OK, get your geek-goggles (nerd noodles?) on, and take a look at this. This is a floating swingarm design that allows the pedals, mid-drive and belt to all live in harmony and peaceful co-existence with each other, yet remain a moving swingarm suspension unit. From the BMW press release:
The drive unit swing arm is a new kind of frame technology for full-suspension eBikes featuring a mid-motor. The concept allows the drive train, which was previously firmly attached to the main frame, to float freely, eliminating the need for the conventional chain tensioner. This permits for the first time the combination of a rear suspension and the durable, maintenance-free carbon belt drive on full-suspension eBikes, resulting in outstanding propulsion and handling characteristics.
The BMW i patent for the drive unit swing arm principle facilitates for the first time the integration of mid-motor, gears and belt drive into an innovative suspension module, thereby dispensing with a belt tensioner.
The Heisenberg XF1 suspension detail
Apparently, this was developed with automotive applications in mind, but then had no real product targeted - thus the release of the patent to Heisenberg.
Heisenberg XF1 blet drive detail
This gives the bike the following:
- Mid-motor and even axle load distribution
- Maintenance-free belt drive with hub gear, without chain tensioner
- Highly stiff frame
- No pedal recoil
- Grip and traction in all riding situations, as there is no stiffening of the rear arm swing
- Possibility of implementing a modular drive system
- Freedom in the design of the main frame
Interestingly, this design harkens back to the old one-piece motor-final drive swingarm of the venerable Honda Hobbit, Cub, mopeddy thing where you get the motor, swingarm and drive chain all enclosed in one piece suspended from the frame. What is old, is new (and electric) again.