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diff --git a/docs/TMC_Drivers.md b/docs/TMC_Drivers.md index 2f456d4a..581fe2b2 100644 --- a/docs/TMC_Drivers.md +++ b/docs/TMC_Drivers.md @@ -83,6 +83,33 @@ setting `stealthchop_threshold` to 999999). Unfortunately, the drivers often produce poor and confusing results if the mode changes while the motor is at a non-zero velocity. +## TMC interpolate setting introduces small position deviation + +The TMC driver `interpolate` setting may reduce the audible noise of +printer movement at the cost of introducing a small systemic +positional error. This systemic positional error results from the +driver's delay in executing "steps" that Klipper sends it. During +constant velocity moves, this delay results in a positional error of +nearly half a configured microstep (more precisely, the error is half +a microstep distance minus a 512th of a full step distance). For +example, on an axis with a 40mm rotation_distance, 200 +steps_per_rotation, and 16 microsteps, the systemic error introduced +during constant velocity moves is ~0.006mm. + +For best positional accuracy consider using spreadCycle mode and +disable interpolation (set `interpolate: False` in the TMC driver +config). When configured this way, one may increase the `microstep` +setting to reduce audible noise during stepper movement. Typically, a +microstep setting of `64` or `128` will have similar audible noise as +interpolation, and do so without introducing a systemic positional +error. + +If using stealthChop mode then the positional inaccuracy from +interpolation is small relative to the positional inaccuracy +introduced from stealthChop mode. Therefore tuning interpolation is +not considered useful when in stealthChop mode, and one can leave +interpolation in its default state. + ## Sensorless Homing Sensorless homing allows to home an axis without the need for a |