Limiting the movement of a motor.

[matellinid]

I am wondering if a component such as a motor exists which can be limited in terms of how far it rotates. In the diagram, the orange is the pivot point and the black is the piece that the motor would move as shown by the arrows. It is the top view of the component. For example if i wanted the black piece to only rotate 90 degrees before stopping and then goes the opposite direction once the current is re-applied. Also it would be activated by one signal and that would cause one rotation. Then another signal created from for example a button being pushed, causes the black handle to rotate back to the original position.
Thanks!!

 

[kellys_eye]

Two ways.

Servo motor or stepper motor.

The servo motor requires a pulse width signal - the width of the pulse determines the absolute position of the motor shaft.

The stepper motor requires individual pulses (and a circuit to count them) sent in a specific pattern to enable rotation in one direction or the other.

The servo solution would be easiest to implement - a couple of 555 timers each preset with the required pulse width (position) and simply selecting one or the other signal.

Another 'clunkier' method would be to fit limit switches - this would be a mechanical solution rather than an electronic one though.

 

[Minder]

The only difference is the servo motor will require an encoder of some kind with PID control for precise positioning over limits.
The basic stepper move in 1.8° steps.
M.

 

[kellys_eye]

The servo I reference to is the type as used in radio controlled models where the position is purely a function of the pulse width applied.

 

[Minder]

The servo I reference to is the type as used in radio controlled models where the position is purely a function of the pulse width applied.

AFAIK RC servo's have a internal pot feedback for position registration.
M.

 

[kellys_eye]

Indeed they do. Those servos are self-contained but, whilst they might work on a PID basis, as far as the user is concerned it's just a 'pulse position' system. The feedback signal isn't passed 'back' to the user.

 

[hevans1944]

At the risk that the OP has already solved their problem and moved on, I hereby bump this old thread to mention a device called a rotary solenoid. This is an ordinary solenoid whose armature is pulled in and forced to rotate by means of three ball bearings mounted between inclined planes. The range of rotary motion is quite limited, but torque is fairly high. Restoration to the original de-energized position is accomplished with a spiral-wound spring that is compressed when the solenoid is energized. Mechanical stops can also be used to further limit the range of rotary motion, although this is seldom done.