Foreward:
We happy to answer questions about our robot (our kids especially love talking to anyone in the pits). We do not upload our CAD because we feel that incentivizes people to merely blindly copy and develop their own design skills or understand why we did things the way we did.
Another note about our designs, just because we are 254 doesn’t mean it’s perfect, we have only a 6 week season like everyone and sometimes that means “just sending it”. Do we overbuild things and rely on custom billet parts a lot? Yes. Do we overvalue aesthetics? Yes. Should we have built a turret in the first place and made our season feel like a dumpster fire? Perhaps not, though it turned out well in the end. This was by far (a solid order of magnitude) the team’s most ambitious, stressful, and challenging build/competition season in recent memory and I’m not sure we’d make all the same decisions again. That said, here’s some details that you won’t find in our technical binder (which will likely be uploaded sometime in the summer).
Wire Management:
Due to the limitations of the bi-directional IGUS (“Bigus”), the turret could only rotate +135deg and -310deg, the code told the turret which way to spin to point to the target, and sometimes if the drivetrain was quickly rotated the turret would have to whip around to keep pointing whilst not going past the hardstops. The Bigus was constrained above and below by a shelf and cover made of bent 1/16" polycarb that attached with velcro onto the bumper rails and could easily be removed to replace batteries/bumpers and service wiring.
Turret Design:
The bearing design for the turret was done to maximize stiffness and strength. Making a turret that was strong enough to withstand the moment generated from our arm running into a rocket or other robot with the elevator at max travel and drivebase at full speed was the driving spec.
The turret shaft (highlighted in blue) consists of a giant billet part which holds an upper, 6.5" ID, 7.25" OD, 0.375" WD Kaydon X-contact bearing we purchased from Ebay. This bearing outer race was held from below by a counterbore in the fixed 3/8" plate that was bolted to the 1x1x1/8" crossrails that were welded to the drivetrain. The outer race is clamped from above by clamp ring via screws into tapped holes in fixed 3/8" plate. The inner race of the bearing rotates with the turret and is held from below by a clamp ring via screw into tapped holes in the turret shaft, and above by a shoulder on the turret shaft.
Lower on the turret shaft a shoulder exists where a #25 72T vex sprocket with a milled-out center is attached (#10-32 screws clamp and transmit torque). This sprocket is driven by #25H chain from a 22T 1/2" hex sprocket that is the output of the turret gearbox. An SRX Mag Encoder counts rotations 1 gear reduction back from this output due to packaging issues. The gearbox is driven by 1 775pro.
On the bottom of the turret shaft another 1" ID, 2" OD, 0.5625" WD high load radial ball bearing is held from above and below by internal and external retaining clips, respectively. It is held radially in another billet piece that attaches down to the drivetrain weldment’s bellypan via standoffs (this billet piece just barely sits above the breakers on the PDP). This extra bearing greatly increases the moment capacity of the turret, giving it a second bearing point 1.75" away that can transmit load into the bellypan, which is very strong in inline tension.
