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About slyowl

  • Birthday 12/30/1992

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  1. That's an interesting point. I wonder whether it's possible to use that connection to crudely control something (ie. no feedback), such as using a relay to switch on a cutting blade.
  2. That would be the ideal solution. It could either trim off the tails, or cut through the filament itself (there tends to be a deformed section about 12mm long, which has been melted and solidified before the tail, which is normally slightly wider than the filament). You'd probably be best off having a blade which cuts the tail as soon as it exits the hotend, to avoid having tail remnants in the bowdens. That way you don't need to find a way of removing the cut off tails, as there shouldn't be any. Perhaps a disk which can spin, with a hole drilled in it. The filament normally passes through the hole, but to cut the tail, the disk is spun one revolution. It wouldn't necessarily have to be sharp - the hot tail should be cutable by shearing it. We thought having a cutting blade was a bit too much mechanical complexity - as well as taking up an extra motor slot.
  3. We've been working on a similar concept at Open Bionics. The aim is to prevent the filament stripping if it jams, so we avoided using metal gears in tandem. Our first design used gears that were too small, and skipped before it could extrude. The metal gears here were inspired by yours - but it worked much better without! The different diameters of the metal and ninjaflex gears mean you have to be careful how you design the gears, as you need the perimeter moving at the same rate. I think you got away with it because your two gears on the stepper have the same diameter - ours didn't! Note the "stacked" extra gears - this was an attempt to increase the friction. It worked, but modifying the ninjaflex wheel diameter and surface pattern (sanding it?) is simpler and probably less prone to failure. Our revised design uses much better gears, which can all be whatever size we like (no metal gears!). We had to lower the e_steps, because of the increased diameter. It works nicely, and the stepper skips before the filament slides or gears skip - proving the principle works. However, the filament tends to move up and down the wheel, and pops out the top, or gets caught in the gears. We haven't made the changes yet, but propose to have interlocking ninjaflex teeth above and below the wheel, to stop the filament getting out. There would still be the PLA gears to transfer the force! We think that having guide holes for the filament just before and just after the wheels would also help. Experiments with butting the top/bottom of the wheels up to a flat surface failed, as the ninjaflex deformed and filament got stuck between the wheel and surface... Have you had issues with the filament moving around? Perhaps the metal gears keep it nice and central... For this layout, we could stack the gears the other side of the stepper, which would only use 5 gears, instead of 6.
  4. We've got ninjaflex and PLA printing well out of 2 nozzles, as per my post in the Flex3 thread, linked below. This is usable, though not totally reliable (though often bizarre non-recurring errors, such as z-shifts mid way through a 20 hour print...). We've also got a Diamond Nozzle (discussed below). For now, the yield rates are unsatisfactory, so multi material is going on the back-burner. We'll look into The Palette, or a 3mm Diamond Nozzle, when released. Interchangeable heads plus diamond nozzle would be fantastic (6 filaments!) - but we need to get the individual components working well enough first. This demultiplexing idea is also on hold, until we muster up the courage to try it again! I don't see the Flex3drive as mutually exclusive to any solution. I've designed parts to allow it to be mounted on each of the diamond nozzle heatsinks - and it could work on interchangeable heads too. Simply, where there is flexible filament, we're going to need a flex3. Reducing the hot zone could work. We've also been experimenting with the Diamond Nozzle (on a Lulzbot), which has produced decent results printing with PLA and ninjaflex. The temperature difference doesn't seem to be too much of a problem. The main issues have been with the nozzle oozing during the print (both materials), and filament jamming in the bowdens (we're using 3mm filament in a partially drilled out 1.75mm diamond - so not ideal!). See here. Will hopefully get the U2 flex3 STLs up soon.
  5. At Open Bionics, we've been experimenting with automatically changing the filament in the hotend. The goal was a solution which could accept as many different filaments as we could control off the board, with only one hotend. In theory it wouldn't require complicated parts, and could be highly expandable. The idea was to withdraw the current filament from the hotend, and push another one in, extrude that, and repeat. We used a "tight" demultiplexing part, where the filaments were fully enclosed by bowden tube for as much time as possible. This part screwed onto the top of the U2 head. The filaments slided through easily, although some chamfering with a knife was needed on the inside of the receiving bowden tube to enable a smooth transition. Withdrawing the filaments (we are experimenting with PLA and ninjaflex) caused significant stringing on the withdraw - which blocked the bowdens. We experimented with different withdrawal rates, and temperatures. We found some success with double and triple "dipping" techniques - where instead of pulling the filament straight out, it was dipped back into the hot end, and then withdrawn again, to detach the string. A similar technique is used in industrial cake decorating robots! We managed to develop dipping techniques for both plastics which avoided any stringing, and produced the most consistent head. However, even our best attempt was temperamental - one day it would work, the next not... The dipping process was implemented by altering the Tool Change Command in Cura. We gave up feeding flexible filament through a bowden, and switched to the Flex3drive (a direct drive). This posed a problem with our technique: the flex3 could only withdraw filament as far as just above its gripper wheel, meaning we could extrude extremely well, but couldn't change filament. We developed the idea of using bowden extruders simply to change the filament, with the flex3drive providing the actual extrusion force. We had some success with pushing through the bowden, and then switching to the flex3 and getting it to grab the filament and push it through - but again, it was temperamental. Ideally both steppers would be pushing at the same time to get a good grab, but the firmware mods were taking too long... Worth noting that the you need to disable the bowden stepper whilst the flex3 is extruding (this is a firmware bodge) - it is strong enough to pull through the disabled stepper (but not enabled!). Even when this is done, the filament tends to build up tension and then ping through, leading to an inconsistent extrude volume. Further difficulty is added by the e_steps being different between the drives, so no easy electronics fix there. The upside to using the flex3 is that the filament path behind the flex3 doesn't have to be fully enclosed. We used an "open" demultiplexer part, where the deformed filament heads are stored when unused. This avoids the heads getting stuck in tight bowden tube (the bowden down to the flex3 was drilled out to 3.5mm). This part was very easy to make - and works well. It also eliminates compression in the filament between the drivers because of the open section. So... we made some progress with this technique. However, there were too many points of uncertainty introduced: the strings, the flex3 grabbing the filament, the tension between extruders, clogging in the demultiplexers. We concluded that it's a road fraught with difficulty! On paper it works, but printers will be printers. Would be very interested to hear if you've managed to get this to work! TLDR: - Retracting filaments from hotend causes strings - difficult to get rid of - Need to use flex3 to consistently extrude flexible filament - Difficult firmware mods to get flex3 to grab filament from bowden tube - Filament changes are very slow - Poor synchronisation between extruders leads to inconsistent extrude volume - Don't try this at home!
  6. At Open Bionics, we've managed to crack the second filament issue. We started with the Flex3drive U2 head, and with a bit of tweaking managed Ninjaflex out of the Flex3drive, and PLA out of the bowden. Firstly, we redesigned the coupler between the stepper and flexible shaft, as it was skipping badly. We stuck a bit of bowden above the nozzle to stop the filament bulging out the gap (circled, A). The flex3drive head is slightly taller than the U2 head, which meant it hit the casing when the head homed - so we had to fudge the endstop a bit. The trick to adding the second filament is to rotate parts A and B through 90', so that the Flex3 extrudes down the right hand nozzle, instead of the left. Parts C and D are rotated 180', so they face the front of the U2. It's necessary to cut a groove for the linear bearing in part B (circled, B) to allow this change to happen. You can see the unused original groove on part B at 90' to where it should be. It should then be possible to thread the bowden down to the left hand nozzle (you may need to trim a few bits of plastic to get it down easily). The Flex3drive axle goes down the far left corner in the picture. Finally, we popped a grub screw through the top part (circled, C), to hold the bowden in place for the extra filament. It may be necessary to do this for the linear bearing as well, depending on how good your cutting was! ... and it works beautifully.
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