Loose arms - normal or not

Mr Phantom · Sep 24, 2015

I know this issue has been brought up earlier and i have read the threads on the forum, but all those three threads i found was from January 2015, so i wanted too see if there has been any new info about this issue from DJI?
Also i read many different answers regarding the loose arms. The most common answer back in January was that DJI has said that a little bit of play is considered normal.

My Inspire has a play on both arms and the left arm has more play than the right, i guess that can't be considered normal?
And some people have no loose arms at all, so if its normal with a little bit of play are their units defective then?
My unit is manufactured March 21 and is a B version. I have only two flights on the aircraft and have not noticed any oscillation but i haven't looked for it either. But i notice that the camera/gimbal is vibrating when hovering, but haven't noticed anything yet in the video recordings.

So whats the deal with the loose arms? Should they be loose or not?
And if they should be a little bit loose whats a little bit? And won't the arms get more loose with time?

Derfmen · Sep 24, 2015

I had the same questions after I received my I1 back in March, I had an A version. The arms were as you said "has a play on both arms and the left arm has more play than the right". It never affected the birds performance, and DJI said it was normal.
Then in June I accidentally flew into the barn and broke it, I sent it in for repair, to make a long story short, DJI sent me a NEW D version. The arms on this one are tight, there is no movement in them at all, But now I notice that there is more wobble in the gimbal when the landing gear is raising or lowering and that when hovering in higher winds I can detect a very slight movement in the video image. I suspect that the looser arms absorbed some of the air frame flex, which would produce smoother images. I don't recall any posts about the arms actually breaking in flight, but I may be wrong on that.

johnmont250 · Sep 24, 2015

one of my I1s is loose as a goose and its a tripod in the sky-stable.

JoffaDan · Sep 25, 2015

johnmont250 said:
one of my I1s is loose as a goose and its a tripod in the sky-stable.

+1

Aussie Pete · Sep 25, 2015

There is a video around that shows you how to remove the "loosness" of the two motor arms.
( put Inspire into Transport mode first ) ...Simply remove the 4 silver hex head screws in each of the outer clamp around the arms..do one at a time...see the black shims DJI install as a tension shim around the silver sleeving/bushing.
I used black electrical insulation tape the same size as the shim....one or two pieces of tape ...only enough to take up the looseness...not too tight as to restrict the rotary action when transforming from flight modes to transport mode etc.
"Do not" over tighten the 4 silver hex head screws when you are finished...its only screwed into the plastic.
....Pete
The loose arms do have a effect on the aircraft when in forward flight.

johnmont250 · Sep 25, 2015

my loose arms have no effect whatsoever on full forward flight all the way to 50+mph.

PB30X · Sep 25, 2015

JoffaDan said:
+1

+2

Mr Phantom · Sep 25, 2015

The thing that strikes me is that some people have loose arms and some don´t, so if DJI says that loose arms are normal then it would mean that the people that has no loose arms has defective units, which i doubt, or if the units with tight arms are normal then our units with loose arms are the defective ones.

Also my left arm has more play than the right one, i guess that is not considered normal, regardless if the arms should be loose or tight they should at least have the same tightness or looseness.

There was a guy making a new thread on this forum back in January where he announced that DJI has confirmed that there shall not be loose arms on the Inspire 1, but on questions where he got that info from he never gave an answer, instead there was several people saying that DJI says there should be some looseness on the arms.
But at the same time i can imagine that because it was a brand new model back in January when lots of people started to complain about this problem that DJI didn't want to admit that their new drone had this problem so they just said its normal?

I need to make a flight as soon as possible so i can record the aircraft and check for oscillations, or maybe i will be able to see them on the craft at hovering, i haven't thought about looking for oscillations on my two earlier flights.

johnmont250 · Sep 25, 2015

i made a slow mo video to make sure it wasnt shaking/vibrating

Aussie Pete · Sep 25, 2015

I rest my case....there is a oscilation with loose arms......but the camera gimbal is doing its job to eliminate the vibration from the video....look at the Inspire with your eyes when it is hovering.
This "will" increase in more gusty conditions....the more the arm movement the worse it will get.
If you say this is normal...well what can I say.???.

johnmont250 · Sep 25, 2015

Aussie Pete said:
To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

I rest my case....there is a oscilation with loose arms......but the camera gimbal is doing its job to eliminate the vibration from the video....look at the Inspire with your eyes when it is hovering.
This "will" increase in more gusty conditions....the more the arm movement the worse it will get.
If you say this is normal...well what can I say.???.

not normal thats for sure. slomo videos are great for that. that sucker needs help, they must be really really loose, and maybe an unbalanced prop.

Mr Phantom · Sep 25, 2015

That was what i was thinking to do, to make a slow motion video of my aircraft. Maybe its normal to a certain degree but when its too much it causes oscillations?

But i still think that everybody's craft should have the same degree of looseness in the arms, and definitely both arms should have the same amount of looseness.

I mean if its suppose to be like that then DJI must have a predetermined value of the looseness that should apply to all crafts, now it feels like some crafts have a little bit of loose arms, some have much looseness, and some have no looseness at all, that is surely not the way it suppose to be.

jhardway · Sep 25, 2015

johnmont250 said:
not normal thats for sure. slomo videos are great for that. that sucker needs help, they must be really really loose, and maybe an unbalanced prop.

that looks like something is out of balance, I would look at the motor bell, or prop on position 2 or 3

Over all I feel the play helps more then hinders, because vibration is a common trait in the design having the play in that plane of the arm allows it not to translate down into the main body. the looseness dithers down the vibration allowing for a better result for the camera.

Aussie Pete · Sep 26, 2015

If a Octo copter had this much play in all the arms with the motors attached...how would it behave ..????
I think stability would be a problem...you would hear the motors changing rpm to compensate trying to keep the stability within normal range.....bottom line is the flight controller is working harder to keep the craft stable.
If this is a normal thing ..why not rubber mount the motors to reduce transmitted vibration through the frame....have floating motors...Hmmmm.
I suppose everyone is different.

jhardway · Sep 26, 2015

I agree if the vibration on an octo can give some unique flight characteristics, what I call twitching, the aircraft will give off some odd adjustments like the gains are to high. Part of the reason here has everything to do with on a standard quad, hexa, and octo, the motors are mutually independent to each position. Each position will adjust from the commands of the FC. The flight controller will through out the adjustment but with vibration or looseness causing inadequacies in the thrust causing twitching and the FC to over work.

Where I think the inspire design becomes intuitive, is in the small play in each arm that connect two motors on a solid arm (the carbon fiber arm connecting motors 2 and 3 - left side, motors 1 and 4 - right side) From there they then connect to the aircraft in the middle of each side's arm and allow a little play, so when you get some vibration the play basically translates on the arm between the two motors. With the aircraft's connection point on that arm sitting in the middle, its balance point, helps null out any vibration resonating down the arm attaching to the aircraft's body, just like if you sat in the middle for a seesaw.

If any of the motor positions are out of balance enough then it will pass the limits of the tolerated play, run down the arm connecting to the body and show up in your video, The majority of the inspire are not having these issue, and looking are one of those video you can see one of the motor positions is out of whack, either on the motor bell or in the prop pulling the motor to heavier side.

Tarrot has played with the rubber mounts on the motors for some of their frames, I have one but to be honest I have not seen a difference in flight. I have read in situation people have found better results when they take away those rubber mounts, but i can not say on my end.