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Apr 01, 2013, 07:51 PM
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otlski's Avatar
Just to quantify some numbers to the static CG balancing process, I ran some tests and posted the results in this post...

https://www.rcgroups.com/forums/show...1&postcount=11

Dan
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Apr 02, 2013, 01:52 AM
mutski
Here is a good discussion of eliminating vibrations with link to a YouTube video on balancing a brushless motor.
http://fpvlab.com/forums/showthread....-Footage/page4

I used electrical tape to balance the motors on my quad. It didn't take much tape, and it seems to stick when I fly. I downloaded an Iphone app that uses accelerometers in the phone to measure and graph vibrations, then put the phone on one arm of the quad, disconnected the other three motors and experimented with tape. You can vary both the size and position of the added tape, and finding the best combination of weight and position is tricky.
Apr 02, 2013, 07:19 PM
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FlyBoy20's Avatar
Quote:
Originally Posted by NACA0012
Can't assume holes are drilled perpendicular to back face, nor can you even assume pitch is consistent between the two blades or matched the label.
Jeez...I never even thought of that, is ever nothing simple in this world?
Apr 02, 2013, 08:38 PM
Registered User
R Zielinski's Avatar
Quote:
Originally Posted by FlyBoy20
Jeez...I never even thought of that, is ever nothing simple in this world?
No, and Ugh, I gotta say...that avatar is really ugly!
Apr 04, 2013, 10:08 AM
Wings that Swing
iheli22's Avatar

Prop & Motor Balance


Quote:
I used electrical tape to balance the motors on my quad. It didn't take much tape, and it seems to stick when I fly. I downloaded an Iphone app that uses accelerometers in the phone to measure and graph vibrations, then put the phone on one arm of the quad, disconnected the other three motors and experimented with tape. You can vary both the size and position of the added tape, and finding the best combination of weight and position is tricky.
There's a guy local in NC who is selling "Balance Rings" for DJI motors. Has anyone else tried these?

I knew that there must be a better (easier) way to balance motors and props. I tried them on my Hex 550 and they actually worked pretty well..
I didn't use a vibration App, but I could definitely feel the difference in my ship with balanced motors.

Here's his link: https://www.rcgroups.com/forums/show....php?t=1847484
Apr 04, 2013, 12:28 PM
Closed Account

Or, as another option, laser and mirror


Several self-evident weaknesses, but an option.

www.flitetest.com/articles/Laser_Balancing_Props
Apr 07, 2013, 12:56 AM
quad lover

several disagreements


Awagar, I have to object here. You seem to be spreading false information, speaking on the subject as though you are an authority. I usually have no problem with that, except when someone isn't merely responding to a question posed, but rather starts a thread as a thread of advice/knowledge sharing. In my opinion, the way you started this thread puts more of a burden on you to be sure you know what you are talking about, and I don't think you do.

Specifically, I'm talking about where you refer to balancing the "hub". First, this is misleading terminology, however frequently it may be used (and this terminology gets spread by way of people purporting to be knowledgeable).

My explanation refers to the same general concept that yours does when you refer to the "hub", but I don't say it like that, and in fact I will leave it to my drawings to say what I mean, because I have tried before to use words, and people still misunderstand. But a picture says a thousand words.

But a few words to describe the drawing: the prop can be balanced such that each blade is equal in mass to the other blade, but the front and back of each blade can still be off balance. The drawing I made that shows the prop split right down the middle long way shows this, with example numbers.

Let me know if any questions remain, or if you disagree, why you disagree.



My main gripe is about telling people to actually put balancing material on the hub. It doesn't make any sense. It's far too close to the center to have enough leverage to balance things out.
Apr 07, 2013, 11:20 AM
Registered User
R Zielinski's Avatar
I agree with John Doe that the term "balancing the hub" is not an accurate description. His drawing is correct. The imbalance could be at the hub or anywhere along the length of the prop. If you're going to complain about the term "balancing the hub", why not also complain about the term "balancing the blades". It's equally incorrect because true balancing of the blade requires balancing on BOTH axes of the blade.

The term "balancing the hub" is universally recognized and understood to describe what your drawing shows. Unless you have a better term and a method for spreading if virally to the entire modeling community, we'll have to stick with it. What WOULD you call it? Balancing axially, or coronally? No term I can think of would be any more accurately descriptive than "balancing the hub".

I do NOT agree with your complaint about adding material to the hub. Sure you have to add a lot of material because you're close to the axis. But again, do you have a better solution?

The prop blades don't usually get that much further off axis than the hub anyway (except maybe on slow fly props). You'd have to add almost as much material there, which would then affect your "blade balance". Adding or subtracting significant material along the leading or trailing edge of the prop is likely to change the aerodynamics of the prop a bit. That blade is also moving a lot faster than the hub, where forces are more likely to cause blade failure (if you removed material) or fling off your layer of tape or CA or paint or whatever you used. It's also uglier there. Lumps of CA on velcro hide pretty well at the hub.

Are you advocating balancing the "hub" first by adding material equally to one leading edge and one trailing edge on the opposite blade? Good luck with that. Once you're balanced "axially", you'd then have to add more material to balance the blades, which would screw up your initial efforts.

That points out the other advantage of adding material to the hub AFTER "balancing the blades". That material is pretty much on the longitudinal center of gravity of the two blades so it has no affect on your initial "blade balancing". That's also probably why it's called "balancing the hub". Capiche?
Last edited by R Zielinski; Apr 07, 2013 at 11:28 AM. Reason: clarity of terms
Apr 10, 2013, 08:43 AM
Closed Account
Hey guys, Awagar didn't write the article, I did.
I wasn't trying to get into an argument about semantics, and in no way was I trying to say that the article was the end all and be all for balancing a prop.

I invite you to post all the information you have. The whole point of internet forums is to share information. So please spread some knowledge.

Also, the fact that the article has caused a discussion, and that many people will get a chance to come away with more knowledge on the subject is a win.
Apr 10, 2013, 09:14 AM
Registered User
richard9999's Avatar
I just got a batch of black 10 x 3.8 props which were badly out of balance. I tried tape but it came loose. Instead, I balanced them by first giving a light spray all over with matt black paint and then adding more paint to the front and back of the light blade - maybe three coats. Fortunately it was a sunny day and the paint dried fast enough that I could complete balancing two props before I had to clean the spray can. Result - invisibly balanced props.

I also had to recently balance the recommended GWS 5443 props for my V929 quadcopter. These have a single 3mm hole at the bottom and a much smaller hole at the top and will not fit on my magnetic prop balancer. I balanced them instead by finding a spare 3mm prop shaft long enough to support their weight and resting this on a level, flat piece of glass - a level kitchen counter would have done as well. Almost zero friction, and then it was just a question of adding bits of tape to the light blade.
Apr 11, 2013, 12:26 AM
Registered User
Quote:
Originally Posted by R Zielinski
My bad. Never saw those props and didn't imagine they'd design a hole like that. On looking at photos of those DJI props, I agree that cones will not center very reliably in those holes. (The hubs also sure look too thin for both cones to point in without hitting each other). I really don't know what you could do to center those props on a balancer shaft reliably.

My only idea is not a great one: use a tapered prop reamer (one that's totally cone shaped) or a cone-shaped diamond file and ream off both of the flats on one side of the prop only. Ream just until the reamer touches the round parts of the prop hole. You'd have to be careful to remove material as symmetrically and centered as possible. Then you should have a centered circular hole on one side that the cone will seat in. Might work while maintaining the "O" shaped hole at the other side of the hub.

Hopefully someone here has a better solution.
I have no problems centering my DJI 10 x 3.8 props using the DU-Bro balancer.
Apr 11, 2013, 03:51 AM
Registered User
jcansdale's Avatar

Balancing a keyed DJI prop


Quote:
Originally Posted by hoggdoc
I have no problems centering my DJI 10 x 3.8 props using the DU-Bro balancer.
I recently discovered the flat parts inside the DJI props don't start right at the bottom. This means you can put the pointy end of a cone at the bottom and the flat end at the top. Before I was struggling to get the prop completely aligned.
Last edited by jcansdale; Feb 12, 2014 at 01:48 PM.
Apr 12, 2013, 11:37 AM
Registered User
A tip when using CA - Common baking soda (Sodium Bicarbonate) works better than commercial 'kicker' and adds mass. Put a small amount of CA in place, then dust a little Bicarb on it. Also works good for filling holes or building up areas - fileable, sandable, in general machinable.
Jim
Apr 13, 2013, 03:53 PM
Registered User
If anyone has experience balancing helicopter blades, they understand you can not just 'balance' blades and have it be physically correct.

Think about a helicopter blade; I may weigh each blade separately, and come up with (made up numbers) 100 grams and 101.5 grams. Ok so I know there is 1.5 grams difference, BUT, depending on where I put that weight on the lighter blade, may or may not lead to them being level balance compared to each other. The closer to the hub I place the weight, the less static balance weight it will have. Finding the point at which the 1.5 grams cause level balancing indicates the correct dynamic balance point.

But in the case of quad props, you do not have the option of weighing the blades separately, so you are best guessing, at best, when just using the 'level' method.

Truth is, only vibration measurements, motor and prop together, are actually producing balanced systems.

Everything else you try is a rough estimate and may or may not work. If it works, great, you're lucky. If you go through the magnetic prop balancer motions, blade and hubs, and still have a vibrating system, do not be surprised.
Apr 13, 2013, 05:34 PM
Registered User
jcansdale's Avatar
Quote:
Originally Posted by spiked3
Think about a helicopter blade; I may weigh each blade separately, and come up with (made up numbers) 100 grams and 101.5 grams. Ok so I know there is 1.5 grams difference, BUT, depending on where I put that weight on the lighter blade, may or may not lead to them being level balance compared to each other.
I've heard this before but never understood why it would matter.

If having the blades weigh the same amount is important, why doesn't NightFlyyer's one bladed helicopter shake itself to bits? I'm sure the counterweight he uses will weigh considerably more than the normal blade.

1 blade Helicopter. Both rotors. These are Blade 400 experiments. (6 min 21 sec)


Does anyone have an explanation why it would matter?


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