Electric bike throttle command

Purpose

Two years ago, I bought an electric bike. I bring it everyday to go to work and sometimes (without the battery...) for a trek. Well... why an electric bike ? It is sometimes hard to have enought motivation for a 7km trip with a very difficult slope.

In France the law is very clear about electric bikes. The power is limited to 250 watts, the speed is limited at 25km/h and also you have to make a minimal effort with the pedals. It is only an assistance.

The neomouv chronos I bought

Pedelec (this is the name of the assistance) is simple and no smart at all. It would like to know if I can make something different with a throttle command.

Drive the motor

Pedelec only mesure rotation speed. On this system, the three-phase motor is usually in the rear wheel (sometimes on the front). A controller brings the power at the right time. Behind the pedals, there is a wheel with magnets next to a hall effect sensor.

There wires are plugged : +5v, ground and signal. The signal wire is always at 3.2v, except when there is a magnet it goes down to 0v. 3.2v comes from the controller, the hall sensor is like a contact to the ground. In fact, when I made manualy some impulsions between the ground wire and the signal the wheel turn.

Arduino limit

Plug the signal wire to a digital output on an Arduino nano does not work. The internal resistor is too high and the wheel will never start.

With a transistor it can work easily, but I only have opto-couplers. By the way, the circuit works !

In and ground connected to the arduino, out to the signal wire and the last on the ground. The 5v wire is enough for the arduino, this is the good news !

            digitalWrite(2, 1);
  
            delay(20);
            digitalWrite(2, 0);
            delay(400);
    

This code a 20ms impulsion with a 400ms low. At this point, the motor starts.

Decreasing from 400 to 60ms shows differents steps. 60ms is the minimal value for max speed.

Add a throttle

I bought this throttle on Amazon. It is design for electric bikes, with a special "throttle" input the mine does not have.

It has 3 wires, it operates like a variable resistor.

On my arduino input the value is between 200 and 865.

    
        // the loop routine runs over and over again forever:
        void loop() {
        int sensorValue = analogRead(A6);

        int amplitudeSensor = sensorValue - 200;
        // amplitude : 665

        // amplitude : 340 factor 1.95;
        int amplitudeMotor = 400 - (amplitudeSensor / 2);
        // delay is from 400 to 60
        
        digitalWrite(2, 1);
        
        delay(20);
        digitalWrite(2, 0);
        delay(amplitudeMotor);
        }
    
    

But this code does not work. The wheel never stop. The mistake comes from the 5v power that has variations (5.5v to 4.3v). The button is too sensitive. I added a gap with a slow mode :

 
        
        // the loop routine runs over and over again forever:
        void loop() {
        int sensorValue = analogRead(A6);
        int writeValue = 1;
        // sensor is from 200 to 865
        if(sensorValue < 230 )
            writeValue = 0;

        int amplitudeSensor = sensorValue - 200;
        // amplitude : 665

        // amplitude : 340 factor 1.95;
        int amplitudeMotor = 400 - (amplitudeSensor / 2);
        // delay is from 400 to 60
        
        digitalWrite(2, writeValue);
        
        delay(20);
        digitalWrite(2, 0);
        delay(amplitudeMoteur);
        }
    
    

Works great !

Next step ? Maybe a speed regulator, or a screen on it...