bug: Error 2003 STALL_OR_COLLISION_DETECTED

[sbalula]

Overview

Flex 1-Channel 1000µL pipette (v3.6) triggers Error 2003 STALL_OR_COLLISION_DETECTED consistently after approximately 10±4 tip ejections. The error occurs during pipette.return_tip() operations with no visible collision.

Cause identified: The plungerPositionsConfigurations.default.drop value (90.5mm) in shared-data/pipette/definitions/2/general/single_channel/p1000/3_6.json causes the tip ejection motor to push too hard against its end limit, resulting in cumulative encoder slippage that exceeds the 500µm threshold defined in ot3-firmware/include/pipettes/core/configs.hpp.

Proposed fix/workaround: Reduce drop from 90.5 to 89.0mm.

Steps to reproduce

1. Mount a Flex 1-Channel 1000µL pipette (model v3.6, serial format P1KSV36*) with about 1 year of usage.
2. Run any protocol that performs repeated tip pick-up and return operations
3. After approximately 10±4 tip ejections (~3 minutes of pipetting in our test), Error 2003 occurs

Current behavior

20260107_160251.2.mp4

The pipette triggers a stall detection error after repeated tip ejections. The tip ejection mechanism travels to position 90.5mm, which presses too hard on the mechanical linkage. Each ejection causes partial motor slippage that accumulates until it exceeds the 500µm threshold:

// ot3-firmware/include/pipettes/core/configs.hpp
constexpr float STALL_THRESHOLD_UM = 500;

Observable symptoms:

• Error occurs right after or immediately before tip ejection
• Clear clicking noise (3x) is audible
• Gantry homes and protocol stops
• No visible external collision

Log output:

"StallOrCollisionDetectedError: Error 2003 STALL_OR_COLLISION_DETECTED (StallOrCollisionDetectedError) (pipette_left)"

Expected behavior

The pipette should complete tip ejection operations reliably without triggering stall errors. The ejection end position should have sufficient margin to avoid motor slippage against the mechanical end stop.

Operating system

None

System and robot setup or anything else?

Robot version 8.8.0

Notes

It's unclear why the error only manifests itself after one year of light use of the pipette. There might be a hardware root cause that remains to be identified.
This issue was reported to support with ref:!00Df404lpsm.!500UV0iCZLk:ref

@cristian-peca contributed equally for the diagnosis and fix/workaround of this issue.