Hi All,

I'm not sure if this is the forum to place this, but it just might be interesting to some of us..

A while ago I was waiting for having my car-tires balanced when I thought that must be possible with my motor-prop combination as well.
So what I did...
Got an old 9DOF razor board from Sparkfun, a motormount, a laserpointer, old transistor uses as light sensitive element, ESC and some programming skills and assembled this into a "Dynamic outrunner and propellor balancing Unit".
The razor board is equiped with an 8 MHz Atmega 328 chip that drives the ESC and reads the light sensitive transistor. Communication to a PC application is done by serial I/O
How it basically works:

- connect the razor serial port to your PC running the visual basic application.
- place the outrunner with propellor mounted on the stand. This stand is flexible mounted on the wooden base plate.
- mark one blade of the propeller with a marker. With each succesive balancing-run this marked blade should be on the same starting position.
- on the pc-application click the "RUN" button.
- now the motor runs from 1000 to 3000 RPM while the accelerometers on the razor board are constantly read. The measurements are sent to the PC-app.
- this pc-app shows the place where a counterweight should be put. It also kind of indicates the mass of it.

Done this several times to test the system and till now it works very well :-) I noticed that not only propellors need balancing, but also the outrunner itself. Could just be poor chinese quality as well :-(
All video's I shoot with my quad are without any halo-vibration-effect since and the quad is vibration free.

What else did I do:
- motors are mounted with shock absorbing supports.
- I removed the circlip from the outrunner-axle. This not only makes the balancing action very easy (just pull off the propellor unit) but also saves the bottom ball-bearing from excessive wear. I know some people may say
this is dangerous, but I never experienced a lost propellor. Every 50 flying hours I replace all bearings with quality european bearings.

Config:
motors: 4 X KDA 20-22L from Hobby King
Prop: APC SF 4,7 * 10
APM 1.4 Hotel & Oilpan with selfmade MS5611 baro-modification
ESC: Turnigy 25A basic 3.1 met simonk firmware, all calibrated manual
3DR radios 900 Mhz, HF decoupled by ferrite ring
sparkfun compass removed from frame by Starship Enterprise construction, shielded cable
Ublox LEA-6 GPS
RX/TX 40Mhz Robbe/Futaba F14 8 channel, ch5:6-way diy-mode-switch, ch6:potty, ch7 extra switch
No sonar
Lipo 4000 1p3s
2 X ubec DE-SW050 Fixed 5V switching regulator(http://www.dimensionengineering.com/products/de-sw050) both with 220uF, 10uF tantal and 100nF parallel. One system for apm + RX, the other for, leds, 3DR radio
4 Ledstrips, discrete driver 2n2222 (yes, leftovers from the stone age)
quad made of: carbon en forex (= foamed PCV). The carbon arms are two crossed rods of 1 meter each.
motors on flexi mounts
apm, dampening with 2 millimeter neoprene + aluminum.
Powerboard: diy 2 * Y, wires to motors not yet twisted, but no effect on compass
No bullet connectors to ESC and motors, all soldered
Camera Canon A3300 with CHDK hack for interval shots and RAW images, even movies are good (love it)
Camera gimball: some chinese carbon thing, works well. 2 X Hitec HS-322HD servo

Total weight: 1.8 Kg w/ camera & gimball, Flighttime 10 min, without camera 12 minutes.
Size M2M diagonal 75 cm

See attached files for pictures and pc app screen dump

Off course, I'll be happy to share code and more insight information if anyone is interested.

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This sounds like a product. You should sell these.

Balancing the motor and prop together is a splendid idea.  As Jason suggests, you should kit this together and sell it.

This is amazing!

Are you doing a 2D balance, or a 3D balance?  The tire balancers actually do a 3D balance, that is why there are different weights on the inner and outer lip of the wheel.  You can still get a little wobble if you don't do this.  I requires measuring not just accelerometer readings perpendicular to the shaft, but also the rotational vibration across the shaft.

If this could be set up such that you could leave your motors in place, on your multirotor, have the system simply drive the existing ESC, and then balance the prop/motor on the airframe, that would just be... mind blowingly awesome.

Very nice! This is very similar idea to what i've been using for years with 1:1 size experimental helicopter rotor balancing :) 

If anyone wants really vibration free copter this is the way to go. I have only balanced separately my quad motors and props, but now after this info i'm thinking to do it dynamic too....

I'm very intrested to see more information and perhaps code, although i'm noob with programming.

-Jani-

Sweet. Let me be the 3rd person to say, you should sell a kit. I'd buy!

Thank you all for your comments, I really appreciate it!

Well, I don't have that much experience in assembling kits (none actually) so a few answers would help me understand the kind of kit that would fit the most of us.

- should it be a nice little plug-and-play box having connectors for battery, usb, motor and optical unit, or

- a little diy action like assembling the parts together is allowed.

In both cases the only thing you will have to bring in is your own motor and heavy-mass baseplate. A little action is also required to mount the motor to the motor base and mount the optical unit.

@R_Lefebvre: Thanks for your remark! I do a 2D balance. I didn't explore the realm of 3D yet because the results of 2D are really good already. However, I like the idea of making it next to perfect, so I think I start experimenting reading the Z axis also and see what happens. It also may require a second acc-meter on a different position.

Mounting the unit to a motor fixed on your craft should be the end picture. Ohhh you just got me inspired: there is an accelerometer, atmega, USB and ESC to every motor allready mounted close the the motor: it's called APM :-) I will definetely try this!

@Jani, I'm working on more info...keep folowing this thread..

Greetz, Frank

Frank,

could You make a part list and a short assembly instruction on how to put the parts together?

The approach is really good and in the very spirit of DIY!

Of course, balancing directly with the apm would be very nice, but I would like to have a standalone solution to be able to balance all of my props/motors of my flying circus!

Regards

Marc

Hi Marc,

The code only runs on the razor 9dof board at this time. Is that the one you have ?

Running on APM didn't work well. Due to the filter capacitor on the accelerometer-analog-output-line the max sample frequency is too low to detect vibrations effectively (and that's why they are there of course)

Regards, Frank

Frank,

I currently do not own a Razor IMU, but I don't mind to buy one if i get well balanced props and motors as result.

Hi Marc,

Ok, then you can buy one and be the first beta-tester of the software :-) The current one sold on sparkfun.com is not exactly the same as the one I have, but the ADXL345 is on board so it will work for sure. Also make sure you have something like the ftdi breakout board to connect it to your pc-usb. The razordboard runs on 3.3v and can be powered by the ftdi breakout board. Please don't blame me if after selecting other hardware for the kit it ends up being cheaper than this set.

There's no kit yet, so you will have to make some kind of optical system that produces a logical high or low (doesn't matter) when a prop enters the beam. Can you do that ?

For the ESC I advice you use a Simonk flashed one. It runs smoother so causes less interference in the accelorometer. The motor needs to be mounted flexible obviously.

I suggest to take this part offline until we have produced a working setup and than return with results and conclusions. Is this ok with you ? Please PM me to discuss details.


Regards, Frank

Frank,
right now I am flashing my Esc's with SimonK's firmware. First results look promising, the motors run a lot calmer.
I have an ftdi flasher board and several atmega developer boards, so this should be enough hardware to play with.
The light barrier for counting the revolutions shouldnt be a problem, i will have to look for some parts to accomplish this.
Lets discuss the rest via email or skype.
Regards
Marc

Looking at your quad's frame, that is a nifty idea to have longer arms, and pay a few grams of extra weight to get some protection from walls and other collision hazards. (and like others have said, I would buy a kit if it were available...)  Oh, and thanks for making me feel old ( "...2n2222 (yes, leftovers from the stone age)"...) LOL

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