GenX™ drive by wire system

The Generator

In 2017 the GenX™ was brought to life. This to reduce the complexity of specialty bikes since these often have complex chain setups that require custom parts not readily available. Going all electric was the logical choice after studying all the alternatives to a chain.

The GenX™ only needs an electrical wire to your battery giving you ultimate freedom when designing while keeping the “feel” of a regular bike. It fits on a standard 68mm bottom bracket and only weighs 3.36Kg. It supports up to 70 Nm pedaling force and an unlimited amount of gears between a cadence of 18 to 102 rpm. It automatically lowers/disables its power output power when the battery is near full to prevent overcharging.

The Controller

The generator is only half of the solution. It integrates seamlessly with the the TwinDrive™ sinewave controller. The controller works as a switch regulating where power is send. Its decision making depends on your brakes being engaged or not, the level of assistance desired, your speed, how hard you are pedaling, and the charge level of your battery. It allows for a portion of power to be drawn from the battery as electrical assist. Alternatively it allows the battery being charged by pedaling at standstill, or engaging the e-brakes. Another great feature is that it lets you drive in reverse by using the walk assist button.

Each Controller supports up to 4 independently working GenX™ generators. (A controller supporting more could be made on request as this limit is only due to the technical limitation of the current sensing chip.)

The Display

The TwinDrive™ controller interfaces with the display. This shows you how much power you’re generating, your battery level, speed, and many more. On top of this it has a background menu that allows the customization of many bike characteristics. Maximum speed, boost, regenerative brake strength,…. Since the software was developed by Geminus bikes from the ground up we can make customizations to any part of it or add features.

About the Efficiency

The GenX™ system has an efficiency between 70% and 85%. This means between 70% and 85% of the energy you put in ends up at the rear traction motor or into the battery. Extensive testing has been done for all the gears. Below you can find the results for a torque sweep that was done for each gear. The green line is the torque being gradually increased from 0 Nm to 70 Nm for a number of different pedal cadences.

Most people will put out about 10~20 Nm of torque at a cadence between 50 and 90 rpm when cruising. This corresponds to between 50W and 180W. This is where the efficiency of the GenX has proven to be the highest (around 80~85%).

Below is a detailed plot of one of the gears to better understand how the efficiency(bottom brown line) first builds up and then declines in respect to the torque (top green line).

  • First the efficiency builds up quickly. This when the input torque becomes higher than mechanical losses of the gears and bearings. The excess is converted to electric energy.
  • Once the peak has been reached; the efficiency starts to decline as the current in the electric motor becomes higher. This increases the resistive losses of the motor. Here we had to make a critical choice between generator weight and generator maximum generated power.
  • Higher gears do lose a bit more efficiency because of hysteresis in the metal core. Hysteresis losses are due to the generator resisting fast changes of its magnetic field. The magnetic field rotates along with the generator, the faster you pedal the faster the field rotates and the more it starts resisting.

Implementing the GenX™ drive by wire system

Currently implementing the twin drive needs some support from our technical team. This is only worth it if you’re looking into manufacturing a number of your bikes.