View Single Post
Old 10-25-2013, 08:44 PM
bluegoatwoods's Avatar
bluegoatwoods bluegoatwoods is offline
Motorized Bicycle Elite Member
Join Date: Jul 2012
Location: Central Illinois
Posts: 1,576
Default Re: Small engine testing equipment

I've had a dyno design in mind for some time. I might get around to building it one day. Or I might not. But I'll offer it to anyone who might be able to use it.

I'll include a simple diagram.

Picture your bike hung up with the wheels free to spin in the air. Now you take something like a 2 x 4 and mount a bicycle rim brake on it. Put this brake on your drive wheel. Somewhere further back the 2 x4, or 'torque arm' rests on a fulcrum. Beyond that is a bathroom scale. Start your bike up and start applying this brake. You can see that the torque arm is going to act as a lever, applying the bike's torque to the bathroom scale. The scale will then 'read' just how hard that bike is pushing against itself.

I really don't know what sort of torque, at the wheel, to expect out of a china girl engine. But let's imagine it is 50 ft/lb. If it were 3 ft to the fulcrum and then 1 more foot to the scale, then that scale would feel a torque of 150 ft/lb. This is right in the scale's most accurate range. So you could get pretty good torque readings.

You'd need a bike speedometer, or some method of measuring wheel RPMs, in this mix in order to calculate horsepower. But this shouldn't be a major difficulty.

I suppose the bike would also have to be fastened to the ground to keep it from bucking around. Also that brake will get hot. But it shouldn't be too hard to rig up a way of running a little bit of water over that brake to cool it.
Which will also smooth out the braking, helping the possible bucking issue.

This dyno might be a bit crude. But any reasonably handy guy could surely get it working without too much trial-and-error. And it would be pretty inexpensive.
Attached Images
File Type: jpg bicyle dyno 3.jpg (18.8 KB, 51 views)
Reply With Quote