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docs: Warn against using the TMC2208 in standalone mode

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Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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Kevin O'Connor
2019-02-20 16:12:33 -05:00
parent 834b9e3d92
commit 328bd89fc1
3 changed files with 135 additions and 10 deletions
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49
docs/FAQ.md
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@@ -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.
![tmc2208](img/tmc2208.svg.png)
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