Bosch ebike mechanical derestrictor


Finding my (electric) wheels
Jun 2, 2012
Readers may be interested in my attempt - not quite successful - at a mechanical derestrictor for my Bosch system. Electronic systems are available - the BadAssBox series, for example - which detect the magnet passing their own sensor and pass every second pulse back to the Bosch system to fool it into thinking that the bike is running at half the actual speed. I wondered if this could be done mechanically and came up with the following.


Figure 1. The original magnet is converted into a striker which rotates the star-wheel 1/4 turn every wheel rotation. A pair of magnets on the star-wheel pulse the sensor every second wheel rotation.


Figure 2. The star-wheel is 50 mm diameter and the prototype is cut from acrylic. Magnets are taped to two of the spokes. I suspect that these are too far from the pivot and that the Bosch sensor is closer to the mounting hole.


Figure 3. Star-wheel mounted on M5 x 30 mm bolt. Assembly is flat-washer | star-wheel | spring washer (to provide friction and prevent run-on) | flat washer | nylok nut 1 | nylok nut 2 (sets the offset from the sensor) | flat washer (not shown) to avoid distorting the sensor.


Figure 4. The assembly. An M6 nut is taped onto the Bosch magnet to extend its reach to the star-wheel.

- I have left the magnet screw a little loose so that if it hits one of the star-wheel spokes edge on then the magnet will rotate on the spoke to avoid damage.
- There is a soft audible click in use. This is useful to hear that the device is working.
- The numbers on my speedo jump around fairly wildly. I suspect that the magnets may not be strong enough.
- I made sure that the magnet polarity was the same as the original actuator.
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Esteemed Pedelecer
Jun 18, 2013
A + for the idea, I’ve Been there and done that, the soft audible click gets louder the faster you go and the constant impacts will break stuff sooner rather than later.
my zero impact pulley system worked well back in May 2019