Electric scooter upgraded to three wheeler.

A couple of years ago I converted a standard kick scooter to be electric for my younger son. I had the motor controller, battery and motor in a single unit simply bolted to the rear of the donor scooter. He loved it!

                                            

 I described the conversion here. 

However, whilst recently browsing AliExpress I came across these, a dual brushless motor drive unit for mountain boards.

It just so happened that my oldest son got the taste for mountain boarding about 5 years ago, then lost interest in it and the board has sat in the shed since. With #2 son spending quite a lot of time on the scooter, and me trailing him on foot I thought it might be time to awaken my skateboarding talent that has lain dormant since the '70s.

I ordered a rear wheel only kit , battery and controller and bolted them together.

No surprises here. Just a few holes and a bit of wiring and I was off.

Problem with this is #2 son realises the mountain board is significantly faster than the scooter and confiscates it.

This does of course mean, once again, I'm trailing him on our outings..although at least I can use the scooter. This was less than ideal given his new speed, so the only course of action is to put the same mountain board motor unit on the back of the scooter to make an e trike.

As the original had an all in one design, I just CADed up a replacement with the dual motor drive instead. 

I used a combination of manual milling and CNC milling on DIY CNC to create the new parts.

15mm aluminium plate for cross pieces....

Bolted to a 6mm aluminium plate....

Which in turn bolts to the scooter body. The electronics sit in a box cavity to keep them safe.

The mountain board controller is a bluetooth hand held device. It has a simple self centering thumb throttle potentiometer which you push up to move forwards and pull back to e-brake. In particular, it has a nice feature where if you release the throttle then immediate push push it up again, the motor controller switches to a faster motor speed, kind of like a gear change.

I quite liked the idea of this, but decided that using a traditional scooter twist throttle it would not be easy to operate it fast enough to get the same operation. I then realised I could achieve a good alternative by using two thumb throttles. One on each side of the handlebars. Right side for brake and left side for throttle.

To make the two potentiometers act as one I was going to need something more than simple wiring to connect them to the original handset. 
I designed an Arduino circuit to take the inputs from both throttle and brake pots and with some software filtering drive an electronic potentiometer which I simply used to replace the one in the hand held controller.

The board also has a DFPlayer mini on it as my son wanted a horn/siren facility as well.

I designed the schematic with my go to PCB package: Design Spark.

And a PCB:

Which I routed on Bertha, my DIY CNC:

With the PCB made up and a test jig for the thumb throttles I was ready for a test. Here I demonstrate the controller action of the mountain board controller and my version of it. I was initially planning to replace the 3.7V LiPo on the handset controller with an Arduino controlled power supply to replace the battery and the power switch of the handset, which was one of those press to power on, press and hold to power off types.

Luckily, I found that the handset is quite happy to power on with just 5V from the micro USB charging port, so in the end it just shares the 5V feed with the Arduino.

The software always prioritises the brake function over the throttle and the braking is or variable strength. I also added a digital input to the Arduino so that I could connect up a traditional brake handle with a built in switch to apply full braking when it is applied.

Happy that the electronics and software were OK. I designed a simple 3D printed box to house the handset, Arduino and a switching PSU to drop the 42V battery down to 5V.

This was 3D printed with some clamps to hold it to the steering column.

I also transplanted the original controller battery voltage meter into the new housing and added a key switch.

So with everything together it's time for a trial run, which of course I didn't get to do. I just rode wingman on the e mountain board. The smile at the end says it all!.

I'm happy with the way this turned out. It's great fun to ride and it's certainly different from the run of the mill two wheelers everyone else has.