What do you think of this proposal:
V1 is your power source, the voltage set to the max. acceptable voltage for fast operation.
Resistors R1 and R2 are set such that the motor operates at the expected medium or slow sped, respectively.
The 3-way switch to the left selects either of the 3 possible speeds.
To the right there is a switch (lower) and a pushbutton (upper).
The switch is a
limit switch which is open in the end position of the motor, closed while the motor is running (away from the end position).
The pushbutton is a normally open type which will short circuit the limit switch when pushed.
The operation is as follows (assuming the motor is at rest in the end position):
- Select the desired speed by setting the 3-way switch to low, medium or high.
- Start the motor by pushing the pushbutton until the the motor has left te end position.
- The motor having left the end position, the limit switch will now be closed. The motor will continue running.
- When the motor reaches the end position, the limit switch will open. As the pushbutton is no longer pressed (for one cycle operation), the motor will stop in the end position.
If you need to run multiple cycles, simply keep the pushbutton pressed so the limit switch will not interrupt the power in the end position.
You may have to tweak the mechanical setup such that the motor really stops in the end posistion even when set to high speed. Since the motor will not stop immediately when power is turned off, there is the risk of the mechanical inertia of the machine letting the motor run past the limit switch which in turn will re-close the limit switch and the motor will be powered again.