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### Topic: Stepper Motor's and Sixteenth Stepping (Read 1 time)previous topic - next topic

#### 9Vortex

##### May 11, 2012, 09:41 pm
Hey,

I am working on a project that is going to involve multiple motors that need a wide range of speeds.  I need the resolution of the stepper motors to be 0.01 degrees, which is very small. And at maximum speed I need them to be able to do 60 RPM (1 revolution per second). So I was wondering if I used a stepper motor with a resolution of about 0.16 degrees, and then used sixteenth stepping with a motor driver would that be equivalent to a resolution of 0.01 degrees?  What are the drawbacks of this?

Also one (or two motors) need to control wheels on the cart of my project.  Which need a minimum speed of 0.1mm/s and maximum of 1m/s.  Is it wrong to use steppers for these motors?

Thanks for the help,
James

#### Grumpy_Mike

#1
##### May 11, 2012, 10:39 pm
That would suggest you need a stepping rate of 36 KHz, that is very fast for a stepping motor, you might have to supply it with a very high voltage to get any torque at that speed.

#### MarkT

#2
##### May 11, 2012, 11:57 pm
And there's no such thing as a 0.16 degree stepper motor to my knowlege, 1.8 degrees per step is the standard fine resolution.

Secondly microstepping is not very mechanically accurate as the arrangement of magnet poles is not purely sinusiodal in response, so 1/16 microstepping might give you about 0.2 degrees or so with a light mechanical load, but significantly worse with high-torque loads.
There's also mis-registration (eccentricity) of the stator plate stack w.r.t the rotor to consider that will give slight errors in angle (above 0.01 degrees quite likely).

What is needed for that precision is a high-resolution encoder on precision bearings and a servo-motor (probably with zero-backlash gear train).  Its quite an extreme requirement really.

You realise the wheels of your cart are unlikely to be precise to 0.01 degree and 200ppm in radius (the same level of precision)
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### 9Vortex

#3
##### May 13, 2012, 09:59 pm
So you bring up a good point... why is that this motor below claims to have a step resolution of 0.07 degrees but then when I click on the second link I provided below the step angle is 1.8 degrees?

http://www.robotshop.com/ca/geared-bipolar-stepper-motor-3v-416-oz-in.html

http://www.robotshop.com/ca/content/PDF/mechanical-drawings-3318.pdf

Is it safe to say that the smallest step angle is 1.8 degrees in stepper motors? And with a micro-stepping I could at most reduce this to about 0.2 degrees pre step?  (Pretty much confirming that I understand what you stated before Mark)

#### kf2qd

#4
##### May 14, 2012, 07:12 pm
Not sure about your budget, but you might want to look into a brushless servo - the motion is smoother, and the resolution is higher, but it would probably also require a gearbox - they are also expensive...

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