Monday, March 30, 2009
Three heater barrels and a new drive
(click on the links for more pictures, design and test results)
quick and dirty extruder
Version 2 - Welding tip
version 3 - wider feed channel (3.5mm through PEEK) for the filament
And I mucked around with a minimalist drive (Keep it Simple)
Simple - shove a screwdriver in a hole
This worked OK - as long as it was driven at a slower speed than the screwdriver default (2.4v instead of 3.6v)
I also had problems driving the screwdriver motor from the RepRap electronics
Version 2 used the BfB motor. Plenty of torque, but I can't drive it slow enough!
Below about 50/255 the motor stalls: above, the speed and torque is good but it stalls the filament once it hits the end and chews up the filament.
It works well (filament speed is aprox 5mm/sec at the 3mm diameter end) and as much drive as the filament can stand. The star screwdriver bits work well and seem to drive well. Perhaps I'll have to get a stepper motor and driver circuit for the extruder to get the speed down?
I'm going to try and reconnect the original BfB screw thread drive to my version3 heater barrel, and see if that drive will screw down at a slower rate.
*embarassed* I can't exactly use the original BfB heater barrel anymore- I was drilling some out stuck filament when the drill snatched and ripped off the ends of the nichrome wire and threw the thermistor circuit across the garage. I still haven't found it...
If you don't want to mess around with optical encoding right away (but you're going to need closed loop at some point to get your accuracy down), try pulsing the PWM drive in software; ie, figure out the minimum PWM to get the GM3 to turn, then give it a quick pulse of that PWM, then 0% PWM. The GM3 will pulse along like a clock mechanism, but the give in the extruder smoothes it out. Someone on the forums was experimenting with this; Geert I think, but my encoder controlled extruder ends up doing the same thing when I set the speed really low.
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