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Heavy build platform. Two stepper motors on Y axis?

Posted by t357 
Heavy build platform. Two stepper motors on Y axis?
October 14, 2012 10:24PM
Would it be possible to have dual stepper motors on the Y axis? am putting together a larger mendelmax with a 300x300 mm build platform and am concerned about wait. One option would be to build a super light weight, but expensive heated build platform. The ther is increasing the power available to move the Y axis. Would it be possible to run two nema 17 motors on the Y axis? What issues would I have in this situation? Can the Azteeg X3 electronics support a higher torque nema 23 motor?

Re: Heavy build platform. Two stepper motors on Y axis?
October 15, 2012 01:27AM
I know someone running a 220mm x 450mm build platform (standard prusa style machine otherwise) with a standard single Y motor.

My suggestion is make sure you have good belts.
Re: Heavy build platform. Two stepper motors on Y axis?
October 17, 2012 06:58AM
You'd need to run a single motor with the current actuation design. (Prusa, mendel etc)
Re: Heavy build platform. Two stepper motors on Y axis?
October 17, 2012 05:48PM
Actually not really.

You simply need to mirror the motor on the far end of the design, and then wire the motors in parallel (same as the Prusa Z stage).

The issue will be that you don't really get much more bang for your buck in this way (with one belt), as all you'll do is pull with one motor (you can't push a belt), and the second motor will simply be 'taking up the slack' as it were (as it will only be pulling the belt from the other motor, which might simply stretch a steps worth in that length, so you won't get any actual pull).

What it will possibly reduce is the belt under the bed 'bouncing' and the rest of the bed moving/wobbling in response just after a move. This is because instead of the belt being stopped by only one gear/motor (which is trying to stop the inertia in the moving bed), you will have two gears, one at each end. The effect would be most noticeable when stopping movement furthest away from the motor by belt length. (eg: movement toward the motor on a standard design, as the belt is longest in that direction). At high speeds, I see this on my Mendel, and it's always more pronounced on the side that has the longest belt length to the motor.

You could also set up two belts instead of one, which MIGHT be a little better, but set them up in the same opposing style (one on each side of the printer). Apart from distributing the motor weight (which only helps for carrying it), you gain the above belt bouncing reduction, as the belt length to either motor will be reduced on a specific side.

Either way, unless you're moving a lot of weight, I don't think this should be an issue, and adding a second motor doesn't gain you that much. You would be better getting a stronger/bigger motor.

Sorry if I'm not explaining this clearly.
Re: Heavy build platform. Two stepper motors on Y axis?
October 18, 2012 07:16AM
I dont think there should be 2 motors on a screw or a timing belt (e.g. positional system). Have anybody seen anything like that? Why not just use a bigger motor? The case of double Z motors in prusa is different because each motor has its own screw.

But to put 2 motors on the same screw, (e.g. one motor at each end of the screw): how do you ensure that the microstepping position of each coincides perfectly with the position of the other? In other words, dont you need to align the two motors coils perfectly? If you dont do that, what can happen? Is 0.6 degree difference a big quantity or can it be ignored? May they end up with motors rather fighting each other instead of delivering actual torque to load? I dont know, what do you think?

Two motors, lets think in extremis maybe with a trapezoidal belt and non-timing non-positional system, because trapezoidal belt based on friction is more forgiving in positional regard. But even then how do you ensure that each motor works 50-50? If you think that its pretty hard next to impossible to ensure an perfect exact the friction of the 2 pulleys to be exactly the same and engage in the exact same manner and have same distance from pulley to load especially in our case as the load is moving between motors. So you end up with very bad imbalances, since you couldnt ensure a perfect 50-50 friction engagement of each motor then one motor will be used more than the other, so further you get efficiency issues, then perhaps reactive power issues, etc. From the belt loop between the motors half of it would have a different belt tension than the other half, so belt is wearing out trough a spring mechanism, going from each cycle through high belt tension to low belt tension.

Not to mention that 2 motors have to cost much more than a single slightly bigger one.
Re: Heavy build platform. Two stepper motors on Y axis?
October 18, 2012 08:02PM
It'd be 0.9 degree for a full step (or 0.225 for 1/4 step, or 0.05625 for 1/16th step, as tends to be used on most reprap electronics). If they're not perfectly in time, you'd get tiny amounts of stretching in the belts, but as long as you step each somewhat reasonably in time you could do it. I wouldn't consider it with screws, because even with decent couplers, you'd probably put undue wear on them.

That said, I don't think you would get any extra power with them on the same belt. If you used two belts in parallel, then you might get a small improvement, and you get a lot more tolerance for timing of the steps (as there is twice as much belt length involved between motors), but you're far better off just putting a better/bigger motor on it.
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