pic: Sheet Metal Swerve Chassis



This is a sheet metal swerve chassis based heavily off 342’s chassis this year. Each swerve module can drop out of the bottom of the chassis by unscrewing 4 bolts. The modules rotate around an HDPE bushing made from round stock and two HDPE sheets. The sheet metal frame can be cut with a waterjet or CNC router, and only needs 90* flanges. The total weight for the chassis and 4 modules is just under 50 lbs.

Right now it’s geared for 11.3 ft/s adjusted drive and 130 rpm module rotation (w/ 63:1 VP), but these can be adjusted easily by changing the sprocket reduction and VersaPlanetary.

The swerve module:


CAD:
https://workbench.grabcad.com/workbench/projects/gcDxN3nkUEpnol_eAbFENPy43g6WbnJVi7nsyA6hslDc7E#/space/gcj4wZbYc0–yELsmLDSPW1MwzIGiuEqAOH2XbBZ4dOcZu

Looks great! :smiley: We never actually had to swap a module last season (other than replacing the wheels between events), but man were we ready. Are you doing encoders on the drive motors? That was the most annoying part of our module (mechanically, at least). Also, if I had to do it again I would add a designated spot/mounting holes for a Talon SRX on the module itself.

I’m intrigued. What is the advantage of putting **one **SRX on the module? Assuming quadrature encoders, it seems like a swap of four encoder wires and two motor wires for four CAN wires and two power wires. On the other hand, if you move both the drive and steering controllers down, you are saving connectors for four signal wires. Either way, the wrinkle with putting controllers on the module is that on swapping modules, you need to change the addresses on your controllers or in your RIO software.

Definitely good points. I meant to say both Talons would mount on the module, but didn’t think of the re-addressing issue. Probably wouldn’t do that after all, then.

Another option would be to put the Talons on the empty spot between the two modules on each side. Put the Anderson disconnects for power on the motor side, and just unplug the encoder cables to switch modules. You don’t need disconnects for the encoder cables and you won’t have to deal with re-addressing.

I’m wondering if anyone has any input on the HDPE bushing idea. I’ve never seen a swerve module actually built with bushings instead of bearings, though I would think that they are spinning slow enough for them to work. On 423 we used HDPE blocks with semicircles cut in the bottom as bushings to support the ends of tank drive shafts. We didn’t notice any significant resistance on the shafts, and they were spinning at the same if not faster speeds as the modules would be. I was debating using HDPE for the radial component and regular thrust bearings for the thrust component if the HDPE would have too much resistance taking the thrust load from the weight of the robot. Any thoughts?

FWIW, the Team221 Revolution Pro uses a large bronze bushing for rotation. The Wild Swerve just puts steel on steel. Plastic has its own oddities, but a bushing can certainly work with some testing.

We have used Igus bushings on a bronze inner liner. They worked but over the season wear became a problem. We prefer a 1" flanged bearing for the bottom with a ball type thrust bearing riding on the flange. For the top we use a 6805zz bearing. It may be a over kill solution but the bearing show no sign of wear and are a very lo friction solution. The big question is how many hour of operation will the module see and the shock impacts different games give.

If your swerve is similar to the 221 geometry, I don’t see a need for fancy bushings. Over time we ran bronze on aluminum, aluminum on aluminum (got to be wise and using the correct aluminum), and finally cast nylon on aluminum. On ours, not only does the bushing go round and round but also up and down for the suspension. Lots and lots of run time, no wear or breakage. Check out the white paper for more details.

https://www.chiefdelphi.com/media/papers/3375

On team 2471, we used flanged igus bushings in our swerves for two years with no issues. I can’t speak directly about HDPE bushings, but I know that plastic can work.

How are you attaching the outer coaxial tube to the top of the wheel module?

I’m not 100% sure what you’re referring to by “outer coaxial tube”, so let me know if I’m not responding to the right question.

The HDPE bushing is made of three parts. The “radial bushing” runs through the mounting extrusion and is made from a 3" diam. HDPE rod. It has a 1.125" center hole and standard FRC bolt circle milled into it. The mounting extrusion is sandwiched on the top and bottom by “thrust bushings”. They are made from 3/16" HDPE plates, with the same center hole and bolt circle and a rim for a bearing flange milled in. The bolts that hold the module rotation gear go all the way through the gear, both thrush bushings, the radial bushing, and the module top plate with nuts under the top plate.