Drive Train Questions

[Ryank]

The thought for us is to be able to turn with minimal voltage (after assembling the kit of parts into a minimal chassis robot we realized that it drew the battery down to 10-9.5V constant when turning with about 110 pounds on it). We obviously would like to cut that 2.5V hit on every turn to about 1 to .5 volts (or you could think of it in terms of amperage draw, whatever you like, I think that voltage draw also draws enough amps to come pretty close to blowing the 40 Amp breaker). Anyway, sorry to ramble, our idea for drive train, admittedly derived from other very successful robot in the past is the standard six wheel design with two omnis in front and in back and two 2" roughtops in the middle, directly driven by two super shifters with the 48:17 tooth gear set. My question is, will having only the middle two of the six wheels lead to problems? I know that it will cause the robot not to drive straight but we could fix that with a gyro and a little programming right? Or is there a better way to straighten it? We also don't think we'll put any cradle or rocking in the wheels like some, because we have a moderately top heavy robot.

[AndyB]

Sounds like you have a good start. You are correct on your 6 wheel design and it should turn pretty easily for you. You will be ok if you decide to only drive the middle wheels even. With 6 wheels and omni's on the corners, you will not need to lower the middle wheels. Although if you are using the kitbot frame, you will have to move the center set of wheels either one hole forward or backwards as the center hole is already lowered.

Just as easily though, you could try the kitbot and replace two wheels with omni wheels.

You could try front omnis, rear omnis, or corner omnis and it should make turning much much simpler. If you do decide to do corner omnis, make sure you check out the Martians (494 and 70) who both rely on the design consistently and successfully from year to year.

[Ryank]

What is the difference between the six wheel and four wheel drives, in terms of pros and cons for each? Also, would it be just as fine to direct mount the super shifter to the drive wheels or is it better to use chain and sprocket?

[AndyB]

If you direct mount the wheel to the supershifter (which is very possible), I would advise getting the 2" longer shaft that is sold seperatly and supporting it on the other side of the wheel as well to prevent ugly side loads.

4wd and 6wd are very similar if you are using a combination of omni's and conventional wheels. It's just a matter of the location of the turning axis. It is also important to know if you want to do a 6w or a 6wd. 6w like I think you are talking about would be 4 unpowered omni wheels and 2 powered conventional kit or traction wheels in the center. So it would be a 2wd.

However, 4wd with wheels in the back and omnis, casters, or skids in the front should be nimble enough to get you where you want to go. The rotation of your turning will be in between your two conventional wheels.

On a 6w design, your turning axis would be centered on the robot.