Motor control

Of course, main use of this robot is to drive around, and for this, we need to control the motors.

Basic control

set_motors(power_L, power_R)

Set power for left and right motors. power_L is power to left motor, power_R is power to right motor. Each of them should be between 100 (full speed forward) and -100 (full speed backward).

Note that because no two motors are exactly identical, even if you give both motors same power (e.g. set_motors(60,60)), their speeds might be slightly different, causing the robot to veer to one side instead of moving straight. To fix that, use PID control as described below.

stop_motors(): Stop both motors.

Encoders

Both motors are equipped with encoders (essentially, rotation counters). For 75:1 HP motors, each motor at full speed produces about 4200 encoder ticks per second.

reset_encoders(): Resets both encoders

get_encoders(): Gets values of both encoders and saves them. These values can be accessed as described below

encoder_L

encoder_R: Value of left and right encoders, in ticks, as fetched at last call of get_encoders(). Note that these values are not automatically updated: you need to call get_encoders() to update them

get_speeds(): Gets the speeds of both motors and saves them. These values can be accessed as described below

speed_L

speed_R: Speed of left and right motors, in ticks/second, as fetched at last call of get_speeds(). Note that these values are not automatically updated: you need to call get_speeds() to update them

PID

PID is an abbreviation for Proportional-Integral-Differential control. This is the industry standard way of using feedback (in this case, encoder values) to maintain some parameter (in this case, motor speed) as close as possible to target value.

Yozh bot has PID control built-in; however, it is not enabled by default. To enable/disable PID, use the functions below.

Before enabling PID, you need to provide some information necessary for its proper operation. At the very minimum, you need to provide the speed of the motors when running at maximal power. For 75:1 motors, it is about 4200 ticks/second; for other motors, you can find it by running motors_test.py example.

configure_PID(maxspeed): Configures parameters of PID algorithm, using motors maximal speed in encoder ticks/second.

PID_on()

PID_off(): Enables/disables PID control (for both motors).

Once PID is enabled, you can use same functions as before (set_motors(), stop_motors()) to control the motors, but now these functions will use encoder feedback to maintain desired motor speed.

Drive control

Yozh python library also provides higher level commands for controlling the robot.

go_forward (distance, speed=50)

go_backward(distance, speed=50)

Move forward/backward by given distance (in centimeters). Parameter speed is optional; if not given, default speed of 50 (i.e. half of maximal) is used.

Note that distance and speed should always be positive, even when moving backward.

turn(angle, speed=50): Turn by given angle, in degrees. Positive values correspond to turning right (clockwise). Parameter speed is optional; if not given, default speed of 50 (i.e. half of maximal) is used.

Note that all of these commands use encoder readings to determine how far to drive or turn. Of course, to do this one needs to know how to convert from centimeters or degrees to encoder ticks. This information is stored in properties bot.CM_TO_TICKS and bot.DEG_TO_TICKS. By default, Yozh library uses CM_TO_TICKS = 150, DEG_TO_TICKS=14, which should be correct for 75:1 motors. If you find that the robot consistently turns too much (or too little), you can change these values, e.g.

bot.DEG_TO_TICKS=15
bot.turn(90)