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Topic: Stepper motor precision (Read 947 times) previous topic - next topic

andrefsl

Hello,

I'm new to the stepper motor world so I would like to get some information about them from more experienced users.


I'm trying to understand if it's possible to have and control with some accuracy a stepper motor with a step angle of by example 0,05 deg (7200 steps per revolution)?

To have this kind you step angle the stepper motor must be provided with some kind of gears?

I would need some kind of close loop (encoder?) to control the stepper motor for this kind of precision?

Thank for your help
André

jremington

#1
Jun 30, 2018, 02:57 am Last Edit: Jun 30, 2018, 02:58 am by jremington
For 7200 steps/rev resolution, you could use a stepper with a gearbox.

However, the gearbox will have backlash, which can be dramatically reduced by always approaching the target angular position from the same direction of rotation.

Shaft encoders with resolution that high are available, but very expensive.

andrefsl

Hello,

Thanks for your help.

I could also use microsteppig? It could be a cheaper alternative?


jremington

#3
Jun 30, 2018, 03:48 am Last Edit: Jun 30, 2018, 03:49 am by jremington
Microstepping does not produce accurate steps, and steps are easily missed. It is intended for smooth rotation, not accurate positioning.

MorganS

I disagree that "steps are easily missed". If the motor is configured correctly and not overloaded then microsteps are just as good as full steps. Otherwise most 3D printers would not work.

The precision of the exact position of a microstep within a full step is debatable. But the steps aren't missed.
"The problem is in the code you didn't post."

groundFungus

Microstepping does reduce the available torque of the motor, though (versus full step torque).

jremington

#6
Jun 30, 2018, 05:26 pm Last Edit: Jun 30, 2018, 05:57 pm by jremington
Quote
But the steps aren't missed.
Yes, they certainly can be, under load.

I and many other people have personally observed the phenomenon. Either you have been fortunate, or you didn't check.

This may be quite surprising, but I've actually seen a stepper motor stopped completely, missing ALL steps!

MorganS

If the motor is configured correctly and not overloaded.
"The problem is in the code you didn't post."

jremington

#8
Jul 01, 2018, 09:18 pm Last Edit: Jul 01, 2018, 09:52 pm by jremington
Conversely, if the OP failed to follow your sage and detailed advice, a stepper would skip microsteps.

MarkT

Microstepping does reduce the available torque of the motor, though (versus full step torque).
I disagree, microstepping moves smoothly between the full step points exhibiting the same
torque at those points, but with less risk of resonances that can jump steps.  Resonance and
vibration will full-steps is very problematical unless the mechanical system is very well damped.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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