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Archive for August 29th, 2012

Longboard Speed-Sensing Ground Effect Lighting

After our Larval Engineer tweaked the code to track the maximum speed for the current run, so that the color always hits pure blue at top speed and red near standstill, we can prove it happened: we have a video! It’s much less awful than the First Light video, but with plenty of cinéma-vérité camera shake, lousy focus, and bloopers:

Longboard In Action

Longboard In Action

That’s a frame extracted from one of the raw videos files using ffmpegthumbnailer:

for t in `seq 0 10 100` ; do ffmpegthumbnailer -i mov07117.mpg -o Longboard-$t.jpg -t $t% -q 10 -s 640 ; done

This view of the 3D printed case shows the power switch and the Hall effect sensor cable snaking out of the truck just below the near axle:

Longboard RGB LED Electronics - right front view

Longboard RGB LED Electronics – right front view

She filled the case corners that pulled up from the build platform with a thin layer of epoxy, getting a plane surface by curing it atop waxed paper on the shop’s surface plate, to keep the polycarbonate sheet flat. I didn’t have any acorn nuts to top those nylon lock nuts, alas.

The 4-cell Li-ion battery lives in the slice between the white aluminum plates, where it takes about four hours to charge from 3.0 V/cell. The Arduino Pro Mini lives behind the smoked polycarb sheet, where its red LED adds a mysterious touch. Maybe, some day, she’ll show the 1/rev pulse on the standard Arduino LED for debugging.

A view from the other side shows the hole for the charger above the circuit board, with the Hall sensor out of sight below the far axle:

Longboard RGB LED Electronics - left front view

Longboard RGB LED Electronics – left front view

Yes, the cable to the LEDs deserves better care. She learned that you must provide strain relief at cable-to-component junctions, which we achieved by pasting the wires to the board beside the LED strip with double-stick tape. The rest of the LED strip interconnections live atop similar tape strips. There’s nothing much protecting the LEDs or their delicate SMD resistors, but it works!

Actually, one red LED in an RGB package went toes-up and wasn’t revived by resoldering its leads. So we jumpered around the package, subjecting the remaining two red LEDs in that string to a bit more current than they’d prefer, and that’s that.

There’s a whole bunch not to like one could improve in both the mechanics and electronics, but it works! If you’ll grant it alpha prototype status, then I’d say it’s Good Enough; this is her project and she’ll learn a lot from how it works and how it fails, just like we all do.

Not shown: crazy-proud father…

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