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Friday, January 27, 2012

2x4 Scooter Build

Ta daa!
I just finished building 2x4 Scooter!  Its mostly functional, although the steering is a tad floppy and the throttle is a bit scary.  From the previous CAD design, I put in a few extra pieces including a piece to brace the wheels and a front bumper to help make the steering more rigid.  I also made the motor mount adjustable so I can tension the drive belt over time.

Most of the body was straightforward.  I cut the 2x4 stock down to size with a radial miter saw.  The hardest part to make was the steering column, which I used a bandsaw to cut down and sanded it with a belt sander until circular and smooth. Using 2.5" wood screws, I assembled the frame with a hand drill (although I wished I had a hammer drill).

Once the frame was together, I had to put together the wheels.  Everything I had came in parts, so I had to press some bearings into the hubs, stuff the wheel with an inner tube, screw the hubs together, and then pump up the tire.  I mounted the wheels on 200mm long M10 screws, which made for a simple axle.

Next I had to figure out the electronics.  First I went to work on the battery pack.  With some help from Charles Guan and some spare A123 26650 cells, I was able to solder up a 8S3P pack which would give 26.4V nominal (the maximum for my ESC) and over 6Ah of charge.  It took me in a few hours to make, partially due to having to hand crimp and assemble the appropriate connectors to balance the cells, but after I shrink-wrapped the whole thing it turned out nicely!

The last part to tackle was the throttle.  Using a force sensor I had leftover from a class, I wrote up an Arduino program to give me throttle control that was dependent on how hard the sensor was pressed.  Its very sensitive, but since I have some other things to work on, I'm leaving it for now.  In the future I plan to fix the throttle issue, make a new drive pulley (the current one isn't centered), and possibly stabilize/redesign the steering.  For now, here's a video!

By the way, I did pretty much all of the work at MITERS, so many thanks to them for their hospitality!

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