Monday, March 6, 2017

Torque Sensor or Speed Sensor?

torque sensor

A torque sensor can increase the range of you e-bike. And they will keep the law enforcement from classifying your vehicle as a moped. But they are not cheap.

Torque or strain sensors, so the bike cannot be driven with out pedaling, are not absolutely necessary but every thing helps when it comes to building a legal vehicle.

But you don't really to need to sense the pressure on the pedals, you can use a Cadence sensor, it is the same as the speed sensor; when the crank arm passes a magnet it sends a pulse to the controller.

However torque sensors apply power more smoothly than a cadence sensor. On a quality torque sensor, you can forget the bike is electric, the bike just becomes easier to pedal. The harder you push on the pedals, the faster you go like on a regular bike, but with the electric power you just go a lot faster.

One method to build a pressure sensor involves using the CycleAnalyst, but needs you to build a chain idler for the top chain of the bike, then attach a strain gauge to the arm the idler is mounted to, and program the CA to work off it's input range. 

Electric bikes are generally super inefficient when accelerating up to speed. A torque sensor forces you to help the ebike when it needs it the most, when it is accelerating and when climbing

speed sensor

In the state of Washington a speed sensor connected to the controller to calculate wheel speed, is absolutely needed if your gear ratio, in conjunction with the motor's maximum RPM, is enough to move the bike faster than 20mph on flat land. That is one reason why washington state e-bike laws must change!

DIY Torque Sensor Pedal Assist!

TorqueSensors on Electric Bikes

PAS (Pedal Assist Sensor) installation problems

Some brushless motors will produce more than twice the wattage that is on the label. Making it even more difficult to engineer an e-bike.
BionX 250 and 350 are both nominal wattage ratings. Those who have ridden them know that they give much more power when climbing hills. I have measured well above 1000 watts with a Watt's Up meter spliced between the battery and motor.

washington state e-bike laws must change

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