# 1440 degrees rotation. What to use? servo/steppermotor or something else?

#### digitsboy

Joined Dec 29, 2016
40
Hi,

I am working on a small project.
To open a panel i need to use a servo or stepper motor or something else haha. But i am not sure which one is best to use.
The panel is fully open with 4 rotations. this means 1440 degrees.
I also want to open it in degrees in between. So the servo / stepper motor also needs to know the actual position

I am not very known in the world of servos and stepper motors.
But what i read is that the stepper motor does not know it's position but is very secure with angles etc.
and for servo's can't just rotate 720 degrees. Then you need timings and that is very insecure i think.

What is the best solution for this problem?

Joined Jul 18, 2013
22,011
The stepper motor can be operated in a predetermined number of steps of course.
200 pulses per rev.
So all you need is something to operate the stepper controller a pre-determined number of pulses, the input is know as (number of) step, and direction, (1 or 0).
Max.

#### ronsimpson

Joined Oct 7, 2019
1,125
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#### Marley

Joined Apr 4, 2016
387
A stepper motor can easily be made to turn 1440 degrees (or any other angle or number of turns). I doesn't know where it actually is so the usual method is to turn it in reverse to a known "home" position first - which is detected with a sensor or an end stop. Remember, it is possible for the stepper motor to jump steps and get out of position especially if its overloaded.

Two ways to solve this problem:
• "Home" before every move sequence
• Add an incremental encoder so that the driver knows its relative position at all times.

What you need is a device called an "indexer" that takes a command - "Move a certain number of steps at a certain speed" or "Go to home sensor and zero the position counter", etc. from a computer or a PLC. The indexer also controls the acceleration and deceleration of the motor.

Some of these simply produce pulse and direction outputs that can be fed to a stepper motor driver. Some are extension modules of a PLC system. Some have the stepper motor driver built in. Better ones (more expensive) can also accept an input from an incremental encoder to give a feedback of actual position.

Joined Jan 15, 2015
5,720
This is a pretty good read on stepper motors. Stepper motors are available with the shaft extending out on both sides of the motor. What this feature does is allow one to include an incremental encoder mentioned above in their scheme / design. To avoid pole slips or skipped steps just make sure your choice of stepper motor can easily handle the required torque necessary. Today incorporating a PLC or uC (micro-controller) makes for easier control of the stepper motor. You also want to know how fast you want things to happen and since you mention points between a damper fully open or fully closed what resolution you want.

Anyway given the choices in most applications I worked with involving a damper we used stepper motors. Another feature was adding limit switches at full closed and full open positions. The switches sent Hi / Low signals to a PLC so a comparison could be made to make sure the damper was wide open or fully closed. There are also other motors used for dampers, I want to recall one which used a 4 ~ 20 mA loop. Been awhile and I can't recall exactly what they were.

Ron

#### Bernard

Joined Aug 7, 2008
5,719
Is it possible to attach encoder to the panel ? IF not then:
Might use Gray code absolute encoder with digital comparator then by inputting a digital number, motor knows which way to turn & when to stop.

#### techman-001

Joined Jan 13, 2021
1
I also think a stepper is a suitable choice and agree a 'home' sensor will be needed to 'register' the motor/gearbox position. After the registration is acquired one can just use a position counter to know where the motor is *providing* it is not overloaded and loses steps as a result.

If that is a problem, then position sensing such as a optical encoder may bee needed to ensure the motor is where it should be.

I made a Youtube video a while ago showing one method to control a stepper:
Stepper motor Demo

#### Phil-S

Joined Dec 4, 2015
177

#### RPLaJeunesse

Joined Jul 29, 2018
139
An alternative to optical incremental rotary encoders is the low-cost hall-effect magnetic rotary position sensor. Since it is an absolute sensor just read the position at the end of the move and see if the final angle is close to where you expect it. Take a look at AMS: https://ams.com/as5200l