Roscoe Bear IDEX as of March 2023
This is a remix of @gregsaun's excellent Prusa i3 Bear frame upgrade for the Prusa MK2 and MK3 printers.
I made it wider, taller and use most of the original Bear plastic parts to create a much longer X gantry to make room for a 300mm x 200mm bed and parking space for the two independant extruders. Print height is approximately 230mm, but I'm hoping to improve on that slightly without spending too much money.
The design has been ongoing since 2017 or so and there is now a working prototype albeit lacking in certain features. The prototype has done useful work, but mainly as a single extruder printer :-)
Looking back at some of the design files, things have changed greatly from the earliest concept.
The printer currently runs Marlin 2.1.3 and is controlled by a BTT Octopus V1.1 control board with TMC2130 and TMC2208 stepper drivers along with an ancient RepRap Full Graphics Display. A Raspberry Pi 3B+ acts as an Octoprint host and provides WiFi network connectivity and 4.3" touch screen with Octoscreen (or Octodash) for control. The printer can be operated from either screen and files printed from either SD card or via Octoprint. A CSI or USB webcam can be fitted if required.
Of course, Klipper firmware could be used but I feel there would be few advantages except perhaps that of input shaping which has some better capabilities than Marlin2 current has. I doubt there would be much speed advantage being a "bed-slinger" although firmware updates would be more convenient than loading a microSD card into the slot after compiling Marlin in VScode - Horses for Courses.
If you decide to go down the Klipper firmware route, I would be interested in hearing how you get on.
The main departure from the Prusa Bear design is of course the X and U carriages (AKA: X and X2) which need to allow for the extra U (X2) stepper motor, belt and idler. For the moment this takes the form of taller X carriage components to make room for it all. The printed components comprise the XmotorUidler, UmotorXidler, Xcarriage and Ucarriage. The carriages are formed from two printed parts encapsulating some LM8UU linear bearings in fairly standard Prusa fashion. The arrangement allows for fairly easy assembly of the extruders to the carriages and also allows some early testing with just the carriages fitted. This keeps things fairly clear to setup homing, parking positions and check for clearances.
The X and U extruders are basically Prusa MK3S but with the wiring harness exiting the top of the units - there's not enough room between all the belts to provide the Prusaesque wiring egress. The endstop sensor boards will need their pins bending carefully so the three pin dupont socket attaches vertically rather horiontally. The rest of the assembly is pretty much as per Prusa's build instructions for the MK3S extruder with the ball bearing switched filament sensor. I have not used the earlier MK3 optical sensor variant which sensed filament movement.
The left hand extruder carries a PINDA2 probe for Z homing. This currently runs successfully at 3.3 volts with the spring steel flexplate. The righthand extruder being offset in the Marlin config to allow for any differences. At the moment, this means that the printer will only work in IDEX mode 1 - Auto Park. Mirroring and Cloning (modes 2 and 3) will not be highly successful. A SuperPINDA could be utilized instead. The benefit being that it is temperature compensated and does not rely on a separate thermister setup. So far the PINDA2 has worked fairly reliably.
Filament runout on both extruders is supported as per the Prusa setup. Just utilize a spare endstop port on the Octopus board - see Endstops
X, U and Y endstops are handled by the TMC2130 drivers (TMC2209 as an alternative). Z endstop is, as stated, a PINDA2 probe.
The Endstop configurationis as follows
X - Xmin (Stallguard)
U - Xmax (Stallguard)
Y - Ymin (Stallguard)
Z - Zmin (PINDA2)
E0 runout - Zmax
E1 runout - Ymax
The BTT Octopus board allows for up to five thermisters. I have them as follows:
T0 - Hotend 0
T1 - Hotend 1
T2 - Reserved for PINDA2 thermister
T3 - Spare (Maybe for ambient sensor one day)
TB - Heated Bed
The heated bed is a generic 24 volt 300mm x 200mm MK2-B (I think) with a BuildTak flexplate print surface from 3DJake
The Roscoe uses a string of NeoPixels arranged on a bracket above the bed. There is good Marlin support and only one pin is required from the control board. Indeed the BTT Octopus board has a dedicated NeoPixel pin. All that is required is a strong 5V supply to power it. I use a cheap eBay buck converter set to slightly above 5 volts. Marlin can be configured to provide printer events to generate various colours as the printer heats up and successfully completes a job. But this only works when printing from the SD card at the moment. From Octoprint you can just set appropriate commands in the Custom G-code routines to turn the lights on, off and different colours if you wish. Manual control via the menu is also available.
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Height adjustment for the U carriage and extruder so IDEX modes 2 and 3 can be used.
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Purge buckets - and/or a far more reliable purge tower control to improve multi material print quality.
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Move to Prusaslicer from Cura to improve print quality and simplify configuration - which requirest the next item:
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Twin part fan control which - Prusaslicer doesn't generate - However, using a post process python script sensible part cooling fan control is available. See the Post Process page.
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Shorten the height of the X and U carriage to increase the available print height.
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Switch to a textured PEI sheet from the exisitng BuildTak setup
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Finalize the Marlin2 config files.
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Control board could be a FYSETC Spider board - the Roscoe IDEX requires seven stepper motors to fully enable twin extruders and two independant Z motors. I did originally use an MKS RUMBA32 clone, but this only has support for six steppers and you have to do without the twin Z steppers and automatic gantry levelling. However this can be hacked reasonably well with a gcode script if a RUMBA32 or other six stepper board is all you have.
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Stepper drivers could be TMC2209 for Stallguard on X, U and Y axis with TMC2208 for the extruders and Z motors. Although TMC have moved on now with driver options, the 22xx series drivers are more than adequate for the motor current requirement. You could always modify the endstop arrangement to something more tradiitonal if that is what you or your budget requires. There's nothing wrong with A4988 drivers and microswitch endstops. But I do like the quietness of the TMC drivers. You can hear the bearings squeak when they dry out!
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Heated bed - In order to keep the weight down I have used a lightweight PCB heated bed with a flexible spring steel sheet system carrying a BuildTaK print surface. I originally inteneded to fit an aluminium bed carriage - Suitably laser or waterjet cut. But I started building the printer shortly before the first COVID lockdown in 2020 and getting special stuff made became quite difficult - as well as travelling around the country to collect parts. So, my Roscoe Bear IDEX has an acrylic bed carriage. I printed out the DXF outline and stuck it on a sheet of 5mm acrylic and got to work with drills and hacksaw. It is of course a lot lighter than an equivalent aluminium carriage although I doubt it would work too well in an enclosed casing as it would warp when it got hot. Marlin's BiLinear Mesh Bed Levelling appears to work sufficienty well for the moment. Of course a glass sheet and blue tape could be used if that is your preference but will increase the bed weight somewhat. Definitely a candidate for input shaping algorythms of some sort. My favourite, especially for PETG is a textured PEI surface which will be a future upgrade, once I find one - Maybe when the BuildTak surface wears out.
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Extruder options are of course to use the E3D Revo 6 hotend or a Voron Stealthburner hotend with Clockwork 1 or 2 extruder and blingie RGB LEDs in it. - up to you really. There is a lot of work involved in getting the Stealburner to fit onto the exisitng carriage arrangement though.
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Another option is to keep the existing MK52 Prusa print bed and make a slightly narrower printer but still have a twin extruder IDEX machine. The standard bed is 250mm wide (instead of 300mm) but offers 210mm in the Y axis (instead of 200mm). Taking 50mm off the X and Top frame members would make the machine slightly more compact.
This is very much a work in progress and is a long way behind things like the BCN3D Sigma and Voron IDEX projects. As a "bed-slinger" its is never going to be as fast as either of the above, but is a fairly simple build from a frame point of view. The open frame means you can see whats goong on and work on the printer fairly easily. The Prusa extruders are fairly easy to build and maintain and there's plenty of life left in the E3D V6 ecosystem. Especially with the new innovative Revo 6 nozzles.
If you have questions or ideas, please contact me.