Electric Brompton? DIY Friction Drive Solution

07Sep2019 Updates
Upgrades for Turnigy Aerodrive SK3 6364 6374 190kV brushless motor
See: https://www.thingiverse.com/thing:3849507

Instruction for wrapping SBR around the motor for best performance
See: https://docs.google.com/presentation/d/1FQdWPTe3nYMLmk8AB0c-IvsF8gwB6K-7bOEx_NRSsPg/edit?usp=sharing

Hello Redditers! (┛❍ᴥ❍)┛

Google Doc - Assembly Guide:
https://docs.google.com/document/d/1Bp1OWOW-BHIptmso75VmstHCjkk27gZrm52MQJ5cX-I/edit?usp=sharing

The uploaded photo should be self-explanatory to assembly, if not download link to google doc below, including a PDF version here for our friends in China, without Google services.

Hello 3D world,

Preface
I present to you a solution, minus the exorbitant cost of an electric Brompton bike, to convert you bike (not just a Brompton) to an electrically assisted bike.

It is also very easily removed, as such, you're not saddled with a heavy hub motor (like the electric Brompton) should you prefer naturally aspirated sweat and muscle power and retain your £$ investment in those Titanium parts)

Description
This is a friction drive solution, it dates back to the French VéloSoleX, where a small internal combustion engine is mounted on top the front wheel of a conventional bicycle, to date, these collectable classic still roams the street of France (Hi Xavier ^_^ ).

https://en.wikipedia.org/wiki/V%C3%A9loSoleX

But before excitement overwhelms you...

WARNING

I worked on perfecting this design over a year, my other 3D printed Brompton upgrade for the front carrier block forms part of this design. It carries the battery pack and VESC brushless motor controller.

http://www.thingiverse.com/thing:3178214

My design is printed with ABS at 0.2mm layer height, 100% infill and tested >100KM of regular use, wet and dry.

I am satisfied with the strength of the material and the durability of the design, especially the fully 3D printed securing mount to the heavy brushless motor, it transfers the radial force like a tire), when compressing the motor with the wheel (hence the friction drive), to a lever beam (i.e. a 8mm carriage bolt), and securing this bolt, is a re-purpose Brompton front reflected mount. For this purpose, the bolt is threaded through yet another 3D printed part, which secure the motor mount as a fixture to the reflector.

This reflector mount is a key component of this design, which provide some gives, for it being flexible, enabling adjustment to the compressing friction (between the motor and wheel). The levering force also minimised, as bolt 'pivot' around the reflector mount at half length.

The reflector mount also allows for securing an extra bolt in the name of safety, in case the mount flies off!

BUT do regularly check the component, in case of wear and tear (or lose bolts)

Use threadlocker (e.g. Loctite)

CAVEAT

This solution does not fair well in wet weather, but hello dry weather and sunshine, it works like a dream, enabling pedal assistance >45KM/h (unladen speed registered by the 16 inch wheel is about 70~80KM/h).

It is also able to accelerate unassisted (NB: this is dependent on your brushless motor controller current limit, battery max current draw and your motor kV ratings)

Another key requirement to enable good traction with the wheel, the preference is to wrap and adhere SBR rubber around the (Outrunner) brushless motor.

https://en.wikipedia.org/wiki/Styrene-butadiene

For a (durable) solution, tested to >100KM, I use sheet SBR rubber of 2mm thickness. It is sufficiently flexible for this purpose.

Buy here (in UK):
https://www.ebay.co.uk/itm/RUBBER-SHEET-VARIOUS-SIZES-X-1MM-TO-25MM-THICKNESS-AVAILABLE/141120177410?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Cut it in width and length to fit the circumference of the motor (also accounting for material thickness), glue the cut ends with Cyanoacrylate (Super Glue), use sparingly, as it dries hard, we do not want hard rubber! NB: this cylindrical tube should fit snugly around the motor.

To adhere the cylindrical rubber tube to the motor, use expanding polyurethane Gorilla Glue, this is the kind activated by water, generally looks and is viscous like honey.

Alternative is to look for a rubber tubing of suitable diameter... For which I have yet to locate.

Okay, you have been forewarn, read on

Bill of Materials

There's also a fair bit of fasteners to gather. I have reduced this requirement to minimal, including the required bearings..

1 x 6364 KEDA 190KV brushless motor.

Other 6364 motor will also fit, diameter should be 63mm, motor length. excluding shaft, 67mm.

https://hobbyking.com/en_us/kd-53-30-high-voltage-brushless-outrunner-190kv.html

1 x M8 (8mmØ) CARRIAGE BOLTS WITH NUTS & WASHERS CUP SQUARE COACH SCREWS ZINC PLATED), threaded length is 65mm.

4 x M4 x 16mm Button Head Bolts, to secure motor mount to motor

4 x M3 x 10mm Countersunk Bolts, to secure the cool looking external blower fan

1 x M5 x 25mm Socket Cap bolt and nut, a security bolt, in case either the motor mount laminates or flips backwards (e.g. if motor wiring inverse)

2 x Bearings F688Z, (8x16x5mm) Metric, one on motor mount, one on fixture mount, it may be necessary to place washers as spacer to aid free movement.

2 x M5 x 40mm Button Head Flanged and Flanged nut, this pair of bolts secures the fixture to the reflector mount. Releasing this two bolts removes the motor, takes just a minute!

1 x M5 x 20mm Socket Head bolt and nut, this is an extra security bolt, just in case.

1 x Vedder VESC V4.12 (Firmware updates and software can be obtained from VESC Project site)

http://vedder.se/2015/01/vesc-open-source-esc/

https://vesc-project.com/

https://www.aliexpress.com/item/33057761841.html?spm=2114.search0104.8.19.6ad162eejjIxmp&transAbTest=ae803_3

https://hobbyking.com/en_us/turnigy-sk8-esc-v4-12-for-electric-skateboard-conversion-w-bec.html

1 (or 2) x 36V 4.4Ah high drain Hoverboard battery pack with BMS

https://www.aliexpress.com/item/32796539334.html?spm=a2g0s.9042311.0.0.42084c4djxfdV4

https://youtu.be/a-QQpKlPf8s

https://youtu.be/mfbv9bPSNcI