49 lines
2.3 KiB
Markdown
49 lines
2.3 KiB
Markdown
# Multiple Micro-controller Homing and Probing
|
|
|
|
Klipper supports a mechanism for homing with an endstop attached to
|
|
one micro-controller while its stepper motors are on a different
|
|
micro-controller. This support is referred to as "multi-mcu
|
|
homing". This feature is also used when a Z probe is on a different
|
|
micro-controller than the Z stepper motors.
|
|
|
|
This feature can be useful to simplify wiring, as it may be more
|
|
convenient to attach an endstop or probe to a closer micro-controller.
|
|
However, using this feature may result in "overshoot" of the stepper
|
|
motors during homing and probing operations.
|
|
|
|
The overshoot occurs due to possible message transmission delays
|
|
between the micro-controller monitoring the endstop and the
|
|
micro-controllers moving the stepper motors. The Klipper code is
|
|
designed to limit this delay to no more than 25ms. (When multi-mcu
|
|
homing is activated, the micro-controllers send periodic status
|
|
messages and check that corresponding status messages are received
|
|
within 25ms.)
|
|
|
|
So, for example, if homing at 10mm/s then it is possible for an
|
|
overshoot of up to 0.250mm (10mm/s * .025s == 0.250mm). Care should be
|
|
taken when configuring multi-mcu homing to account for this type of
|
|
overshoot. Using slower homing or probing speeds can reduce the
|
|
overshoot.
|
|
|
|
Stepper motor overshoot should not adversely impact the precision of
|
|
the homing and probing procedure. The Klipper code will detect the
|
|
overshoot and account for it in its calculations. However, it is
|
|
important that the hardware design is capable of handling overshoot
|
|
without causing damage to the machine.
|
|
|
|
In order to use this "multi-mcu homing" capability the hardware must
|
|
have predictably low latency between the host computer and all of the
|
|
micro-controllers. Typically the round-trip time must be consistently
|
|
less than 10ms. High latency (even for short periods) is likely to
|
|
result in homing failures.
|
|
|
|
Should high latency result in a failure (or if some other
|
|
communication issue is detected) then Klipper will raise a
|
|
"Communication timeout during homing" error.
|
|
|
|
Note that an axis with multiple steppers (eg, `stepper_z` and
|
|
`stepper_z1`) need to be on the same micro-controller in order to use
|
|
multi-mcu homing. For example, if an endstop is on a separate
|
|
micro-controller from `stepper_z` then `stepper_z1` must be on the
|
|
same micro-controller as `stepper_z`.
|