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Stepper or DC motor

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Kryten

New Member
Hi im trying to decide whether to use a stepper or a geared down DC motor to achieve the best precision for positioning control by using a PIC18F series uC.

Can any one please advise me or point to different projects so i can get hints or tips..

Oh yeh the motors will be traveling both ways ( ie left and right, up and down). Not much mass (just a kilo or so)
 

Chippie

Member
Hi im trying to decide whether to use a stepper or a geared down DC motor to achieve the best precision for positioning control by using a PIC18F series uC.
QUOTE]


Just how precise does the positioning have to be?

Steppers can be quite accurate if controlled correctly, a geared dc motor would need some form of feedback to determine position..
 

Kryten

New Member
Sorry i forgot to write it..

The idea is to have feed back either way. It will control a pan tilt head. I am planning on having it so that you set "outer" limitations in all four directions, then set a frame and the unit will calculate how many times it must stop and take picture to cover the entire outer limit.

My initial idea was to count the number of steps, but i think it will take a lot more uC power than use a feedback (pot meter or similar).

Precision wise i think it needs to be with 0.1mm at the unit..
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Driving a stepper is simple enough, the amount of processor 'power' required is tiny - the main problem is that it's not an absolute positioning system, whereas a servo is.

A stepper is OK if it NEVER misses a step, and NEVER gets moved mechanically - a servo has absolute positioning, it goes where you tell it - and if it's moved mechanically it will move itself back, and actually fight against mechanical movement.
 

Kryten

New Member
Ok.

Thanks Nigel.
I was thinking but im only familiar with RC servos and dont think they are strong enought. Althou I bet there are servos that are big and strong.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Ok.

Thanks Nigel.
I was thinking but im only familiar with RC servos and dont think they are strong enought. Althou I bet there are servos that are big and strong.
Yes, you can get bigger servos - but even RC ones are amazingly powerful, far more so than steppers many times the size.

Bear in mind with servos though, they only have a very limited degree of movement.
 

Chippie

Member
An S148 servo (as made by Futaba ) can be modified to turn thru' 180 degrees...Even if you got a bigger servo there's no reason why it too cant be hacked to do the same....
You would need two servos..pan and tilt
 

Kryten

New Member
Yes i know that i need two servos. But i was actually thinking of usa a planetary gear on pan. This combined with a lazy susan will make for exelent weight handling..
 

Kryten

New Member
Does it matter wheter its a analog or digital servo? This is some thing i really dont know any thing about.
 

Russ Hensel

New Member
I think when you hack a servo to go 360 it is not a servo any more just a motor.

Generally a servo motor is any motor with a position sensor.

Steppers can be geared for more torque.

A gear head motor with an encoder prior to the gear reduction can have very good positioning and high torque, think it is more complicated than a stepper.

I would use a stepper geared down a bit.
 

Chippie

Member
I think when you hack a servo to go

A gear head motor with an encoder prior to the gear reduction can have very good positioning and high torque, QUOTE]

Thats a servo.....albeit the encoder is a potentiometer giving position feedback....
 
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