Required motor power

I'm trying to get a handle on the amount of output motor power required for typical printer applications.

What is the largest moving mass in a typical printer? I'm guessing that the moving bed in a 200x200mm printer is about 500g or so, and maybe about the same for a typical print head carriage with a Wade's extruder. Is that about right?

And what accelerations are people using? Is 10,000mm/s/s (about 1G) typical?

And finally, what peak speeds would be considered medium performance these days? 200mm/s? 500mm/s?

By way of example, a 500g carriage mass, accelerated at 10,000mm/s/s to a speed of 500mm/s requires about 2.5w of power (not includng any friction). A typical 1.7A, 48mm long NEMA 17 can deliver about 10-12w of output power with a 24v supply. Curiously, much shorter 34mm long NEMA 17's can deliver about 8w or so. (Note: your actual mileage may vary.)

Many thanks for help with real data.

I think maybe you are getting some ideas confused. Power consumed does not necessarily equal mechanical output. Anyhoo... when people talk about the mechanical power of a stepper motor, which I think you are asking about, they talk about the holding torque. There is a certain upper end given that you are working within a small mechanical package (the nema 17). There is a page devoted to this topic already.

I'm not sure why you find it curious that a smaller motor consumes less power. I may well be misunderstanding your inquiry.

From what I've seen more torque is better. I haven't seen anything in a nema 17 package exceed 60 oz/in holding torque. The larger the motor the more the torque and the more heat it will produce. Regardless, all of these motors will come in under 2Amp. More than likely 1.5. Power is simply current times voltage.

[reprap.org]

The Kysan 1124090 is a NEMA 17 that specs at 76 oz/in holding torque.

And now I have never seen anything in a nema 17 package that exceeds 76 oz/in.

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Dorian
Power is simply current times voltage.
[reprap.org]

What I'm actually talking about is the required mechanical output power of the motor, which is equal to force x speed. The output power (Pout) is equal to the input power (Pin = voltage x current) multiplied by some efficiency factor.

For systems with little friction and no gravity or spring loading etc. (like most printer mechanisms), the force is equal to the mass x acceleration (F=mass x accel). The peak power required from a motor is just as it finishes accelerating to the top speed, or Peak Power = mass x acceleration x max speed

Most motor companies publish speed / torque curves for their motors, and you can calculate the max. output power as the torque x RPM x appropriate conversion factors. This helps in picking the correct motor for the load.

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Dorian
I'm not sure why you find it curious that a smaller motor consumes less power. I may well be misunderstanding your inquiry.
[reprap.org]

What is curious is that a smaller motor with about 50% of the holding torque of a bigger motor provides 80% as much power.


What I'm looking for is real numbers for the mass, speed and accelerations used on typical printers.

Edited 1 time(s). Last edit at 11/23/2013 08:44PM by LoboCNC.

you need to look at inductive load of motors.



quote '10,000mm/s/s to a speed of 500mm/s'


that is a setting in software. time any video you see and the software can not keep up to a 4th of those settings. it is very doubtful that any acceleration ramp using arduino would process that fast.


for more speed raise the voltage, but do so with caution. chips may be rated to 36v, but this is absolute maximum. voltage spikes limit practical voltages to 24-30 volts on ramps for example.


the resistance of the motor coil increase the faster the pulses per second. this is why we use higher voltage and a current chopper circuit. we keep current constant but provide more voltage to overcome the winding resistance at higher speeds. for example a typical motor is limited to 12v at 2500pps, at 24v it increases to 10000pps

I would look for a hybrid motor with an coiled arrangement to allow for higher pps. do a web search for high rpm stepper motors.

Edited 1 time(s). Last edit at 11/24/2013 03:00AM by jamesdanielv.

a while back i read an article about stepper motor windings, if you have an 8 wire stepper motor you can wire up the motor a few different ways. and any 6 wire motor can be converted to an 8 wire motor with a soldering iron some wire and a razor blade. anyways if you rewire the motor into the parallel configuration you can lower the inductance value to 1/4. basically you get 4 times the max speed out of the motor, i think.

[probotix.com]

Edited 1 time(s). Last edit at 11/24/2013 04:45AM by aduy.

I think there is some confusion here and people are talking at cross purposes.

As I understand it the OP ASKED for information about typical Reprap hardware and ASKED if an acceleration of 10,000mm/s/s (~1G) and a top speed of 500mm/s are typical.

It seems as if people think the real figures are much lower than this, but nobody has said what the realistic figures would be.

I see nothing strange about the OPs power calculations, but they are probably not often considered by Reprap builders.

If my maths is correct a 1G accln would reach 0.5m/s in 0.05 secs ?

...R

Reprap has evolved seemingly by trial and error. I don't think anyone sits down and does power calculations before designing a new printer. And I don't think anyone takes proper measurements on working systems.

Mass should be easy to measure. Numbers for acceleration and max speed I would take with a pinch of salt. At some point the Arduino tops out and it will be running as fast as possible, but not at the claimed speed. To find the actual performance you need to hook up a scope and measure the pulse train. I don't think anyone bothers to do that.

So in order to get accurate numbers for a typical printer you would have to get hold of one and measure it.

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Perhaps some background might help clarify what I'm after. I'm working on a closed-loop stepper controller (see previous post) that I think will most useful for CNC machines and higher performance printers, but I'm trying to figure out if it would also be useful for more middle-of-the-road printers. I'm trying to sort out whether or not typical printers are bumping up against any motor performance limits that could be helped with a closed-loop control system.

When I mention motor power, I think people reflexively think I'm talking about the input side and the driver electronics. I'm trying to get information on the output power requirements - masses, speeds, accelerations. Once I know what the mechanical power requirements are for a typical machine, then I can look at different motor/driver combinations and see if closed-loop control offers real benefits.

Regarding actual speeds and accelerations, I know what these are for my own machines, but they are odd-ball designs of my own that aren't representative of what most people are building. I 'm hoping that some power-hackers on this forum might have actually measured their speeds and accelerations and also maybe weighed their machine components. Anyone?

some one could build in the sketch an output debug that tells of the actual time to move.
somewhere in the setup()
long timemove;


then in the actual stepper planner ad
#ifdef debug
timemove= millis();
#endif

then at end of stepper planner ad:

#ifdef debug
timemove= millis()-timemove;
serial.print("time of move:"); //choose correct serial setup. marlin now has a variable to control serial port used.
timemove *=1000000 ; convert to seconds
serial.println(timemove,6); //print number several places past zero
#endif


or along those lines. timing the moves is the best way, if the move complete and does not skip a step then the steps are valid. take the time in seconds at output and calculate the distance traveled for the move in 3d space.

code is example it won't work unless a creative takes it over.

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output power requirements - masses, speeds, accelerations

Unfortunately, a lot of power is going to go into friction and that's not consistent between printers -- nor is it necessarily constant along the linear rod or consistent in time as bearings age, lose lubrication, even between two different LM8UUs due to sloppy manufacturing tolerances, etc. You probably can't operate a printer at the exact output power "required" because its not constant. Suppose the printer changes direction and becomes slightly misaligned and catches. Suppose it works when the bearings are brand new and then not once they wear in. To really do it well, measurement on the exact same system is probably what you have to do. Set something up to monitor the power over the course of a print and plot it.

@lobocnc, it looks like "nobody knows or cares". Maybe the best you can do is draw inferences from the sizes of stepper motor actually used in successful projects.

On the other hand if the project is successful why bother changing to a different type of motor? I'm guessing your motors will be more expensive but may allow greater speeds.

But can the extruders cope with higher speeds? There seems to be no shortage of threads about extruder problems and extruder improvements.

I suspect that for hobby printers the "complete" working system has evolved rather than been designed.

...R

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iquizzle

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output power requirements - masses, speeds, accelerations

Unfortunately, a lot of power is going to go into friction and that's not consistent between printers -- nor is it necessarily constant along the linear rod or consistent in time as bearings age, lose lubrication, even between two different LM8UUs due to sloppy manufacturing tolerances, etc. You probably can't operate a printer at the exact output power "required" because its not constant. Suppose the printer changes direction and becomes slightly misaligned and catches. Suppose it works when the bearings are brand new and then not once they wear in. To really do it well, measurement on the exact same system is probably what you have to do. Set something up to monitor the power over the course of a print and plot it.

Friction is always a bit of a crap shoot in machine design, but in a belt driven linear drive system, it should be maybe only 15 - 25% of the load. You still want to start with the basic power requirements (mass, speed, acceleration) and then take a guess at the worst case friction.

Having an axis cock or jam (if minor) is something that a that a closed-loop system can help with, particularly if it occurs during reversals where you are at a low speed. This is because a closed-loop servo has the ability to over-current the motor safely to power through sticky spots. You may end up with a glitch in your prints, but you won't end up with shifted layers as you would with lost steps.

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Robin2
@lobocnc, it looks like "nobody knows or cares".

I suspect you are right - that most people are happy enough with open-loop steppers to not bother thinking about the issue. But then, most people are happy with their computers until they are shown a faster one. I'm trying to figure out if closed-loop control would improve performance for the average printer.

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Robin2
On the other hand if the project is successful why bother changing to a different type of motor? I'm guessing your motors will be more expensive but may allow greater speeds.

Yes, exactly that - more expensive (maybe $50 or so per axis more) but higher speeds. The question is, is it worth it to add $200 or so to the cost of a printer for some level of improved performance and reliability.

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Robin2
But can the extruders cope with higher speeds? There seems to be no shortage of threads about extruder problems and extruder improvements.

Extruders are a more interesting question. Here, the high speed may not be so much of an issue, but motor heating and load variability are, and closed-loop control can help on both fronts. Because in a servo, the motor current is continuously adjusted to exactly match the load, the motor runs much cooler. This also lets the controller safely over-current the motor for short periods to deal with extrusion load variations.

Lastly, closed-loop control can provide feedback that the extruder has stalled (or is about to stall), providing an opportunity for the firmware to slow down the print. (This sort of feedback could also be used to help prevent stripping the filament.) Of course, this would require some non-trivial mods to the firmware.

The most loaded motor in a reprap is the one driving the extruder, and builders usually use the same model of motor everywhere.
Assessing the force required for that motor is a bit dificult as is depend of material, extruder design and temp.

On other axis, acceleration is severely limited by the lack of rigidity of most linear systems, hence reduced loads.

commonly available nema 17 packages rate 4.2 to 4.8 kg.cm or 58-66 oz.in for 2.5A. Those are the most used in repraps i would think

That is not an upper bound as at least 5.4 kg.cm ones exist (mine are) and larger systems with nema 23 can go at least to 12, but something over 6 kg.cm seems a reasonable one.

I think only scara robots could perhaps have acceleration needs that would induce axis load above extruder, and it is simple enough to add then a separate encoder.

When I wondered if the extruders could cope with the extra speed I wasn't thinking about the power needed to drive the motors but the more important question of whether the goo can be made to come out quickly enough while remaining under control.

...R

Oh, I see what you are saying - why move the axes faster when extruders are already close to maxing out. I suppose if you are printing really thin layers, then you do want to move fast but the extrude rate is fairly low. For some of the all-metal hot ends that don't like extruding at low rates, you may actually want to move the axes faster to keep the extruder happy.

What I've gleaned from all of these comments, though, is that for the most part, the garden-variety printer wouldn't benefit much from closed-loop control, except for maybe the extruder which might be made more reliable.

there was something interesting mentioned in this post. extrude issues and stalling could be detected. if it could then reliability of the machine would improve, however the feedstock usually stops feeding, and the motor shaft rarely stops. the place to control the extruder feedback should be somewhere else other than the motor.

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jamesdanielv
there was something interesting mentioned in this post. extrude issues and stalling could be detected. if it could then reliability of the machine would improve, however the feedstock usually stops feeding, and the motor shaft rarely stops. the place to control the extruder feedback should be somewhere else other than the motor.

The way you could handle the filament stripping would be to set the internal current limit parameter of the closed-loop controller to a value just below where the filament would start stripping. This prevents the filament from stripping in the first place. You'd then run the fault output of the closed-loop motor controller back into the printer controller so that it could detect that the filament had stopped feeding.

Handling the error is another issue. In theory, you could alter the print speed or hot-end temp to reduce the required feeding force. This may not be so straightforward, though. If it's an issue of the cold-end getting too hot on a long print, you could maybe just pause the print, cool off the hot end for a few minutes, and then restart everything.

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LoboCNC
Oh, I see what you are saying - why move the axes faster when extruders are already close to maxing out. I suppose if you are printing really thin layers, then you do want to move fast but the extrude rate is fairly low. For some of the all-metal hot ends that don't like extruding at low rates, you may actually want to move the axes faster to keep the extruder happy.

What I've gleaned from all of these comments, though, is that for the most part, the garden-variety printer wouldn't benefit much from closed-loop control, except for maybe the extruder which might be made more reliable.

dont want to discourage you, as a cheap closed loop system is indeed worthy, but in repraps only the extruder is worth the added cost. However, did you look in the DIY CNC milling crowd like shapeoko ?
Here, the higher loads on axis make a closed loop system highly desirable.

As I said earlier, if scara types become common in reprap (which seems to be a trend), very high accelerations make closed loop good too.

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alj_rprp
However, did you look in the DIY CNC milling crowd like shapeoko ?
Here, the higher loads on axis make a closed loop system highly desirable.

Actually, I'm already selling a 3-axis closed-loop controller board for the Lobo CNC milling machine.