Drop-center drivetrains: Why?

[JamesCH95]

Originally Posted by billbo911

Now, if you want to climb a ramp, or go over a bump, then omni's on the corners add a whole new level of difficulty. I'm not talking so much about traction, but the need to hit the incline squarely. If you are out of alignment by only a few degrees then the robot will tend to slide out, or fall back to the level surface. The steeper the incline, the greater this effect will be.

Although we did not use omni wheels this year, we did us mecanums, and we noticed that the robot wouldn't glance off inclines, but rather tend to align with them. There probably is some angle where the robot would tend to glance off rather than self-align, but my experience tells me that this angle is sufficiently wide to easily drive over a bump or up a ramp.

Originally Posted by Chris is me

I really think "just use omnis" can be a pretty poor solution depending on the game challenge. If you have a long arm, a gentle tap moves your game piece several feet away and there's not much resistance to speak of. Really, it's not that hard to do "all of the analysis". I can tell you what the analysis will say right now: The more rigid your chassis, the better your 6WD can perform. Building a rigid chassis doesn't take tons of time and energy. Even if you do want to do careful and thorough analysis for such a drivetrain, it's not exactly a huge resource drain, and depending on the challenge it could result in a much, much better chassis for your needs.

While some games you probably could get away with a chassis with four omnis, in the past I think more often than not you couldn't. Being spun off target in Aim High, knocking you away from your spider leg in Rack 'n Roll, or taking a mid to long range shot in Breakaway are all situations when I'd rather have a bit more resistance to being spun.

Perhaps you did not understand that I was referring to a 6wd chassis with two traction wheels in the center and four omni wheels on the corners. In my experience these have been fairly resistant to being spun and do not rock much, if at all; a good compromise in my opinion.

I was not referring to a chassis stiffness analysis, but rather keeping track of CG location for the purposes of reducing rocking while manipulating a game piece. While these are both straight-forward analyses to perform, not every team has a lab full of CAD-capable computers and/or trained operators ready to do them.