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Better Grip: Part One

A project log for Autonomous RC car

My attempt at robot Folkrace

Martin PĆ„lssonMartin PĆ„lsson 12/07/2016 at 19:280 Comments

This thing can be quite fast. Banggood promise 35 km/h and yes it felt that way when I tested it on tarmac. Id like to be the one finishing most laps in the competition, so it would be good if I could use a lot more of the available speed.

What Ive found is that it in higher speed than about 50% duty cycle it goes straight in the curves. Since the car is 4x4, could adding friction (and perhaps weight) give the car a bit more steering in high speed? We'll see.

My plan is to cast tires out of polyurethane onto 3d printed wheels. I designed the wheel to be 3d-printable (no overhangs or overly complicated features), so I split the wheel into an outer ring and a hub. The wheel with tire will have the same dimensions as stock, but (hopefully) better friction against the floor. In Minisumo polyurethane rubber is the most used material because it really "suck" onto the ring. I will also use a 3d printed mold to cast the tire directly on the wheel (with or without the hub mounted).

Exploded view of the wheel assembly. The inside of the wheel towards the screen.

Wheel centered in the mold.

Wheel assembly from the outside. It looks a bit dull (even worse with black hub!)

I forgot to document the test print but the hub, with the dimensions given during design, fits perfectly into the wheel.

I use CPE for the outer wheel, white ABS for the hub.

The tire will be cast from Xencast PX30, which is a polyurethane rubber with a shore hardness of A30. I use a black tint to this.

To suck out trapped bubbles in the rubber I constructed a small vacuum chamber. I don't have too much confidence in the syringe as a pump, I'll have to put a little bit more work into this. It was cheap though.

The wheels are being printed as I write this. Hopefully I have the molds done printed when the resin arrives, I'm very eager to get the casting done since it has to cure for at least a week.

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