This instructable is designed around my particular model of wheelchair which is an Invacare model. To make this work with your wheelchair may require some modifications. Also, be sure to check the warrenty on you wheelchair before making any modifications. This instructable will require drilling into your wheelchair which could void the warrenty of your wheelchair. Before making any modifications, make sure that all electrical connections are away from where you will be working. It should also be noted that this bumper will have to be removed when it comes time to replace the battery in your wheelchair.
For my particular wheelchair, the frame of the chair consist of two hollow metal pipes. Ordinarily, the ends of these metal pipes are covered by a plastic cap. For this project, the caps were removed and careful measurements taken of the size of this hollow metal pipe. On my chair, the pipe was large enough that two blocks of wood could be inserted into the frame on both the right and left side of the chair without interfering with any electronics.
The wood blocks have to fit tightly into the frame of the wheelchair as this will be the support for holding the bumper on the rear of the wheelchair. If you do not have a place to insert wood blocks, you may have to find another way to mount your bumper to the chair. The other principals for the bumper you may still find useful.
For my chair, the two scrap pieces of wood block, approximately 4 inches long and 2 inches wide where cut and sanded to fit tightly into the frame of the wheelchair. I painted these to match the color of my chair, though this is optional as not much of the blocks is visible. Measurements were then carefully taken to measure the distance between the center of these blocks of wood from the right to left-hand side of the chair. This will be the distance between the two drill holes you will need in your bumper. Next, measurements were taken of how long the bumper should be. For me, I didn't want the bumper to be longer than the width of my chair.