How to measure position of motor

[GenghisHan-op]

I have a Motor connect to a gear like in the image below, controlled by an Xbox controller, please teach me how can I make it run within the upper and lower limit only, if it reach the limits, the motor stop. Starting position of the gear is always at lower limit. I tried using control.target_tolerances()→ Tuple[[int], [int]] as instruct from the document but no luck. Sorry for my bad English. Thanks in advance.

[BertLindeman]

Hello,

Do you have an example of what you tried and tell (show) us how that fails?
If you show us the program it is easier to point you to improvements.

Bert

[GenghisHan-op]

motor = Motor(Port.A, Direction.CLOCKWISE, [8, 26],False)
speed = controller.joystick_right()[1]
if speed != 0:
        if speed < 0:
            motor.dc(speed)
            angle = motor.angle()
            if angle < -8600:
                motor.dc(0)              
        if speed > 0:
            motor.dc(speed)
            angle = motor.angle()
            if angle > 0:
                motor.dc(0)
else:
        motor.dc(0)

This is my code. The limit is 0 and 8600 (angle). The motor is controlled by the controller, with this code, the gear never move pass the 2 limits. If you can improve, please show me. Thank you.

[BertLindeman]

I see no loop in this snippet. If this is the complete test program, then this is all done only once and the program is ready in no time.

After the define of the motor you might need something like:

while True:
    # do the speed control like you show
    wait(100)  # just a small wait

Bert

[GenghisHan-op]

Ah, this is not a complete program, just a chunk of code that do the work in the first post.

[BertLindeman]

I simplified the snippet a bit, but kept the logic:

while True:
    speed = controller.joystick_right()[1]
    if speed < 0:
        if motor.angle() < -8600:
            motor.dc(0)
        else:
            motor.dc(speed)
    elif speed > 0:
        if motor.angle() > 0:
            motor.dc(0)
        else:
            motor.dc(speed)
    else:
        motor.dc(0)

And this works ok on a primehub, so I can see some debugging.
Might there be some error in your complete program?
Due to the disconnect on the TechnicHub for the xbox controller you cannot see the runtime error.

[EDIT] You might simulate (if you have a port free) the joystick with a color sensor. Say RED makes speed -100 and GREEN does +100. By running without xbox controller you may find out where the problem is.

[EDIT 2] The motor has inertia, so stopping at -8600 will have the motor stopped at (say) -8634 or so.
Keep the deceleration in mind.

[GenghisHan-op]

Thanks for your reply, the code work without any problem on my technic hub. Maybe I'll change to primehub later. The error ratio of the motor is small and acceptable. I do have color sensor but I have no room to install it, the technic hub still have 1 port free.