Unlike most motor conversion kits, which place a motor at a hub, the Revos instead uses a driven roller that wedges between a frame seatstay and rear wheel.
A magnetic sensor placed at the cassette then determines exactly when and how much power is sapped from its bottle cage-mounted 100Wh or 209Wh battery pack. This powers the roller, which turns directly against the bike’s rear tyre and provides pedal assistance right up to the UK’s limit of 15.5mph / 25km/h.
The beauty of the system is that it consists of only three main components: the drive unit, pedal assist sensor and the battery. Its design also means that it can be fitted to most bikes within minutes using just a couple of tools and a few cable ties. There’s also no controller at the handlebar to worry about, and switching assistance on an off requires nothing more than a slight backpedal at the crank.
This larger battery version weighs just 2.5kg (5.5lbs) and will retail for £499, though early Kickstarter backers will save £90 over that priceOli Woodman / Immediate Media
It’s also particularly light — just 2kg / 4.4lbs for the smaller battery option, or 2.5kg / 5.5lbs for the larger 209Wh battery pack. Once converted, your bike will be good for around 15–40km of riding, depending on the size of the battery pack you opt for. That’s hardly a class-leading range, but Revos is confident that, with the UK’s average cycle trip lasting a little over three miles, it’s a range that will suffice for most of its customers.
Should you end up with a flat battery then the Li-ion cell will be able to be charged to 80 percent in just one hour, and will be fully charged within two hours, but if you can’t reach a charging point then the roller of the drive unit can be manually retracted with an Allen key to remove any drag from the bike’s drivetrain.
Both the 100Wh or 209Wh battery packs attach to a frame bottle cage mountOli Woodman / Immediate Media
The Revos won’t fit every bike, but will fit most. To make it work you’ll need room for at least a 50mm x 50mm space between the seat tube and rear wheel of the bike it’s being fitted to. The roller needs to work against a relatively slick tyre, so a knobbly tyre would have to be switched out.
The Revos is the work of father and son duo Mark and Hugo Palmer, who started the project back in 2006 and have since left their careers to devote all of their time to getting the Revos to mass production. Now listed on Kickstarter, the Revos has already reached more than 50 percent of its funding goal, which should see a production version available for September of this year.
The roller uses a 30mm section of silicone grit tape to transfer power directly to the rear wheelOli Woodman / Immediate Media
Revos first ride impressions
The Palmers stopped by our Bristol HQ to allow for me to have a quick ride on a bike equipped with the system. I was very impressed by its smooth and predictable power delivery and never felt a need to alter from its predetermined assistance setting.
The unit was noisier than most mid-drive models, but I wouldn’t go as far to say it was loud. The drive unit showed no difficulty, slippage or strain when tackling some of Bristol’s steepest climbs. This has to be one of the most impressive e-bike conversion kits I’ve seen to date.