Sunday, December 18, 2011

Razor Wind: Motorpod Edition

Shortly after the demonstration video shoot for the Clough Undergraduate Learning Commons, I burned out the version 1 wheelmotor. I knew the motor was running hot, I thought I had seen some sparks fly out the side, but I wasnt alarmed. Not until smoke billowed from the nearly air-tight electronics compartment was I actually worried.

Turns out some screws loosened, some wires shorted, and magnet wire combusted. Some serious weld marks were left inside my frame.

So I disassembled it and left it aside. I got pretty tired of fiddling with wheelmotors after rebuilding neumotor 2-3 times so I designed an alternate power system: The Wheelpod.


A separate power drive system that easily slips into the space of the old one. This particular design slipped in between the two main frame rails and bolted/pivoted about the old wheel axle location. Mechanical tabs prevent the module from rotating in any undesirable direction. When a person stood on the scooter, the rotation about the pivot point applied a counter rotational force on the rear footrest spoiler and the from plate about the speed controller cover.

But what for drive? I spent a fair amount of time perusing the new line of Hobbything Turnigy SK3 motors when I realized Xo and I had one remaining unmodified Turnigy 6364-280 from Hardboard.

I never thought I would be reassembling one of those motors.

Some quick calculations: 280kv @ 22.2V, with 4" wheels and a ~2.2:1 belt ratio leaves about 30 MILES PER HOUR. YESSSSSSSSS!

The device went together about as quick as the waterjet could sneeze its watery sand snot.

Waterjet timing pulley using the low-taper cut settings to prevent belt deviations due to taper. The bore was turned to accept a giant-ass ball bearing. Eight holes run through the entire assembly to secure all parts.

 Wheels were also bored out. The preferred Colson 4" x 1.25" was selected because it offered the most thermoplastic core. The 1.5" and 2" wide versions has much more rubber and made turning difficult. For this design, I decided to enhance the rigidity of the wheel by adding aluminum plates to each side. This would give the bearings a better material to sit in and provide a more positive material to tap and thread.

The stack, not yet ready to be pressed in.

For some reason I managed to epically fail with hole placement. It did not occur to me the THRU diameter of #6 hardware, but I was left with this case regardless. So I did what any 'sensible' engineer would do and take a reamer to it. Don't hurt me too much.

The results were actually reasonable. It was very tight, but enough screws passed through to finish the piece. The way I see it, I have some potent 'thread locker' in this assembly. 

The protruding screws were screwed into the timing pulley above. After turning some spacers, boring out timing pulleys, and screwing stuff:

One thing I neglected to do was design the sensor module. As a result, it is currently running sensorless. While it is less a headache for me, I would like to someday add a data collection module in the scooter so I can produce REAL values for comparison. Someday...

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