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Old Nov 15, 2012, 09:37 AM
kitesurfer
United Kingdom, Blackpool
Joined Dec 2005
1,537 Posts
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Prop balancer balancing?

big question i thought of..

Is your prop balancer balanced?
i have been struggling to get my props balanced, and i think its down to the balancer not being balanced. because every time i put the props on the balancer, its different.
i have the turnigy balancer, http://www.hobbyking.com/hobbyking/s..._Balancer.html
but i think the rubber bits are out of balance (they never side still, always fall one way)

so how balanced is your balancer? do you recommend a better balancer?
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Old Nov 15, 2012, 09:42 AM
I never finish anyth
United States, TX, Houston
Joined Jan 2012
2,585 Posts
Did you balance your hubs (with prop vertical)? I forgot to balance a hub once and couldn't get my props balanced to save my life. After 20 minutes of messing with it the light bulb turnd on and I was done 1 minute later.
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Old Nov 15, 2012, 09:51 AM
kitesurfer
United Kingdom, Blackpool
Joined Dec 2005
1,537 Posts
yeh, i can balance the prop perfectly, but then i take the prop off then on again, or twist it on the balancing shaft, and it will be out of balance again
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Old Nov 15, 2012, 09:55 AM
I never finish anyth
United States, TX, Houston
Joined Jan 2012
2,585 Posts
If you can't consistently put the props on the hub there is a problem with the balancer. Other than that it's magnetic and it shouldn't come "out of balance"
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Old Nov 15, 2012, 09:57 AM
Registered User
United States, NV, North Las Vegas
Joined Sep 2009
1,075 Posts
Balance the rubber bits... my topflight balancer tells you to do this in the instructions, something lacking when it comes to most turnigy products.

I added a drop of CA at a time to the "light side" of the rubber cone until the shaft and cones will stay in what ever position I put them in... just like a well balanced prop

John
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Old Nov 15, 2012, 09:58 AM
I never finish anyth
United States, TX, Houston
Joined Jan 2012
2,585 Posts
Quote:
Originally Posted by shultz View Post
Balance the rubber bits... my topflight balancer tells you to do this in the instructions, something lacking when it comes to most turnigy products.

I added a drop of CA at a time to the "heavy side" of the rubber cone until the shaft and cones will stay in what ever position I put them in... just like a well balanced prop

John
^^ Never considered this. Mine is a dubro and is aluminum and is very balanced.
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Old Nov 15, 2012, 10:08 AM
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United States, NV, North Las Vegas
Joined Sep 2009
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Quote:
Never considered this. Mine is a dubro and is aluminum and is very balanced.
Yep, I have the Dubro as well and use it for my larger props, well made and balanced. The friction makes getting smaller props balanced difficult.

My top flight magnetic balancer I use for small under 8 inch props as its more sensitive. I had to add a couple of drops of CA (per the instruction) to get the shaft and cones balanced, once done I can balance 4 inch props with no issue... something my Dubro cannot do.

John

Edit:
Mcrites... you quoted my TYPO!!!! and here I thought I edited fast enough..... Add CA to the "light side" of the hub not "heavy side"
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Old Nov 15, 2012, 10:10 AM
I never finish anyth
United States, TX, Houston
Joined Jan 2012
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I only balance 8+" props. Mainly 10in so i haven't come across it. Good to know though and makes sense.
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Old Nov 15, 2012, 10:17 AM
Registered User
United States, NV, North Las Vegas
Joined Sep 2009
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Quote:
I only balance 8+" props. Mainly 10in so i haven't come across it. Good to know though and makes sense.
Yeah, I used my Dubro for years on larger props without issue... then I got a micro quad that uses 5 inch props. No matter how I mounted the small props they would just sit on the balancer... just too much friction and not enough prop weight for a reading. So, I picked up the top flight magnetic balancer and solved my problem. I even went back and found my "balanced" 8 inch props were not as good as they could be using the magnetic balancer

John
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Old Nov 15, 2012, 10:18 AM
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United States, FL, Miami Beach
Joined Jun 2012
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Quote:
Originally Posted by AliB View Post
yeh, i can balance the prop perfectly, but then i take the prop off then on again, or twist it on the balancing shaft, and it will be out of balance again
Same here. What gives?
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Old Nov 16, 2012, 09:27 PM
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Joined Feb 2008
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Experiment...

I have a top flight magnetic balancer and ran some experiments. I balanced a prop very carefully, shrouded from external air currents, to the best of my ability. For the experiment I used tape. I achieved the level of balance where the blade would stay put no matter what position I moved it too. At this point, either friction (which always exists) or magnetic hysteresis must dominate over any residual imbalance. Next I added extremely small pieces of tape to create a purposeful imbalance until I could reliable detect it via the motion. At his point I weighed the tape (0.00194 grams) and measured its located radius (80 mm). Multiplying the two terms yields a sensitivity of 0.1557 g-mm.

Some maths...

Now, the shaft of the balancer is not a perfect machining/grinding job. Assume for a moment that the slightly rounded points at the ends of the shaft are eccentric from the outside diameter of the shaft. Let's say they are 0.001" (0.0254 mm) off center. This means that the prop will be held off center by 0.001" creating an error torque (moment). A 12" APC prop weighs 17.96 grams. Multiplying 0.0254 X 17.96 g yields 0.456 g-mm, creating a potential error three times the established sensitivity. This means that it is possible that you can do a perfect job balancing but because the blade was off axis, the balancing job ended up offsetting the effects of the eccentric shaft exactly. Exactly.... until you pull the prop off and remount it clocked 180 degree from original. Now the two effects are additive instead of subtractive.

The same hold true for the plastic cones that locate the prop. If they mislocate the prop by the same amount then a second potential source of error creeps in.

Not to be neglected, the shaft itself has mass, it weighs 5.043 grams and given the same offset as before has a potential moment error of 0.128 g-mm, or equal to the sensitivity of the balancer.

Based upon the observed repeatability, I happen to believe that the shaft on the top flight is better than 0.001" but these are example numbers just to point out the realm we are dabbling in. It is rather easy to imagine that the cumulative sum of all these errors rises to a factor of two or three above the sensitivity. At that point you can get different readings every time you mount a "finished" prop.

One thing I always do is to use one cone to engage the cylindrical side of the prop hole. For the other side I have removed any plastic flashing on the hub face and use the flat side of the other cone to establish a solid plane against the hub face. This way the prop's mounting position is more repeatably established. The intended cone establishes centering, the backside flat established the plane. When I'm done I rotate the prop 180 degrees as a reality check. This is a work reversal method where perhaps you can split any difference.

Dan
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Last edited by otlski; Nov 18, 2012 at 08:07 PM.
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