on the Engines I have made recently I have tried to make them as free running as possible sometimes using ball bearings instead on plain and have measured my success by timing how long they would run on one charge of air from my small airbrush compressor, several of them would run on 1psi or less but then I found the looser they are the quicker they use up the air, and some of the air also leaked away pass a slack piston so this plan is flawed. Perhaps I should time them at a steady speed of say 100 rpm.
What I have been playing with to day is I found a way to measure the force of the piston when powered by compressed air, I have this part finished Benson which lends itself to the job. I set it on scales under the pillar drill so when I applied air pressure the con rod pushes up against the chuck an gives a readout. Here are the results with a piston of 12mm.
Psi Grams of force
2 180
3 280
6 600
9 900
12 1200
as you can see they are quiet linier, here's a pic as well
Geoff
