Power Board
A few years ago I built the nifty electric skateboard pictured below.
Unfortunately it was stolen on the way back from the 2007 Maker Faire (where the photo was taken — courtesy of Max from ZedoMax.com).
What made it special was a weight-sensing control system that I came up with in college. Basically, if you lean too far forward on a conventional skateboard, it’ll shoot out behind you in a maneuver called the Wilson (after Mr. Wilson of Dennis the Menace). This board would sense the forward lean and apply motor torque to counteract the Wilson effect, which in turn allowed you to intuitively control the accereration and decelration.
This made the whole thing completely hands-free (well, at least until something broke and you had to carry it). The experience was a bit like playing one of those skateboarding video games, where you can effortlessly skate uphil without having to push the board. Even a bit like snowboarding on pavement.
It started out life as a three-wheel design, based on a Mongoose Slalom 132 mountainboard. I had lopped off the rear truck and replaced it with a BMX bicycle fork holding a small hub-motor wheel. The control system was some basic analog electronics amplifying the signals from a set of force-sensing resistors placed between the frame and the deck. This signal was fed to a small industrial servo amplifier that controlled the torque of the brushless DC hub motor. Power came from 36V worth of RC-car battery packs, and later from a set of 10Ah high-current NiMH cells. I eventually added a keychain remote to turn the thing on and off.
At an EV show in Vancouver I met Justin Lemire-Elmore who had a few neat EVs with him, including a self-balancing electric unicycle. He had planned a project quite similar to mine, and we decided to collaborate on version 1.5. We eventually re-attached the original truck and machined it to accept a pair of small hub motors directly driving the wheels. He designed a digital control system to condition the weight signals (now provided by strain gauges) and drive the (now two) servo amplifiers. This is the unit you see above that we had as a ride-and-drive at the Maker Faire.
I started a blog way back when on this project which has tons more information. And at some point I’d like to build another one: it was quite a blast to ride around the streets of Bellingham on.