The accompanying swerve module for the swerve base I posted. Built around the excellent Revolution Pro 2 wheel module. Currently geared at 5.75:1 for an adjusted free speed of 10.6 ft/s, but that can easily be changed up or down by swapping out sprockets. VP encoder at 1:1 for turning and SRX encoder for speed. Shout-out to the Robostangs for the SRX encoder mount from their off-season swerve base (I’m using a slightly modified version here).
CAD can be found here!
This view has the tube transparent.
This shows the pocketing on the bottom of the turning gear which leaves room for the VersaPlanetary’s mounting hardware.
What’s the gear ratio for the VP?
I figure if we actually build this I’ll go with 90:1. The Robostangs’ off-season swerve had the same steering setup but they used 50:1 (which I thought was surprisingly low when compared to something like the AndyMark Swerve & Steer module, but they said it worked well for them). I think you’d need something like 120:1 in order to match the steering RPM of the AndyMark module, but I didn’t want a 3rd VersaPlanetary stage because I felt that put the BAG motor too close to the ground.
Have you considered putting an idler gear on there and doing one reduction in the spur gear stage? Probably a bit more weight and part count but it would give you some flexibility.
I was thinking about that, but wondered if it would compromise the steering encoder setup. Currently the steering encoder is a VP integrated encoder after the last stage, and the external gears are 1:1, which means the encoder is 1:1 with the wheel. Does that mean you can use the VP encoder as an absolute encoder? I should probably make a point of knowing more about the encoders needed here… If you had such an external reduction, would you need to mount a separate absolute encoder somewhere else?
You don’t need a 1:1 reduction for an absolute encoder to work, you just need to be sure you account for reduction in the code (and if your encoder has a deadband or something you need to make sure that isn’t a problem). The VP encoder can be used as an absolute encoder. I don’t know too much more about the details of electronics, but your mechanical design isn’t necessarily constrained by your encoder here.
Adding idler gears after your encoder increases the potential for cumulative position error from backlash. Granted, there’s already a 1:1 spur gear relationship after the encoder, so that risk exists already. But more gears just compounds that risk further.