1640, Sab-BOT-age, is proud to present our 2020 CVT Swerve Module.
Our 2017-2019 CVT swerve was designed to add CVT functionality on top of our standard swerve module, which has only seen iterative changes since its inception in 2010. While this provided us a lot of success and the base swerve module was robust, proven, and reliable, it provided for a suboptimal implementation of CVT. Over the last 2 years, we have spent countless hours redesigning our swerve module from the ground up. Our new module borrows many great features from 2910’s MK2 and MK1 modules and combines them with an integrated CVT. This amalgam of the best features swerve has to offer will greatly enhance the performance, precision, and reliability of our swerve drive trains.
-Integrate CVT as core feature of design vs treating CVT as an add-on to an existing design
- Low possibility of V-belt misalignment with pulleys causing thrown belt
- Increases reliability vs older & more fragile 3D-printed servo arms to actuate CVT
-Achieve a near-linear relationship between servo angle and CVT ratio (see CVT description below)
-Decrease height of module to reclaim important real estate on the robot
-Integrate the modules into a Versaframe chassis as huge gussets.
-Reduce weight of module using non-standard materials and 3D printing
-Use NEO Brushless Motors for both Driving and Steering
We utilized many of the same standard COTS parts from other swerve modules, 3D printed parts as much as possible, and G10/Garolite plates for further weight reduction. The G10 is easy and fast to route for our team though we did implement a new vacuum system on our router to protect our lungs. The most significant weight reduction from 3D printing is found on the wheel supports. They are reinforced with 2 10-32 bolts inserted vertically into each support. Initial testing of repeatedly crashing the swerve modules into a barrier (à la 2019 ball corral) has yielded no failures.
Free speed: high -> low gear 16ft/s -> 7.5ft/s
1.029->2.25:1 CVT range + 26:18 gear reduction + 4:1 bevel gear reduction
Total reduction: 5.95:1->13:1
Steering reduction: 24:1 -> 4rps
Size: 7.4’’ x 5.75’’ length x width
1.5’’ Ground to bottom of wheel mounts
3.6’’ Ground to bottom plate
6.1’’ Ground to top plate
8.45’’ Ground to top of NEO
True drive speed sensed by AMT-102 encoder
Steering sensed by 6127V1A360L.5 hall effect sensor connected using plastic
The main feature of this swerve module is the integrated CVT. For anyone who needs a refresher in how CVT works, the gist is that you have a variable diameter pulley that you can control to change your gear ratio. In previous years we used external 3D printed arms controlled by a servo to introduce tension to the belt and alter the gear ratio. This was hard to control, unreliable, and delicate. This year, we instead move the CVT pulley itself to introduce tension and vary the gear ratio. In the video you can see the NEO and CVT pulley are mounted to the “pie gear” which acts as a curved rack to interface with the servo’s pinion. The servo precisely moves the CVT assembly to introduce tension. This opens and closes the CVT pulley and allows us full control over our gear ratio.