I kept a lot of the original geometry because this seemed like the most sensible configuration to use. I compared it to commercial delta trikes and they often matched, but for various reasons some aspects have changed or added to.

The biggest constrain I have is materials. You do not always have a wide variety of choice when you are looking for cheap second hand donor parts and materials. You have to design with what you can get and that can have major ripple effects throughout the design.

for the rolling frame, I knew that I wanted full suspension, but the design and dimensions of these features were greatly depended on what donor material I ended up with. The first real buy was a parts bike for tuppence.

This is a kids dirt bike. Not the best, but it can take a beating. The frame is steel, as it should be so I can weld it and this basically dictated that the front and rear wheels wanted to be 20" with a 9cm wide hub. It also gave me a front fork with suspension, rim brakes, a 6 gear cassette and a crank shaft. So all the designs you seen with a crank motor you can forget about. Parts of the steering wheel could come in handy as well as the remaining tube sections.

It also came with a ridiculously oversized stand which I fitted to another bike that needed a replacement (That part alone in the shop would have cost me more than this entire bike did!)

The rear suspension was semi-dependent on the steel I could scavenge and what shocks I ended up with. I now have the shocks.
 

This set is for a scootmobile. A electric mobility scooter for people with various types of disabilities. These are quite simple and can take a lot of weight. These are 20cm from axle to axle and require very little redesign of the rear suspension albeit I decided that one major modification was needed. This is now the rough design of the rear section.

Looks pretty sane, but there is one problem here....

You see the problem here. Not having 4 springs, I did not want them to be mounted outside the suspension arms to reduce load. Well, put them in the middle then! that would be alright for the right arm, but unfortunately the left arm also has the drive shaft running through it and I designed the original to small. So this changes the dimensions of the arms, the steel box section, the attachment points for the upper frame bars and much of the gearing and drive system placement.

And still the final frame design has not been set in stone. Well, that is what scrapyard iterative design gets you!