technical issue on paralleling 4 z-azis stepper motors

hello:

I am current plan to have DIY 3D printer that need 4 z-axis stepper motors.

I have tried traditional wire connection with mainboard with one single output step motor source, and parallel connecting two stepper motors on Z-axis,


However when same case happen but sharing four motors, it may not have enough current to run it, although from electronic theory that the voltage should remain the same, am I correct?

So my question is,
Does any hardware device that I can input extra electric power on this device in order to multiply the existing current, so that it have enough current to run 4 stepper motor?

Thanks,

You could connect the motors in 2 chains, each with 2 in series, then connect the 2 chains in parallel. Or use a 24V supply (if your printer electronics can handle it) and connect all 4 motors in series.

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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].

I have 24v input into Mainboard already, but Not 100% sure how the driver work.

first, my board only have one output for z axis,
if using your way, which mean connect all 4 stepper motor in serie, then it will yes keep the current all same, but spread voltage among all motors, am I correct?
, I know my Mainboard build with A4988 driver,
so does the driver would automatically regulate voltage if connected in serier, or regulate current if connected in parallel?
if both answer is yes, the solution is already there,
but if no, I still need to return my original question that I need to find other device to balance current/voltage for more demand of extra motors.

Quote
hamonic
I have 24v input into Mainboard already, but Not 100% sure how the driver work.

first, my board only have one output for z axis,
if using your way, which mean connect all 4 stepper motor in serie, then it will yes keep the current all same, but spread voltage among all motors, am I correct?

Yes. Unless your motors have higher than normal inductance or resistance, there will be adequate voltage for running 4 Z axis motors in series. Do you know the specification of your Z stepper motors?

If they are high inductance/low current motors, then 2 parallel chains of 2 motors is series may be better.

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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].

The motor is 2.8V and 1.68A
I have 4 for z axis, but still need as regular one y, one x, and two for extruder, all same type of motor.
that in total with rest of mainboard other output such as hotbed....., I am not sure my 24v 10a power supply is enough to go?

However, for x and y axis, do you think I need less power motor to run it, as I think the extrude isn't that heavy that it may not need that big power motor?

thank

With 2.8V 1.68A motors and a 24V PSU, connecting all 4 Z motors in series should work well, and better than a series/parallel combination.

You will probably run your motors at 1.2A or less, much more and the drivers will overheat (even 1A is probably enough for reliable operation). But the motor current draw from the 24V supply will be much lower than this. With the motors at rest, the X and Y motors will take about 150mA each on average from the 24V supply, and the four Z motors in series will take around 600mA. So about 1.2A for all 8 motors. That's the magic of chopper stepper motor drivers. The current will increase when the motors are moving, but is unlikely to exceed 2.5A. Each hot end will take less than 2A if it is a 24V 40W heater. That leaves the heated bed. For dual extrusion, I reckon you need at least a 300W power supply, assuming a standard 120W bed heater.

Edited 2 time(s). Last edit at 04/22/2015 04:39AM by dc42.

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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].

Thank you for your advice, I think my motors can work from the driver.

it comes my interested to understand the logic and calculation.

let say, my single motor require 2.8V 1.68A.
If I have 12v PSU, the current I need for this motor is proportional to PSU, which is (2.8/12)×1.68A=392mA
and for same logic if using 24V, the calculation is (2.8/24)×1.68A=196ma

Above is correct situation for the driver work?
I though the driver would regulate power to the need/requirement of individual motor, even the input power is 12 or 24 or whatever voltage. Which mean if the motor need 2.8V, then the driver would automatically adjust voltage from 12 or 24V down to 2.8V, isn't it correct?

Another interesting question is,
for total power from PSU, if I am about making a super large print platform, something like 1meter by 1 meter hotbed, then I may need to have PSU exceed 120W x 25= 3000w (multiply by 25 because one regular hotbed is 200mm by 200mm, 1meter × 1meter is about 5×5=25piece of regular hotbed size)
do you think the mainboard can support that much power?
for people making that big platform, which kind of board can be an option?

Quote
hamonic
Thank you for your advice, I think my motors can work from the driver.

it comes my interested to understand the logic and calculation.

let say, my single motor require 2.8V 1.68A.
If I have 12v PSU, the current I need for this motor is proportional to PSU, which is (2.8/12)×1.68A=392mA
and for same logic if using 24V, the calculation is (2.8/24)×1.68A=196ma

Above is correct situation for the driver work?

If you ran the motors at maximum current and the drivers were 100% efficient, that would be true. But you will run the motors at less than maximum current, because you don't need the full torque and they get very hot at full current. Also the drivers are not 100% efficient, more like 90%.

Quote
hamonic
I though the driver would regulate power to the need/requirement of individual motor, even the input power is 12 or 24 or whatever voltage. Which mean if the motor need 2.8V, then the driver would automatically adjust voltage from 12 or 24V down to 2.8V, isn't it correct?

Correct, although the 2.8V is just the average voltage. In reality it will be switching rapidly between +12V and -12V, or +24V and -24V..

Quote
hamonic
Another interesting question is,
for total power from PSU, if I am about making a super large print platform, something like 1meter by 1 meter hotbed, then I may need to have PSU exceed 120W x 25= 3000w (multiply by 25 because one regular hotbed is 200mm by 200mm, 1meter × 1meter is about 5×5=25piece of regular hotbed size)
do you think the mainboard can support that much power?
for people making that big platform, which kind of board can be an option?

For large heated beds, AC mains heating power is the practical solution. The mainboard is then used to drive a zero-crossig solid state relay (SSR), which in turn drives the bed heater. So the 12V or 24V power supply no longer has to drive the heated bed, just the hot end heaters, motors, electronics, fans etc. My printer with a 330mm diameter bed uses AC mains power for the bed heater, and a 12V 100W PSU for everything else. Of course, you need to take additional safety precautions when using AC mains voltage for the bed heater.

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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].

Quote
hamonic
it comes my interested to understand the logic and calculation.

let say, my single motor require 2.8V 1.68A.
If I have 12v PSU, the current I need for this motor is proportional to PSU, which is (2.8/12)×1.68A=392mA
and for same logic if using 24V, the calculation is (2.8/24)×1.68A=196ma

Above is correct situation for the driver work?

Depends on the mental frame in which you want to represent the things. For a dc motor, as the voltage is increased, the current also increases (like the ohms law with supply voltage and coil resistance/impedance). So for a dc motor the voltage can be increased with purpose of increasing the current and this way to produce more power. For the stepper motor, when the voltage is increased, the current does not increase because the driver limits the current instead. And the 2.8V number its as much a "requirement" as much as a representation of the coil resistance in relation to the maximum current. From the 3 it suffices that manufacturer gives 2 so user can deduct the missing one. So from that 2.8V and current number you can deduct that your coil resistance should be ~1.67ohms (measure it with an multimeter).

In reality the parameters of the motor come down to what is maximum current, which depends on the wire used to make the coil. Specifically the wire sectional area, a thicker wire would allow for more current and vice-versa. So a certain wire section (gauge) is used in coil, and with the number of turns comes to a certain coil length, which further begin to show as other two parameters, inductance and coil resistance (or impedance). These and only these are the "hard-coded" parameters built into the motor. The voltage at which users are going to run the motors is not a such thing, but its a user choice, you can choose to run at different voltages.

If you run the motors at 12v you can set the driver at 1A (the peak current). If you feed a psu 24v, then again you can set the driver at 1A also. Just the frequency would be different because in 2nd case the coil flux builds up faster, or in other words the coil energizes faster, potentially providing more speed, better said more power at higher speed. But voltage as parameter mostly depends on driver board max voltage input. The coil is insulated with a laqeur which should hold like mains voltage rating, so the coil wont fail because of voltage, but only because of current. The 4 motors in series would make a 6.68ohms coil and the inductance would be 4 times of a single motor, so you probably "really" need 24v to make the Z axis able to move practically, even with a low speed, depending on load too. You could try maybe find a construction solution with a very lightweight Z and only 3 motors, imo that should be better than four.

Quote
NoobMan
... The 4 motors in series would make a 6.68ohms coil and the inductance would be 4 times of a single motor, so you probably "really" need 24v to make the Z axis able to move practically, even with a low speed, depending on load too. You could try maybe find a construction solution with a very lightweight Z and only 3 motors, imo that should be better than four.

I agree that he needs 24V to run 4 motors in series - he was intending to use 24V anyway. As to whether 3 or 4 Z motors are better, I think it depends on size. For a small to medium size bed that can be made rigid enough over the whole area so as not to deflect more than about 0.03mm at the unsupported corners, three Z motors would be enough, and 3-point support is easier to set up. For large beds where it may be difficult to make the bed rigid enough for 3-point support, 4 motors might be a better option. Or perhaps 3 motors supporting a truss, which in turn supports the bed.

Ideally, the 3 or 4 motors would be drive independently, so that in conjunction with a Z probe the bed could be levelled automatically.

Edited 1 time(s). Last edit at 04/24/2015 02:23PM by dc42.

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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].

That a lot with both advice, very in deep and detailing.
However, about using AC power for extra size of hotbed. I would like to know the connect method of physical device.
Now I only experience one single board control everything from stepper motor to hotend to bed itself.
But if running on AC power, it should have some sort of connection/signal from mainboard that telling new AC device to offer certain power need for hotbed.

As far as I know the hotbed working logic is, it is set to have stable temperature on hotbed. Way of doing it is, thermistor tells current temperature, throught DIP control, then device tell how often, and how much power is given to hotbed.

If this operation is correct, then using AC power for hotbed can work individually without signal/connection from mainboard. Let say, if I want to have 78 degree temperature stable one. Then I just need to have individual device with thermistor feature, and simply have a feature on this device that I can adjust a designated temperature, or even have add on DIP manual control. Then this device can run by itself without any connection with mainboard. The only bad thing on it is, every time I turn on my 3D printer, I need turn both mainboard and hotbed device on separately. And the information LED (let say if the mainboard have connected one) doesn’t show all information at once, but need two indication/LED monitor telling the complete store of system status.

What should I search for this device?


I am curious to know your way of AC powered hotbed.


Another question is, I am looking for cheap DIY way to build hotbed platform, the components would be a large size of aluminum piece, with hotwire underneath. Do you know what type of hotwire I should use for this.

Many thanks,

To control an AC mains power heatbed, you use a zero-crossing DC-AC SSR (e.g. SSR-10DA or SSR-25DA), with the output side connected in series with the heater, and the input side connected to the heated bed output from the electronics. This is what I do on my large-bed delta printer.

Edited 1 time(s). Last edit at 04/30/2015 07:13AM by dc42.

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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].