Description
Support problems are one of the most common problems with Stromer bikes. The central element for regulating the assistance is the torque sensor in the left dropout. It measures the force acting on the chain when pedaling and converts this into a voltage. This is evaluated by the riding computer, the OMNI, and forwarded to the motor controller (MCU = Motor Control Unit) depending on the gear setting and the so-called pedal sensor value (designation in the Omni app). This in turn controls the hub motor.
The torque sensor has a working range or voltage window within which the voltage supplied to the Omni must lie. If it is above or below this defined, model-dependent threshold, a calibration error is displayed in the Omni and support is discontinued.
The factory adjustment of the sensor and the tightening torque of the thru axle in the rear wheel and the sensor plate in the dropout are responsible for ensuring that the tension is within the working range.
Stromer has repeatedly made improvements over the years. For example, the TMM sensor models have been changed, the tightening torques of the thru axle or sensor plate have been adjusted and a 'Use Trace' function has been implemented to compensate for fluctuations in the sensor.
Problems
- Pumping / waviness of the support
- Weak or over-motivated support (self-propulsion, scooter)
- Tough or incomplete support (lack of Stromer-Wums)
- Sudden loss of support
- Delayed support after braking
- A perceived braking effect when pedaling, the bike does not 'pull'
Checklist: '+Stromer- | Solve support problems'
Bracket open [
The TMM sensor is not the only source of support problems. Before tackling the checklist relating to the TMM sensor, it is also worth checking the following sources of faults physically or with the SIT (Test Runner) to be checked.
- Motor defects are rare. If this is the case, it is usually caused by a Hall sensor, the temperature sensor or rust in the engine due to water ingress.
- Motor cablewas a particular problem with the ST2(S)
- Motor plug loose or damp on the left chain stay
- Motor cable connections in the bottom bracket area, especially in older models, not insulated. This led to corrosion and subsequent faults
- Controller
- Reed switch in the brake levers (for recuperation). Rarely defective but possibly incorrectly adjusted.
> See BREMSEN - 'Reed contacts: Setting brake light and recuperation' - Battery has too much play in the battery slot (especially ST1 / ST2)
> See PROBLEMS - MISCELLANEOUS - 'ST1/ST2 switches off while driving'
] Bracket closed
If hardware defects can be ruled out, there are various approaches to solving support problems. These range from simple calibration to replacing the TMM sensor. There are also curious solutions such as honking the horn or fitting a jacket wave filter to regain assistance (see below).
Checklist
My Checklist lists 14 different problems and phenomena and describes possible solutions. [Print version] / [Web version - translatable]
Feedback in forums
Waviness of the support
Here is a representative report from forum member 'Georgio' in the Dutch speedpedelecrevie.com forum. He describes his experiences as follows and defends the 'sensor'.
Irregular support is experienced by many (including myself). Based on the design of the sensor, the sensor is a pretty simple concept, which means it does its job "well" or "not". There is no in-between.
A fluctuating sensor?
It often happens when you have to wait a while at traffic lights (I make sure that I never leave my feet on the pedals) that you suddenly have a much better response when starting off. A restart or offset reset often helps here, but not always. The whole thing looks like a software problem. You can't do much with the values coming from the sensor. The measured voltages vary continuously, so they have to be converted into a usable "moving average" by the software. After that, many more processes are probably carried out until a signal is sent to the motor support. In any case, nothing to go to the FM with, as the complaints depend on interpretation and cannot be reproduced. The measured values of the voltages during the cycle also give no indication that the sensor is doing anything wrong.
Forum greetings from Georgio
(translated from Dutch with deepl.com)
Horns
Posts occasionally mention the sudden loss of support. The 'voltage' output voltage of the TMM sensor drops sharply without being caused by potholes or rough road surfaces and is then usually outside the operating range. If 'voltage' Outside the working range, the Stromer stops assisting, but if it is still within the 'offset' range, the Stromer is strongly inhibited.
An effective workaround, which has been proven by various accounts from electric drivers, is to honk the horn. Honking brings the 'voltage' in the Omni back to the starting level and you can continue riding. If you don't believe it, see the Video.
Stromer drivers report the problem in these threads:
The actual cause is still unknown. An attempt at an explanation can be found in the NL-Stromerforum. The solution to the problem is usually to replace the sensor and, in the case of sensors with connectors in the chain stay, also the cable to the Omni.
Sheath wave filter
A special and probably rare problem is a sensor voltage far above the operating range. The stromerforum.ch user 'Faithlesslorin' reports this problem. When driving, the assistance suddenly fails, calibration is not possible due to a much too high sensor voltage value. The sensor value jumps from normal ~1.2 V to approx. 2.8 V. The phenomenon also occurs without moving the bike, e.g. overnight. If you touch the sensor cable, the voltage drops back to the normal value. Replacing the sensor did not solve the problem. After a lot of forensic work, the solution seems to be to fit a Folding ferrites (sheath wave filter) on the connection cable directly at the sensor. This attenuates or eliminates coupled interference via the sensor cable. The sustainability of the solution is not known as of June 30, 2023. The post here is a good starting point for further information.
My experience
I run with a slight advance of the sensor voltage 'voltage' compared to the value 'offset' (negative offset). The voltage difference is approx. 20-30 mV. This way my ST3 runs optimally, has a good response behavior, is agile but still has no propulsion.
What actually happens in practice is similar to the above descriptions of Georgio' that the support develops a kind of 'life of its own' although nothing has been changed on the bike. The support lacks the usual 'pull', you have the feeling that the bike is 'braking'. It happens, for example, overnight, at a stop, less often during normal riding. Sometimes the problem solves itself, sometimes calibration helps, but not always.
I can reproduce the effect of the inhibited assistance after using recuperation. If I use this on a long descent, I have noticed that the 'voltage' sensor voltage falls below the 'offset' voltage (approx. 20-50 mV). This means that the Stromer rides with inhibited assistance and has no traction. The effect usually disappears again and the motor simply continues to run. If you nevertheless calibrate to the new, lower value of 'voltage' and the sensor voltage recovers, it can happen that the Stromer develops more and more propulsion of its own.
> See also BREMSEN - Recuperation and recuperation'‚
My current workaround - after the problem occurs - is to pedal hard in a long gear for a few revolutions so that the support bar in the Omni is red. However, this does not work reproducibly. I then ride on and things usually work out again. Honk the horn too 🙂
Update
With the Fimware SUI 4.5.0.3 dated March 5, 2025 a bug was fixed which in practice made calibration necessary again and again. Stromer writes in the release notes:
A bug that caused the vehicle to no longer provide support if the TMM sensor value was slightly too low has been fixed.
The engine tuning setting 'Agility' for mode 2 did not work as intended - this issue has been fixed.
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