Use Continuous Servo as extruder filament feeder HELP!

Hello, we are designing our own extruder and looking at various ways to feed the filament. Other than steppers and DC motors, we were thinking of using a continuous rotations servo as we have a nice compact high-torque servo, which we think would work well for this. The question is: does the extruder controller directly support this function, is it configurable in the code, or possible otherwise?
Thanks,

Anyone?

I don't know of any current electronics set that supports PWM hobby servos for anything. There might be a PWM fan header. If there are enough pins left on one of the Arduino boards, you could modify one of them and hack the firmware to support it.

I'd recommend you just go ahead with a stepper which is already implemented and working well.

There is servo control built into the Arduino examples that can be used with standard RC servos it works just fine.

The servo support is for the common Radio control type servo. They uses a potentiometer for positional feed back thus these types of servos have a limited movment. On instructables there are at least two items were the pot is removed and the stop on the gears removed then a multiurn pot is used for positional feed back. again this would be limited to say 10-20 revolutions or so.

Im not sure if you could count Makerbots original extruder with its Magnetic Rotary Encoder v1.0 Kit as a complete servo extruder system. Makerbot.

However Makerbot apper to be moving away from a DC motor drive to a stepper based extruder so maybe stepper is better option to stick to. Reprap has been a stepper extruder drive for at least two years now I think..

[en.wikipedia.org]

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Changing an RC servo to continuous rotation is simple, and we were mostly considering this since we have one already, it has quite a bit of torque, and is small and lightweight. But guess we'll be going with a stepper drive now, to keep things compatible and easy from the software side.

Thanks.

You are probably better off getting it done with a stepper initially, but a hobby servo is actually a great idea in some ways. It is much lighter than a stepper and has equal or greater torque. You don't need much speed so that is OK too. The mass is a big plus if you want to drive the axes at higher speeds, but since there is no (maybe there is now?) per axis acceleration yet you are still limited by your heaviest axis which is probably the Y axis anyway. On a Darwin/ultimaker style bot where the platform moves only in Z, the idea might be great. The unknown is quality and consistency since modifying the servo destroys position information so the speed can't be precisely controlled. It would end up being a DC gear motor. Also unknown is whether it can reverse fast enough to control ooze. I have thought about those little bundles of joy too. It might be a fun project once you get your bot done. I think the extruder control software already does PWM for DC motors by the way, it would just be a matter of hacking the fimware a bit to get the pulse lengths you want.

The print axis on all standard ink jet printers are direct servo drive mechanisms all using DC motors with optical positional feedback. So speed is not a problem just the optical encoder strip and reader device in DIY quantitys creation of the software to controll the sevo. Most printers seem to be Arm processor based as well.

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Bodge It [reprap.org]
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BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]

My Epson Stylus has two steppers inside, no encoding strip in sight.

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