Sep 29

All-terrain Mobility Scooter, Part 1

A few months ago I decided to build an all-terrain mobility scooter for a handicapped friend. This blog series will show the machine taking shape.

This is an Ortho-Kinetics Triumph Model 4390 mobility scooter, circa 1990. This works OK for Pete, but isn’t too good over boggy or bumpy ground in the paddock. I bought two of them as a cheap package deal (neither of them were working).

By the time I purchased the scooters all of their electronics were non-functional, so this one has been adapted to use a $20 eBay motor controller.

This children’s quad bike (with dead engine) is going to supply most of the parts needed to build an all-terrain mobility scooter.

Here’s the first “trial fit” of the layout, using the seat from the second Triumph scooter. I’ve used a plank of wood and some clamps to see how high we can raise the handlebars.

A side view, with the steering at full lock.

Side view, steering straight ahead.

These two drive motors have come from another donor scooter with dead electronics (this time a mid-1990s Fisher & Paykel)

We’ll be driving each rear wheel with its own motor, 200 watts per wheel.

Here I’ve cut the front end off the quad bike, and tilted the steering column back to give an easier reach to the handlebars.

A view with the front wishbones and hubs refitted. This quad had mechanical drum brakes on the front wheels, which will come in handy. We’ve also used the quill stem from a children’s BMX bike to get some adjustability.

Full right steering lock.

Closer view of the front suspension assembly. The new extended steering column is a different diameter to the original, so I made a “splicing plug” on the lathe to bolt the two together. This will also allow us to dismount the handlebars if this machine ever needs to be transported in a vehicle without much vertical space (i.e. a Toyota Corolla station wagon).

I had to cut and re-weld the steering pivot to tilt the steering column.

An assortment of useful pieces from the scrap dealer, and some 5mm thick disk blanks from the steel shop. The disks are usually welded to fence post tops as caps, but I’ll be cutting them into sprockets for the chain driven rear wheels.

A solid rear axle like this has to spin the “inside” rear wheel on tight corners. I’ll be cutting this one into two stub axles, and driving each rear wheel with its own electric motor.

Checking the layout. The final chassis will use 4 parallel 25x1mm steel tubes, with a topping of aluminium tread plate. I’ll add triangulation bracing to the high-stress areas. The turning circle won’t be as good a a 3-wheeled mobility scooter, but that shouldn’t matter because this one isn’t intended for indoor use.

The two “inside” chassis rails are a different diameter to the existing quad bike frame, so I’ve made some adaptor plugs to bridge them.

The adaptor plugs are hammered into the ands of the existing frame (they’re a “snug friction fit”).

I’m also slipping a piece of intermediate-sized tube over the skinny quad bike frame tube.

All welded up. I drilled 10mm holes in the chassis rail tubes so that I could weld through into the adaptor plug.

The frame bracing will be made from these old 1980s chairs. These were the high-quality “made in Italy” variety.

The chair frame is made from a single piece of thick-walled 25mm steel tube, with lots of useful 90-degree bends.

Squeezing the end of a tube to make it easier to weld onto the chassis rail.

This was a little optimistic of me, but it would have been much quicker to construct.

Unfortunately I didn’t take either steering lock or suspension compression into account.

90 minutes later, all better.

Assembling the outer chassis rails parallel to the inner ones.

Back outside the shed for an ergonomics and component fit check. The chassis tubes will be cut to their final length once everything has been checked and tested.

The rear axle is just sitting there for show at the moment. I’m hoping to get the new rear stub axles constructed this week so that we can do some billycart testing next weekend.

Front view.

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