AS5600 "dead spot" around 0


I have slightly modified the example code for ESP32 + I2C magnetic sensor to allow motor commands as suggested by @Antun_Skuric.

here is the code (just for tracability, nothing special)

   ESP32 position motion control example with magnetic sensor
#include <SimpleFOC.h>

// SPI Magnetic sensor instance (AS5047U example)
// MISO 12
// MOSI 9
// SCK 14
//MagneticSensorSPI sensor = MagneticSensorSPI(10, 14, 0x3FFF);

// I2C Magnetic sensor instance (AS5600 example)
// make sure to use the pull-ups!!
// SDA 21
// SCL 22
//MagneticSensorI2C(chip_address,bit_resolution, angle_register_msb, bits_used_msb)
MagneticSensorI2C sensor = MagneticSensorI2C(0x36, 12, 0x0E, 4);

// Analog output Magnetic sensor instance (AS5600)
// MagneticSensorAnalog sensor = MagneticSensorAnalog(A1, 14, 1020);

// Motor instance
//  BLDCMotor( pin_pwmA, pin_pwmB, pin_pwmC, pole_pairs, enable (optional))
BLDCMotor motor = BLDCMotor(25, 26, 27, 14);

void setup() {

  // initialise magnetic sensor hardware
  // link the motor to the sensor

  // power supply voltage
  // default 12V
  motor.voltage_power_supply = 12;

  // choose FOC modulation (optional)
  motor.foc_modulation = FOCModulationType::SpaceVectorPWM;

  // set motion control loop to be used
  motor.controller = ControlType::angle;

  // contoller configuration
  // default parameters in defaults.h

  // velocity PI controller parameters
  motor.PID_velocity.P = 0.5;
  motor.PID_velocity.I = 20;
  // maximal voltage to be set to the motor
  motor.voltage_limit = 6;

  // velocity low pass filtering time constant
  // the lower the less filtered
  motor.LPF_velocity.Tf = 0.01;

  // angle P controller
  motor.P_angle.P = 1;
  // maximal velocity of the position control
  motor.velocity_limit = 30;

  // use monitoring with serial
  // comment out if not needed

  // initialize motor
  // align sensor and start FOC

  Serial.println("Motor ready.");
  Serial.println("Set the target angle using serial terminal:");

// angle set point variable
float target_angle = 0;

void loop() {

  // main FOC algorithm function
  // the faster you run this function the better
  // Arduino UNO loop  ~1kHz
  // Bluepill loop ~10kHz

  // Motion control function
  // velocity, position or voltage (defined in motor.controller)
  // this function can be run at much lower frequency than loopFOC() function
  // You can also use motor.move() and set the in the code
  // motor.move(target_angle);

  // function intended to be used with serial plotter to monitor motor variables
  // significantly slowing the execution down!!!!
  // motor.monitor();

  //  // user communication
  // user communication

// utility function enabling serial communication with the user to set the target values
// this function can be implemented in serialEvent function as well
//void serialReceiveUserCommand() {
//  // a string to hold incoming data
//  static String received_chars;
//  while (Serial.available()) {
//    // get the new byte:
//    char inChar = (char);
//    // add it to the string buffer:
//    received_chars += inChar;
//    // end of user input
//    if (inChar == '\n') {
//      // change the motor target
//      target_angle = received_chars.toFloat();
//      Serial.print("Target angle: ");
//      Serial.println(target_angle);
//      // reset the command buffer
//      received_chars = "";
//    }
//  }
// utility function enabling serial communication the user
String serialReceiveUserCommand() {

  // a string to hold incoming data
  static String received_chars;

  String command = "";

  while (Serial.available()) {
    // get the new byte:
    char inChar = (char);
    // add it to the string buffer:
    received_chars += inChar;

    // end of user input
    if (inChar == '\n') {

      // execute the user command
      command = received_chars;

      // reset the command buffer
      received_chars = "";
  return command;

I have noticed a strange behavior (or side effect ?) (or still a bug on my side ?) that I would like to share with you.
When the target position is set to 0, then I can feel a dead zone (very small) where the motor seems to be unpowered. I can’t feel force feedback and even hear a small “clac” as if it was a mechanical backlash.

If I set target at 0.1 (or any other value) then this “backlash” disappears and the force feedback is immediatly present.

Any idea please ? Is it something that you already noticed or am I alone with this “dead spot” ?
Thanks in advance

Hi @freedom2000,
I had the same problem with the “dead spot” and I think I could solve it.

In “MagneticSensorI2C.cpp” the angle is read from adress 0x0E. That is an angle which contains a hysteresis.
I changed the adress to 0x0C to read the raw angle and it seems to work fine.

1 Like

This looks fine :slight_smile:

I thought I was alone to get this behavior !

@Uli you just saved me a batch of AS5600 I was about to throw away. Thanks for an excellent workaround.

I’m thinking, if all of the AS5600 suffer from this dead spot jerk, it would warrant a pull request to the library.

1 Like

Absolutely right, its going to be integrated into the new release!