Fighting with computers

Computers are not always friendly.

Wednesday, October 19, 2016

My Printrbot experience

While some friends were waiting for their first Printrbot off Kickstarter I had already built one with the parts Brook Drumm posted on Thingiverse. That was quite a while ago. It was a cute little machine that I sold to a fellow reprapper.

Last year, while I was working on a closed-loop DC motor controller for replacing the steppers of our 3D printers, Brook Drumm offered to help and sent me a free Printrbot Simple Metal, fully assembled to be used as a testbed printer for such type of motion control. I had a difficult time trying to convince the taxman that the printer was really a gift and eventually I had to gave in and pay some custom taxes although that was not really a product I was buying and the sender was charging me no money for that.

I was surprised of how compact the thing appeared and how smooth and solid all the axis moved. However, the 3d printer was not intended to be used as a 3d printer and the first thing I had to do was to partially disassemble a brand new unit and to start to adapt the other type of motor.

Adapting another motor while keeping the functionality of the printer was a dead end given my limited mechanical skills and how tight fit all the parts on this model of printer. I managed to get a motor working on Y axis but then I would lose Z-axis functionality as it was not possible to get both axis working with the type of motor I was using.

At then end, the mechanical limitations made the task to lay in my project's table for a long time without any new development. I want to stress that when I mentioned the problem I was having to Brook and the inability to get the test of operation he offered to send another model but I already felt embarrassed enough for not achieving the original goal to go on that path.

So one day I decided it was about time that I reassemble the Simple with its original motor and get it work as a regular 3d printer. Once it was up and running I did a sample printing while the printer sat on a stool in my office and I left the printer unattended for a coffee break with some colleagues. When I returned I discovered to my horror that the printer had fallen on the floor due to the carriages acceleration (metal feet of the frame on a hard plastic lab-type stool was a deadly combination). To make things worse the USB cable had almost ripped apart the micro-USB socket. My attempts to fix it did not succeed, so I ended up cutting the micro USB connector off and soldering the four wires directly (incidentally I discovered the schematic had the wiring to D+ and D- reversed on the Reprap site).

Luckily the torn USB connector was the only damage occurred to the printer after the fall. Once fixed it is working I hope as new and giving very good prints using PLA. While very good output quality, I have to admit it is not as good as the i3 MK2, but one of the reasons maybe that the Simple feels faster (in fact it uses default higher accelerations on XY axis than the Prusa i3) which can account for both the faster printing and the small difference in output quality.

All in all, I am impressed at how well this little printer handles. One minor detail is that while the printer profile is small, you need to have good clearance on the sides and on the back so X and Y carriages can move freely.

I can understand why this model has so many good reviews, it is just not intended for tinkering much as all the parts are held in a really compact space.


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