Swerve Drivetrain.

[Joe G.]

Originally Posted by PAR_WIG1350

I was under the impression that coaxial module swerve was (usually*) the more flexible of the two due to the deletion of electrical connections to the module thus allowing the module to rotate directly to the desired position (for example, a 10 degree rotation in a coaxial setup could translate into a 350 degree rotation in a MOM (motor on module) setup). I am currently working independently on coaxial swerve and how to unlock it's full potential. Technically, due to the allowance of slip rings this year, MOM swerve is superior due to the greater efficiency that can be gained by eliminating the 90 degree transmission necessary for coaxial modules and the removal of MOM's limitations by the slip rings allowing unlimited rotation of the modules. One key design feature to fully utilize the abilities that swerve can give you is the independent steering and drive of all modules. After venturing into the 'branch' of swerve that I have, It is difficult to look at front/back // left/right linked swerve and say that it is even approaching all of the benefits that a fully functional swerve drive train has to offer. (NOTE: I plan on releasing that white paper I promised eventually).

My statement is based around the fact that non-coaxial modules are, by nature, independently powered, while many coaxial swerves power the modules in pairs, or even from a single "power plant" swerve, as 118 often does. Putting multiple modules on a single power source limits some of the motions you can make.

For example, say you have your modules steered in front/back pairs, and powered in left/right pairs, as many (most?) coaxial swerves do. This setup excels at akerman-style steering. But tank style steering is impossible in any module orientation other than "forward," and in long orientation, with four traction wheels, may even be difficult there. Motor-in-module setups, however, would allow tank-steering in any orientation; forward, sideways, and probably diagonally to some degree.

This downside of coaxial is considerably more apparent in a 118 style setup. With all wheels tied to the same motor, there can be no variance in their speed. This makes any kind of tank steering just about impossible, and for this reason, all robots that I know of built this way have been either turreted, or had no real "front" (think 148 in overdrive). Which is something that a team may or may not be able to fit into their design.

Admittedly, it's not a huge downside. And you're correct, ignoring the possibility of slip rings, having infinite rotation of the modules is a big plus for coaxial. If you can do a independently powered, independently steered "pivot drive," more power to you, but that's not an easy undertaking. Which system is right? It depends on your robot, what you have experience making, and which set of pros and cons you think is best.