Sunday, January 11, 2015

Bicycle-Powered Air Compressor

bicycle compressor gif
After Halloween, I was looking in the dumpster for free pumpkins to cook.  Unfortunately, there were no pumpkins, but instead a free air compressor.  I figured this was a better find.  I tried plugging it in, and the motor started sparking like crazy and spinning.  This was nothing I wanted to try repairing, so I decided to rig it up to a bicycle instead.
Campbell Hausfeld extreme air compressor

First of all, taking off the plastic housing to reveal all of the inner workings.  It wasn't as complicated as I expected, basically a motor spins a flywheel connected to a piston to compress the air, like a backwards combustion engine.  My modification was to take out the motor and attach a bike sprocket to drive the flywheel.
compressor without plastic housing
Due to the original design, this meant I would have to make a new shaft since the original one didn't have any space to mount a sprocket.  To add to the problem, I couldn't get the shaft out because the bearings were press fit and glued into the compressor's casting.  My only recourse was to do the impossible and drill out the entire shaft.  I was very lucky that the shaft was not hardened because otherwise the drills wouldn't cut.
 compressor diagrammodified compressor diagram
Taking the motor out.
removing motor from compressor
Starting to drill out the shaft.  I had to wedge a piece of metal in the flywheel to stop it from spinning while drilling.
drilling out flywheel shaft
After a lot of drilling, and using nearly every tool in the toolbox, I finally got the shaft and the bearings removed.
shaft and bearings removed from compressor
Starting the new shaft in the lathe.  I don't remember the dimensions since they were metric, and therefore, not important.
turning new shaft
Turning the other end of the shaft.
turning other end of new shaft
Milling set screw flats on the shaft.  The original shaft didn't have flats for set screws because all the components were press fit with tighter tolerances.
milling set screw flats on shaft
Now turning the hub for the sprocket.
turning compressor sprocket hub
Drilling the set screw hole after welding the sprocket on.
drilling set screw hole in sprocket hub
To start the set screw hole in the flywheel hub, I used a long center drill.  Of course I could've just cut off the belt teeth since they weren't needed anymore, but then it would look ugly and imbalanced.
center drilling flywheel
Tapping the set screw hole.  Good thing the tap was long enough for this.
tapping flywheel set screw hole
All the new shaft components are in place.
new flywheel shaft with sprocket in place on compressor
The only information I could find on bicycle-compressor conversions was from an Instructable where they made this:
I decided that I didn't want to destroy a perfectly good bike for this project, and also since this compressor is so small, I figured I could just mount my bike directly on it in place of the rear wheel.  Also look at that gear ratio! that looks like it'd take a fortnight to get any decent amount of air.
sizing the compressor with the bike
Perfect fit!
I designed this mess for the drive train:
complete diagram of bicycle compressor conversion
Here's the same thing, except less coherent and hand drawn.
hand drawn compressor diagram
First the piece for the big sprocket was made of some welded pieces.
welding pieces for sprocket adaptor
I took the big sprocket off some terrible old riveted crank.
drilling out big sprocket from terrible riveted crank
Now turning an undercut on the piece of plate to mount the sprocket. This was a pain because the interrupted cut caused enough torque to stall the spindle if the depth of cut was too deep.  Also boring the inside to accommodate the aluminum sleeve/bushing.
turning under cut to mount big sprocket
Afterwards, drilling holes to bolt the sprocket.
drilling holes to mount big sprocket
Then drilling and tapping a setscrew hole to secure to the aluminum sleeve.
tapping set screw hole in sprocket adaptor
Finally, welding on another small sprocket.  This is the one that connects to the bike's chain.  The big sprocket connects to the small sprocket on the compressor.  This way I've reduced the gear ratio twice, so it will spin fast.  During welding, I plugged the hole with a scrap piece of aluminum so no spatter would mess up the bore.
welding small sprocket on sprocket adaptor
Here I am milling a flat on the aluminum sleeve.
milling set screw flat on aluminum sleeve bushing
Now making the bushing shaft bits that the aluminum sleeve will spin about.  These thread onto the ½" threaded rod that goes in place of the rear wheel axle.
turning bushing shaft bits
The rod needed relief grooves in order to fit into the bike's dropouts.
cutting relief grooves on 1/2" threaded rod
For mounting all of this, I used the conveniently placed threaded holes that the original plastic housing screwed into.  I used some angle iron from a bed frame.
new angle iron mounted on original compressor housing holes
Then I welded the support rails on top.  Just to be safe, I covered all the compressor stuff with some sheet metal so I didn't accidentally ruin anything with weld spatter.
welding bicycle compressor support rails
For the slot the threaded rod mounts in, I started by drilling a lot of holes.
center drilling rails
Then bigger holes.
drilling rails
Then milling it out to ½".  Drilling the holes first made milling it a lot easier.
milling mounting slot in bicycle compressor rails
Everything ended up fitting together perfectly.  The first time I tried spinning it without putting oil on the bushings which caused the aluminum to gall and stall, not good.  After some lubrication, it would spin more freely.
bicycle mounted on air compressor
It looks pretty funny to have the rear wheel replaced by a compressor, but that was the plan, essentially an exercise bike that stores your energy as potential energy of the pressure difference between inside and outside the tank.
bicycle mounted on air compressor top view
Now the test.  I believe the chain keeps falling off because it is my old bike chain which was stretched by some ¼" per foot, and thus doesn't mesh with the sprockets correctly and therefore, loose.


  1. Great article on Air Compressors, very informative, thank you

  2. Well this is definitely a neat way of taking the seemingly pointless activity of riding an indoor bike and putting it to good use!

  3. I had a plan like this but could not manage it. It can be the alternative of generator powered air compressor where electricity is not available. I have gone through all your images given step by step and really understandable. I have a plan to try at home. I do some engineering works like this at home. This post will help a lot if I try to do it at any time.

  4. This is a good idea to infuse exercise while yielding something useful. The procedure seems complicated but I'll have my team work on it. I or my wife can be on that bike. Thanks for sharing this.

  5. Please provide full information in PDF format

  6. Wow great article
    Best for those who want to save money or having no electricity in there area. Never the less any one can built this.


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