2.007 Milestone 5: Shopping + Steering


We finally ordered our motor controller last Tuesday, but we still have a ways to go! We’ve only ordered our motor controller and motor so far, even though we’ve also picked out parts for the rest of our drive train. So, we actually made a schedule, and we realized that if we wanted our parts by spring break, we’d want to order approximately…well…this coming week. So Aisha and I split up the subsystems and decided to cement down our list of parts! I worked on drivetrain and the frame while Aisha tackled the steering.
  • #25 chain: Found cheapest price on a site where you can build your own CNC. o.O
  • Front wheel: Charles gave us an option to get 2 bad wheels, but we’d have to replace the bearings ($10 total) and add spacers (?!?) or 1 good wheel. We’ll get the one good wheel and then order the exact same one from monster scooter parts ($24)
  • Sprocket: 11 teeth
  • Masterlink for the #25 chain (Electric scooter parts, Item # CHN-HD25ML) – it turns out that Charles has a great stock of these
  • Tensioner: buy a block of delrin – we wanted a gear ratio of 1:5, meaning that we wanted a pretty small sprocket – of 11 teeth! However, to prevent the teeth from shearing off from the force, we asked around (Thanks Jamieson!) and found out we could use a tensioner that would apply force and allow contact with more teeth. Something like this:
  • Pedal: Hall effect – This is for our throttle.
  • Brake: Funny story… I didn’t know how to install the bike cable to the band brake assembly that came with our wheel. So I decided to carry that wheel back home with me and ask my bike-friends. On the way home, I decided to go to my urop, go do my readings at the library, and I promptly left the wheel near the stapler garden at the library. Oops. Don’t worry, I frantically wrote emails to the library staff and called them at the library opening to get it back. On another note, I still haven’t figured out the bike cable assembly, but it should be resolved this week.
  • Seat + Seat Mount: This thing is surprisingly expensive. This seat is the cheapest one I could find. Or youtube tells me there are lots of people out there who make their own. I eventually found a treasure trove of old tractor/lawn mower seats on ebay. We’ll be getting one of those! The dimensions of the seat mount were on ebay. Assuming they’re correct, we made a H seat mount. Seat H Mount
  • I started to CAD all these parts in to figure out the motor place w.r.t the giant sprocket on the wheel. I used my trusty calipers to dimension the wheel and CAD in the band brake + sprocket assembly to figure out how how far away the motor should be in order for the tiny sprocket to align with the large sprocket. At the same time, we need to mount the wheel somehow, so I spent lab looking at all the other karts and asking Banks about his kart. CAD is fun. (Edit 3/17: I decided I wanted a low-riding kart without remembering that Aisha was designing the steering and so had set the height of the front wheels. Oops! I redid this).
We made a prototype of the steering mechanism in real-life size by lasercutting the MDF parts! We quickly realized a problem: the steering mechanism is too cramped. In our CAD, we didn’t account for the bearings adding 0.1″ to the top of the hole; so we decided to redesign the mechanism next week. We’ll simply need to add washers and an extra 0.25″.
The rest of our budget looked like this.
Other milestone assignments we had to do this week included:
1) Submission of a part for waterjet:
[add picture here]
Things we have learned: waterjet tolerances 😦
0.25″ aluminum-6061 is heavy
2) We used an arduino to control a servo (and then a motor) in a certain range.
3) Technical drawing of 2 parts we can machine!
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