Author Topic: stepper motor vs servo  (Read 4241 times)

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Offline RebelgiumTopic starter

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stepper motor vs servo
« on: October 07, 2007, 04:46:47 PM »
Since every self respecting electronics hobbyist has a few old floppy drives lying around, and there is a small stepper motor inside each one, I'm thinking over twice if I can't use one of those steppers before I decide to purchase a servo...

I have 12 floppy drives that I don't use anymore (don't ask how I got them...) And I was wondering why I shouldn't use one of these small steppers (to rotate my IR Sharp sensors for scanning). And I couldn't find any really convincing arguments.

The downsides of using a stepper motor vs a servo are:
-it's easier to mechanicly attach an IR Sharp sensor to a servo.
-you need a stepper controller circuit.
- ?

Both these arguments are no problem for me at all.
Did I miss aything here? Do you know more downsides?
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Offline benji

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Re: stepper motor vs servo
« Reply #1 on: October 08, 2007, 03:31:22 AM »
the servomotor control is just easier to program
in case of steppers your program should provide smooth rotation ,adjusting delay times between each new 4 bits.
just use a servo but if u dont wanna buy ones and u prefer to use your own ol'steppers u just need to worka lil more in the program.
good ol' BeNNy

Offline Ro-Bot-X

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Re: stepper motor vs servo
« Reply #2 on: October 08, 2007, 08:36:31 AM »
If you connect the stepper to a L297D driver and that one to a L297 stepper coder, all you need from the microcontroller is one pin to provide steps and one pin for direction. The normal resolution of a stepper is 200 steps per 360 degrees. So send a pulse to the stepper, take a sensor reading, send another pulse... The speed will be dictated by the sensor reading time. The stepper will be energised even when it doesn't move, so it will hold the position. You may want to have a homeing touch sensor for initialisation.

So the downsides are:
- more pins from the the microcontroller: 2 for the stepper and 1 for the homeing microswitch,
- more parts on the board: 2 IC (with their capacitors of course), one microswitch.
« Last Edit: October 08, 2007, 08:42:27 AM by Ro-Bot-X »
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Offline Ro-Bot-X

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Re: stepper motor vs servo
« Reply #3 on: October 08, 2007, 08:47:23 AM »
For the money you pay for the stepper driver and coder, you might want to purchase this little servo:
http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5456
Of course, shipment may be more costly than the servo...
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Offline Admin

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Re: stepper motor vs servo
« Reply #4 on: October 08, 2007, 01:13:25 PM »
Just a thought . . . wouldnt the floppy drive also have a stepper driver?

I think the main issue you might have is torque limitations . . .

Offline RebelgiumTopic starter

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Re: stepper motor vs servo
« Reply #5 on: October 08, 2007, 02:48:23 PM »
Quote
Just a thought . . . wouldnt the floppy drive also have a stepper driver?

I think the main issue you might have is torque limitations . . .

The driver was already soldered out, and it's waiting for me to use it ;)
And I suppose that little stepper (diameter 1,5cm) will have enough torque to rotate 2 Sharp IR's right?
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Offline garriwilson

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Re: stepper motor vs servo
« Reply #6 on: October 22, 2007, 10:36:06 PM »
I want some motors!! How do I take the floppy apart without breaking anything inside?

Offline RebelgiumTopic starter

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Re: stepper motor vs servo
« Reply #7 on: October 25, 2007, 04:35:34 PM »
turn the screws loose, and pull...
there's really nothing to it.
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