As a rookie team last year, Team 3489 (Category 5) knew little about what build season would hold, but we were pretty sure we’d need wheels. Looking at the simpler COTS options, all had drawbacks. We decided to develop a custom molded urethane wheel that would allow us to pick the geometry and hardness of our wheel tread. A goal was also to eliminate/reduce “throwing” of treads sometimes seen on the Plaction wheels. What we arrived at was a fiberglass reinforced 50 Durometer wheel with a subtle (crowned) tread, molded in place on a 6 inch Performance Wheel.
At our only regional, our 4WD setup on toughbox tubes showed good traction but only fair turning. When we committed to our defensive strategy we were not easily pushed. Integrated jackstands made it really hard to move us when deployed.
For fall scrimmage at SCRIW, we changed out the front wheels for 6 inch omnis, since we already had the jackstands. Much better maneuverability, and still managed to do some pushing against some 6WD drop center drives. Through it all, we have yet to lose a tread on carpet (sound of wood being knocked).
Anyhow, here’s some pics, let us know what you think…
The material is EP1150, a 50 durometer urethane from Eager Polymers. The molds are made on a FDM 3-D printer. The mold is made in 3 sections to facilitate removal of the finished wheel. I also printed a small funnel to facilitate pouring the urethane into the small crevice (it seems that a shorter sidewall holds up better). The performance wheel is a COTS item, and I wrap the wheel with a couple of wraps of fiberglass drywall tape before overmolding to help adhesion and strengthen the tread.
No empirical data yet. The initial thought behind the overmolded tread was the ability to crown the tread for better turning, and to avoid throwing the belt tread (which we’ve seen happen). We tried a teat setup with a bathroom scale up against the wall last year, but ended up mostly burning a hole in the carpet:yikes: . Maybe this year I can find a fish scale/strain gage with a peak hold function. If I can make that happen in my spare time :rolleyes: I’ll post the results here.
On the real world application side, we went up against a few West Coast drives with belt tread last year and held our own. We had sort of a “hybrid” 4WD with our molded urethane tread on the rear, omnis on the front, and integrated jackstands to hold firm if we were getting pushed.
Have any videos of this you are particularly proud of? Not that I’m questioning you, I’m just genuinely curious to see it.
I think you’ve done a nice job of implementing a urethane molding process. The nice thing is you can use this process almost everywhere on the robot (linear bearings, intake rollers, etc.)
Not a lot to see as the jackstands only lift the bot about 1/8", but from about the 1:20 mark on, when the bot is not moving, the jackstands are usually deployed. With our bot broadside to the West Coast drive of Exploding Bacon, we held our position, despite the omnis on the front.
