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Stepper motor

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GatorGnet

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Can a typical stepper motor be run at 800+ rpms? Also, when a motor is rated at x amps per phase, how do I figure the total draw? Lets use a standard bi-polar setup as an example.
 

3v0

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Reloadron

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To add to 3v0's post this link is a pretty good and informative read. As to speed, it depends on the motor. However, there are cases where if we applied a full speed frequency to the motor it would just sit there and hum but if we ramp the speed up slowly to full speed it will run just fine.

Ron
 

shortbus=

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Assuming a 1.8 degree/200 step motor, for 900 rpm, your driver would need to run at 3000 Hz. Correct?
 

3v0

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A 1.8 degree motor has 200 steps per revolution.
It takes 4 patterns applied to the stepper to make one step.
So we need 800 patterns per revolution.
For 900 RPM you need 900*800 patterns per minute which is 720,000.

So the output of the controller is 720kHz.

Did I get something wrong ?

EDIT: As diver300 points out above this needs to be divided by 60 to get patterns per second. 720kHz/60 is 12kHz (thanks diver300)

What are you planning to use as a controller ?
 
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Diver300

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A 1.8 degree motor has 200 steps per revolution.
It takes 4 patterns applied to the stepper to make one step.
So we need 800 patterns per revolution.
For 900 RPM you need 900*800 patterns per minute which is 720,000.

So the output of the controller is 720kHz.

Did I get something wrong ?

Yes. You forgot to divide by 60 to convert from pulses per minute to pulses per second, so it's 12 kHz

Thanks I fixed it in my post below. 3v0
 
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The first question, you ask about current draw.

Some datasheets are described differently, for my college project I'm using stepper motors running in unipolar (just cheaper to build). My datasheet says 2.8A and 2.8V per phase, so you'd think that this would be a total of 2.8V at 5.6A - nope. My datasheet counts "phase" as the total current drawn, so its actually 2.8V 1.4A per coil.

Do what I did, wired it in either the unipolar, bipolar series or parallel and connect to a variable power supply. Set it at the rated voltage and then see what the current draw is, then you will know what you datasheet actually means.

Are you building or buying the controller, if you are building then you wont get anymore than 100rpm without a current chopper and higher power supply voltage - I have built mine including a current chopper and only get about 5-600rpm before it resonates and stops spinning. Many of the controllers can get 1000rpm, someone on youtube has managed 18,000rpm with a 3Nm motor - no load, 2000rpm with a load. Steppers have tonnes of torque so you can always gear them to spin faster.
 
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shortbus=

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A 1.8 degree motor has 200 steps per revolution.
It takes 4 patterns applied to the stepper to make one step.

Did I get something wrong ?

I think your wrong about the 4 patterns per step. Each step is one pattern, the next step is the next pattern and so on.

200(steps = 1 revolution) x 900(revolutions per minute) = 180,000(steps per minute) / 60(second in minute) =3000Hz
 

shortbus=

Well-Known Member
Most Helpful Member
The first question, you ask about current draw.

Some datasheets are described differently, for my college project I'm using stepper motors running in unipolar (just cheaper to build). My datasheet says 2.8A and 2.8V per phase, so you'd think that this would be a total of 2.8V at 5.6A - nope. My datasheet counts "phase" as the total current drawn, so its actually 2.8V 1.4A per coil.

Do what I did, wired it in either the unipolar, bipolar series or parallel and connect to a variable power supply. Set it at the rated voltage and then see what the current draw is, then you will know what you datasheet actually means.

Are you building or buying the controller, if you are building then you wont get anymore than 100rpm without a current chopper and higher power supply voltage - I have built mine including a current chopper and only get about 5-600rpm before it resonates and stops spinning. Many of the controllers can get 1000rpm, someone on youtube has managed 18,000rpm with a 3Nm motor - no load, 2000rpm with a load. Steppers have tonnes of torque so you can always gear them to spin faster.

If your running the motor at only the 2.8V in the data sheet thats part of the resonating, most motor when moving something (a machine) are powered by much more voltage than the rated spec.

Another thing about steppers is that to get RPM's under load, they have to "ramp - up". If you just try to give them full frequency/step command, from a stopped position, they lose their step and just sit and chatter/resonate.
 
My motors are rated for 2.8V, I run them at up to 30V. The faster the stepping speeds the less time the current has to rise therefore I increase the voltage to increase rise speed. When running at low speed the current will rise far above the 2.8A therefore I use a current chopper that turns off the controller for a short period of time to allow the current to fall.

And yes I have to ramp up the speed otherwise it will resonante, I will be bringing my project into college in the next few weeks so I can use their frequency generators to ramp the speed up slowly. I couldnt ramp it up slow enough before because I havnt got any heatsinks on my transistors, they would overheat before I could.

I'm limited to 30V so cant see how fast my driver can get them, college does not have bigger power supplies and will not let me wire my own SMPS.
 
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