So the method called reset is an additional way to cause the motor to reset it's internal tachometer to 0 at the current location.Ĭ.reset() #Set the internal tachometer back to 0Ĭ.run_position_limited(position_sp = 150, speed_sp = 150)
If you scroll down that page you see this command: from ev3.lego import MediumMotor We need to learn to read and comprehend the source code ev3.lego documention, Defined here: If you run this python program many times, the motor will rotate forward by exactly 150 each time, rather than the default behavior: "rotating to exactly position 150", which only holds true until the EV3 brick is rebooted." Store this value permanently so every time we want to move ahead by 150, we add that value to the location it was at start. Then we read the current position of the angle of the motor on start. Then we instantiate a new connection to the Motor on Port C. Position_sp = int(initialMotorLocation) + 150,įirst we import the Motor library from ev3.lego. InitialMotorLocation= c.read_value("position") Python 2 code: which gets the initial position of the Motor on program start: from ev3.lego import Motor ) to spin the motor to a certain angle position. Setup: I installed Debian Linux on the Mindstorms EV3 brick and I'm using Python 2 to use the ev3.lego package to use the method: run_position_limited(. Get the initial position of an EV3 Motor and return to it. Your admonition of 'no other helpers' could be interpreted to mean you don't want the first solution in which case you are left with using the encoders and figuring out the differential motion of your chassis design (which may be non trivial). (the accelerometer is too but not as bad I think.) It's also prone to accumulation of errors. This is harder because you have to account for the geometry of the wheels and keep track of the robot heading - lego also sells a compass sensor if you don't want to deal with finding your heading, but you'll still have to deal with non-spinning turns. You can record each displacement into a variable for x and y directions using the servo readings from the motors - remember to reset the encoder value from the servos after each reading.
That is it accounts for motions that cancel out so you can set a straight line path back. This nice thing about this is it gives you absolute displacement. The way to do this is to put it in your control loop and sum up 0.5*dt*dt*a where a is the accelerometer reading (there will be one for each axis of motion) and dt is the time between samples. You have to then integrate this information twice to get positional change. This allows you to independently measure the acceleration of the robot.
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