Torque Sensor for Electric Bicycles | NCTE S-BB-RT

The NCTE S-BB-RT uses the physical principle of reverse magnetostriction to measure the torque applied to the bottom bracket axle.

When the cyclist exerts force on the pedals, the axle experiences a twist that produces variations in its magnetic properties. The integrated electronics detect these variations and generate an electrical signal related to the applied torque.

The measuring system works without electrical contacts between the rotating shaft and the reading electronics, avoiding the use of brushes and slip rings.

This technology allows for the integration of a robust and compact torque measurement directly into the bottom bracket of an electric bicycle.

The S-BB-RT has a 2.5V center-offset analog torque output for a zero torque condition.

Its nominal sensitivity is 10 mV/Nm, which allows the bidirectional torque of ±200 Nm to be represented.

Nominal conversion:

Torque (Nm) = [Output voltage (V) − 2.5] × 100

Intermediate values are calculated from the nominal sensitivity. Actual accuracy should be evaluated according to the manufacturer's metrological specifications.

Safety note: NCTE indicates that certain electronic faults can generate a constant signal of approximately 2.5 V, equivalent to the nominal value of 0 Nm. Therefore, the controller should not rely solely on torque voltage to determine if valid pedaling is occurring.

The sensor incorporates an analog torque output and two digital channels to determine the speed and direction of rotation.

The Hall sensor outputs use an open collector with an internal pull-up resistor of 37 kΩ at +5 V, according to the NCTE data sheet, revision 4.0.

Before connecting the sensor, the power supply, logic levels, controller inputs, and the type of connector supplied must be checked.

The NCTE S-BB-RT is designed for installation on bicycle frames with a BSA 1.375 × 24 threaded bottom bracket shell and widths of 68 or 73 mm, depending on the axle configuration.

Tolerances: total length ±1 mm and L2 dimension ±0.5 mm. Shaft ends square to 12.73 mm.

For 73 mm BSA gearboxes, an additional spacer is included. Final compatibility must be verified against the dimensional drawings and connecting rod specifications.

NCTE bottom bracket sensors have been developed for the typical mechanical and environmental conditions of electric bicycles.

• Level of protection: IP64 in installed condition.
• Serving temperature: −20 to +70 °C.
• Dynamic test: Test for city and trekking applications according to DIN EN 15194:2018-11, indicated as passed by NCTE.
• Environmental resistance: 96-hour salt spray test passed, according to the manufacturer's documentation.
• Mechanical system: two 61902-16-2RS bearings and shaft with zinc-plated surface.
• Encapsulation: TECHNOMELT.

The manufacturer states that the measuring system does not require periodic recalibration under the intended conditions of use.

The IP64 rating and the declared tests correspond to the installation conditions specified by NCTE. They should not be interpreted as authorization for cleaning with high-pressure water.

The sensor is designed to be installed on 68 or 73 mm BSA bottom bracket shells compatible with the geometry of the selected model.

The NCTE instructions state the following precautions:

• Avoid powerful magnets and magnetized tools, which can permanently alter the magnetic field of the shaft.
• Do not open or modify the sensor.
• Keep threads clean and free of grease, in accordance with the NCTE assembly procedure.
• Respect the tightening torque of 30 Nm indicated for the cups.
• Prevent the cable from being excessively bent, caught, or damaged during assembly.
• Preferably install the wiring inside the panel.
• Protect the power supply by adequately limiting the current; NCTE indicates a fuse of approximately 1 A.
• Check polarity and avoid overvoltages.

The controller must validate plausible sequences on both turn detection channels before enabling motor assist.

The detailed installation and safety procedure should always be consulted in the official technical data sheet corresponding to the version supplied.

A PAS cadence sensor detects pedal rotation and can provide information on speed and direction of rotation. A torque sensor also measures the torsional force applied by the cyclist.

The NCTE S-BB-RT combines both functions, allowing the development of electric assistance systems based on the force applied to the pedal.

The S-BB-R and S-BB-RP models are designed to detect speed and direction of rotation. The S-BB-RP offers a higher number of pulses per revolution.

He S-BB-RT It also incorporates the measurement of torque of ±200 Nm, so it is geared towards assistance systems based on the cyclist's effort.

NCTE considers applications in urban bicycles, trekking bikes, and cargo e-bikes. For each project, the permissible loads, bottom bracket geometry, electronic integration, and usage conditions must be verified.

Not necessarily. The controller must be compatible with the analog torque signal, digital rotation outputs, power supply, and system safety requirements.

Integration should be verified during product development, especially in OEM projects.

The manufacturer's documentation covers supplies for small, medium, and large production runs. Samples for prototypes and project validation are also available.

GUEMISA can manage configuration, availability, quantity and commercial terms inquiries with the manufacturer.