I got the idea of modifying my back-pack bag on the wheelchair to hold a roof canopy that could be quickly attached to my wheelchair, and when not in use, returned to the bag. Before you begin this project, you must keep in mind that all wheelchairs are not built the same, and every individual in a wheelchair is a different height, and so you may have to modify my design to suit your own needs.
Material (Approximately 4 yards)
2 Dowel sticks or metal spreader bars
6 Eye Loops
4 Metal trigger clips
2 metal rods
needle and thread
Step 1: Step 1: Measure twice... three times
In the illustration, the Bar Bracket is labeled and is shown as attached to the wheelchair. This bracket may be attached higher or lower depending upon what works for a particular wheelchair model. Depending upon the height of the individual in the wheelchair and the angle you wish the canopy to rest, the lengths of the canopy bars labeled BAR F and BAR G may change. You will want to measure the Height of BAR F first using a yardstick measuring from the position the Bar Bracket will be attached to at least three inches above the head of the individual who sits in the wheelchair. Keep in mind, you'll want this bar to be at a slight backward angle so that the roof fully covers the individual's head. It is better to add extra height to your measurement then be too short. Keep in mind, the canopy will be made of material and will sag some in the middle. Next, measure how long BAR G must be. You can vary the angle of this bar which will lengthen or shorted its length. The shorter the bar at any given angle, the more forward sloping the canopy will be. The longer the bar, the more upward sloping the canopy will be. The angle must be taken into account in your measurements. The greater the angle, the longer the bar must be, and the greater the canopy length. You can either measure the angle of this bar with a protractor, or can do it the easy way and take a piece of paper to mark down the angles of the two bars and the length they must be. Work out on paper with pencil first the bar angles and lengths. Next, measure how long the canopy must be given the angle and length of those bars.
Once you know the length and the angle of the two poles, you can solve for the length of the canopy using some trigonometry (The first time ever found a use for trigonometry!). Unfortunately, I was never very good at trig, and so I laid out the angles using three yardstick rulers to get the appropriate dimensions and traced the angles onto a piece of paper. If you want to do the math, you can look at http://www.teacherschoice.com.au/maths_library/trigonometry/solve_trig_sss.htm for how to calculate the dimensions.