Description
Unterstützungsprobleme gehören bei Stromern zu den häufigsten Problemen. Das zentrale Element für die Regelung der Unterstützung ist der „Drehmomentsensor“ (TMM-Sensor) im linken Ausfallende. Er misst die Kraft, die beim Pedalieren auf die Kette wirkt, und setzt diese in eine Spannung um welche vom Omni ausgewertet wird. Je nach Einstellung der Fahrstufe und des Tretsensorwerts in der Omni-App wird damit die Leistungselektronik im Motorcontroller (MCU = Motor Control Unit) angewiesen die Unterstützung des Nabenmotors zu steuern.
Operating range / Voltage range
The torque sensor has an operating range or a voltage window within which the supplied voltage must fall for the Omni.
If it is above or below this defined, model-dependent threshold, a calibration error is displayed in the Omni and support is discontinued.
To ensure the tension is within the working range, the factory setting of the sensor is responsible on the one hand, and on the other hand the Thru-axle tightening torque (torque) in the rear wheel and the sensor plate in the dropout.
Stromer hat im Laufe der Jahre immer wieder Verbesserungen vorgenommen. So werden immer wieder neuere TMM-Sensor-Modelle eingesetzt, Anzugsdrehmomente der Steckachse oder Sensorplatte angepasst und es wurde eine Funktion „Use Trace“ implemented to compensate for sensor fluctuations.
Problems
Despite all the improvements, there are still problems with the support. They can manifest as follows:
- 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 through'
- Spontaneous loss of assistance while driving
See PROBLEMS → MISCELLANEOUS → „ST1/ST2 shuts down while driving“
See BATTERY „SoC recovery after a trip (rebound) / Spontaneous failure“
Checklist: '+Stromer- | Solve support problems'
The TMM sensor is not the only source of errors in support issues. Before tackling the checklist regarding the TMM sensor, it is worth checking the following sources of interference, either physically or with SIT (Test Runner) to check
- Motor defects (electric) are rare. If so, the reason is usually a Hall sensor, the temperature sensor, or rust (bearings) caused by water ingress.
- Motor cable – was a particular problem with the ST2(S).
- Motor plug on the left chain stay loose or damp.
- Motor cable connections in the bottom bracket area – on older models, partly not insulated, which led to corrosion and follow-up malfunctions.
- Controller
- Reed switches in the brake levers (for recuperation) – rarely defective, but potentially misaligned. See BRAKES „Reed switches: Adjust brake light and recuperation“
- The battery has too much play in the battery compartment (especially ST1 / ST2). See PROBLEMS → MISCELLANEOUS → „ST1/ST2 shuts down while driving“
- Spontaneous failure of support, especially at colder temperatures. See BATTERY „SoC recovery after a trip (rebound) / Spontaneous failure“
- Country Configuration in Omni Incorrect: It can happen by accident that the Stromer is configured with the CA C1038 profile. This limits the top speed to the legally mandated value of 32 km/h for Canada. See more info in this topic.
If hardware defects can be ruled out, there are various approaches to troubleshooting support issues. These range from simple calibration to replacing the TMM sensor. In addition, there are unusual solutions such as honking or attaching a common mode choke to regain support (see below).
My Checklist (incl. torque table) lists 14 different problems and phenomena and describes possible solutions.
Print version (EN)
Web version translatable
Torque table separate
Feedback in forums
Waviness of the support
Representing here a report from forum member „Georgio“ on the Dutch forum speedpedelecreview.com. He describes his experiences as follows, defending 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
In forum posts, one occasionally reads about the sudden loss of support. The output voltage („voltage“) of the TMM sensor drops sharply without encountering potholes or rough roads and then usually moves outside the working range. If „voltage“ is outside the working range, the current stops providing support. If it is still within range, but significantly below the „offset,“ it drives with significant resistance, as if constantly braking.
Ein wirksamer Workaround ist das Hupen. Es bringt die „voltage“ im Omni wieder auf Ausgangsniveau, sodass man weiterfahren kann. Wer es nicht glaubt, findet hier das Video.
In the following posts, Stromer riders report on the problem:
- stromerforum.chHorns – Posts„ 1 | 2
- speedpedelecreview.com: 1 | 2 | 3 | 4
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, for sensors with a connector on the chainstay, also the cable up to the Omni.
Sheath wave filter
A special, likely rare, problem is sensor voltage far above the operating range. Stromerforum.ch-User „Faithlesslorin“ Reports on it: While riding, the assistance suddenly fails, and calibration is not possible due to an excessively high sensor value. The voltage jumps from the normal approx. 1.2 V to approx. 2.8 V – even without the bike moving, for example, overnight. Touching the sensor cable causes the voltage to drop back to the normal value; replacing the sensor did not solve the problem. After extensive troubleshooting, it appears that a component attached to the sensor Folding ferrite (Common Mode Filter) as the solution, as it dampens or eliminates coupled interference via the sensor cable. The sustainability of this solution was not known as of June 30, 2023. The starting point for further information is this post in the Stromer forum.
My experience
Until switching to the latest P218 sensor, I ran my ST3 with the P211 sensor and a slight lead of the sensor voltage („voltage“) over „offset“ of approx. 20-30 mV. The bike ran optimally in this setting: good responsiveness, agile, but without self-propulsion.
However, in practice, similar to the descriptions by „Georgio,“ the support exhibited a mind of its own, even though nothing had been changed on the bike: the usual „pull“ was missing, and the bike felt more like it was braking. This occurred irregularly, for example, overnight or after a stop, and less frequently while riding. The problem sometimes resolved itself, and sometimes calibration helped – but not reliably.
Reproduzierbar war der Effekt nach Rekuperation: Bei längeren Abfahrten fiel die Spannung „voltage“ um ca. 20–50 mV unter „offset“, was zu gehemmter Unterstützung und fehlendem Durchzug führte. Meist normalisierte sich dies bei der Weiterfahrt. Kalibrierte ich dagegen auf den neuen, tieferen Wert von „voltage“ und erholte sich die Sensorspannung danach wieder, konnte dies zunehmenden Eigenvortrieb zur Folge haben. See also BREMSEN - Recuperation and recuperation'‚
Update: Since I switched to the latest SPL042 sensor (P218), the support has been very consistent. I also no longer have a slight negative offset when tightening the rear wheel axle. The SUI 4.5.0.3 update might also have contributed to the improvement. See the „Update“ section below.
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 „Agility“ engine tuning setting for Mode 2 was not functioning as intended – this issue has been resolved.