[Taiwan] little geared stepper motor, 1:50, 7ohm, 12V, 0.4Amps, 147Oz

Little geared stepper motor that will work as direct drive for extruder.

1 pcs $15, Buy link http://www.2engineers.com/shop/motor-1/

to see the direct drive motor in action click this link http://www.youtube.com/watch?v=NYF8tm0hxXo&feature=g-upl

Here are the specs of this little motor.
Phase 4/2
Step Angle 7.5 degrees
Voltage 12V
Drive Mode 4-2 unipolar
Current 0.4A/Phase
Resistance 7 +/- 10% ohm/phase
Pull in torque 100N.cm min(100PPS)
Insultaion Class E


Best Regards,
2engineers

What does "Moderating Ration 1/30" mean?

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[www.hydraraptor.blogspot.com]

i think this is a case of wrong translation by Google..

it should be Reduction ratio..

I was jus reading this wiki: [en.wikipedia.org]

I have been testing several motors with different gearboxes.. one is a 97Oz - 1:30 Geared motor
the other is the 1:50 147Oz Geared Motor

The 1:50 (147Oz) geared motor gave me the best test result so far.

hp_

Any problems reversing fast enough?

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[www.hydraraptor.blogspot.com]

yep no problems reversing fast enough.

check out this filmclip where blddk is using same type of motor. only different with that motor was it had 30 ohms resistance. and it would get to hot.

i've ask the manufacterer to make me the same motor but with 7ohms

[www.flickr.com]

hp_

Edited 1 time(s). Last edit at 08/10/2012 09:54AM by hp_.

Restocked the website after running out of motors.

Cheers,
Hp_

Like the idea of compact and light design, have you a working design for a 3mm extruder using this motor?

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Richmond, New Zealand
Thingiverse ~ YouTube

You plan on testing this motor Nophead? Would be very interested in your results.

So after a move back to Belgium our motors are back in Stock!

http://www.2engineers.com/shop/geared150/

this time shipping from Belgium.

Cheers,
HP

Just bought one of these so I'll let you'll know how it goes when it arrives.

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Richmond, New Zealand
Thingiverse ~ YouTube

I've got one running and I like it a lot. It does not get too hot (as the PG35L it replaces did) and it has plenty of torque. It is quiet and light.

And hp_ has been very helpful while I was setting it up. What not to like? :-)

What extruder and filament are you using it with?

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Richmond, New Zealand
Thingiverse ~ YouTube

I am using this hotend [www.ebay.com] which starts not going ok if you go faster than 40mm/s and I am using 3mm filament and 0.5mm nozzle.

And this extruder (on a Prusa i3) [github.com]

No such thing as a 7ohm, 12V 0.4A motor. They have to obey Ohm's law!

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[www.hydraraptor.blogspot.com]

Nophead you are probably right.. lets see:

U = volts
I = amperage
R = Ohms

U = I . R
12/7 = I

I = 1.7 A

in the next post i need to change this

hp

My guess is that 7ohm is the coil resistance, that will limit maximum current to 1.7A if supply is 12V as hp_ calculated, but the 0.4A is the nominal current.

What I have done is to adjust my Pololu to 160mV so it delivers 0.4A to the motor winding. This way the motor hardly gets warm.

If the coils are 7 Ohm then it is either 12V 1.7A which seems too much for such a small motor or 2.8V 0.4A, which seems more likely.

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[www.hydraraptor.blogspot.com]

I'll have to measure the coils resistance when I am back home, but this is datasheet of a similar motor:

[www.baolai-cn.com]

There is going to be some impedance from the pulsing nature of the stepping currents so that might explain why Ohm's law isn't working for the winding resistance

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Richmond, New Zealand
Thingiverse ~ YouTube

I have just measure coil resistance at it is 7.5ohm.

Having such a low resistance means that if you apply 12V to the coil the motor will heat up quite a lot, but using a current-switching driver like Allegro's or TI's will keep the current to the desired value without a problem. Still, I guess nophead is right and this motor nominal voltage is not 12V.

Which by the way is actually good news as you always want your motor nominal voltage to be several times lower than your power supply voltage so the switched-current drive can do its work properly.

Hi,

I had some of these motors lying around so I tested them.

Unfortunately, the shaft of these motors cannot turn faster than around 18RPM = ~280mm/min = ~4.7 mm/sec. I have tested this for different current levels and different step-rates - same result. How come the vendor's website (2engineers 1:50 geared stepper) suggests a MAX_FEEDRATE of 45 mm/sec ?? This would imply over 80RPM (e.g. for an MK7 drive gear)!!!

I hope someone can explain where the error is

The max speed of an stepper motor is connected with the voltage of the supply. The same motor that stalls at 12V at a certain rpm, can run faster if you double or triple the supply voltage (still the same current on the driver). Steppers are known to show a significant drop in torque as they speed up.

No idea what the maximum achievable speed on these motors is though.

I understand. This is plausible since the winding resistance of these motors is around 4Ohm, and the current rating is 0.4A yielding around 1.6V "rated" voltage (12V in the datasheet is wrong!). Usually around 10x to 20x higher voltages are used to decrease the rise time of the current by the chopper driver; hence the best driver voltage would be between 16V and 32V. I use 12V, which is maybe a bit too low for this motor - however it is the "standard" driver voltage for RepRap systems (RAMPS, etc.)

Nevertheless, I wonder why the suggested firmware speed setting is so much higher compared to what the motor can actually handle. So I was wondering if I had overseen something...

Quote
andin
Hi,

I had some of these motors lying around so I tested them.

Unfortunately, the shaft of these motors cannot turn faster than around 18RPM = ~280mm/min = ~4.7 mm/sec. I have tested this for different current levels and different step-rates - same result. How come the vendor's website (2engineers 1:50 geared stepper) suggests a MAX_FEEDRATE of 45 mm/sec ?? This would imply over 80RPM (e.g. for an MK7 drive gear)!!!

I hope someone can explain where the error is

Most steppers have trouble getting above 1000 RPM using Pololu drivers and 12V (maybe 7.5 degree motors can go a bit faster?). Geared 1:50, this would give an output speed of 20 RPM, so your finding of 18 RPM max seems reasonable. An MK7 gear has ~10.5mm diameter, giving a ~33mm circumference. At 20 RPM, this is ~660mm/min or ~11mm/s (~10mm/s with 18 RPM). I could see them claiming ~10mm/s max speed, but I don't see how you could possibly get 45mm/s out of it.

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Help improve the RepRap wiki! Just click "Edit" in the top-right corner of the page and start typing. Anyone can edit the wiki!

Hi,

the direct link to the motors have changed to:
http://www.2engineers.com/shop/geared150/

be-aware, the 45mm/sec in the configuration file is a suggested configuration. where the max_feedrate is set to 45 mm/sec was working pretty well for me, the thing to take notice of is the acceleration and E_JERK.
with these geared motors you have to reduce the acceleration.

cheers,
hp_

@hp_:
well if you suggest a value of 45mm/s, than it needs be technically plausible. The fact that it is working for you may indicate that your other settings (slicer speeds, feedrate for X/Y, etc.) never allow this value to be reached.

I have set the acceleration and jerk as you suggested on your website - no problem with that. What we are talking about here is the maximum feedrate of about ~10mm/s, as it was well pointed out by Cameron above. This yields an absolute theretical maximum printing speed of around 10*(1.75/0.35)²=250mm/s (1.75mm filament and 0.35mm nozzle) - which is e.g. lower than what has been achieved on an ultimaker (claimed to even go beyond 300mm/s). I guess the real maximum speed will be lower due to the decline in the stepper torque at higher extrusion rates. This is an important limitation which should be documented... 45mm/s is very misleading.

PS: If you have the phase inductance of these steppers, it is not difficult to estimate the maximum RPM using the time constant (simplified calculation w/o moment of inertia, etc.).

Quote
hp_
be-aware, the 45mm/sec in the configuration file is a suggested configuration. where the max_feedrate is set to 45 mm/sec was working pretty well for me, the thing to take notice of is the acceleration and E_JERK.
with these geared motors you have to reduce the acceleration.

Something must be limiting top speed then. Probably the max step frequency of your firmware and a 16MHz Arduino. You are using 1,100steps/mm for the extruder, which is appropriate for a 11mm diameter drive gear and 16x microstepping. Max step frequency of Marlin on a 16MHz Arduino is ~16kHz (AFAIK; it may be even less than this. I can't find any recent documentation of the actual max step frequency for Marlin). 16,000steps/s divided by 1,100steps/mm gives a max feedrate of ~14.5mm/s, or 25 RPM of the output, or 1250 RPM of the stepper motor.

I would guess that if you reduced microstepping on the extruder to 8x or even 4x so that the firmware would be able to step it at a higher speed, that you would find the extruder motor skipping steps as it tried to keep up.

On a side note: As I do more research and calculations, I believe this issue applies to the standard geared extruders in use on most RepRaps. A standard Wade's-type geared extruder at 16x microstepping is usually around 1000steps/mm as well, meaning the max feed rate would be firmware/processing limited rather than mechanically limited. However, since the gearing is less severe, the max feed rate wouldn't be limited by stepper RPM to nearly the same level. I will have to do some testing. 45mm/s may very well not be actually achievable with a standard Wade's-type geared extruder either.

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Help improve the RepRap wiki! Just click "Edit" in the top-right corner of the page and start typing. Anyone can edit the wiki!

I thought about this as well (I am into upgrading to an ARM-based solution for this reason in order to drive my X/Y steppers faster ). Hence, I removed microstepping at my extruder driver when I was testing this geared stepper - it's pulsing in a single-step mode (i.e. 0.25deg per step after the gearbox) and still yields low RPM. Wade's extruder has a much lower gear ratio (i think ~1:4 or something close) which would yield more RPM i guess...

Hi andin, NewPerfection,

Thanks for your info, i've never made those calculations

what i did was just put in the motor and test hours on hours..
if your interested checkout this youtube clip

http://www.youtube.com/watch?v=NYF8tm0hxXo

running pretty good speeds

cheers,
hp