I’d like to preface this post by stating that if you or your team is considering doing swerve, please save up money and get some nice SDS or WCP modules. Seriously. It’s not worth the money or time to do something cheap.
With that said…
GBX-173, the Aliexpress Swerve
GBX-173, or Aliswerve, has a BOM cost of under $160 not including motors and motor controllers, with a total cost of only $1350 for four modules including motors and motor controllers. Featuring a brushless drive motor, a 1:1 absolute anti-backlash encoder, a 5.3lb assembled weight, and no machining beyond what can be achieved with a hand drill and bandsaw, this design cuts no corners on features other than reliability and strength. And really, who needs those with a price tag this low?
This design was inspired by the recent influx of “cheap” swerves to Chief Delphi. Many of these designs feature expensive gear setups, premium printer filaments, or assume access to CNC equipment. Aliswerve makes none of these assumptions, and was designed ground-up to be as cheap as possible and manufacturable with the bare minimum of tools.
Aliswerve is designed to be printed on a stock Ender 3 in PETG and contains exactly 1 “machined” part, which can be made using an included 3D-printable jig. STL files designed for printing are included in the repository. There is also a 3mm carbon steel plate that can be lasercut for $25 from Send Cut Send’s online lasercutting service.
The “printable” versions are versions designed to be printed in PETG on an Ender 3 Pro with a 0.6mm nozzle, 40% infill, 3 wall layers, and 0.3mm layer height, as determined by the shrinkage measured by a friend of mine who owns an Ender 3 Pro. At these settings, one module’s worth of parts takes about 25 hours to print. If anyone has a fully stock Ender 3, I’d be interested in hearing about your experiences with repeatability and shrinkage so I can update my clearances. Holes and bosses get about a 0.25mm adder right now, depending on the size.
At the heart of the design lies a 3mm steel baseplate.
When nested as shown, the price for 8 plates drops below $26 each. The lack of lightening ensures that you can count each piece as a 30-minute part for re-usability purposes.
The one machined part is the plate used to link the TTB bevel to the Higrip wheel.
This is a fairly difficult part to make by hand due to the six 6-32 tapped holes (Ryan pls), but I’ve included a 3D printable jig model to aid in layout and cutting. Frankly, I don’t trust this to hold up, and drilling out the bevel gear for an 8-32 screw is probably the right way to go. The outside profile doesn’t need to be very round; it can easily be a square or octagon. The bore is a simple step drilled 7/8" hole.
M4 screws, locknuts, and threaded inserts are used throughout the design due to their impressively low cost and ease of use. 6701 bearings are used where possible due to their low cost and small size.
The use of a generic all-metal 500-size planetary gearbox saves money over the more popular Versaplanetary or Ultraplanetary gearboxes favored in custom swerves.
Using metric gears, an 8mm shaft, and the WCP bevel gear set could save an extra few dollars on gears and bearings (and skips tapping 6-32 to interact with the TTB bevel), but I felt that sticking to 20DP gears was best for this design. Chinese gear and bevel gear suppliers on Aliexpress can often be unpredictable in their stock, so sticking to local sources for all gears was the safer option. I was also on the fence about using a 5mm HTD belt, but for the same reason I decided it was safer to stick to an American supplier.
A cross-section view for those curious. Just the standard swerve stackup here.
And a closeup of the anti-backlash gears. These are “sprung” so that they maintain contact with the small encoder gear 100% of the time. This is a nice technique that I think can be used more often in off-axis encoder situations.
Overall, there’s a few improvements I’d make to the structure of the module, but I’m pretty happy with how everything turned out. Would it be a great option for an FRC season? Probably not, but for years like 2018 or 2019 with few obstacles, I think something like this could work well. I’ll leave it to someone more talented to shore up any weak points I missed in the design.
Here’s a chart comparing the price of various swerve options.
Questions and comments are welcome as always.