3175 Off-Season Swerve

During the end of competition season, and all of the off-season (until now) we have been designing a swerve module, hopefully for use in 2020. Our focus with this module was simplicity and ease of manufacturing. We tried as best we could to stick to designing/manufacturing processes that we already have experience with. Both the base and top plates require a CNC machine, but all other parts can be made with common drills and saws. A few pieces will be made on a 3D printer (printing PLA). The base plate is made of 5/16 inch aluminum and the top plate is 1/4 inch lexan. we are using two 15t Vex bevel gears and 3.25 inch VersaWheels. The drive motor is a CIM geared 5.83:1 using a 12t pinion and a 70t spur gear. The azimuth motor is a BAG geared 63:1 using a Versa Planetary gearbox. The speed of the swerve as calculated by this calulator is 12.92 ft/s. Each module weighs approximately 9.37 pounds, heavier than ideal so any suggestions about reducing weight would be greatly appreciated. This design was influenced by the designs of team 33 and team 2910. While the actual design is not similar, the technical paper by team 2767 about their third coast swerve was a huge help.

Team 33’s swerve
Team 2910’s swerve
Team 2767’s technical paper

This is our first year trying Swerve so design suggestions are greatly appreciated, This is also my first year doing CAD, so suggestions on improving the CAD would also be appreciated.

Full CAD: 3175OffSeasonSwerve.STEP (32.7 MB)

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Very nice simple design - given the objectives.
Obvious suggestion is some lightening of plates - but I also like the focus on robust, then simple to make.

Suggestions that maintain simplicity: reduce height of standoffs so that steering gear is not as far cantilevered. We also have found it preferable to use a belt between steering motor and pivot to reduce backlash (the bane of swerves driving straight) I like the one to one gearing vs requiring another set of gears for an encoder.
You could consider using the AM 40/20 bevel combination which then you could reduce the size of the drive gear by half and achieve same drive ratio. (the AM gear set uses a 3/8" hex bore on the gear with the wheel, and a 8mm keyed bore on the other, you would then use a 8mm to 1/2 hex adapter - from VEXpro or WCP - to mate with gear - still no machinhing there required)
Personally we prefer using Colsens wheels with hex bore ( you can also use a 3/8 hex to 1/2 hex converter) than the vexpro wheels as the wear better and are easy to use.
Also would encourage use of either retaining clip or bolt and washer threaded into THunderhex axle vs. clamp which may loosen and fall off at some point.

Your not showing it , but I assume you are including a VP encoder in the steering transmission - we like those for that application.

I can’t quite tell what you are using for the main pivot bearing which can be the key point of failure.

Nice work.

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Can you nest the motors closer to each other then position them in such a way that the mounting plate starts to look triangular?

If you use screws instead of clamps LOCTITE them! The screws also make it easier to adjust the bevel gear backlash.

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+1 To Mark’s comment on using screws in your main axle. While wear can be minimal, there is still wear that needs to be adjusted for over time to prevent malfunction.

You are correct in that we are using a versa planetary integrated encoder. The main bearing is the same used on 2910’s MK2 module.

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I cant move the motors closer together, due to the spacing of the gears, but moving the placement of the motors could help. If I re position them so that they are on the left and right side of the drive axle instead of in front and in back I might be able to cut off some of the base plate. I’ll change the placement in the CAD and see if it helps.

Sorry, I didn’t mean smoosh them together, I meant move them radially around the module axis. Looking at the top view and pretending it’s a clock face, move the azimuth to 1 o’clockish. Move the drive motor to 10 o’clockish.

After messing with the CAD I got this. the first picture is the base plate with the corner cut off. If I could move the bearing closer to the corner of the frame I would be able to cut off more. Due to the width of the wheel cage I cannot move the main bearing any closer to the corner of the robot. Cutting off that corner saved about 0.13 pounds on the base plate. EDIT: I realized that I can cut off two corners of the plate, not just one. Cutting both corners saved about 0.3 pounds combined. The last picture is the base plate with both corners cut off, the second to last is the whole assembly with the corners cut.

I would work on getting the wheel location closer to the edge of the frame. Getting as large of a wheel base as possible is one of the most important things you can do when improving drive dynamics.

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I’ve thought about that, and the only way I have come up with to achieve it is to make the wheel cage smaller. In order to do that I would have to use a different (and more expensive) bevel gear set. The Andy Mark bevel gears that @page2067 suggested would help, but it would require changing the drive axle to an 8mm round instead of a 1/2 inch hex, a big change for a small decrease in the width of the wheel cage. Is there any other way to move the bearing closer to the corner of the robot frame that I haven’t thought of?

Not use 2 wheels for your module. Do a single wheel with the bevels either beside the wheel or above. This will definitely decrease the size of the module and allow you to move everything a lot closer to the edge of the robot. See our module that you linked above for reference, or some other teams such as 910, 2910, 1323, etc.