Alternate to a proportional linear solenoid

[TammyHere]

I am trying to build a circuit using gears, motors, and relays only which mimics the motion of a proportional linear solenoid i.e. Hold a spring compressed at a certain distance depending on the current passed, and push/ release it further based on the increase/ decrease of current. (V=12 V, Spring Force in Kg = 25, distance = 10 cms). For now, I am seeking help in the design, what to use and how to use.

I am trying to use a cam follower mechanism but it doesn't work out. Can you please help me out in this regard?

Thanks in advance

 

[Mike_In_Plano]

For your typical DC motor, the shaft torque will follow the current, and the motor free speed will follow the applied voltage. The torque will also dip as the motor's shaft angle varies. Some high quality motors (like Maxon) are designed to have a more consistent torque versus angle. You will also have all the difficulties that stiction bring. With a good quality motor, a spur gear, and a rack it should behave somewhat like a solenoid drive.

 

[meBigGuy]

I don't see how you do this with a "normal" motor unless you are running it "stalled". You need a servo or stepper motor, I think. Am I missing something?

http://en.wikipedia.org/wiki/Servomotor