Low Mass Extruder driving thoughts

[Windshadow]

I have been following the Titan threads and this afternoon i was down in my machine shop cleaning up a cast iron part of its casting flash before mounting it on the Bridgeport for machining. (it is or will be a steering gear box for Pre WW one truck (a FWD Model B)).
I was using a flex shaft grinder (a hand piece connected to a motor mounted on the bench sort of like a very thin dremel tool in your hand. I guess the connection to the bench mounted motor is via a cable like a beefy speedometer drive cable (from the days when you had a mechanical connection to drive things like the speedometer and tachometer)

This got me to wondering if anyone has tried mounting the extruder stepper to the top of the printer but putting the extruder itself either directly mounted to the hot end the way it is done with a lot of cartesian printers or on a flying mount just above the hot end with a very short tube connection between them for the filament. the torque required is not huge and the cable and its sheath while not as flexible as the teflon tube could be of far lighter construction than on my 1/2 hp bench mounted die grinder.

Here is a cheap($45)Harbor freight flex shaft grinder which is I know too heavy for this use but we don't need high speed and I wonder if a speedometer drive cable might work i put the picture here to be clear about what i suggest
[img]http://www.harborfreight.com/media/cata ... _18086.jpg[/img]

[Captain Starfish]

What problem are you trying to solve by getting the extruder to the hot end? If it's the inaccuracy in feed caused by the bowden tube, I suspect that the twist under load of the flex drive core would be an order of magnitude worse...

[Polygonhell]

Been done

http://mutley3d.com/Flex3Drive-1/

So many things have been tried by various people and forgotten about, then rediscovered and derived from. Johann always gets credit for the Linear delta printer, but his was based on http://reprap.org/wiki/Helium_Frog_Delta_Robot and that was based on http://builders.reprap.org/search/label/tripod which even used magnetic balljoints. That's not to say that Johann didn't greatly improve the design, he did and perhaps most importantly he hacked the Marlin firmware to allow a delta to work in a useful way.

The reprap forum is a great browse if you interested in off the wall idea that have been tried.

[Windshadow]

Oh well back to the thinking spot (TV and a beer) I guess it must have the twist problem you highlighted Cap. or these Mutley3d folks would have a hit on their hands and everyone would be using it...
Polygon have you seen it work?
thanks for the heads up

[Polygonhell]

I've never seen one run, I don't know how many he actually made, he sold a number to people on the reprap forums, then there were delays, eventually I think they were delivered.
It would guess it probably works about as well as a bowden tube, with the same hysteresis issues, which when it was first released meant it couldn't justify the additional complexity. Now it might be different, mounting the extruder on the platform, even with the same hysteresis would be a win for flexible filaments.
I'm sure someone will reinvent it at some point.

[geneb]

From what he's told me, the flex shaft is stressed in such a way that there isn't any hysteresis.

g.

[Jimustanguitar]

I know people who've played with the idea of using a full NEMA17 or larger at the frame and then using a tiny stepper at the hotend. The heavy lifting is done by the big stepper, and the little one just keeps it accurate at the business end of the bowden tube...

[Windshadow]

The end game goal is to keep mass at the effector (note not weight) as low as we can to get the speed as high as we can get it for a filament deposition printer.
Jim that idea of using 2 steppers is intriguing how fare have your friends gotten with it>
If we can do that and keep up the needed extrusion rate for even an e3d volcano hot end I wonder how fast can we push a future delta design?

[Jimustanguitar]

Jim that idea of using 2 steppers is intriguing how fare have your friends gotten with it

Just toying with the idea so far, I don't know that anyone's actually started throwing parts at it yet.

[ipcalit]

Just some heads-up on recent work using DC motors posted on reprap forums.

http://forums.reprap.org/read.php?1,661444

Best design so far is 15g with 2kg force. Should be easy to adapt to any Delta.

[img]http://forums.reprap.org/addon.php?1,mo ... embled.jpg[/img]

[Tincho85]

Why not just mount the Titan with a pancake stepper (like the ones used here: http://forum.seemecnc.com/viewtopic.php?f=35&t=10225) directly to the extruder? with no bowden tube, like any cartesian direct feed.
If it's too much weight, then add a counterweight pulley system.

Or it's still a lot of mass moving around?

[Jassper]

Why not pull the extruder out of a 3Doodler?
I have often thought about it but have not tried it. .... yet.

[ipcalit]

Why not pull the extruder out of a 3Doodler?
I have often thought about it but have not tried it. .... yet.

Because you'll be spending at least $50 for one and you still don't have the encoder there. The parts discussed in the reprap forum are less than $10.

[ipcalit]

Why not just mount the Titan with a pancake stepper (like the ones used here: http://forum.seemecnc.com/viewtopic.php?f=35&t=10225) directly to the extruder? with no bowden tube, like any cartesian direct feed.
If it's too much weight, then add a counterweight pulley system.

Or it's still a lot of mass moving around?

The lightest NEMA SANYO pancake is 70g. Add the Titan and you're past 150g. If you use a short stack NEMA17 or NEMA14 you start at 120-140g and get in the neighborhood of 200g. Our initial prototype was 30g total, and currently we have a design at 15g with similar torque.