replace the electric motor of an air compressor with modified bicycle drivetrain. pedal. keep pedalling...
Step 1: Get Rid of the Motor.
use the existing motor mount to install an axle with one fixed cog and a belt pulley. You'll need bearings. try a 1/2" axle with radial ball bearing cartridges. make the bearing housing out of a slotted tube that has a drilled out nut and a regular nut to allow a bolt to tighten the tube around the bearing. (should i include more desciption?)
Step 3: Weld on the Rear Triangle of a Bicycle, to Allow the Use of the Dropouts and Bottom Bracket. Horizontal Dropouts Are Best.
Step 4: Attach a Heavy Flywheel to the Compressor to Smooth Out the Resistance.
Step 5: Make Handlebars, Rig Up a Chair, Add Gears If You Want, and Go for It.
Step 6: Toe Clips Really Help.
Step 7: This One Takes 15 Minutes or So to Reach 50 Psi, and I Think It's a 30 Gallon Tank.