Over Christmas I spent considerable time looking at the properties of different metals to find which is suitable for building the mountain wheelchair frame. Steel is far too heavy; even this smaller “prototype” which I built earlier in the project weighs 40kg. That’s half a grown man!
The other two likely candidates are aluminium or chromoly. In the end, I decided to go with 6061-T6 (or its UK equivalent 6082-T6) aluminium. This alloy is used in a wide variety of applications where appearance and better corrosion resistance with good strength are required. However, everything I’ve read and all the advice I’ve received have suggested that welding aluminium is not for the beginner.
First Full-Size Test Vehicle
Before building the full mountain-going wheelchair, I figured it’s best to get the rocker-bogie part made first, with some kind of platform in-between for batteries (see image below), make this radio controlled, and then run some tests. At this point it should in theory be capable of getting up Snowdon, if not then it’s back to the drawing board. Eek!
Quotes for Building the Frame
With this in mind I’ve obtained some quotes for making six sets of bicycle forks to accommodate the hub motors. Quotes have been in the region of £1,200 – £1,500.
With £1,500 just for the forks, I imagine I’d be looking at 5/6k for the full thing. In light of this, I’ve decided to continue with the same mindset that I’ve adopted thus far and attempt to weld an aluminium frame myself. Not only will this keep costs down, but it means I will have complete control of “deadlines” and be able to make modifications both during the initial build and at a later date after having conducted some tests.
Pre-made Bicycle Forks
To try and simplify some of the fabrication I went ahead and purchased 6 pairs of pre-made BMX forks. The forks have the correct dimensions for my needs, are made from the same 6061 aluminium that I plan to use for the rest of the frame, and are intended for trials riding (jumping over rocks) so should be perfect for the mountain wheelchair.