Back in April, i posted my first attempt at swerve. I had a lot of fun making it, and while i made a whole bunch of mistakes the one thing i was really unhappy with was its size. It was really big, both because of the design limitations and silly mistakes on my part. Now we’re actually building a swerve drive for 2021, which is better but still fairly big, with a footprint of 180 x 142mm or 7x5.6 in.
The real swerve however has been optimized to death. We dedicated several weeks to the design review process to make sure there are no design flaws. Its size problem comes from our self-imposed design limitations. With that, and inspired by the (really cool) CMS swerve, i wanted to see just how small can you possibly make a swerve module.
Before i got into CAD, i wanted to compare some pre-existing modules to see what i’m aiming for:
Not too detailed, but this is a comparison the smallest modules i know of, along with my swerve and the Mk3. At first i thought i could just compare footprint, but this would make it impossible to compare square and rectangular swerves, so while it’s more abstract, i decided to use area. I also did not include the area taken up by the drivetrain tube as part of the footprint, since it’s unrelated to the design of the module itself and would make the comparison inconsistent (not everyone uses the same tube, in some module the plate goes over the whole width and in others not etc). Height is measured overall.
I also wanted to have some design limitations to make the module more practical for us:
- Have as many parts as possible that can be manufactured with the machines we have in-house, those being primarily the CNC router and the lathe
- Only use COTS products vendors we have good access to through international shipping (so no WCP, McMaster or KHK)
- No COTS gearboxes (our team has a policy against them, we have our reasons)
The final result after some CAD is the Galactic Swerve Mk4
- The drive reduction is 5.45:1 with a 75mm (~3 inch) wheel, for a free speed of 4.6 meter or 15.07 feet per second
- The steering reduction is 30.76:1 with a NEO 550
- Uses the Lamprey Through Bore encoder
- Bearing is used is an x-contact 3x3.5x0.25 In from The Thriftybot
- Swerve turns using a modified 20DP Vex Gear
- Bevel gears are 20:40 1.25 module from Andymark
This module beats the rest that i’ve included in the comparison by most parameters:
- The footprint is 4.9 x 3.65 Inches or 124.3 x 92.4 mm (again, not including the tube). That’s an area of 17.8 In^2, or 11490.7 mm^2.
- The overall height is 8.34 In or 211.75 mm, losing out by a bit to the SDS Mk2, though as far as i can tell this parameter depends mostly on motor choice (NEO vs Falcon, what with the NEO being shorter)
- The module weighs 3.76 lbs, or 1.7 kg
There are however some drawbacks that make it a little impractical, at least for 5987 at the moment:
- The team has never worked with Spark Maxes or NEOs in the past, which is also why we chose the 775pro for turning in the Mk3 Swerve. There are plans for it in the future, but currently the team has no access to REV motors.
- The wheel is live-axle with a triangle bore, same as in the SDS flywheel. While it may have worked well with the brass flywheel, as far as i know it’s never been tested on a drivetrain before, let alone with a 3/8 In shaft.
- While the azimuth gear saves space over a pulley, it would be harder to manufacture, especially on a router. If this design is ever considered it might be worth getting a waterjet or other sponsor to make it for us.
I don’t think these issues are deal breakers, but if this design is ever implemented it will only be for the 2022 season at best.
CAD can be found here: https://grabcad.com/library/frc-team-5987-galactic-swerve-mk4-1