Duet3 + BTT Hermit Crab can-bus tool changer?
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Does anyone know if the Duet3 can connect to (and control) the BTT Hermit Crab and, if so, where I can find any documentation online to help me get that working?
Thank you in advance!
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@abitsean the Klipper CAN is not compatible with Duet3 CAN-FD
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@t3p3tony Is the hardware incompatible or the software?
i.e. the btt hermit crab can can be flashed with klipper firmware... would it be possible to flash it with a firmware that is compatible with duet3d in order to achieve quick tool-change ability using duet hardware? that would be the best of both worlds -
@abitsean as far as I know they do not support CAN-FD only original CAN.
So a hardware incompatibility unless the Duet hardware is configured to run CAN. If the BTT breakout board was the only thing on the CAN bus then that would be possible in hardware. It would require work in firmware as well
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I have a hermit crab can bus unit that I can't seem get to work (it takes the klipper firmware without issue and appears to respond to the bus query script on my R-Pi, but the script fails to identify it on the bus) and their support never bothers to respond (thanks for the quick replies, btw... very refreshing in comparison).
So, if this is at all a possibility to request as a feature, that would be outstanding and I'd be willing to donate my hermit crab in the name of getting that firmware change created, if it would help at all...?
(it is essentially a paperweight collecting dust at this point, so I'd be happy to donate it in the name of "science"
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@abitsean it'll need not just firmware changes to the duet side but more than likely firmware changes to the hermit side too.
Unfortunately I'd be inclined to say it will continue to be a paperweight -
@abitsean when we first looked at using CAN to connect expansion boards, we did the sums and concluded that plain old CAN has too little bandwidth to handle motion. It's fast enough most of the time; but when slicers generate long sequences of short movements, it's too slow. That, and our desire to produce a solution that scales well, is why we chose CAN-FD to interconnect Duet 3 boards.
It may be that if an expansion board has just a single motor controlling an extruder, and there very little other CAN traffic in the system, and especially if the firmware performs extruder smoothing (which RRF doesn't do) and/or you can control the minimum segment length generated by the slicer, then controlling a single extruder over plain CAN is feasible. So I'm not saying that the Klipper solution isn't feasible under those conditions; but I doubt that it is scalable in the way that RRF + CAN-FD is.
Duet 3 MB6HC and MB6XD have a second CAN bus intended to use plain CAN protocols to communicate less time-sensitive data to other devices. It is already being used by one of our users to program the behaviour of external stepper drivers, but not to command actual motion.
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Thank you for the detailed explanation. I understand what you're saying and appreciate that you guys (and gals?) put the forethought in during the R&D phase to avoid issues like these down the road for your customers.
So, back to my problem... do you know if there will be a similar type of "quick (or even automated) disconnect" type system for the duet can-fd ecosystem?
I'm sad to have wasted the money on this turd but such is the nature of the sunk cost fallacy. For that reason, I'd be eager to purchase something similar (or better) that is compatible with the Duet3 can-fd family, and I'm sure I'm not alone, given the size of your loyal and enthusiastic fan base
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@abitsean said in Duet3 + BTT Hermit Crab can-bus tool changer?:
"quick (or even automated) disconnect" type system for the duet can-fd ecosystem?
The E3D system with Duet toolboards.
The disconnect is only mechanical, the toolboard stays connected to the machine via CAN and 24V cables.
You cannot safely disconnect motors while the control system is powered, anyway, and this system allows "live" toolchanging for multicolour or multimaterial printing.
The E3D system is an open design and there are compatible DIY ones such as the Jubilee printer version, which is cable operated rather than having a motor in the head.
https://www.thingiverse.com/thing:3805144I got a basic TronXY printer and converted it to a Duet toolchanging machine using the E3D stuff & a lot of home made parts..
https://forum.duet3d.com/topic/25709/meet-the-frankentron
If you want more tools that can fit in the machine - you can connect the toolboards via plugs and fit different sets, while power is off.
(I use 15 pin D connectors, with four pins parallel at each end for power and ground, then the CAN in & out in the middle). -
@abitsean from what I can tell, the CAN version of the Hermit Crab only does CAN up to the tool holder, and it's then the same as a conventional Hermit Crab to connect the tool plate.
In principle you could use a non-CAN Hermit Crab to connect tools to the Duet, either directly, or by using a single Tool Board on the tool holder so that you use CAN up to the tool holder. The caveat (as @rjenkinsgb has pointed out is that disconnecting stepper motors while they are powered is bad for the drivers and may cause them to fail. Therefore it's necessary to be very certain that the driver has been disabled before disconnecting the tool.
It may be that what you have in mind is an automatic tool changer with pogo pins or similar spring contacts to connect power and CAN bus. This would be possible in principle, although precautions would need to be taken to limit the surge current when power is connected. But sadly there is a patent on using CAN + pogo pins on 3D printers, which is now owned by Stratasys.
