Dual motor extruder

[tray]

For a printer I'm working on, I'd like to get the nozzle pretty much line up with the extruder center of mass in the XY plane. Looking at popular extruders, the center of mass usually hangs off to one side.

Has anyone played with a pair of motors sprung against each other to drive filament? That would meet my goal, plus give two-sided filament pushing. That would require a drive gear style where the teeth aren't too deeply dished, like the hob goblin, so the drive gears don't hit.

[Steven Butterfield]

Tray, check out bondtech, flexion, E3d.
The bondtech has dual hobb extruders and is designed to attach to a hot end with a groove mount like you find on an E3d hot end. You would have to calculate the center of mass and make a custom bracket.

[Ryan Carlyle]

Steven, I think Tray meant TWO motors. That has been done a few times. Can't think of a good link example I can share without doing a lot of forum post digging though. Somebody posted one on the Deltabots google group a while back. 

Question is, does aligning your nozzle closer to the CoG with a second motor accomplish more than the added mass of the second motor costs you? I'm not sure.

Where double motors makes sense to me is when you're using little tin can steppers and the motor is already light, but a little weaker than desired. 

[Steven Butterfield]

When I read this I thought he said I'm looking for extruders instead of at popular extruders. That changes the meaning a bit :)

In curious why would you be looking at using dual motors?

[Ben Holmes]

Walter Hsiao over on Thingiverse has published a few dual motor extruder designs. You can read about them here: http://thrinter.com/2wd-dual-drive-extruder-designs/

His collection of extruder designs is here: https://www.thingiverse.com/walter/collections/extruders

Ben

On Thu, May 3, 2018 at 9:01 AM, Steven Butterfield <steven.butt...@gmail.com> wrote:

When I read this I thought he said I'm looking for extruders instead of at popular extruders. That changes the meaning a bit :)

In curious why would you be looking at using dual motors?

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[Bob Bilbrey]

Yeah, I've designed, built and used this effector mounted unit on my homebrew Delta for over a year now.  Very reliable but not super muscular like a Bondtech.  But I reliably push +20 mm^3/sec ABS through a 0.40 nozzle ( 130 mm/sec @ 0.30 layer ).   Light weight and simple - one-piece FFF ABS housing , no gears or other reduction, low parts count, speedy assembly/dis-assembly.  The secret sauce is a pair of  very small shaft mounted asymmetric hardened steel drive spurs ( I can hear the arguments ).  The steppers are low cost off the shelf pancakes with modified shafts.  

[tray]

Having two motors allows symmetry making it much easier to align the COG with the nozzle.

[Ryan Carlyle]

Dual motors gives twice the pushing force, too :-) plus it’s easier to fab DIY than a geared dual hob setup like Bondtech.

[tray]

>Question is, does aligning your nozzle closer to the CoG with a second motor accomplish more than the added mass of the second motor costs you?

Maybe. Reducing z-torque would certainly help in my case, although 2 motors does cost you a bit in torque/mass.

[tray]

That looks interesting Bob! 

The spur gears/modified shafts are to get a smaller diameter? (Could be a killer for me - I lack machine tools.) 
Are the metal plates for cooling?

Is filament pressure spring loaded, or fixed spacing?

>+20 mm^3/sec ABS
What are you using for a hot end?

[Bob Bilbrey]

    First off you are dead right - good quality machine shop capability is required and luckily I retain that from an earlier incarnation.  The stepper shafts are either stock modified or a custom shaft is manufacturer assembled to accept a very small diameter filament gripper.  The grip wheel is  a uniquely ( I think ) profiled non-dished  4 mm diameter of hardened steel.   

    The formed metal thingies are indeed heat sinks added as a thermal band-aid - they lower the motor face peak temperature by about 5-7 degrees Celsius ( measured at the shaft end ).

    Spring loaded - the triangular gizmo in the photo is a leaf spring which drives the two steppers together.  The shaft with the orange lever actuates the filament load/release action.   

    Note the grey ABS extruder body is a single FFF fabrication where the only added parts/labor consist of 1-2 minutes of handwork/cleanup and 5 heatserts.   I print the body in about 80-85 minutes.  I have quotes for the same body from production quantity sources in Nylon in the $10 per unit vicinity ( domestic USA vendors $ dependent upon quantity ).

    The hotend system from the top of the heatbreak downward is pure E3D V6.  Heatbreak upward is a dramatically shortened circular E3D style heatsink directly fastened to the underside of the effector platform (eliminating the abominable groove mount).  The net-net of these mods is a very short-straight distance of grip wheel to nozzle tip of ~55 mm.  About 35% of that distance is in Teflon.  Good stuff for flex filaments.