A lot of people want an electric boost while they're cycling, but don't want to replace their perfectly-good existing bicycle with a costly new e-bike. That's why several types of add-on motors exist. One of the latest, the Swiss-made bimoz, is not only a lot less obtrusive than most, but at 1.97 kg (4.3 lb) including battery, it's also claimed to be one of the lightest.
Similar to the low-profile Bionicon e-ram, the 250-watt bimoz motor attaches to the bottom bracket, taking the place of the existing left-hand crank. It's powered by a removable seat tube-mounted lithium-polymer battery pack, and the amount of pedal assistance is controlled by a hard-wired bar-mounted remote.
A torque sensor measures how much pedalling force the rider is exerting, then augments that with electrical power – there is no throttle-only setting. It has an electronically-limited top motor-assisted speed of 25 km/h (16 mph), and a stated range of approximately 130 to 150 km (80 to 93 miles) depending on use. A full battery charge takes three hours.
One thing that the direct-drive bimoz lacks, however, is a gearbox. Instead, it uses a proprietary electromagnetic system to engage the bike's drivetrain. This reportedly helps keep its weight, complexity and operating noise down, while also eliminating added friction when the bike is being pedalled in full-manual mode, with the motor shut off.
The bimoz system can reportedly be added to just about any bicycle, in under 20 minutes. It can also be used with an accompanying app that does things like increasing the amount of electrical assistance as the rider's heart rate increases, or even adding friction in order to simulate a hill-climbing workout while riding on flat ground.
If you're interested, the bimoz is currently the subject of an Indiegogo campaign. A pledge of US$899 will get you a kit, when and if they reach production.
More information is available in the following video.