Killough platforms (A.K.A Holonomic/kiwi drive)

[jgannon]

I don't know much about kiwi drive, other than watching the original video and the 229 parody, but maybe I can still help you.

The vast majority of DC motors are designed to run more efficiently in one direction. This is a function of how the motor is wound. This difference was very drastic in the drill motors last year; I haven't found it to be as severe in the CIMs this year. If I had to fix this in software, I would take a CIM motor, and hook it up to a Victor. Pick a few different clockwise PWM values, and measure the speed with a tachometer (you can make your own with an encoder). Then output the equivalent values to spin the motor counterclockwise. Keep note of the speeds, and then do a calculation to slow the motor when it's running clockwise. For example, if the motor runs twice as fast clockwise as counterclockwise (a gross exaggeration):

if(pwm15>127)
   pwm15=(pwm15-127)*.5+127;

Hope this helps.

[Joe Ross]

I beleive it took 1083 several regionals before they were able to get thier robot driving straight last year.

[Adam Krajewski]

The way we controlled our Killough platform back in 2002 was a completely analog solution. We used three joysticks mounted in the same orientation as the drive wheels (120 degrees apart), mounted together using ball joints like so:

This was back in the PBASIC days. It may be low-tech, but it certainly worked: http://stuweb.ee.mtu.edu/~alkrajew/FIRST/kiwi.mpg

[Alan Anderson]

Originally Posted by Adam Krajewski

Wow. Just...wow. $@#$@#$@#$@#, that's awesome. The forums don't like the words going through my head as I see this, but I can't find better ones to replace them.

[MattB703]

In my dream of a 4 wheeled Killough drive bot I was going to turn the handle of a joystick to 45° from the base of the joystick. If you push the joystick strait up you get full + X and full + Y. You can map the drive motors directly to the joystick values in such a way that the bot moves in the direction that the joystick is pressed. You would also need a rotary pot to control the rotation of the bot.

[Greg Ross]

Originally Posted by MattB703

In my dream of a 4 wheeled Killough drive bot I was going to turn the handle of a joystick to 45° from the base of the joystick. If you push the joystick strait up you get full + X and full + Y. You can map the drive motors directly to the joystick values in such a way that the bot moves in the direction that the joystick is pressed.

I did this last year. It worked, but I couldn't get used to the way the joystick felt in my hand. I had a hard time moving the stick along the diagonal when going straight forward and reverse.

You would also need a rotary pot to control the rotation of the bot.

I used the joystick thumb wheel for this (NOT the trim wheel!). Again, it worked, but I didn't like it because it didn't self center when released.

[ajlapp]

as adam already posted the analog joystick solution is very easy to construct and works flawlessly without any programming....i repeat, no programming!

my suggestion is to build one and then work on a slick programming solution if you still feel it's necessary.