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Laser Balancing Props

fliteadmin

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#1

laser-balance7.JPG laser-balance3.JPG

Lasers can help you visually see the vibration that your motors and props are creating. By reflecting a laser off of a mirror that's attached to your plane, tricopter, quadcopter, or multi-rotor you can easily see and and correct balance and vibration issues!

laser-balance8.JPG

The effects of an unbalanced prop or motor can be seen with your FPV with the onboard camera causing a jello-like, wavy, warped video playback. You can also sometimes simply feel the vibration by touch as well.

laser-balance2.JPG laser-balance4.JPG

The idea is simple, point a laser towards a mirror which is attached to your multirotor arm, plane or where your onboard camera is setup. Reflect that laser off of the mirror and onto a wall.

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The dot that is formed on the wall while the engine is off is what you want to match when your props are running. Unbalanced props will result in wavy or elongated deformation of that laser dot reflection.

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Add or remove tape from your prop and try again until the vibration is to your satisfaction.

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This is a great way to test the vibration of any area of your RC plane or multi-rotor, attaching the mirror to any place you want to 'see' the vibration.

We got the idea from this youtube video:
http://www.youtube.com/watch?v=QnjflLDxQQU
 

colorex

Rotor Riot!
Mentor
#2
Amazing cool trick! And really useful! I guess if you get the reflection further away it amplifies the visibility. Also I think it should work well if you place your mirror on the camera mount.
 

colorex

Rotor Riot!
Mentor
#4
If you have a small pointer laser, you could simply mount it on the boom. No mirror needed!
OK, now you beat us all.

Except the mirror multiplies the vibration by 2 - because say a 1 degree rotation of the mirror (caused by vibration) will increase the angle at which the laser hits it by 1º AND the angle of the reflection by 1º. If you only use the laser, 1º rotation will mean only 1 degree laser deflection which isn't as good.
 
#8
I salvaged surface mirrors from an old SCSI scanner and stuck them to my Quad. I used a cross laser to make it even more visible if the vibrations was up/down or left/right

Quite useful

//UndCon
 
#9
Has somebody an idea where to get upfront mirrors. Would disks out of an old hard disk work? I have so many old hdds around I would not care much about loosing one. Or is there another way to get those. Are they used somewhere else and you can get them hardware store?
I have just bought a big nice Prop Balancer from but it would be a cool way to balance the motors like he did in the original video.
 

colorex

Rotor Riot!
Mentor
#10
Has somebody an idea where to get upfront mirrors. Would disks out of an old hard disk work? I have so many old hdds around I would not care much about loosing one. Or is there another way to get those. Are they used somewhere else and you can get them hardware store?
I have just bought a big nice Prop Balancer from but it would be a cool way to balance the motors like he did in the original video.
Yeah, if I remember correctly and a hard drive disc is like a mirror, then it should work. Just shine a laser on it and see if the reflection is perfect or not.

Hard drives don't have glass on them :p so they should work as long as they are reflective.
 
#11
Yes the HDD-surface is shiny - almost mirror like (I have a bunch at home)

Surface mirrors are also on overhead machines but they are usually rare nowadays
 

Joker 53150

Mmmmmmm, balsa.
Mentor
#12
This looked like a really good idea so I decided to give it a shot on my Super Cub, as I had just balanced a couple props for it (it's too windy to fly, so I've got to do SOMETHING...).

I found an old DVD and tried to break a small section off. No dice, it just bent in half. I'm not sure if this means it's a cheap DVD or a high-quality one... No problem, an "L" shaped piece would be easy to set on the wing, and could be held down with a little tape. I taped it down far enough out to avoid the prop-wash and tried it with a laser level, and found there was a fair amount of vibration starting at around 1/3 throttle. Not a ton, but I could feel it as well as see it now.

Before I started trying to balance the prop more to reduce it, I remembered that the inspiration video for this segment was showing it to reduce MOTOR vibration, not prop-balance vibration. I pulled the prop from the SC and tried it again, and found that just the motor without prop still gave me vibration starting again at about 1/3 throttle. I'm running the stock HZ motor, which probably isn't the highest quality unit on the planet, and I'll assume that the prop vibration I was getting was originating from the motor vibration.

Considering the motor is providing at least some of the vibration, I assume there isn't much sense in trying to get the prop balanced using this method since I'll be back at square-one once I swap props or remove it and re-install it again. As a new pilot, there is always some prop replacement happening after my flights. :p
 
#13
You can balance the motor as well as the prop.

Sometimes it can help by loosening the prop and turn it a bit on the axle - than fasten it again and try.

//UndCon
 

colorex

Rotor Riot!
Mentor
#14
True. But even a well balanced motor running a well balanced prop can give you vibrations! Especially if you need to drill out the props yourself!
 

JayFly

Junior Member
#16
Im Confused???

True. But even a well balanced motor running a well balanced prop can give you vibrations! Especially if you need to drill out the props yourself!
What is the difference between a magnetic balance and the laser shown on the video? I can see that it can also do motors but how??:confused:
 
#17
What is the difference between a magnetic balance and the laser shown on the video? I can see that it can also do motors but how??:confused:
do you mean magnetically balanced props? If so ill try to sum it up in as few words as i can. Even if you "balance" a prop and "balance" a motor, it does not mean it is perfect. Both will be off to a certain degree and if some how both prop and motor are in the right spot, it could be out of balance as a whole unit. This laser method would be the optimal way to "fine tune" the pair together. There is also a subject called harmonic balance. A vibration can get worse at certain speeds and cause a harmonic disturbance and this can help fine tune that as well. Best way to find the best balance spot is to fly your plane,quad....etc and listen and see if you hear any type of unusual vibrational noises at certain RPM or positions on the throlle of the Tx. make a note where your throttle is at and test it out with the laser balancer.

Hope this helps and if it wans't what you were talking about then just ignore all my blabbering lol
 
Last edited:

Cyberdactyl

Misfit Multirotor Monkey
#18
Yes, +1 for Bigshow. Harmonics can find its way into many systems, even though everything seems to be finely balanced.

Another problem multi-rotors have, and is over-looked ALL the time, is the rather large planform under, or over (V-tails) the prop disk projection. I'm sure everyone has seen quad designs with no real consideration of the obstruction of the air flow. Every time the prop passes over (or under) the boom it gives a little thump to the boom, which is in turn transferred to the center structure.

Another phenomenon that probably results from the prop passing over the boom is known as Aeroelastic Flutter. However, this effect is not a structural safety concern unless the boom is severely under-designed, but may add minutely to vibration.

It would be fairly difficult to empirically estimate the severity of any harmonic or flutter effect from simply looking at the prop diameter and planform obstruction, since there are several variables within each component. Prop distance above the boom, prop profile, prop pitch, boom size, boom rigidity. motor torque etc., all are playing a part.



 

LokaDesign

Just starting!
#19
This looked like a really good idea so I decided to give it a shot on my Super Cub, as I had just balanced a couple props for it (it's too windy to fly, so I've got to do SOMETHING...).

I found an old DVD and tried to break a small section off. No dice, it just bent in half. I'm not sure if this means it's a cheap DVD or a high-quality one... No problem, an "L" shaped piece would be easy to set on the wing, and could be held down with a little tape. I taped it down far enough out to avoid the prop-wash and tried it with a laser level, and found there was a fair amount of vibration starting at around 1/3 throttle. Not a ton, but I could feel it as well as see it now.

Before I started trying to balance the prop more to reduce it, I remembered that the inspiration video for this segment was showing it to reduce MOTOR vibration, not prop-balance vibration. I pulled the prop from the SC and tried it again, and found that just the motor without prop still gave me vibration starting again at about 1/3 throttle. I'm running the stock HZ motor, which probably isn't the highest quality unit on the planet, and I'll assume that the prop vibration I was getting was originating from the motor vibration.

Considering the motor is providing at least some of the vibration, I assume there isn't much sense in trying to get the prop balanced using this method since I'll be back at square-one once I swap props or remove it and re-install it again. As a new pilot, there is always some prop replacement happening after my flights. :p

Hi Joker,

You can balance your motor without the prop on, you just put a zip tie around your motor. Or 2. I ve seen our Swedish David do this in one of his vids.