EPuck2 Motor - EPFL-MICRO-315/TPs-Wiki GitHub Wiki

⚠ wiki page used in TP2

Introduction to EPuck2 Motors

  • The e-puck2 robot is equipped with two stepper motors
  • These motors have two windings
  • The power in these windings is controlled by 4 signals (a, b, c and d) for each motors
  • Look at the figure 1 showing how these four signals have to be activated to make the motor turn
  • Every signal transition is considered as a step
  • A rotation of 360° of the wheel corresponds to 1000 steps
    • 20 steps per revolution of the motor combined with a gear reduction of 50:1
  • To calculate the distance run by the robot, one must consider the robot wheel's perimeter of 13cm.
  • More information on stepper motors:

Figure 1

Activation sequence for the motor 1 control signals

Implementation in Code

  • The control of the motors can be managed for instance by this state machine where the direction (backward and forward) and speed can be handled

Figure 2

State machine with the states of motor control

[!WARNING] Avoid staying too long in a state that powers the coils of the motors or else they will heat very strongly and this can even destroy material.

  • So be careful when handling GPIOs managing the drivers of the motors.
  • On the state machine figure it misses the state 0000 where the 2 coils are not supplied at all. This is the state in which the motor must be when it is stopped so as not to consume and especially not to heat.

[!IMPORTANT]

  • It is really IMPORTANT to test your motor management code by simulating the states of the state machine with the 4 Red LEDs (1-Front, 3-Right, 5-Back and 7-Left).
  • Start by changing the states at very low frequency (≤1Hz) so you can visually see and validate the main part of your code without powering the motor then without risk.
  • When your code seems ok, before to replace the LED's GPIOs with those interacting with motor driver:

[!WARNING] Don't forget that driver motor GPIOs have a different configuration (external pull-down and positiv logic) and work exactly like FRONT_LED or BODY_LED

[!IMPORTANT]

  • Then test your state machine by replacing 2 of the 4 previous Red LEDs with these 2 new LEDs. You will know better how to configure the GPIOs of the motors
  • Again if your code seems ok, replace all the LED's GPIOs with those interacting with motor driver
  • Finally do the same with the second motor.

💡 Tips and Tricks

  • The 4-bit value in the state machine figure indicates the values you have to put in the 4 binary signals that control the windings of the stepper motor
  • To make the motors turn, these signals have to change in a cyclical way according to the FSM (Finite state machine)
  • Two timers, one for each motor (timers 6 and timer 7 are recommended) must be used:
    • each timer interrupt makes the motor performing one step
    • the interval of timer interrupt must be set accordingly to the desired speed of each wheel
  • There must be a step counter allowing the robot to move for a given number of steps
  • Do not consider trapezoidal speed profiles but just rectangular (on-off) speed profiless