Question about RELATIVE and ABSOLUTE movement.

[PawelKulesz]

Hi,
Im doing some tests with UART control and as far as I understand, ABSOLUTE movement doesn't work for UART (with function run_to_position_steps, which I guess isn't intended to use with UART). Is it a STEP/DIR feature only and if it is, does the TMC2209 driver know where it currently is (on which step) or should I create a variable and store that information in it?

[Chr157i4n]

Hey,

ABSOLUTE movement doesn't work for UART (with function run_to_position_steps, which I guess isn't intended to use with UART)

Do you mean VActual? VActual is time based. using run_to_position_steps on it would be an approximation. Only with STEP/DIR is it guaranteed that the motor has performed exactly the desired number of steps.
But nevertheless it should work with Absolute and Relative movement. The difference between these is:

run_to_position_steps(400, MovementAbsRel.RELATIVE)
run_to_position_steps(100, MovementAbsRel.RELATIVE)   # <-- 100 Steps forward

run_to_position_steps(400, MovementAbsRel.ABSOLUTE)
run_to_position_steps(100, MovementAbsRel.ABSOLUTE)   # <-- 300 Steps backwards (back to position 100)

Can you please share the relevant part of your script (how the Tmc-object is created and which movement function is being called).

[PawelKulesz]

Hey,

this is how I create the TMC Object:
tmc1 = Tmc2209(TmcEnableControlPin(21), TmcMotionControlVActual(), TmcComUart("/dev/ttyAMA0"), loglevel=Loglevel.DEBUG,driver_address=0)

This is the config of it:
tmc1.tmc_logger.loglevel = Loglevel.DEBUG
tmc1.movement_abs_rel = MovementAbsRel.ABSOLUTE
tmc1.set_direction_reg(False)
tmc1.set_current(800)
tmc1.set_interpolation(True)
tmc1.set_spreadcycle(False)
tmc1.set_microstepping_resolution(2)
tmc1.set_internal_rsense(False)
tmc1.read_ioin()
tmc1.read_chopconf()
tmc1.read_drv_status()
tmc1.read_gconf()

And this is the function that we call:
tmc1.run_to_position_steps(200)
time.sleep(1)
tmc1.run_to_position_steps(200)

So as I understand, default type of movement is ABSOLUTE, as stated in the config code above. So second movement call should not do anything, but the motor moved. I will be switching to STEP/DIR movement, I'm just curious why the absolute movement didn't work in this example.

[Chr157i4n]

well, i just looked into the code and absolute movement is not implemented for TmcMotionControlVActual()

PyTmcStepper/src/tmc_driver/motion_control/_tmc_mc_vactual.py

Lines 56 to 72 in 74d6c43

	def run_to_position_steps(self, steps, movement_abs_rel:MovementAbsRel = None):
	"""runs the motor to the given position.
	with acceleration and deceleration
	blocks the code until finished or stopped from a different thread!
	returns true when the movement if finished normally and false,
	when the movement was stopped
	Args:
	steps (int): amount of steps; can be negative
	movement_abs_rel (enum): whether the movement should be absolut or relative
	(Default value = None)
	Returns:
	stop (enum): how the movement was finished
	"""
	rps = tmc_math.steps_to_rps(self.max_speed_fullstep, self.steps_per_rev)
	self.set_vactual_rps(rps, revolutions=steps/self.steps_per_rev)

The function run_to_position_steps even has the arg movement_abs_rel, but just ignores it and moves relative.

I have created an issue, feel free to create a pull request if you want.