Offseason Swerve Module

As a small offseason project, I decided to design a swerve module with the main considerations being as compact as possible. The entire module is only 6.4" tall and has a footprint of 7.125"x7.125".

This module uses 3D printing extensively for the wheel mounts, the azimuth and the azimuth driving gear, the steer pulley, as well as the MA3 encoder mount. The azimuth itself has two teeth profiles, each of them offset from the other by half a tooth to help reduce backlash. The free speed is 16.1 ft/s.

Some pictures:

CAD:
https://workbench.grabcad.com/workbench/projects/gcXV6lTLgzTby417nqfjeoAGxndqYYqNjnilg7zfp8o89c#/space/gcD2ALIKPie-yfblIn57KRmy2za7ztNBsRBvWSiY8129IF

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I might be wrong but looking at that, the 4 corners of your drive base would be held together by the swerve module. Wouldn’t that put an unnecessary load on them and reduce structural integrity as opposed to a rigid frame?

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Yes, they would be held together by the swerve module, but also by the belly pan. The reason for this is to push the wheels further out leading to a more stable drive base. The idea comes from 33’s 2019 Offseason Module

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To be clear, we still brought the frame tubes to the corner of the modules so that it was still a rigid frame. I would have some concerns about the above frame holding up.

Also, I would remove the plate material outside the falcons as they are not adding any rigidity and would make it easier to remove the falcons when needed.

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I’d add a 1/4" aluminum bracket to the bottom of the frame, so you can switch modules without the frame coming apart, and to add extra strength, because idk if one plate will hold super well

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How do the offset azimuth pulleys help reduce backlash?

Here’s two pictures demonstrating the idea. The gear with the red arrow cannot rotate counterclockwise anymore since there are two points (next to the red dots) on the gear tangent to the other gear. Hence, it is in the position with the most backlash.

However if you look at the profile on the other side of the gear, motion in the clockwise direction (since its the opposite side) is reduced due to the fact that next to the green dots the teeth profiles are intersecting. Hence, the position shown in the first image is only possible with one tooth profile, however if the second offset profile exists, the position in the first image is impossible. Hopefully this gives an idea as to why there’s less backlash.

Edit: This wireframe should make it more obvious the intersection of the teeth profiles in the second picture

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That makes sense now. Thanks!

idk but I feel like this is semi unnecessary, we 3dprinted our gears, and they have no backlash (almost the same setup as you)

It cuts down the backlash by almost 50%. Was it cool to experiment with: yes, is it necessary: not really.

ah, interesting.

While it’s a neat idea, I think your backlash reduction is in the wrong spot. Right now, it doesn’t matter that you eliminated the backlash in the rotation drive gear, since you didn’t eliminate the backlash in the encoder gear pair as well. Since your encoder still has the same degree of uncertainty as to the location of the azimuth, the extra precision on the motor doesn’t matter.

Generally, precision on the sensor matters much more than precision on the motor, since error on the sensor side results in a faulty position, while error on the motor can be compensated for in many ways.

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That’s something I didn’t think of. It shouldn’t be too hard to offset the encoder gear’s profile
for even less uncertainty.

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This is cool. Very cool.

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quite hot - 10/10

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Thanks!

Why are you bolting up from the bottom of your robot? Looks really good though.

We have the bolt heads on the bottom so that we don’t have bolts sticking out from the bottom for better ground clearance and for a spot to mount bumpers.

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You could use the bumpers as an integral stiffener in the design, assuming the corner is jointed well and you’re using quality plywood… Might address concerns around chassis stiffness

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#SummerCD ridiculous marginal gains that don’t matter:
You could use the Falcon casings to replace some of the standoffs, if you pulled the set screw out of the side vent and ran an L-bracket from there to the lower plate? Bonus points for using a vented screw there. Extra bonus points if that hole lines up with the lower plate height and you just need to add an operation to put holes in to take advantage of it.

Pretty sure this doesn’t actually save weight, just adds complexity, but feel free to draw it out and prove me wrong. (“Throw a hole in it” probably only works if the plate is already ~1/4".)

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