Hi Joe,
I kindly ask you to confirm/deny if there are calibrated counterweights in bell of 3510H motor, and if such counterweights are axially asymmetric? What such weights would counter, if everything else is axially simetrical (hubs, props...)? It is for sure that you put so much more time in your research then anyone of us, so I kindly ask you to shed some light to this basic topic which got me confused.
If my mechanical engineering knowledge is complete, when all masses are symmetrical over axis of a motor, then no vibration should be present? Therefore we balance props to be symmetrical over their axises. Therefore motor bells as well as prop hubs should be symmetrical over motor axises.. So, I can not comprehend why there would be asymmetrical balancing counterweights incorporated in motor bells when hubs and props are symmetrically balanced? I have just one idea - that these tabs are balancing points for bell itself (to fine tune bell balance by shaving tabs as appropriate)... I know that it can be that different props, as well as different hubs and bells have different total masses, but if any of these masses are axially symmetrical then rotation should be without any vibration - am I right?
Please comment and advise material for further reading if I missed some point.
Thanks for your effort and contribution.
Hi,
You are right. If that counterbalance is in line with the blades (with the right axis), it wouldn't matter.
If you'll look at this page,
How to balance the new 1345T quick release props...
There are a couple of photos that I posted that show the depths. You'll see that there is a 3mm difference in depth from the side of the bell to the counterweight mass.
The shallow part does not line up with the prop blade. The shallow (13mm) part lines up closer to the notches in the prop than it does with the blades.
So, through much testing with spinning the bell while using an X and Y axis measuring tool (highly precise) it was determined that without the prop, there is a .1mm vibration at 8000 rpms. However, with the prop on and after being properly balanced, vibration was down to less than .005mm.
It doesn't seem like much.
It's difficult to feel a .1mm vibration with no prop but with an unbalance prop, it's very noticeable.
It was determined that it takes the prop, counterbalanced housing and the locking tabs to make it work with the least amount of harmonic distortion.
I'm sure you are familiar with harmonic distortion. It will vibrate at some rpm no matter how well balanced it is.
Every car will vibrate at a certain speed.
Ha, some vibrate at all speeds. Lol
I should have referred to this phenomenon as self resonant frequency.
Sorry, I've driven a couple of thousand miles in the last three days and I'm tired.
Try measuring the hubs as I have in the photos and I think you find that the counterweight doesn't line up with the blades.
The blue blobs are there for fine balancing and was in fact done with a simulated prop at DJIs plant. I was finally able to speak with someone that could tell me how they were balanced at the factory.
It is balanced while spinning the same as a tire shop would balance the tires for your car. The computer tells them where to put it and how much to use.
I guess what I'm trying to say is that the motor, prop and locking tabs were designed to work as one unit or system.
That means that I need to simulate the prop locking hub and motor counterbalance for static balancing the props.
I would guess that DJI has a tolerance they go by when spin balancing the motor and maybe .1mm on the X, Y axis is acceptable?
I hope this helps.
I'm in Arkansas in a campground at the moment but headed toward Tx. I'll be starting a filming tour on Monday.
I won't be back at my shop till the second week in April.
I'll try to keep my eye on this thread.
All the best!!
Joe
Edited the morning after getting a little rest.
