Over the past couple of months, the mentors of 3419 participated in the NYC Corporate Challenge, where companies in New York City compete in a FIRST robotics game. The original Corporate Challenge was in 2019, where the teams competed in a Deep Space tournament. Last year’s event was cancelled because of the pandemic, and this year teams built robots to compete in “at home” version of the 2020/2021 FTC game, Ultimate Goal.
We decided to build a swerve drive for our robot, which we probably overkill for the game, but an fun engineering challenge nonetheless. Doing swerve on an FTC robot presents some unique constraints:
-Robots are only allowed to use 8 motors total, so a typical 8-motored swerve was out of the question as it wouldn’t allow for any motors for other mechanisms.
-Robots must fit in an 18" cube, so space is very limited
-We didn’t have access to our machine shop because of COVID, so our machining capabilities were limited. The only things we had access to were hand tools and 3D printers.
Here are some pictures of the module:
To overcome the motor limitations, we used a servo ( 2000 Series Dual Mode Servo (25-4, Super Speed) - goBILDA ) to orient the drive. We were concerned that the servo wouldn’t have the speed or torque perform well, but it turned out that it worked just fine. The servo is in continuous rotation mode and drives the rotation through a 4:1 gear ratio, which means that the wheel rotates at 47RPMs This is quite a bit slower than we’re used to for an FRC robot, but it didn’t have a significant adverse affect on the driving quality. The stall torque at the wheel was 16.7 kg-cm, which would seem like not enough for an FRC robot, but for the much lighter FTC robot, it was sufficient.
To keep the module as small as possible, we used a wheel that was only 2.5" diameter. We struggled to find a COTS wheel that we liked of this size, so instead we 3D printed our own. We printed a tread pattern into the wheel, which worked quite well on the FTC floor, which is similar to a gym mat and has a nice squish and grip to it that interfaces with the printed tread well. This allowed us to fit the entire module in a 3.625" x 5.375" footprint, and only 6" tall.
The module used bevel gears from Gobilda ( 2:1 Ratio Bevel Gear Set (8mm REX Bore Pinion Gear) - goBILDA ) which are very small and well-suited for this exercise.
The other gears are 3D printed. We used a herringbone gear in an attempt to make the gears as strong and smooth as possible for a 3D printed gear. The gears transferred the torque and held up just fine without any visible wear. The one down side of this approach is that it made assembly very difficult because you can’t slide these gears into place axially like you would a normal spur gear; rather, they need to placed where they should go and then you have to slide the shaft through them, which was quite tricky in this small assembly.
Overall we were very pleased with the results. It led to swerve drive which was very smooth and easy to drive. I’m happy to answer any questions that anyone has.