08/05/2015 at 18:36 •
We've been working on the grinder tooth profile to create the proper sized chunks with only one pass through the grinder. Depending on the infill percent, shape of the material, etc, the waste can sometimes get shredded into strips instead of ground into smaller bits. While we're optimizing the grinder assembly for longevity, weight, and overall awesomeness we decided it was the perfect time to try and nail down the best tooth profile as well. We're about halfway through right now, as we're now able to grind fully solid stuff without issue (which is something we weren't able to do before), but super thin materials are still creating strips instead of chunks. It seems to be a bit of a trade-off between strength and chip size!
In other news, as we lost the current feedback system from the DC motor (which augmented, but is not required for, the diameter feedback system) there's no way to tell what force is on the auger, unless the stepper begins stalling, which is obviously not ideal. This means that our Intelligent Extrusion feature has to be implemented a different way. We're testing a few different theories to try and re-gain this capability, and one of the ideas that's looking the most promising is comparing the size of the filament at each sensor. We've noticed through testing that filament that's a little too cool gets stretched out overly aggressively - think of a more parabolic profile - than filament that's the right temperature. And, filament that's too hot gets bubbly and rough. Once the temperature has been settled on, adding an encoder to the stepper would allow us to increase the pressure until it begins to stall, and back off again. While it would be a slightly less elegant "searching" process, the end result would be the same - ProtoCycler can learn about what type of plastic it has without needing you to tell it!
The very general process we're going to test is to heat the melting section in 10 degree increments until the plastic is extrudeable at a medium speed. Then, the diameter sizes will be compared to find the correct draw down ratio, corresponding to the correct temperature. Finally, the speed will be increased until the stepper begins to stall and / or the diameter becomes inconsistent. At this point, everything will be properly set for that plastic!
07/08/2015 at 18:37 •
Had a motor issue with our main auger motor, previously a geared DC motor. It turns out that torque ratings for DC gear motors are for peak load only, and not continuous...and that the continuous load is only about 1/10th of the peak (so much for a 3:1 factor of safety...)
After much experimentation, we've switched over to a stepper motor for the main auger. This involved changing both the control scheme and physical implementation of the MixFlow melting section so that the stepper's constant speed could be reliably translated into a constant pressure to the plastic. Performance has improved in a number of areas including reliability, tolerance for non-uniform input material, power efficiency at higher speeds, etc. However, intelligent extrusion is not as reliable at this point as there is no pressure feedback...work is being done on the algorithms to try and restore this functionality, but for now testing and design for manufacturing are moving ahead to speed delivery to our Ingiegogo backers.