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Author Topic: stepper motors and torque  (Read 641 times)
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hi,

I was trying to use a few different stepper motors for a project to swing a 6oz pendulum. i bought a normal little one on sparkFun and also this one: http://smartautomation.en.alibaba.com/product/279733845-211876543/85BYGH_NEMA_34_HYBRID_STEPPER_MOTOR.html

These things seem to have NO torque whatsoever. I can stop them from rotating with my pinky. I can't get it to lift or move or turn anything besides its own shaft. Is this normal? What are stepper motors used for typically? I was using this code: http://bildr.org/2011/06/easydriver/

Is there anyway to increase torque with the code?

Thanks for any advice...
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Well what kind of driver are you using? Are you providing the correct voltage as per the specs of your motor? can your driver supply as much current? Also try running your motor at a much slower speed per step, that generally increases torque.
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thanks so much. i'm using the easyDriver: http://schmalzhaus.com/EasyDriver/

From what I understand you just give the EasyDriver 12V...it has a built in regulator and takes care of powering the motor. Do I understand this correctly? I've slowed the speed waaaay down to no avail. could it just be this EasyDriver in combination with the motors I've been using?
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I cant find the exact specs of your motor, but by the looks of it, it doesnt no look like a 12v one. And no, you will have to provide the driver with the voltage specified by the motor. Try and giving me the datasheet for your motor. I think your driver may be too weak to run this motor.
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That's not a small motor!  Can your electronics supply the current (amps) you need?   

Synchronizing a stepper motor to the natural-frequency and motion of a pendulum... if that's what you are doing...    sounds very...   uh...mathematical....
« Last Edit: May 08, 2012, 03:02:42 pm by DVDdoug » Logged

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Quote
it has a built in regulator and takes care of powering the motor

and yes it does have a voltage regulator BUT that is for the driver IC not the motor. Also you may want to try a bigger power supply, you driver can handle up to 30v, i reckon that's a 24v motor, but im not sure.
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Quote
it has a built in regulator and takes care of powering the motor

and yes it does have a voltage regulator BUT that is for the driver IC not the motor. Also you may want to try a bigger power supply, you driver can handle up to 30v, i reckon that's a 24v motor, but im not sure.
Stepper motors are either fixed voltage low speed (which could be 24V), or they are constant-current driven fast bipolar motors designed to be driven with a chopper drive from a high voltage (anything from 12 to 60V is done...).

Well a bit of searching on 85BYGH NEMA 34 motor suggests its a hefty bipolar motor, 5A perhaps - no way can you drive this with an EasyDriver if so, I think that's limited to about 0.75A

We need clarification on the motor - size, current, winding resistance, number of wires, any other details
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thanks for all the input....the motor has 4 wires....i don't know much about the motor...anything I know is from here:
http://www.globalspec.com/SpecSearch/PartSpecs?partId={F34339A0-00FE-48A1-AEB0-3833FA04664B}&vid=153687&comp=38&RegEvent=new

Step Angle ---------------------------------------- 1.8 deg

Ambient Temperature --------------- -25 to +40 deg C

Temperature Rise ------------------------------------- 85K

Insulation Resistance ----------500VDC 100Mohm Min

Insulation Class ------------------------------------------ B
Specifications
Performance Specifications
DC Voltage    4.4 VDC
Holding Torque    297 In-oz
Rotor Inertia    0.0283 oz-in-sec²
Motor Type
Stepper Construction    Hybrid
Step Angle    1.80 degrees
Shaft Orientation    In-line
Gearing Options
Gearing    Motor Only (No Gearhead)
Housing / Enclosure
Units    Metric
Motor Shape    Square Body
Environment
Operating Temperature    -13 to 104 F

If you think I can't drive this with the EasyDriver....do you know any way I could drive it? Do you think once I properly drive and power it the torque might all of a sudden get strong? I can move the shaft around with my fingers....is that normal on a stepper?
« Last Edit: May 08, 2012, 05:42:51 pm by treebykooba » Logged

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Which SparkFun stepper did you get?

My guess is your Easy Driver can supply enough current for the smaller one, but I think they can only sustain around 750 mA so I don't think it's enough for your bigger stepper.

Like the others say, for better performance you can step up the voltage. The Easy Driver will take care of the current.

The other thing I can recommend is using the AccelStepper library instead of just the immediate on/off of the Bildr example. It's easy to tweak speed and acceleration parameters until you get a good combination.

Good luck!
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