Newbie: Which motor and parts do I need ?

[myuser777]

Hi,

I'm trying to build a project, that will control the position of a part which now done by a cable and a spring.
The cable is the "contra" force to the spring. Pulling the cable to increase the tension in the spring is done manually, and I want to change it to be done with a motor and controlled via arduino.

I've uploaded a small diagram to illustrate it - see attachment.
In this diagram, a green flag represents the movable part, and it can be in 3 positions: A B and C.
In the simplified diagram - I want to control the position of the green flag, using the arduino+motor.

I have some questions that I will be happy to get answer for:

1. Which is the correct motor for this job - servo/stepper, etc ?
2. Is it possible that after the "green flag" is in place, the motor will be turned off (to save battery),
   but it will be kept in place (namely the spring will not pull it when the motor off)
3. I saw that motors have "torque" value in specification, but I have no way to check the value of "K" for the spring I have, so can you give me some real life example for what can and cannot be done with these servos ?

I hope my explanation and questions were clear,
Any help is much appreciated, 10x.

[MarkT]

You will need to tell us the basic forces involved - what's the weight? Is pulling vertically or horizontally as in the diagram? What thickness of cable - how far will it have to move? Are there safety implications if the motor fails?

[myuser777]

Hi,
Here is some more information:

> You will need to tell us the basic forces involved - what's the weight?
The counter force is by a spring which I could not find specification about it's k (spring factor),
but I think it's roughly equivalent to 5-10 lbs.

*> Is pulling vertically or horizontally as in the diagram? *
the pulling is vertical.

> What thickness of cable -
1.1mm

*> how far will it have to move? *
1-2 inches

> Are there safety implications if the motor fails?
no.