the 'Camel' - Brompton/pronto hybrid

Most electric bikes have a hub motor in the front or rear wheel that provides power betwen 0 and 15mph with a single gear ratio.

The Pronto powers the bike through the chainwheel and so it uses the gears to tackle a range of terrain: good hill-climbing and a decent top speed *

all informatio npresented here is my creative work and is copyright 2008-2010

The motor cradle is designed to suit a range of frames and is slotted to allow exact alignment of the cog and chainset. Hidden is the chain exit slot (look at the bottom view of the cradle below). The side is bolted on so that a chain can be installed with a breaker. 3 motor positions are provided - 2 axle slots, and the sides can be exchanged for the 3rd position.

A chain tensioner (not shown) also has 3 positions. 2 frame clamps (with plastic grommet and tube to prevent paint damage and provide grip) hold the cradle to the bicycle frame.

U -clamps hold the cradle to the frame. In some cases a torque arm is required from the motor to the frame to prevent rotation of the cradle under full power


The cog mounting plate is drilled with 'disc brake' hole centres with 6mm stand-offs to mount a fixie cog. Cogs are available from 15T to 19T to suit a range of gearings. Here I used 'rivet nuts' or 'nutserts' fitted to the adapter plate.

The motor fixings depend on the choice of motor - the nano has 6 x 4mm screws.

Top and bottom views of the motor and cradle fitted to the frame tube.

The tube clamps are sleeved and have grommet strip to prevent damage and improve grip. No torque-reaction arm, to prevent the cradle rotating around the frame tube was found necessary (but I may fit one, anyway!)

Brompton Camel

Two views of the 'Camel' that explain the name!

With a 15T motor cog and a 44T chainring, top speed in 1st gear is ~ 8mph with improved take-off and hill-climbing compared to the same motor in-wheel. 3rd gear delivers 15mph

Brompton Camel
Brompton Camel

<< close-up of the drive system ....

The front wheel hub motor is used to compare performance, not actually 2X2.

.....and of course, it folds! >>

Brompton Camel

* The Camel is somewhat 'tongue-in-cheek' as the motor seriously impedes a good riding experience! I offer it as an example of what can be done - I built it to compare a front-wheel hub motor with a Pronto hub of the same spec.

here is a link to all Camel photos