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diff --git a/docs/FAQ.md b/docs/FAQ.md index 0f1eea53..bde845b2 100644 --- a/docs/FAQ.md +++ b/docs/FAQ.md @@ -265,17 +265,46 @@ configured in Marlin. ### My TMC motor driver turns off in the middle of a print -There have been reports of some TMC drivers being disabled in the -middle of a print. (In particular, with the TMC2208 driver.) When this -issue occurs, the stepper associated with the driver moves freely, -while the print continues. +Short answer: Do not use the TMC2208 driver in "standalone mode" with +Klipper! Do not use the TMC2224 driver in "stealthchop standalone +mode" with Klipper! -It is believed this may be due to "over current" detection within the -TMC driver. Trinamic has indicated that this could occur if the driver -is in "stealthChop mode" and an abrupt velocity change occurs. If you -experience this problem during homing, consider using a slower homing -speed. If you experience this problem in the middle of a print, -consider using a lower square_corner_velocity setting. +Long answer: Klipper implements very precise timing. + + + +In the above picture, if Klipper is requested to move along the red +line and if each black line represents the nominal location to step a +stepper, then in the middle of that movement Klipper will arrange to +take a step, change the step direction, and then step back. Klipper +can perform this step, direction change, and step back in a very small +amount of time. + +It is our current understanding that the TMC2208 and TMC2224 will +react poorly to this when they are in "stealthchop" mode. (It is not +believed any other TMC drivers are impacted.) It is believed that when +the driver sees the two step requests in a small time frame that it +dramatically increases current in anticipation of high acceleration. +That high current can trip the driver's internal "over current" +detection which causes the driver to disable itself. + +This pattern of steps can occur on all stepper motors and on all +robot kinematics. + +The TMC2208 and TMC2224 do work well with Klipper when run-time +configuration mode is used (that is, when a wire is routed from the +micro-controller to the PDN-UART pin and the printer config file has a +corresponding [tmc2208] config section). When using run-time +configuration, either configure the drivers to use "spreadcycle mode" +or configure them to use "stealthchop mode" with a reasonable +"stealthchop threshold". If one wishes to exclusively use +"stealthchop" mode with run-time UART configuration then make sure the +stealthchop_threshold is no more than about 10% greater than the +maximum velocity of the given axis. It is speculated that with a +reasonable stealthchop threshold, then if Klipper sends a "step, +direction change, step back" sequence, the driver will briefly +transition from stealthchop mode, to spreadcycle mode, and back to +stealthchop mode, which should be harmless. ### I keep getting random "Lost communication with MCU" errors |