July 12, 2013

The Rebirth of the All-Terrain Scooter

The all-terrain electric scooter has lived a sad and broken life.  A combination of design flaws and user stupidity have caused it to burn through more CIM's than I would like to share, and since the Great Blizzard Snow Storm of this year, the scooter has been folded up in a corner with all three motors in some state of broken.

The basic problem with the scooter was that I wanted both more torque and a higher top speed than 3 CIM's were really capable of producing.  Combined with a motor controller that would happily feed the motors over 100 amps until the battery went flat meant that the motors got really toasty, especially at low speeds or on any sort of hill.

I came up with two basic plans of attack for reviving the scooter carcass:
  1. Rewind the original shorted 80-100 motor from the tricycle for operation at 60 volts, and buy the most powerful Kelly KBS motor controller.
  2. Find some giant DC motor(s) to swap in for the CIMs.  Preferably one or more short magmotor.
Since I did not want the 72V 200A peak brushed controller on the scooter to go to waste, the second option was more appealing.  I checked ebay for magmotors on a regular basis for a few weeks, but found nothing for sale below ~$225 per motor.  Eventually I tried lowballing the seller, and somehow came away with 2 Magmotor S28-200's for 27% of the original asking price.

While waiting for the new motors to arrive, I stripped down the scooter.  I found lots of things that were either beginning to break or were simply too painful to look at to continue using.  The fork fit both these descriptions, as the its aluminum plates were beginning to bend, and it was a real hack job in the first place.  The plate that held the idler sprocket on the high-tension side of the chain was warped from the torque of the motors.  When I got down to the bare frame, I found that the aluminum extrusion the original kick scooter frame was actually slightly bent where the suspension attached.    So, rather than sinking time (and fancy new motors) into a scooter frame that would probably break repeatedly, I plan on rebuilding the scooter pretty much from the ground up.

I will be using the same electronics plus the two new magmotors.  Some of the original gears and sprockets will be used, as will the hubs of the original wheels the original head tube and folding mechanism and handlebars.

In the spirit of the original scooter (and because I'm lazy and don't want this to take all summer) I am not really designing much before hand.  I am certainly not CADing out the entire thing, although I am fairly carefully planning things that require some degree of precision (like the gearbox).  So, when I'm done, this should be an interesting comparison of what I can whip up with a hacksaw and drill and what I can whip up with a mill, lathe, semi-infinite aluminum, and a year of hanging around MITERS.  

Enough text, and more pictures.
Some large aluminum U-channel makes a frame that is much easier to attach things to than the old weird extrusion shape was.  Also, since it's open underneath, the battery pack will be able to fit in a single-pack-thick arrangement, giving another inch and a half of clearance.  The controller also fits in nicely.

I beheaded the old scooter for it's head tube and folding mechanism, and bolted that assembly onto the U-channel with a gratuitous number of 1/4-20 bolts:

There happened to be a pair of whees at MITERS that used the same size hub as my original wheels, but the tires were 14" in diameter rather than 12.5", and had rounded rather than flat tread.  I swapped one of the new tires onto the old back wheel hub, and just used the entire new front wheel.  here's a comparison of the old vs new wheels:

Because the original for was terrible, and also not suited for a slightly larger wheel, I built a completely new one.  The fork crown came from some old moped/motorcycle contraption.  For no reason other than that I think they look cool, I made it a single swing arm fork - the wheel is only supported on one side, not both. Like the Cannondale Lefty forks, but with a leading link suspension design, rather than a telescoping tube.

The fork is supported by this massive chunk of 2" square aluminum stock, turned to round and clamped into the fork crowns:

The wheel is held by this steel axle.  One end is threaded, for a bolt to axially retain the wheel.

And here's the (mostly) finished fork.  The spring/damper was also an old moped part.  The swingarm itself was machined from some more 2" square stock.

The axle is clamped to the swingarm.

With a wheel attached.  The combination of slightly larger wheels than before as well as a spread out battery pack will give this something like a foot of clearance.

Don't miss the next episode, in which I turn an aluminum brick into a dual-Mag-gearbox!

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