For those who follow our blog, you would have seen back in early October that we were working on a special project as part of our fall semester class. We’re now happy to present that to everyone.
No, that wasn’t a typo in the title… WildStang has designed a new swerve module!
Moving away from our previous crab module design, this time we have a coaxial swerve module.
Full details, design iterations, and photos of the built modules are posted on our blog here. You’ll also find CAD files (STEP and SolidWorks files), and assembly instructions. Software will follow later this week.
Looks great! I’m sure you’ve already thought of it, but won’t the turning bearing be under large loads when hit from the side?
What is the final gear ratio? How heavy is a module?
So the dual turning bearings were a big part of the design, and it saw many revisions before the final design was released. This is the bearing used for this prototype design: [McMaster-Carr, however, this will most likely change to something a little more durable for competition (our fall budget was tight, and these bearings, we decided, would do the job fine for our testing). We also suspect that some side loads would be transferred through the thrust bearing as well.
The final gear ratio is 4.29:1, with a theoretical free speed at 16.38 ft/sec and an adjusted speed to be 13.27 ft/sec (all according to the JVN calculator).
The module’s CAD, par the SolidWorks weight analysis, is 6.97 lbs. I am not sure what the actual weight of the module came out to be.]()
Every time I see this style swerve, I wonder why teams didn’t use aluminum box stock for the lower pieces that hold the wheel. It seems like it would greatly improve build time, strength, and decrease complexity since it would be one piece. Did you guys consider that at any point?
I personally did not have that in mind when designing this, mainly due to the limited amount of sponsorship during the fall (and build season). We did not have access to a CNC mill during the fall, so making the wheel cage assembly out of aluminum tubing stock was out of the picture. The current design is tedious to assemble, but it honestly is not that bad as it is lightweight and strong.
For us right now and our build space and tool availability, it is much easier for us to get parts fabricated by our sponsors, than to try to cut and work with box stock accurately enough to have even two identical modules. More so if we wanted cutouts for weight.
That doesn’t mean we wouldn’t consider boxier wheel assemblies for strength/stability, but to fabricate those ourselves right now is pretty much a non-starter.
Having tried making something lime this before, it ends being much heavier and harder to make due to the necessary odd placement of the top bearing and the poorly suited external dimensions of box tubing. In the end it would take more time and probably more money than just using plates.
I just thought I should chime in here to say that team 2471 built a swerve with both the upper and lower mechanisms constructed in aluminum box tubing, and we loved it. Even with zero CNC machining, it was very easy to build, lightweight, and crazy strong. The prototype module.
That doesn’t mean this the right way to build a swerve for everyone, just that it worked well for us. We had freshman and sophomores make the boxes on a manual Bridgeport early in the season when there was nothing else for it to be used on.
The final iteration weighed just under 7 lbs, and we had zero mechanical failures from the system.
There we go. We’re at that end of the spectrum - up till now we haven’t had a decent brake, and we just got an in-house manual mill last year. So box-stock was always the way I pictured a swerve for us, and it seems that just being able to through-drill holes takes a lot of potential alignment and tolerance issues out of the equation. In fact, a number of times in the past we’ve actually welded our chassis and drilled the axle holes after the fact for the same reasons - to eliminate the tolerancing issues that we have with poor tools and students who are just learning =).
Another reason why we decided to go for a sheet metal wheel cage is because we wanted a versatile part. By making it sheet metal, we were able to have both a 3 inch and a 4 inch configuration, so we had the ability to manufacture both easily.
The prototype we built up has the 4 inch configuration, it was supposed to be the 3 inch, but some drawings got mixed up and the 4 inch configuration was sent to our sponsor instead. This resulted brought up a few problems with the design, but nothing a dremel couldn’t fix.
To follow up, our prototype code is now posted up on Github here. This is built on top of our new framework, so you would need the core_framework repository as well to be able to run it.
