By now we’ve sort of succeeded in bringing the fab@home 3D fabber into operational state, thanks to the great help of the Waag FabLab people, especially Jean-Michel Molenaar and Bastiaan Ekeler. The kit we worked with is one that we ordered from KoBa Industries. While the kit is designed wonderfully, we still bumped into a number of challanges.
The fabber kit comes in the form of a white box, a bit too big to transport manually alone, weighs in at about 10kg. It includes almost everything you need for assembly, basically all the custom-made plexiglas parts, motors, cables, etc. The fab@home site provides a list of additional equipment that you need, see here. You can follow the documented assembly process, it’s put together pretty much, though navigating between the assembly pages is quite difficult, as the navigation menu is only provided at the bottom of some of these pages, and it’s not obvious which is the first one. The process is surprisingly easy, but of course you can never get everything right at the first time.
Below I listed some issues we’ve found, and also some improvement suggestions.
Some issues with the kit
We’ve encountered the issues below when trying to get the fabber work.
Some motor orientations were incorrect
Though we’ve followed the wiring color convention suggested in the assembly tips page, at the end it turned out that actually 3 of the 4 motors had opposite orientation then expected. Don’t know how / why this happened. By reversing the cable connections from the motor controller to the motors, this issue got mitigated. We’ve had to reverse the limit switch connections as well accordingly.
We only found out about this issue when we were controlling it from the software, as the 3D representation of the kit and its actual movements contradicted each other. For example, the plate was moving up in reality while moving down in the 3D view. Coincidently, the deposition tool’s motor was also reversed, so it was actually pulling back instead of pushing the material out. No wonder nothing got printed at first 
The controller support doesn’t hold the controller
It seems that the small parts that are supposed to hold the microcontroller on the fabber chassis were added as an afterthought, and they just don’t lock in properly, and thus they don’t support the controller. Maybe a better design would help in the future, so that the controller is held properly on the side of the fabber box.
A Windows-only solution
It’s not mentioned in the required bill of materials, but actually you need Windows to run the fabber software, or even just to connect to the fabber. Seeing that it’s an open source project, actually I didn’t check in advance, but I supposed it most be running on Linux, and possibly cross-platform - well, it’s not.
What’s even more surprising is that the controller is not a regular USB-Serial device that would be generally recognized by operating systems, so one can’t even just connect it to any OS and play around with it via a serial protocol. It needs a special USB driver that is available for Windows only. This also means that if you’re running Windows from a virtual machine within another OS, you need one that enables for USB pass-through from the host OS to the guest OS. (For example, the closed source version of VirtualBox does this, but not the open source version.)
It would be nicer to have the controller as a generally recognized USB-Serial device that is picked up by all major operating systems. It would be even nicer if the whole solution would run on a range of operating systems, especially Linux, so that one can create a complete fabber solution running on nothing but open source software.
Possible improvements
The following would improve the kit building experience.
Include more of the easy-to-break parts
While I know that professionals never make mistakes - me as an amateur, I sure do. And as more and more people try to get into 3D fabbing, more amateurs are entering the scene. It would be nice thus to include more of the easy-to-brake-but-cheap parts in the kit. This is especially true since internationally some are very difficult to replenish, just because of the different markets around.
For example, I ruined all limit switch connectors when putting them together, and took me about 3 days to find replacements. Unfortunately the kind of connectors used are not available here in the Netherlands, so I had to buy replacement limit switches. Fair enough - but these are actually of different shape (the connectors on it are not on the side but on the bottom of the switch), which means they don’t fit into all the locations they are supposed to on the fabber. We worked around it by creating adapters for them using a laser cutter at the Waag FabLab - but not a lot of people have this luxury.
All this could have been prevented by supplying say twice the amount of the small white connectors and the crimp contacts used, which I guess would have cost about $5 more at most, less than 0.2% of the kits overall price. And would have saved me 3 days.
Use fewer kinds of screws
It’s not apparent on the assembly tools page, but putting the fabber together requires a huge range of different screwdrivers. Moreover, it requires both metric and imperial scale screwdrivers. Thus no one is having a good time: actually you have to buy sets of different norms, it’s not enough to have everything from one norm. It’s also annoying to always look for the other screwdriver as the one in your hand is just not the one from the six kinds used.
I’m sure this all stands to reason, but maybe lowering the number of different screws in the construction would make for easier assembly and maintenance.
Provide a JTAG adapter with the kit
A JTAG adapter for the board used in the kit is not easy to get internationally. Took me about 2.5 weeks to finally get one shipped here in the Netherlands, and about €85 including shipping, even though the list price is about half at that at $55. This being about 1.9% of the overall price of the fabber kit, it might be wise just to include the JTAG adapter in it.
Of course one can argue that this is generic, re-usable equipment. But it never hurts to have one, and amateur enthusiasts are not going to have this specific adapter anyway. And yes, you’ll want to have one to upgrade the firmware, even though KoBa Industries sent the controller already flashed with some version of it.
Provide easier adjustment for the Z-top limit switch
One has to adjust the Z axis top limit switch quite often, so as to accommodate the size of the syringe nozzle in the deposition tool. This has to be done by loosening a hexagonal screw, which is opposed by a nut on the other side. Unfortunately the nut is very hard to reach because of the vertical support rods of the plate. It would make life easier if one could loosen and tighten these screws easier.
As a workaround, we glued the nuts to the limit switch, so that they oppose the screws movements without having to manually hold on to them.
Tags: bio.display by akos
Comments Off
