Details and technical data

The assistance control on Stromer S-Pedelecs is initially based on a TMM sensor (Torque Measurement Module) in the right-hand dropout. The TMM sensor is actually a force sensor and not a torque sensor, as it is commonly referred to. It measures the force exerted on the chain/belt by pedaling. The measured force is directly proportional to the torque on the bottom bracket, which is generated by pedaling, hence the term torque sensor. See here also the topic 'Functional principle'.

The manufacturer of the TMM sensors is the Dutch company I|D bike.

The Hall sensor mounted in the sensor plate measures the deflection of the plate caused by the tensile force on the chain (pedal torque). The maximum deflection is 0.1 mm. The Hall sensor supplies 1 V for every 40 Nm of pulling force. So if the rider applies a pulling force of 40 Nm to the chain, the sensor voltage deviates upwards by 1 V. 

In addition to the pedal torque, other factors can also have an influence on the sensor voltage and lead to fluctuations in the TMM signal:

• Cadence of the rider
• Steep uphill and downhill ride
• Selected translation
• Chain line
• Outdoor temperature, solar radiation
• Torques of the thru axle and sensor plate in the dropout
• Unevenness of the road surface

Technical specifications:

Environmental impact

I|Bike writes:

The sensor electronics are protected against moisture, salt and dust by a special coating (IP66). The sensor has been tested by I|D bike under extreme outdoor conditions, including a one-week test in salt water.

However, contamination of this magnitude can certainly influence the measurement and should be removed.

Temperature drift with solar radiation

According to the manufacturer, the temperature drift of the sensor is negligible (< 1 mV/ ºC | < 0.02 Nm/ ºC).

Practice: My experience is that there can indeed be an influence, especially if the Stromer is in the sun. If the right-hand dropout with the sensor is exposed to prolonged sunlight, its temperature rises and can increase by 20-30 mV. 'voltage' are generated. This is noticeable in a more or less strong self-propulsion (scooter effect). It can also happen that the Omni then displays a calibration warning:

If you press CANCEL, the vehicle is no longer ready to drive. The Stromer must be restarted.

Temperature drift and the ambient temperature

If the bike is in a cool cellar, you calibrate it there and then ride it in summer temperatures, the 'voltage' also increases due to the temperature drift and pushes the Stromer better over the road. Conversely, if you calibrate in warm temperatures and then leave the bike in a cooler environment, the voltage drops. If the 'voltage' drops below the value of the 'offset', this can lead to ripples in the support. If you look at the issue over the whole year, you can speak of a necessary 'winter or summer calibration'.

QR code sticker

In the Stromer, the sensor is sometimes additionally covered with a QR code sticker. It only contains the part number. It has its own theme 'QR code sticker - what's it all about? dedicated.