So the lack of budget has made me choose longboard wheels for my first gravity racer build – the LGR-002. They are cheap, larger than skateboard wheels (so roll better, arguably, but at least offer more ground clearance) and have simple atatchment. Basically, the wheel holds the bearings, and then you just slot the whole lot onto an 8mm axle and tighten it up with a nut. Done. No hubs, no spokes, no rims. As i’ve seen with street luge, they are also capable of high speeds.
But there is the tricky subject of brakes, as I have mentioned in my previous blogs.
Well, I think I’ve come up with a design that is simple enough to work, and here it is.
Essentially, each wheel will have a large washer screwed to the inside face to act as a braking surface. I have chosen Abec11 70’s Flashback wheels, as they have a flat inside face to allow this. The washer is 60mm in diameter (less than the 70mm of the wheel) 4mm thick, and with a 22mm hole in the centre which is exactly the same size as the bearing. I’ll mark out the washer for the fixing holes, drill them, and then use a small section of 22mm steel round bar to line it up on the face of the wheel. Then I’ll mark the holes through to the wheel, drill some small pilot holes and then screw the washer to the wheel. The screws will be countersunk to allow a smooth braking surface.
Then it’s a case of making up some pivoting brake arms with pads on the ends. They’ll have a return spring that pulls them against rubber stoppers, to keep the brakes off the wheels when no force is being applied. The tops of the brake arms will be linked together by a brake cable, much like in a bike brake. This cable will run into the cockpit of the car and be connected to a brake pedal.
I’ve not done the maths (primarily because I don’t know how) so I’m not sure how much braking force I can expect to see from this setup. I know that to increase leverage and braking force I’ll need to move the pivot point closer to the brake pad (or make the brake arms longer above the pivot) to give more pedal travel per mm of brake pad travel. ideally the brake pivots would have bearings etc, but I think a fat bolt with nylon washers and a bit of grease will have to do in the first instance. Nip things up nicely and then let the return spring take care of the rest.
Anyway, that’s the plan for now, so we’ll see how it goes.