Mention of this project should acknowledge Ryan McFarland with a link to zieak.com as well as Instructables and this project page.
Step 1: Supplies and materials
3 - 4 crutches
2 bicycle wheels with a 16" diameter (BMX bike size)
4 inner tubes from a 26" tire (Mountain bike type)
Sheet metal screws
Carriage bolts, washers and nuts
Drill and drill bits
Ratchet and sockets
I purchased the metal crutches from the local thrift store. They were $2 per pair. Try to get two pairs that are as close to identical as possible. (You might consider buying an extra pair that fit you in case you need them some day. A few years ago i tore a muscle in my leg and was charged $80 for a pair.) Remove the handles from the crutches. The bicycle rims don't need to be perfectly straight - the ones i used were in horrible shape. I didn't bother trying to true the wheel - i wanted to see if this idea would work first. You can probably get the wheels and inner tubes at any bike shop for free. You'll want to remove the axles. Wash the grease off of the hubs.