New member questions

Yesterday I ordered my hot end bits and ABS filament from makerbot and I have some Noob questions.

1.How much power is used for the extruder motor? (Volts and Amps)
2. In a video it looked like the filament moved backwards when the extruder stopped. How far does it back up and is it just to relieve pressure at the tip?
3.What is a good starting temp for the makerbot ABS?
4.Is there a Reprap FAQ? I found answers to most of my questions by searching the web but a FAQ would have have saved a lot of time.


I am making a extruder for my homemade mill that I control with EMC2 and AXIS. I use sketchup as my main CAD program and use Skeinforge to create the gcode.

1) 12V at probably no more than 1.5A. The driver chips are rated for 2A max. The coils on my makerbot motors are 35ohm, but I'm not sure that ohms law applies with this type of load. You adjust the current with the trim pot on the stepper driver too, so amp draw on the motors can change accordingly.

2)This is done to stop plastic oozing out of the barrel and making blobs on part outlines. My understanding is that the distance you have to back it out is dependent on the material you use (PLA, HDPE, ABS, etc) and what temperature you use. I have not run different nozzle sizes long enough to tell, but it may also depend on the diameter of your nozzle hole (.5mm vs .3mm).

3)Makerbot sells the Mk5 extruder now a days, mine is an MK4. The different thermal mass might reduce temperature swings which could make your temperature a little different from mine. 218 to 223 work well for me. I print the first layer at a higher temperature since that seems to help it stick better. I back it off for the rest of the print to keep shrinkage down.

4)I'm not aware of any. The wiki page might help you though.

Edited 1 time(s). Last edit at 01/02/2011 03:39PM by dazed.dnc.

4.Is there a Reprap FAQ? I found answers to most of my questions by searching the web but a FAQ would have have saved a lot of time.

We've got two:
http://reprap.org/wiki/FAQ
http://reprap.org/wiki/General_FAQ
plus my favorite:
http://reprap.org/wiki/What_Tooling_Do_You_Have

Although this is what you're looking for:
http://reprap.org/wiki/EMCRepRap

irc is good for quick questions:
http://reprap.org/wiki/RepRapWiki:Community

plus you should probably join our technical-but-friendly developermailing list since you're probably a developer:

http://lists.reprap.org/mailman/listinfo/reprap-dev


Welcome aboard!

Edited 1 time(s). Last edit at 01/03/2011 12:04AM by SebastienBailard.

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-Sebastien, RepRap.org library gnome.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

dazed.dnc Wrote:
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> 1) 12V at probably no more than 1.5A. The driver
> chips are rated for 2A max. The coils on my
> makerbot motors are 35ohm, but I'm not sure that
> ohms law applies with this type of load. You
> adjust the current with the trim pot on the
> stepper driver too, so amp draw on the motors can
> change accordingly

Ohm's law always applies. The trick is that it specifies "ultimate" current. So it's what the current will eventually rise to.

With an inductive load, it takes *time* for the current to rise. The "chopper circuit" inside the stepper driver cuts the voltage when the current gets to the pot-adjustable limit. This prevents excessive heating of the motor. Heat loss is I²R, so controlling the current controls the heat of the motor. Torque is = Current though, so you'll also limit the torque. You can usually turn the heat down quite a bit by lowering the current a little bit, so you don't lose much torque. You can't get the full torque rating of a motor with a Mendel anyway, because the plastic mounts would melt - steppers are usually spec'd to run quite hot.

Since the voltage is (usually quite a bit) higher than the motor's rating, the current rises faster than it would with the motor's rated voltage, which is (normally) the voltage without chopping drivers. Because it rises faster, it gets torque sooner meaning that the max speed of the motor is higher and the torque at high speeds is better. This effect is because as the steps get closer together the current still rises far enough to get torque.

Of course, with an inductive load, the current takes time to *fall* to. This is what will kill your stepper driver if you unplug the motor while the power is on. As the current slowly decreases, the voltage on the motor side of the plug spikes, easily to several thousand volts. The current has nowhere to flow, electrons end up piling up at the end of the wire, acting as a very small capacitor. This voltage is high enough to jump across the plug you just unplugged and zap your motor driver chip. Also beware poorly-soldered joints in your motor's wires.

When the driver is still attached, it uses a set of diodes to "short" the coils. When the chopper cuts off the voltage, the current begins to fall, and ends up flowing across the diodes instead of building up to dangerous levels. The diodes too take time to "switch", so there's also a small ceramic capacitor to store the charge while waiting for them.

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I'm building it with Baling Wire

Thanks for the replies.

My other motors are running at 18V 1A or 18 Watts. So i can build another controller to the same design.

I am going to check out the FAQs before i ask any more questions.