January 25, 2016

Snow Bike Part 2: How Does Snow Work?

Snow Bike was more or less finished Saturday night, just in time for playing in several inches of snow before it all got plowed and salted.

Here's the motor mount, made from a couple more aluminum plates.


I cut a ski mount from a section of 3" square tubing, and pressed some brass bushings in.  The axle is a standard bike axle.  I have some long gas springs I might eventually add to the ski to return it to a neutral position, but haven't gotten around to that yet.



With seat and electronics.  The battery and motor controller are held by a bent polycarbonate shell which drapes over the frame.  I also added footpegs at the back.


I wired up all the electronics, only to find out that the hall sensors I had previously repaired the wires for were actually completely dead.  So I cracked the motor open again, and stuffed some new hall sensors in slots that weren't already filled with sensors and epoxy.

Bringing out in the snow immediately uncovered a problem.  The motor shaft was cut very short, and had two flats ground in it, so there was very little interference between my clamping motor sprocket and the shaft.  Any real torque, and the sprocket would slip off.  I thought about making a new shaft for the motor, but in the interest of time I first tried saving the situation with a giant set screw.  I drilled and tapped the sprocket-retaining shaft collar for a huge 1/4-20 set screw, and drilled a matching dimple in the end of the motor shaft, so there's both clamping action and positive interference holding the sprocket on.  Worst case, the shaft gets wrecked and I have to make a new one, but this was a last-ditch effort, so I don't mind that.

Second (and more fatal) problem was the shape of the track rollers.  The tracks would quickly get filled with snow, which was compacted by the rollers and clogged the teeth.  This stopped the track from engaging properly, and caused it to bind.  I think the answer is to just remove most of the width of the teeth, so that there's space between the teeth and the matching part of the track.  A bigger gap should make it much more difficult for snow to collect and jam things up.

Next time there's a good snow forecast, I'll fix the track roller problems and get this running again.

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