First we owe a lot of the design to the work put in by the minds on Team 33. We have never done custom swerve before and also developed this module during the 2019 season, so having a working design was invaluable. The original plan was to use 33’s module wholesale, but after speaking to Jim Zondag at the 2018 MI state championship, and reading Nick Couzens write-up here, we thought it best to implement some of the improvements they discussed, and soon, the project very quickly became a “new thing”. The second factor that pushed our design further from theirs, was wide release of the REV Robotics NEOs. Having the power and mounting of a CIM in the size and weight near a 775-pro was a game changer, and we felt it was worth it to include this in the design.
These changes eventually necessitated every part to be re-designed and re-CADded, however, that doesn’t change the fact that the legwork in layout, design, and engineering were pioneered by 33. Thank you so much for releasing your design!
Our objective with the module was to simplify — reduce the number of components, use COTS components where available, reduce design time, machining time and weight, and to utilize the new technology of the NEOs to package it as short as possible.
We’ll work our way from the frame inwards. The ⅜” lower Nylon plate and upper ¼” nylon plate were a concept used in 33’s module, and they had great results with it. In addition to easier manufacturing than aluminum on a CNC Router, you also get a large amount of impact resistance and a slight amount of suspension. This helps with even weight distribution across the 4 wheels of the module, and can make up for some manufacturing issues in the chassis. The module is mounted at the bottom of the frame so load is distributed across the outer edge of the lower plate. This prevents flexing up in the middle that would happen if the module was mounted on top of the frame.
The large 100mm bearing, how it is clamped in, and the structure of the inner rotating hub are also constructed similarly to the 33 Module. All of the parts were designed from scratch to match up with our frame and the how we power the azimuth of the rotating hub.
Concerning rotation of the hub, we have the first major deviation from the 33 design, and borrow from a concept that 2910, and other teams use. Rather than a 775-Pro and Versaplanetary combo, directly driving a gear that powers the rotation, we have a NEO and a custom gear train. After comparing these two options, we found the NEO and Geartrain are actually lighter. It also packaged significantly better. It took very little time from a machining perspective, as all of the gears used were various COTS Vex-pro 32dp, and 20dp gears. (slimmed down to 0.25” thickness for packaging… <10 minutes each on the lathe) This geartrain connects to a custom shaft. Besides the wheels and bevel gears, it is a fairly complicated part from a machining perspective. It starts as a Thunderhex, with snap ring grooves in it, and bored out for a 3/16” steel shaft to be pressed into it.
The center hub was similar to 33s design. We contacted rapid prototyping companies in our area and one generously sponsored our SLS Nylon parts for us. We also slightly simplified the design and strengthened the hub, as well as increased the grip length of the assembling screws to get more threads into the nylon of the captive nylock nuts.
Using a NEO on the drive and the AndyMark 20t:40t bevel gear combo, rather than a 775 pro and the Vex 15t:15t bevel gears enables a single stage reduction. This brought the layer count of the module from 3 down to 1. The NEO pinion drives a COTS VexPro geartrain. This powers a COTS AndyMark CIM-ulator output shaft, down to the wheel, which then powers the COTS AndyMark Bevel gear combo.
The 40t Gear bore was machined out and mounting holes were drilled to facilitate direct mounting to the Colson wheels and a dead axle. This meant a simpler pillow block design for the dead axle (a ¼” shoulder screw). The wheel we found worked best was a single 3” diameter, ⅞” wide colson wheel.
Pluses and Deltas:
+ Light 4.5lbs weight per module
+ Overall Driving Chassis 5 lbs lighter than previous Tank Drive designs
+ Compact. Overall footprint <7×9” and under 6.5” tall (fits within the bumpers)
+ Outside of the 2 plates and 3D printed pieces, fairly simple to manufacture
+ Effective use of COTS components (Vexpro Gears, AM Bevels and shafts, Thunderhex + Hex shafts)
+ Robust (Never failed during the season despite direct hits to the cargo depot rail)
Δ Steel inserts for the 3/16” portion of the rotational shaft
Δ Custom wheels not feasible for 3” wheels. Tread wear was too fast. Colsons were best
Δ Complicated Machining on Wheels and AM Bevel Gear
Δ Having to machine the wear part (Colson Wheels) is not desirable