Testing, Testing

[frinesi2]

Here's a pic of my overkill junior design project, during testing.

[jminer]

@frinesi2 That thing looks amazing

[RallyDarkstrike]

OK, that is cool....is it powered by that drill back there?

[frinesi2]

@rallydarkstrike Yep. The project requirement was to use an 18V cordless drill to power a vehicle that could pass under a 36" (maybe 42"? don't quite remember) bar carrying a single occupant. The vehicle had to do as many laps of the quad (well half of the quad - so the course was a right triangle which means one 90° turn and two ~135° turns) as possible in a given amount of time, and we were allowed to swap batteries.

Since our group happened to have the entire Baja SAE shop at our disposal, and a member with a lot of contacts in the downhill mountain bike community, we decided to build a reverse-trike with the largest diameter tires we could find. It had rack and pinion steering, hydraulic disc brakes, and a momo race seat (mountain bike guy was also a Subaru guy). I made the chassis from spare Baja roll cage tubing. Lots of little custom fabricated brackets and shafts as well.

It also had an in-hub computer-controlled planetary CVT that would change the gear ratio to keep the drill as close to optimum RPM as possible while wheel speed changed (the laptop in this picture is being used to tweak the program). The drill was the most powerful 18V cordless that DeWalt made at the time, and in fact was one of their bench test models so it had no labels or markings. (Fun fact - I still have that drill and use it to this day, although the clutches are starting to give up the ghost.)

Since the rules allowed for unlimited battery swaps, we lined up 6 or 8 batteries behind the rear seat and wired them up to a relay bank. We then gutted another battery and used it as an adapter to attach to the relay bank. A rotary switch in the middle of the steering wheel let the drive switch to a fresh battery every lap. (Another group member had access to aviation grade relays and wiring so it was a pretty solidly built power system).

We got 2nd place, with two teams tied for first that were more conventional "kiddie bikes with drills". One of them had to deflate their tires to get under the height limit, but the other one was just plain fast with a rider who basically did a superman pose the entire test. It was actually kind of impressive. We could have been faster but we failed to account for how badly the mountain bike wheels dealt with lateral forces. I think if we'd given them a lot more camber and set up the steering geometry with a lot of kingpin inclination we could have taken advantage of camber thrust and maintained a lot more speed in the corners. A smaller rear tire might have helped get some more torque to the ground as well.

I do take some solace, however, from knowing that - being the primary welder in the Baja shop at the time - I essentially built the two first place bikes as well

Why do the emojis look like blob fish?