2.007 Milestone 3: Component Selection and Solid Modeling

This milestone was due at the same time as Milestone 2, leading to procrastination and then mass panic. The milestone this week was to try to figure out the rest of the kart.  We decided to tackle 2 subsystems. Aisha took on Steering, and I took on the Drive Train.

Drive Train: We wanted to design something like this:

Parts:

1) Drive Wheel: After browsing through tons of wheels on monster scooter parts, I settled on this wheel. I decided that I wanted a rear wheel assembly with the band brake and sprocket installed instead of having to buy those separately. Also, Charles also gave us a decision in picking our parts – we could either get 1 nice wheel or 2 pink bad wheels. The 2 wheel pink wheels were bad because the bearings came loose, seen from Banks’ go-kart. Charles said he’d sell us ball bearings at $2.50 a piece, which means $10 for both wheels. We also need to make spacers. We decided thus to order 1 back wheel assembled and use the 2 pink wheels as our front wheels.

2) Small Sprocket: Found one on mcmaster that would give us a 1:5 gear ratio with 11 teeth. The wheel we bought came with a sprocket with 55 teeth. Banks and Charles warned us that it’d be too few teeth because the force might shear them off. To solve this, we’ll make a tensioner.

3) Motor: Already chosen!

4) Chain: Chose #25 to fit the sprockets; We also thought about doing a belt drive, but those are more expensive. We did not want to make a gear box.

5) Motor Mounts: For the last part of our milestone, I made an assembly with our motor (with new dimensions) mounted across an 80×20 extrusion.

MotorAssembly

6) Brakes: We decided finally on using band brakes (which our chosen wheel came with!) because they were the cheaper option and worked fine. Disc brakes would be nice, but they’d be almost twice as expensive, and they wouldn’t give us as big a gain in our braking. Also, who needs to brake…? (jk)

Our resulting budget outlined. Looking into previous budgets, we discovered that people spent ~$300 on drive train and ~$100-150 on steering. How expensive >.<

Budget Estimates (with drivetrain + steering)
Budget Estimates (with drivetrain + steering)

Physical HW: We characterized a motor (Kt and R, internal resistance)

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