extruder motor on PWM?

I have a high power motor for my extruder which the dc motor driver cannot handle. Is it possible to run the extruder motor on the PWM instead? i know i will lose direction, but is it really necessary? I mean, does the RepRap software make any use of reverse drive?

Thanks

All things are possible, if you're willing to hack the firmware to suit your needs.

It might be easier just to pick up a smaller motor though

you could reverse the motor with a second pwm channel, but take care to not have both channels active simultaneously

Maybe you can connect the motor to both dc-motor-driver ports too to gain more power.
It may be worth a try.

But, I'm with Ru personally, I'd choose a smaller motor

'sid

i'm running a 5amp motor because i'm trying to increase the speed of extrusion.

hack the firmware? Does this mean the software makes use of reverse drive?

thanks

korndog Wrote:
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> i'm running a 5amp motor because i'm trying to
> increase the speed of extrusion.
>
Wowzie! How are you planning to get that kind of amperage out of those motor controller boards?

I think the host s/w has the ability to reverse but it is not used at the moment. You can't reverse the flexible drive because it unravels the cable. I made my extruder electronics one way only because of this. Now that I have gone to direct drive I will make my next electronics reversible as I want to experiment with winding back the filament to stop the flow. Definitely not a requirement at the moment though, and not needed with the anti-ooze value design.

While I think a bit more power would benefit the extruder I think 5A is way too much. How big is the motor?

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[www.hydraraptor.blogspot.com]

5A?

THAT is oversized
On the other hand you could print filament at roomtemperature with that ,
not that it makes sense, but I bet you could (if your nozzle don't break of course )

'sid

nophead Wrote:
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>
> Now that I have gone to direct
> drive I will make my next electronics reversible
> as I want to experiment with winding back the
> filament to stop the flow.
>
I did try to do reverse flow with the GM-3 with Tommelise 1.0. When I tried it one of two things happened. 1) I overloaded the antistall device in the gearbox and the GM-3 started buzzing like a baby rattlesnake. 2) the GM-3 stripped off the threads that it had cut into the filament.

My feeling is that we are going to have to have a much firmer grip on the filament than we have with this lead screw arrangement that we are using presently before we can make good use of reverse flow in the extruder.

Quote

i'm running a 5amp motor because i'm trying to increase the speed of extrusion.

Seems... excessive. You'll probably need your own DC motor driver for something that big. The interface is simple enough, so I'm sure you can find something you can attached to the arduino and run using the existing firmware.

Motor power is only part of the problem... the little GM3 puts out a surprising amount of torque, because it is heavily geared. Less than a 5A monstrosity would with a bunch of gears, of course, but consider that people already have had issues with various bits of the extruder barrel popping off under pressure. I'd be surprised if you could get away without a seriously overengineered head to compensate for significant pressure increases, and then you'll need a pretty hefty cartesian bot to carry the whole thing...

A longer drive screw would increase the contact area but would also increase the channel contact area, increasing the amount of friction.

I keep visualizing a set of 3 drive screws surrounding the filament but I can't figure out a sane way to connect a motor to all 3 screws.

Some sort of compromise between a drive screw and a pinch roller might be interesting. Maybe two tank treads in opposition or something.

Hi Steve,

i was thinking of tank threads too, but it seems to be very complex - you need a special narrow shape fitting the filament, what's not common - so you have to build all the parts on your own.

For synchronizing three screws you can build a ring with 6 gears: one is the motor, then every 2th is a screw and two dumb gears between for syncing and closing the transmission. Or imagine planetray gears, where the motor drives the 'sun' or an outer ring - you can find good planetary gears in shutter-drives (blinds?)

Viktor

I am currently working on a tripple roller feeder. The three knurled rollers are carried in a cage which rotates around the filament. The rollers are angled at 5 degrees from the filament axis to give approx 1mm/rev advance.
Pressure is applied by a set of circlips pressing in on the roller shafts.
I am currently working out the best way to mount the cage on a bearing to withstand the axial thrust and radial thrust of the drive gear (or I may use a drive toothed belt)
Ideally I would mount the cage on a hollow shaft stepper in a nice co-axial stack, but they are a bit more expensive than a GM3. (filament would run through the motor, through the rollers and into the heater unit.)

THe three rollers provide perfect balanced pressure on the filament with the only friction being the thrust on the roller ends which I intend to apply grease to until I can devise a better thrust bearing arrangement.

The cage design is currently laser cut 1mm steel, but it could be easily implemented in FFF. The little brass knurled rollers are standard M8 threaded inserts for plastics, drilled out to take a plain 8dia steel shaft.

except that it's somewhat harder to obtain a left-hand threaded screw...
what about four drive screws? two left two right (threaded, not mounted )?
that way
there's no need of dumb gears and the filament wouldn't turn around.

'sid

My design just made another little leap - Mk1 will use mini flanged ball bearings in each roller end to take the radial & axial thrust. 3 quid each from RS, but probably half that from my bearing supplier. I could use one in each end but a simple bush will be ok at the lower ends. Shaft reduces to 4mm which saves space and a smaller set of circlips can be used, which helps with the main cage bearing size/arrangement...

i'm using a car window motor and i upgraded the power transistors on the pwm to handle it. i'm not using the darwin design.
thanks for your help

korndog Wrote:
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> i'm using a car window motor and i upgraded the
> power transistors on the pwm to handle it. i'm
> not using the darwin design.
> thanks for your help
>
I used one of those on another application once. They are really, really powerful. Mine was pretty heavy, though. Is your Repstrap going to have to fling that thing around?

it's pretty much built like a cnc setup so it's fling it around w/o a problem.
the reason i'm using it is because i'm feed up of those hobby geared motors.. it maybe overkill, but at least i don't have to worry about grinding the teeth on the gears.

Korndog Wrote:
-------------------------------------------------------
> it's pretty much built like a cnc setup so it's
> fling it around w/o a problem.
> the reason i'm using it is because i'm feed up of
> those hobby geared motors.. it maybe overkill, but
> at least i don't have to worry about grinding the
> teeth on the gears.

Sounds good to me.

Quote

it's pretty much built like a cnc setup so it's fling it around w/o a problem.

Good stuff. I'll be quiet then

Quote

the reason i'm using it is because i'm feed up of those hobby geared motors

Sounds like a sensible plan. Let us know how it goes... Car window motors seem dead easy to get hold of. I hadn't considered using them for anything before.

yea, they're super cheap too. you could also consider a cordless 12v drill motors or screwdriver motors as well. Although they'll use much more power than a gm3 and are really big, they are much more robust. best part is u can usually get them for free if they have a dead battery and just salvage the parts

The only problem that I ever had was actually controlling them from a microcontroller. There was something about how the winding was made that made running the one I bought from a L298N quite difficult.