the top of the motor housing through the vent holes, you'll see the compound in two or three of the vent holes (depending on how much they had to use). At least if this compound comes loose, it'll just get slung out. The downside is, it should be inside the motor next to the magnets so it can't come loose.

Take your time till you feel comfortable with what you're doing, never be in a hurry with this procedure!

Sincerely,

Joe

4 small pieces, 1 under each leg, is that better than one large piece under all 4? I have some of that closed cell foam, like what they use in the cases for the Inspire, will that work?
thanks,
steve

 

[Joe R]

4 small pieces, 1 under each leg, is that better than one large piece under all 4? I have some of that closed cell foam, like what they use in the cases for the Inspire, will that work?
thanks,
steve

Hi Steve,

One large piece would be fine.
If two of the legs are slightly off of the foam it will be OK as long as you do use one large piece. Not Ok if it's 4 pieces.
The closed cell should also work. It may not work quite as good as foam rubber like a 2 inch memory foam mattress but it should still work.
The idea is to keep vibrations from being transmitted directly to a hard surfaced table.

Please read my post above about testing the motors without any props first.
This is something that I tried this morning to eliminate any vibrations in the motors before moving on to the props (just to make sure those balancing compound blobs are still there, see the photo above that shows the blue compound in the top of the motor).

I'm glad you're asking these questions. Stuff like this makes this an informative thread for all to read.

Please post your results when you're done so others can learn from it.

I don't want to be the only one contributing information, I consider this to be a group effort.

Thank you, Steve!!

Joe

 

[Terry Lowe]

I have some foam, a laser, tie down straps, a table and will be testing first without the props hopefully Saturday morning.

 

[Joe R]

I have some foam, a laser, tie down straps, a table and will be testing first without the props hopefully Saturday morning.

Hi Terry,

Sounds like a good plan. I'll be around and I get notifications on my phone too so if you run across anything odd, get in touch, I'll reply promptly.

You can also start a conversation with me in private and I'll give you my cell number if ya want. We can always try to work through it over the phone as well.
Depending on what you run across, I may be able to offer you some other things to try.
Did you try to find any places that look sort of dull (like where a dab of compound used to be?)
If you're not sure what I mean, have a look at the photo I posted above that shows where the blue compound is located on the motor. I had to use a flashlight and a small magnifying glass to see where one of mine had come off. I'm a little old so I had to use a magnifying glass, you may not need to. . Mine may have been taken of by the factory though cause it's still in balance.

Thanks, Terry and good luck!

Joe