Shock dyno (or Shock absorber dynamometer)

[tonyfoale]

Hi Tony, big fan of the book, very cool to see your build on a forum. Quick question: where did you source the gearbox for the 25:1 reduction of a 5hp motor? It looks neat and small, not like anything I've been finding on the used market.

It was a scrap one from a Segway, originally it was 25:1 but I wanted to test at higher velocities and was after something like 10:1. The Segway box was a double stage device but I modified it to single stage and now have around 5:1. I was a bit worried that the motor wouldn't handle that gearing but it works fine and I can get high velocities at short strokes as well as the longest.
If I was doing it again, knowing now that the motor can handle 5:1, I would do it with pulleys and a toothed belt.

Click image for full size.

Here you can see a stock gearbox on the left and the modified one on the right. Note the different input shaft positions.

BTW. I have made several other posts on here about motorcycle related tools which might be of interest. Look here:
http://www.homemadetools.net/builder/tonyfoale