Pipette crunching during tip discarding (PLR)

Hi everyone,

Does the lh.discard_tips() command assume a specific length of the tips that it is discarding?

I noticed that 50 ul tips are consistently being pushed into the metal surface by a couple of millimeters. Since these tips are very soft they easily bend away under the pressure without causing any harm to the instrument nor flagging up a hardware error but this should still be avoided.

However, if a tip stayed on the channel after an interrupted automation run the lh.setup() command correctly identifies any remaining tips and discards them gently (with what looks like capacitative tip detection).
This raises the question of how the lh.discard_tips() command makes a judgement of the channel height at which it is discarding tips.

PLR knows the length of the tip from the origin tip rack’s definition (using tip trackers) so a perfect discrad should be possible. discard_tips is actually just a wrapper around drop_tips(trash). For the STAR’s trash, I made an educated guess about the z height but apparently was off by a couple of mm. Could you confirm that tips with a different length are also pushed into the surface? The z-location can be edited on line 65 of hamilton_decks.py.

For future reference, the conversation continued on GitHub: Correcting trash z height for discarding tips by BioCam · Pull Request #63 · PyLabRobot/pylabrobot · GitHub. TLDR: some firmware parameters were wrongly computed for place&shift tip drops.

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Thank you, Rick, for the fast troubleshooting - another solution for PLR :slight_smile:

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