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diff --git a/docs/TMC_Drivers.md b/docs/TMC_Drivers.md index 38a9514a..99213cb8 100644 --- a/docs/TMC_Drivers.md +++ b/docs/TMC_Drivers.md @@ -11,6 +11,53 @@ this document are not available. In addition to this document, be sure to review the [TMC driver config reference](Config_Reference.md#tmc-stepper-driver-configuration). +## Tuning motor current + +A higher driver current increases positional accuracy and torque. +However, a higher current also increases the heat produced by the +stepper motor and the stepper motor driver. If the stepper motor +driver gets too hot it will disable itself and Klipper will report an +error. If the stepper motor gets too hot, it loses torque and +positional accuracy. (If it gets very hot it may also melt plastic +parts attached to it or near it.) + +As a general tuning tip, prefer higher current values as long as the +stepper motor does not get too hot and the stepper motor driver does +not report warnings or errors. In general, it is okay for the stepper +motor to feel warm, but it should not become so hot that it is painful +to touch. + +## Prefer to not specify a hold_current + +If one configures a `hold_current` then the TMC driver can reduce +current to the stepper motor when it detects that the stepper is not +moving. However, changing motor current may itself introduce motor +movement. This may occur due to "detent forces" within the stepper +motor (the permanent magnet in the rotor pulls towards the iron teeth +in the stator) or due to external forces on the axis carriage. + +Most stepper motors will not obtain a significant benefit to reducing +current during normal prints, because few printing moves will leave a +stepper motor idle for sufficiently long to activate the +`hold_current` feature. And, it is unlikely that one would want to +introduce subtle print artifacts to the few printing moves that do +leave a stepper idle sufficiently long. + +If one wishes to reduce current to motors during print start routines, +then consider issuing +[SET_TMC_CURRENT](G-Codes.md#tmc-stepper-drivers) commands in a +[START_PRINT macro](Slicers.md#klipper-gcode_macro) to adjust the +current before and after normal printing moves. + +Some printers with dedicated Z motors that are idle during normal +printing moves (no bed_mesh, no bed_tilt, no Z skew_correction, no +"vase mode" prints, etc.) may find that Z motors do run cooler with a +`hold_current`. If implementing this then be sure to take into account +this type of uncommanded Z axis movement during bed leveling, bed +probing, probe calibration, and similar. The `driver_TPOWERDOWN` and +`driver_IHOLDDELAY` should also be calibrated accordingly. If unsure, +prefer to not specify a `hold_current`. + ## Enabling "StealthChop" Mode By default, Klipper places the TMC drivers in "spreadCycle" mode. If |