A friend, Marshall Thayer made the attachment bracket that is on the front of the frame of my four-wheel drive wheelchair. As you can see from the pictures and the diagram, it is a small solid piece of aluminum. A 3/4" hole has been drilled in the front and then an open channel comes out of the hole and runs to the side. Through that channel a screw is passed which allows you to tighten down anything that is placed in the hole. The bracket is attached to part of the wheelcair's frame that runs across the front of the chair. Two allen screws hold the entire device in place. Again it is quite simple but highly functional. All the equipment placed in this bracket must be either 3/4" pipe or tube. I have included these pictures to help you understand the concept but I do not encourage anyone to try and make it themselves. I am almost positive that it would need modifications to attach to different wheelchair frames.
Handihelp as now developed a Universal Chair Mount with a mount based on the principles shown in this bracket. We encourage you to look at and consider having this mounting system made for your chair.