Robot refuses to turn!

[Edoc'sil]

Alright its the last few days of the build season and everything is going fine. Our kicker is looking good, electronics are mounted, and our weight is right at where the CAD model said it would be.

Well almost everything is good, our robot won't turn.

We built a basic six wheel design. There are 6 8in plaction wheels, 3 to a side, all hooked up by a chaindrive, so all 6 wheels are powered. So we take a battery reading 12.5 volts and the thing flies forwards beautifully. Next we switch up the wires so that one side is going forwards and the other back so we can test our turning. It doesn't move at all. We take a look and we realize we made a design mistake, the distance between our front and rear wheels is greater then the distance between the two sets of wheels. Oops. So no big deal we think, we can fix it easily enough. We pop off our front wheels thus halving the distance between our "front" wheels (the old middle ones) and our back wheels. We then go add the power again and it still doesn't turn at all. With a bunch more testing we find out that the only way we can get our bot to turn is if all the weight is supported by one parallel set of wheels.

Our bot has a 24 to 1 gear reduction, so that translates to about 6 feet per second under normal load, and when moving forward our bot does close to that. Perhaps 4 to 5 feet per second. the distance between the one wheel and the next is 12.5 inches and the distance between one drive and the other is 24 inches. Nothing is jamming, the motors are spinning all in the correct direction when we take the weight off the wheels but no matter what we do the bot will not turn under its own power. Are we breaking some kind of cardinal rule here? I would appreciate any input.

We thing the best fix will be to replace the front and back wheels with omnis, leaving just the middle ones being plaction wheels. We hope this will solve our problem, but we do not want to throw $200 bucks at the problem unless we know it will fix it.

Final thought. We were testing this by hooking up the motors directly to the battery. I assume many people will tell me this is a bad idea, maybe for safety reasons, maybe because its hard on the motors etc. I just want to say that I am aware of the risks, but we needed to know if our robot would work at all not two days from now after we have figured out that the problem wasn't an electrical one. If we would have hooked up the motors to the jags and run everything the way it was supposed to would it have any significant improvement in the performance of our bot?