Prop Balancing by Laser???

[Opto-Mystic]

I just watched this vid on using a laser to balance props. As a new comer to this ';science';, it looks interesting.

Flite Test - Laser Balancing Props - FLITE TIP

Any comments? I am going to give it a try.

A laser pen on eBay is less than a tenner - the mirror is a little harder to come by ...BUT if you have a defunct scanner, don';t just dump it, strip it down. It contains an optical grade strip mirror with the mirroring surface on the front, \It also contains stepper motor/s and a myriad of useful bits and pieces that you can use to clutter up the ';Useful Bits'; box. However, there is another very useful bit in the old scanner: a beautiful lens that can be used as an inspection loupe. Very handy for looking for dry joints etc...

[flybywire]

Donald, I watched this clip some time ago, and thought it useful.  However, I believe that it';s possible to balance motors/props by ';feel'; quite well.  Just do one at a time, spin the motor up gradually, holding the arm firmly (of course) as soon as you feel some ';bad'; vibes, turn off and tape a blade and re-test.  I don';t think you can ever get it 100%, but 90% is good enough.  If you buy decent motors & props, you';ll find they';re pretty well balanced anyhow.

[Opto-Mystic]

Thanks - I had thought about the the ';do it by feel'; method but dismissed  it as not accurate.. maybe as I get more experience in these matters, I might be blessed with that skill.

[Hands0n]

A lot of people do simple static balancing with one of those magnetic devices. It works really well, as I found out with my APM 2.5 adventures earlier this year. 

The ultimate form is active, as demonstrated in the video. But it isn';t as straightforward to do.  I would worry, however, about using the "feel" method.  Those props can be very unforgiving if you get it wrong, and it all happens very quickly indeed.

SunnySky motors are factory balanced, so only need the props and their hubs balancing.  I can';t speak for other motors, but I guess others will be.  Turnigy, in my experience, are not!

[Opto-Mystic]

Hi Danny... I have had issues with trying to balance props - I have just tried the laser technique & found it easy to set up and do. The following is a write up of what I did and how I did it... For me, the Laser Method Rocks  


Well, well, well! I am very surprised at the ease of balancing this is. I found it very sensitive and apparently very accurate.

The ethos I adopted was ';consistency leads to repeatability and accuracy'; ...

My kit:
* A small red laser unit salvaged from an old spirit level. (Cost when the level and tripod was new at B&Q £10)
   (Do an eBay search for a laser pointer.)
* A small mirror. (salvaged from a defunct scanner) I put a small strip of double sided carpet tape on the back
* small vice to clamp the laser unit on.
* a roll of sticky insulating tape (for balancing)
* Bottle of  Tipp-ex ( for marking parts)

Once set up, I had balanced the four propulsion units on the quad in about half an hour. I say propulsion unit because following the methodology, balances the outer motor case, prop hub, prop and the prop nut as a whole and not just the prop.

Methodology:
I did not disconnect any of the motors. Each of the 4 motors were powered up in the process.
My quad has the larger landing legs that lift the motor arms above the deck. If your drone relies on the short stubby legs on the arm, you will need to lift the legs free while doing the test. I suggest a book or something similar under the body of the drone.

Preparation:
1) First, remove all props.
2) Mark each arm with its appropriate motor number (I used a CD/DVD pen)
3) Mark ONE tip of each arm PROP with a small touch of Tipp-ex.
4) Mark the orientation of each prop to the orientation of the motor shaft and on the outer casing of the motor. (I used a small dollop of Tipp-ex.)
5) Using the CD/DVD marker pen, give each prop the number of the motor it will be associated with. The same with each prop nut. I don't believe the nuts will be out of balance anyway but there is no harm in being consistent.

Balancing:
6) Still with no props fitted...
7) Connect freshly charged battery
8) Attach the mirror to the stubby leg on the end of #1 motor arm, using double sided sticky tape
9) Put the drone in position with the mirror at 45 degrees to the laser, the laser should be in front of the drone. The reflected laser spot will be projected a 90 degrees, hopefully on to the wall adjacent.
9) Arm and start up the un-propped motors on slow revs. Adjust the laser and mirror so that you can see the projected spot on the adjacent wall.
10) Holding the top of the drone to stop it from moving, slowly rev up the motors and observe the laser spot. Hopefully, the motor will be in balance and the spot will not move.
11) Stop motor.
12) Install the prop and nut in the orientation previously marked.
13) Arm & start motor on low revs – observe the laser spot.  Keeping your hand and arm well clear of the prop, apply gentle downward pressure of the drone. ( You don't want it tipping over during the next steps)
14) Slowly advance the throttle to rake off speed and to flying speed. Observe the laser spot. If it doesn't move, it may well be a well-balanced propulsion unit. However, deliberately unbalance the prop by adding a little insulating tape on one side of the prop (Note which side, the one with the Tipp-ex or the other) and do the test again. This time there will be a marked difference in the behaviour of the laser spot!

At this point you will have to experiment with the size and placement of your favourite balancing tape until you get the spot to be as steadty as possible. Once yiou are happy with the balance of the prop, remove it and its nut from the motor and start over again at (8) above until each motor unit is done in turn.

When finished, remove the battery and assemble each prop on their respective motor, observing the orientation of the prop on its shaft and lock it down with its nut. You're done. Now go for a test flight.


A note on motor balance:
I have only seen the inside of two motors (different manufacturers). Both had some hardened 'goo' that was obviously there to balance the outer case of the motor (as my daughter would describe it: "the spinney round bit"

One of these motors I noticed had some metallic debris (AKA: FOD) stuck between some of the magnets. This could have been ingressed during a crash near metal shaving contaminated ground or even if the motor had been rattling around a tool box or other environment where metal shavings were present. The magnets are extremely powerful and can attract fine metal FOD during its life. At the rotational speed the spinney round bit travels, this could/might//may/will unbalance the motor.

The method I adopted will counteract any unbalances in the motor case, propeller boss, propeller and its nut.

EDIT: correction of (3) above...