Quote:
Originally Posted by Aaron Ng
Ackerman steering sounds quite difficult to design as well as build.
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As you have limited your acceleration by only driving two wheels anyway, steering two
unpowered wheels is not terribly complex. If you're only driving two wheels, drive them together (perhaps with a solid shaft), and have one shifting gearbox that drives it. Hopefully you can get away without a differential. Then, make a parallelogram with hinges, with one edge being the frame chassis and the two adjacent sides mounting idle wheels. Use a motor geared really low (I'm thinking an AM PG188, but the may be a better answer) to steer it. As I read your last post, it seems that you need to steer most early in the run, while you are significantly accelerating. In this case, it may make sense to use front-wheel drive and rear-wheel steer.
Also as for making it aerodynamic, it wouldn't be optimal, but you could do a lot better than having open equipment by simply putting a fairly sheet of plastic over the top and bottom of the robot, a half-cylinder on the front (perhaps a PVC pipe cut lengthwise), and a bit of wedged tail.
Finally, I agree that more shifting range would be better than more CIMs in trying to get an intentionally light robot from zero to 75 using a single FRC battery. I would use cascaded shifters, with one at around 4:1 and the other around 2.5:1 (gearboxes near these ratios are available off the shelf), then you can get composite ratios of 1, 2.5, 4, and 10. If custom designing shifters, I would aim to make one of them the square of the other (e.g. 2.5:1 and 6.25:1, giving ratios of 1, 2.5, 6.25, and 15.625). While I have never tried to shift directly from the CIM, I can certainly see how it would be a problem; moving the shifting as close to the wheel speeds as possible makes sense.
Caveat: I have not built any of these things; just a geek with a couple of physics degrees and three+ years of experience in FRC.