Solution to delta printer falling arms and effector at power off
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This is not specific to a Duet powered printer, but I thought I'd write about it here anyway.
TL;DR Stop your delta printer effector crashing into the bed at power off using this small part.
For a while I've been tinkering with a Tevo Little Monster that I "repowered" with a Duet Mini 5+ board. The printer uses a BL Touch for sensing bed height. What I have found is that when the printer was powered off, the effector and arms would sometimes start to slide down and hit the print surface with a thunk. This wasn't the end of the world, but when powering the printer back on the BL Touch performs a self test, and with the effector firmly on the print surface this self test fails. The upshot is having to turn the printer off again, raise the effector off the bed by hand, and, while holding it off the bed, reach up and power on the printer.
More recently I modded another Little Monster with another Duet Mini 5+ board, and gave it 1.5m rails instead of the 1m rails on the original. This printer has the same problem when the power is turned off, except now it's even harder to reach the power switch on the top of the machine without raising the effector a long way up. A hassle more than anything. Anyway I wondered about how I could fix this issue and here is my solution.
It's a flexible bracket that has enough resistance to stop the arms falling at power off, but not so much resistance as to stop the arms moving while under power. I position it a couple of mm below the rear carriage while the effector is in the parked position.
As these printers use 80x40mm C-beams the bracket I designed works with those only, however I think the idea could be applied to any other design. It's possible others have come up with something similar, but I didn't find anything in my searching. As is often the case the biggest problem may be figuring out what it's called!
Anyway, here are some photos. I use two screws with T-nuts to hold it on the rail.
Here is a photo of the two monsters, showing the bracket in place.
