Can You Convert an E-Bike’s Torque Sensor into a Cadence Sensor?

Converting an e-bike’s torque sensor into a cadence sensor is a technically feasible but nuanced process. While torque sensors are designed to measure the force applied to the pedals, cadence sensors focus solely on the rotational speed of the crank. Understanding the differences and challenges involved can help determine whether this conversion is a practical solution for your e-bike setup.

Understanding Torque and Cadence Sensors

Torque Sensor:

• A torque sensor measures the force applied to the pedals, often in conjunction with cadence, to calculate the rider’s total power output.

• These sensors provide proportional motor assistance based on the rider's effort, ensuring a smooth and natural cycling experience.

Cadence Sensor:

• A cadence sensor measures the rotational speed of the crank or pedals (in revolutions per minute, or RPM).

• Cadence sensors typically provide binary feedback to the e-bike’s controller: either the pedals are turning, or they’re not. This simpler system results in motor assistance that doesn’t account for how much effort the rider is exerting.

Steps to Convert a Torque Sensor into a Cadence Sensor

To convert a torque sensor into a cadence sensor, you’ll need to isolate and use the cadence signal provided by the torque sensor. Here’s a detailed breakdown of the process:

Step 1: Verify the Torque Sensor’s Output Signals

Many torque sensors inherently measure cadence as part of their operation, outputting this information along with torque. Check the technical documentation or pinout diagram of your specific torque sensor to identify if it provides a distinct cadence signal. This might be an analog or digital signal.

Step 2: Analyze Signal Compatibility

E-bike controllers expect specific signal types from sensors. Compare the cadence signal from your torque sensor with the input requirements of your controller:

• Voltage Range: Ensure the cadence signal operates within the voltage range supported by your controller.

• Signal Type: Some controllers expect analog signals, while others work with digital signals (e.g., pulse-width modulation or frequency-based signals).

• If the signal formats differ, you may need additional hardware, such as a signal converter or a microcontroller, to translate the cadence signal appropriately.

Step 3: Rewire the Torque Sensor

Once you’ve identified the cadence signal:

1. Disconnect the torque-related wires if they’re not needed.

2. Connect the cadence signal wire to the appropriate input on your e-bike controller. This may involve modifying connectors or soldering wires directly.

3. Secure all connections to ensure durability and safety during operation.

Step 4: Configure the E-Bike Controller

Some e-bike controllers allow for configuration to ignore torque input and rely solely on cadence. Refer to the controller’s user manual to see if this mode is available. Adjust settings as necessary to ensure the controller recognizes the cadence signal properly.

Step 5: Test and Calibrate

• Test the system by pedaling to see if the motor responds correctly to cadence input.

• If the motor assistance feels inconsistent or unresponsive, recalibrate the system. This might involve fine-tuning the signal output or rechecking the wiring.

Potential Challenges

While the process is technically possible, you may encounter several challenges:

1. Signal Compatibility Issues:

   • Torque sensors and cadence sensors often output different signal types, making direct substitution difficult without additional electronics.

2. Controller Limitations:

   • Not all e-bike controllers can operate solely on cadence signals, as many are designed to work specifically with torque-based feedback systems.

3. Mechanical Integration:

   • If your torque sensor is integrated into the bottom bracket or crankset, converting it might leave some components unused or interfere with normal operation.

4. Technical Expertise:

   • The conversion process requires a basic understanding of electronics, including signal analysis, wiring, and possibly programming microcontrollers.

Alternative Solution: Install a Dedicated Cadence Sensor

If the conversion process seems too complex or impractical, a simpler and often more cost-effective solution is to install a dedicated cadence sensor. These sensors are widely available, inexpensive, and easy to install. Most cadence sensors work by attaching a magnet to the crank and a sensor to the frame, transmitting the cadence signal directly to the e-bike controller.

Advantages of a dedicated cadence sensor include:

• Simplified installation with minimal wiring.

• Compatibility with a broad range of e-bike controllers.

• No need to modify or repurpose existing components.

Conclusion

While converting an e-bike’s torque sensor into a cadence sensor is possible, it involves significant technical effort and may require additional hardware for signal conversion and compatibility. For many riders, installing a dedicated cadence sensor is a more straightforward and reliable solution. Assess your technical skills, tools, and e-bike system’s capabilities before deciding which approach to pursue. If you’re unsure, consult with an e-bike technician or manufacturer for guidance tailored to your specific setup.