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Crazy Idea - Duplicate motors?

Posted by clearlynotstefan 
Crazy Idea - Duplicate motors?
September 04, 2017 01:54PM
Is it possible with a duet wifi to have two motors mirror each other? IE on a delta have 2 motors on each tower doing the exact same thing? I just came up with a crazy idea. Basically I wanna try making a decoupled extruder holder. Essentially I'd like to mount a second set of steppers facing out from the towers with carriages that ride along the backside (the outside) of the linear rail/extrudeision driven by their own belts but matching the motions of the actual carriages exactly. The second carriage is mounted higher than the first but has comparable arms that reach to a second effector holding a flying extruder. In this way, a very very short tube can be used as the 2 effectors would stay aligned, but be completely decoupled for purposes of moving mass. I know it's out there, but hey it's reprap right? Lemme try my crazy ideas haha
Re: Crazy Idea - Duplicate motors?
September 04, 2017 03:19PM
Yes you can do that, use the M584 command.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Crazy Idea - Duplicate motors?
September 04, 2017 04:11PM
Thoughts on my idea? (Besides its obviously overkill) Anything I'm missing?
Re: Crazy Idea - Duplicate motors?
September 05, 2017 12:59AM
I think it will be more useful if the extruder moves independently from the effector.

Actually, I'm in the middle of designing & implementing this for my Diamond Hotend's extruder. The main idea is that in order to have shorter Bowden tubes, we need to move the extruder closer to the effector. The problem is that the extruder's mass is massive we can't move it as fast as the effector. If we allow the Bowden tube to be a little longer so that the extruder's movement doesn't have to exactly follow the effector's movement, we can allow the effector to move fast while the extruder moves slower. For example, while extruding the hexagonal infill, the effector change direction real fast. The extruder, due to its mass, can't change its direction as fast.

To overcome this problem, I'm about to create a lazy follower for the extruder. It follows the real effector's moves, but lazy. We can think about the lazy follower's movement as a low-pass filtered version of the extruder's movement. Ultimately, for this to work we need firmware's support. In the mean time, I'm thinking about using a simple program to parse G-code and insert the lazy-movement to the new motor axis to simulate the lazy follower. (We need the firmware's support because the motors' movement is not linear, we can't accurately simulate the lazy follower by injecting new motor axis into the G-code.)
Re: Crazy Idea - Duplicate motors?
September 05, 2017 01:06AM
By the way, I'll just hang the extruder using 3 fishing line, controlled by 3 motors. They don't need high accuracy.
Re: Crazy Idea - Duplicate motors?
September 05, 2017 01:29AM
Are you not familiar with flying extruders? I'm sorry I don't follow your idea really, might be misunderstanding it. I'm currently using a flying extruder that isn't all that different from yours. I don't really get the distinction between your idea and a typical flying extruder other than having a second set of motors and belts apparently. Maybe I'm misunderstanding, the problem with a typical flying extruder (to the extent that there even is a problem) is that the extruder stays at a pretty appropriate height because it is attached to the carriages, but it stays centered and tilts to face the effector based on the force of the bowden tube pulling it sideways. This is fine and in my opinion is better than a long bowden or a direct drive effector, but if you've watched a flying extruder rattle on fast infill or honeycomb etc, you'll see that the bowden tube is def transferring momentum to the extruder and vice versa. Using fishing line on separate carriages doesn't actually change anything, it might take the weight off of the carriages themselves, but weight at the carriages isn't a problem. The reason I want to use comparable arms to the main effector is precisely so it will follow the effector to xy positions while not transferring any mass or momentum to the effector. It might not even be the case that separate motors are needed. Perhaps a very tall carriage carrying 2 sets of rods vertically (the top for the extruder, bottom for hotend) would do the same thing. It'd be just as heavy as a direct drive from the motors position, but much lighter on moving mass from the hotends perspective. Admittedly I have no idea how much torque a typical stepper motor has as I've never pushed it that far under conditions that aren't normal in a printer.

TL;DR: I might be misunderstanding your idea. Alternatively I understand it fine and it's a more expensive flying extruder that doesn't solve the problems created by standard flying extruders.
Re: Crazy Idea - Duplicate motors?
September 05, 2017 01:59AM
0. I do know about the flying extruders.
1. I don't want to put more mass on the main carriages. More mass = more torque needed
2. The current flying extruders' movement follows the main carriages, so when doing the infills they are forced to follow the carriage's movements. Mine didn't.
3. Yes, movement from the effector affects the extruder due to the stiffness of the Bowden tube. That's why I said I'll use a longer Bowden. Longer than normal flying extruder, but shorter than a fix extruder.
Re: Crazy Idea - Duplicate motors?
September 05, 2017 02:30AM
I forgot another point.

4. Due to the lazy follower algorithm, my extruder will hover over the effector. Not exactly match on X-Y, but close. The normal flying extruder tends to stay in the center, which in turn pulls the effector side way.
Re: Crazy Idea - Duplicate motors?
September 05, 2017 03:54AM
I'm not following how a second set of carriages holding the the extruder via fishing line is going to make the extruder follow the effector I guess. Also I don't think mass on the carriages is a problem at all, mass at the effector is bad news but I don't think steppers are struggling for torque moving the carriages and the effector, the problem is just where the weight is in my opinion. I'm actually now scrapping a second set of carriages and belts with this idea until I prove that taller carriages with 2 tiers of arms doesn't work. If that fails I'll consider a second set of carriages and arms on the back of the extrusion to have them driven by completely different belts and motors. My money is just using 2 tiers of arms with the top holding an extruder and the bottom holding an effector will work without a problem. Then a very short Bowden tube will suffice because the two effectors will move together, but will generate far less momentum on the hotend. Plus because the extruder has it's own set of rods and is constrained the same as the effector it won't wobble around and transfer motion to the hot end, it'll stay still in relation to the hotend. Basically I'm shifting the weight of the extruder from the effector (or attached to the effector) where the machine is weak, to the frame where it is strong and can resist inertia. The only question now is whether I need a whole second set motors and steppers driving it.

DC if you're still following along, my original question wasn't so much "can I use 6 drivers to drive 6 motors in pairs" as it was "what happens if I splice wires and have each driver output splitting to two motors." I don't have enough ports to do it mirrored without an expansion board.

Edited 2 time(s). Last edit at 09/05/2017 04:15AM by clearlynotstefan.
Re: Crazy Idea - Duplicate motors?
September 05, 2017 03:59AM
Driven by 3 motors. I'm not good in expressing in English. I think I'll need time to draw some diagrams.

By the way, I'll just hang the extruder using 3 fishing line, controlled by 3 motors. They don't need high accuracy.
Re: Crazy Idea - Duplicate motors?
September 05, 2017 04:03AM
Oh... They're not hooked into the second set of carriages. There will be a spool controlled by a motor for each fishing line. Better write a diagram. My English is bad.
Re: Crazy Idea - Duplicate motors?
September 05, 2017 04:04AM
Please do, I'd love to understand what you're driving at because my bad understanding of your plan doesn't seem effective, I'm sure there's more to it! Lemme know how it goes if you try it!
Re: Crazy Idea - Duplicate motors?
September 05, 2017 04:14AM
Let me rephrase. The main idea is similar to your design, the extruder's movement is controlled. The differences are:

1. I don't want the extruder to follow the effector 100% on the X-Y plane. I want it to move somewhat lazy.

Imagine you're walking a dog with a leash. You (the extruder) hold the leash (the Bowden tube). The dog (the effector) may run around you freely, as long as it don't go too far from you. You let the dog run anywhere it wants but kept the leash within an acceptable range. This way you don't get tired. (I don't want to move the extruder if not necessary because of its weight.)

2. I intend to use fishing line instead of another set of rail/carriages because the extruder's movement doesn't need accuracy.

I'll draw a diagram. Maybe tomorrow.

Edited 1 time(s). Last edit at 09/05/2017 04:15AM by kasom.
Re: Crazy Idea - Duplicate motors?
September 06, 2017 03:47AM
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