Coaxial Swerve Derivation with Paired Modules

[Aren Siekmeier]

Originally Posted by Tom Line

Has anyone performed a similar variation for a paired-module swerve where 2 have 2 sets of modules, when each set has linked steering and drive?

To more explicit, picture 4 modules where the left side modules are turned and driven together, and the right side modules are turned and driven together.

For the kinematics: first take the equations for 4 wheels. A wheel's velocity is given by:



where i is the index of the wheel, r is its position vector relative to robot center, v is the velocity of the robot, omega is the rotation of the robot (counterclockwise around robot center). However, by pairing up modules, you introduce further constraints on magnitudes and directions of wheel velocities. In your case, you are requiring for some pair i,j:



or very close to zero (the wheels are allowed to scrub a little). But this means either you aren't turning very much at all, or your paired wheels are nearly on top of each other.

For other pairings you can follow a similar process to figure out what motions are still allowed. Calculate wheel speeds and directions as you would normally, then average them for each pair output, so that the pair outputs are the same, and it should work, though some motions may not be possible.

I believe it was 2451 who had a nice table of all the different ways to pair up modules for both power and steering, and the motions it allowed. I've been unable to find this anywhere online however, so I must have seen it in their pit. The paper by Nate Laverdure posted below is what I was thinking of.