Longshot City

Here’s the idea:  It’s an electric skateboard with no hand-held controller.  Instead, it senses the portion of the rider’s weight on the fore and aft trucks with strain gauges and commands motor current (~= torque) according to the differential between them.

So the trucks (where the wheels go on) are actually electronic scales.  It knows which way I’m leaning (toward one end of the board or the other), and accelerates in that direction.  That’s pretty much it.

I and the great Frank Schmitt tried to make one of these back in the 20th century when we lived in California.  He’s carrying the torch presently, while I fired all of my guns at once on this proof-of-concept.

I came up with some way to belt-drive the wheels, glued the strain gauges (the little brown rectangular thingies) down to some custom trucks, and hacked together an all-analog (!!!) motor controller that used the strain gauge signals to compute a current command and drive an H-bridge power stage accordingly.

Upside down to show the complexity. The big metal box housed the batteries, and the 9-volts were to deliver +/- 18V to the analog motor controller! (I forget what the black box is.)

Closer-up of the back end. I think those are Speed-400 motors, one per wheel, belted to pulleys that I somehow screwed onto the polyurethane wheels. The strain gauges are visible as little brown rectangles on the trucks.

Left of the purple truck piece is the analog-output current sensor, and to the right are the battery/controller current fuses (lot of good they did me).

(I like how the photography came out. Thanks to Mom and Dad's 1967 Nikon!)

My Crap-o-Matic H-bridge power stage for the motors. Notice the SOOT emanating from the second MOSFET! (Power electronics is hard.)

Of course it's an all-analog strain-gauge-informed current-mode DC motor controller. What else could it be?

One Saturday night I finally got it all together at work, turned it on, and I swear to God, good people, that it worked for ten seconds.

Ten seconds.

For ten seconds, it responded to my fore/aft shifts in my CG and motored to get under me.

And then the power stage caught fire.

Sadly, that ends my chapter of the story, because I’m just not that into skateboards anymore.  The great Frank Schmitt is making progress a version with just two rolling-pin-style wheels that’ll allow direct-drive motors, which will be very cool.  When he updates me I’ll link to it!  Go go Frankus!

So get a load of this.  I wanted to do some simple playing along to my favorite Oasis and Tears for Fears songs.  Play what?  Well, I tried guitar classes, but man is guitar hard.  So how about a musical keyboard?

I had actually taken a basic piano class across the street from Harvey Mudd at Scripps College (where the girls were), and was indignant to learn how the conventional piano’s “seven-five” (seven white keys, five black keys) layout meant that a C-major chord, while embodying the exact same sequence of half-steps between notes as a B-major chord, for instance, ended up looking very different.  Bullcrap!

The sequence of four, and then three, half-steps between the notes in a major chord is an easy concept to learn and understand, but that doesn't mean that all major chords look remotely the same!

The same goes for scales.  Playing a C-major scale is easy, but an A-major scale is more complicated, even though the sequence of half-steps is exactly the dingdang same:

Same thing with scales. Even though all major scales are the same series of half-steps, they look very different. Learn one learn them all? Nope!

So how about this.  How about a “six-six” keyboard, with six white keys and six black keys per octave?  That way, the geometric patterns (and the shape necessarily made by one’s hand) between keys that correspond to half-step interval patterns will be consistent, regardless of where you’re starting from:

Aha, now that's more like it. The same half-step pattern corresponds to the same geometrical pattern between keys, wherever you start from!

Now we’re talking.

What’s weird now is that the “white” keys are no longer always the “natural” (as opposed to “flat” and “sharp”) keys.  The C, D and E keys look the same as before, but F, G, A and B are black keys now.

It’s all the same notes, though.  All the same notes.

Bingo! I took the brain of a cheap Midiman MIDI controller and figured out how to re-wire it to a new set of key switches. (Now in a storage room at Cornish College of the Arts).

So I got a cheap Midiman keyboard and figured out to wire its brains to a new set of Cherry keyboard keys.  I water-jet cut the “white keys” from a sheet of fiberglass panel and glued the black keys down.

In triumph, I sat on the floor in my underwear for an entire Saturday and played along to my favorite songs with the help of some guitar tabs from the internet.  The regular geometric pattern of the keys meant that most of the time, when I intuitively reached out and played a chord, I actually got it right, like I’m Elton John!  Victory lap!