Cargo bike to tandem scooter conversion build

[glennb]

I haven’t seen this done before, so it might be of interest to someone with similar criteria to me.

I need a form of transport for couriering a mentally disabled person that comes closer to complying with the local vehicle regulations than what I’ve been using to date does.

This is the best that I can come up with to avoid confiscation, huge fines, and loss of driver’s licence.

It’s a compromised design, not really what I want. The small wheels are frustrating, but this has to look as much like a traditional stand-up scooter as possible to avoid attention.

It’ll be ugly, because it’s only required for a year or so, and therefore knocked together cheaply with whatever parts I have laying around.

I’m aiming for total weight around 30kg.

The passenger seat cannot resemble a seat, unfortunately, because the scooter must “be designed for a single person”. The fine for carrying a passenger is only $200. That’s ok, but I cannot run the risk of the scooter being deemed to have been “designed” for more than one person.

It’s also going to be a harsh ride. I have another equivalent full suspension frame, but I dislike the heavy steel and can’t be bothered tuning the suspension.

Anyway, enough of the preamble, it’ll mostly be photos from now on. I’ll snap them as I go, and add brief explanations.

 

[glennb]

This is the gist of it.

The riding position and front end geometry is how I want it.

The main effort will be building the fork.

 

[glennb]

The original fork is unusable, have to start from scratch.

Steerer tube is 300mm.

 

[glennb]

For the fork steerer I’ll use 1 1/4 inch pipe.

The frame barely accommodates it. With paint on it won’t fit through the head tube (which was supposed to be used with 1 1/8 inch steerer).

The headset is easy enough. No head tube modification, just had to make a shim. And will have to change the top cup to threadless.

 

[glennb]

That’s it for a while. I’ll work on the fork now.

P.s. the headset shim is a ground down bottom bracket shell.

 

[glennb]

It’s all going to rough as guts, but there’s a couple of parts that need to be reasonably square and flush, including these things - not sure what to call them.

 

[glennb]

The packers for between steerer and side plates are cut and drilled …

 

[glennb]

The plates were recycled from an old scooter.

Making new ones out of aluminium wouldn’t save much weight.

I might anyway, but no need for now, and it’d be to reduce steering trail rather than weight.

With a straight blades without offset, the trail should (at a rough eyeball guesstimate) be around 50mm, which is likely too much.

With a 1250mm wheelbase, and slow speed, plus an extra 70kg passenger on the back … nothing’s going to make this scooter handle well, so the trail’s probably moot. I’m just mindful of a past scooter fork I built for zero trail, which was problematic at high speeds

 

[glennb]

Completed fork.

I’d like to say it’s only a prototype, given how ugly it is, but that’d be misleading.

 

[glennb]

Brake adapter. Aluminium would be stiffer and lighter, but it is what it is.

 

[glennb]

I told a lie. Fork wasn’t complete.

Assad a bracing plate …

 

[glennb]

Probably should add one to the back face of the crown as well.

 

[glennb]

If I made a bracing back plate with cutouts around the pinching clamps, after affixing it I could actually cut off the protruding clamp sections..

Trouble is, if I ever need to disassemble the fork they’ll spring back out, and I’d need a huge vice to force the assembly together in order to bolt it together again.

 

[glennb]

If it wasn’t obvious, the point of the pinching clamps is to remove any play around the steerer tube. The torque required to achieve this via the long horizontal bolts would likely be more than the nuts could handle … they’d surely strip threads.

 

[glennb]

Added a back plate.

I originally planned three bolts to bind the crown together instead of two, so that if a bolt snaps the fork won’t lose rigidity, but didn’t bother, because the assembly’s so tight that there’s no location along the length of the bolts where them snapping would cause any immediate danger - the bolts practically had to be hammered in.

Anyway, the backplate will prevent the fork from collapsing (pivoting around one of the bolts) in the almost impossible event of a bolt managing to shear off cleanly in two places at once either side of the steerer.