I was recently offered to try out the BIQU Hermit Crab CAN. This was great timing as one of my printers was down due to a bad thermistor cable in the cable drag chain. I was in the process of removing the wiring and also replacing the drag chain to an open style which allows me to open up each segment and easily add or remove wires.
What is the Hermit Crab?
The Hermit Crab is a quick change tool, which allows you to easily and quickly change out your tool. For example, you can change to a FDM extruder, or a laser engraver, or a cutting tool, or whatever you want. The CAN version uses just one USB-C cable (doesn't use USB protocol, just uses that style cable for convenience). The USB-C cable carries the data and power to the hotend. The CAN version has a bunch of nice features such as accelerometer, Neopixel RGB LEDs, and TMC2209 stepper driver.
In this photo, you can see my current setup as I'm in the process of rewiring. I've got an Orbiter extruder with a "Hero Me" mount, using an inductive probe, and also an accelerometer attached (but no wires hooked up as there are too many wires to leave connected to it). You can also see the open style drag chain that I was talking about, with a few of the segments open.
Here's the plan with the new setup. Use the BIQU Hermit Crab CAN and while I'm at it, switch out to the BIQU H2 extruder/hotend. Instead of having a bunch of various wires going to my hotend assembly, I would just have one single USB-C cable.
|Setting up H2 and Hermit Crab CAN. You can see the CAN hat on top of the Raspberry Pi, as well as the CAN Power interface board that adds power to the interface
|Duet 2 Wifi board
|"make menuconfig" configuration for Hermit Crab firmware
|Simple to add or remove a tool head
|Going from a bunch of different wires to just one cable. Yes, I know there are multiple wires inside of the cable sheath but from my point of view, it's just one cable.
|23mm thick with both plates
Also, Klipper is known to have issues with having a probe on one MCU and the Z steppers on a different one. I've ran into multiple warnings of communication timeout during probing. You can find more information here: Multiple Micro-controller Homing and Probing - Klipper documentation (klipper3d.org) . Here's the text from that page:
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.)
Overall, I would have to say that my experience has been positive. I've got a working printer that has simplified maintenance and gives me flexibility to change out the tools on my printer. The biggest change for me is going from RepRapFirmware to Klipper. A couple of features that I miss include the ability to have a macro that runs in the background (daemon macro), the ability to perform actions while waiting for the printer to heat, and the ability to make changes on the fly (every configuration in RepRapFirmware is just gcode, whereas config changes in Klipper require restarting the Klipper service). The new benefits of Klipper include faster data transfers (Duet uses a slow ESP8266 module, Raspberry Pi has faster wifi), a nice LCD UI via KlipperScreen, as well as simpler resonance tuning and the ability to run on additional boards.
I haven't had a chance to mount other tools yet as of this time of writing, but I plan on trying out various setups such as using a cutter tool to cut vinyl, and trying out a pen as well. This particular printer is in my office so I have no plans of attaching a laser module to it as laser etching produces lots of smoke and fumes.
I would not recommend this to the average 3D printer user but would recommend it for advanced users. It does involve a lot of knowledge, figuring out how to mount everything, wire everything up and setting up the firmware for it. There are several use cases I can think of. Perhaps you have a multi-filament hotend you want to use one day, and then another day you just want to use a high-end single filament hotend. You can easily do that with the Hermit Crab. Also, if you want to have a hybrid FDM printer and laser engraver/cutter you can easily setup that up with the Hermit Crab as well. Or if you really like the idea of reducing the number of wires you need to connect to your print carriage as well as having an accelerometer and RGB lights, the Hermit Crab CAN version will do that for you.