BasVanDeursen

Cool idea!

I asked Erik yesterday and he said he used the 400 motor. -Bas

Hi Everybody! We are indeed working together with Mutley3D to make an upgrade kit that would fit the UM2. This kit would be aimed at people who are not afraid to do some tinkering on their machines. However, at the moment we are still in the prototyping phase, so it might take a while before this kit will become available. So "should be available soon" might be a bit too optimistic. Kind regards! Bas

As far as I know all UM2's have 400 steps/rev motors. It might be that Erik did not use his stock UM2 feeder motor for his Flex3Drive setup. I should ask him about that next time I see him. Another comment that Erik made to me the other day: make sure that your retraction length is set to 1.5mm or something in that range. The drive wheel is so close to the nozzle that you won't have to compensate for any slack in the Bowden tube so you can use a low setting on your retraction length. -Bas

But you are building it onto a UM2?

I did not do an awful lot of printing with the Flex3Drive yet but during the first bunch of prints I noticed that there was some stick-slip between the gears. I put some grease on the gears and that solved the problem. -Bas

I can't find them but a 200 steps/rev stepper should do the trick. I think you could probably do with a nema14 because you won't need a high torque because of the worm gear reduction. -Bas

yes indeed! Sorry for the late reply! It's awfully busy here... I think that the problem is that the printer can't handle the enormously high steps per unit that you would need because of the high gear reduction in the Flex3Drive worm gear set. I also noticed that you will run into trouble when using a UM2 extruder motor because it has 400 steps / rev and is on 16 microsteps. Erik van der Zalm also had this problem when he installed it on his UM2 so he adapted the firmware to do "double stepping". However because Erik has a very early version of the UM2 he has a 200 steps/rev extruder motor. Because of this it works just fine on his UM2 but not on other UM2s. The solution would be to install a 200 steps/rev extruder motor. I think we still have a bunch of them here at UM HQ. I'll check out and if we still have some lying around I'll send you one, that should solve your problem. cheers, -Bas

Hi everybody, At the moment I have Erik's design running on a UM2 However I did make a custom shaft for the hobbed wheel. The standard shaft that comes with the kit is about 10mm too short for Erik's design. At the moment we are experimenting with this. Kind regards, -Bas

Hi, I understand, that is of course unacceptable. I know that the current feeder design is critical, which means that only slight changes in the resistance in the "extrusion train" can make the difference between a nice and a bad print. From the material feeder perspective (which is the area of the printer I am working on) I can say that I am doing my best to get some more grip and torque. -Bas

Hi everybody! Just to give some input: I know that Illuminarti did some research about this as well: http://www.extrudable.me/2013/04/18/exploring-extrusion-variability-and-limits/ Besides this Erik van der Zalm also took some measurements with a rotary encoder on the filament (see attached graph). As far as I know, these results were all measured on a UM original. -Bas

Hi! I've never mounted a hobbed wheel onto a UM2, I've only tested it's grip in a test rig that I had built for that purpose. If your knurled wheel keeps getting loose you could secure it onto the motor shaft with a drop of loctite. Cheers, Bas

Hi everybody! Some input that might be interesting for those working on improving the feeder mechanism: Lately I have been experimenting a lot with geared stepper motors. The increased torque on the feeder axis helps a lot in achieving higher extrusion rates. However, printing with a very high number of retractions is still problematic: during these prints the filament gets flattened and obstructs the bowden tube. I have been measuring the temperature of the feeder wheel axis; during long prints (with a room temperature of 22 degC) the feeder wheel axis reaches temperatures between 40 and 43 degC. At this temperature PLA already gets quite a bit softer than at room temperature. During continuous extrusion this is not problematic, however during prints with lots of extrusions it is. Cheers! Bas

I did a quick comparison between the hobbed and the knurled feeder wheel. I fed a piece of PLA through a feeder while measuring the torque on the feeder motor axis with a torque sensor (no bowden tube and no hotend present). I used a hobbed wheel and a knurled wheel of the same diameter (8mm, for the hobbed wheel the diameter at the lowest part of the curved surface). At the same idler setting, a higher torque was needed to feed the material through with the hobbed wheel. However the hobbed wheel also had a higher grip than the knurled wheel at the same idler setting. So in the end it doesn't seem to make too much difference. -Bas

Hi! I've also noticed that the hobbed wheel seems to cut more into the filament while the knurled wheel seems to push and deform more. The only disadvantage that I found was that when the wheel really slips over the filament (e.g. in case of a clogged nozzle) then the grip pattern really clogs which dramatically decreases grip. However the grip was superior to the grip that I could reach with a knurled feeder wheel. I have the suspicion that the hobbed wheel is also a bit more efficient in transferring power to the filament because the grip pattern cuts better into the filament, resulting in lower losses. A while ago I've done some measurements on the grip versus the idler wheel pressure for different grip patterns, If you'd like I could send you the results. I've also done some measurements on the feeder loss versus the idler wheel pressure (the higher the pressure, the higher the grip, but also the higher the losses induced by deformation of the filament). I'll try to repeat this measurement this afternoon but then with a hobbed wheel. That way I can seen if the hobbed wheel is more efficient. Cheers! Bas