A space Elevator circuit!

[MrModelmaker]

Good Morning all,

Well I'll try to keep it short, I'm a model maker and currently working on an exhibition for the science museum, the piece itself is a scaled down model of a space elevator for the atrium of the museum.
The basic principle is a loop of fishing wire with an elevator stuck on it, with one end of the wire looped around a pulley on the roof and the other end of the loop attached to a motor on the ground. Now what I need is the elevator to go up, trigger a switch which would reverse the motor and return the elevator to the ground to trigger another switch and send it back up again repeatedly.
I hope that makes some sense! I can of course clarify with drawings
So could anyone give me any advice or point me in the right direction? I know how to put together circuits and things because I do some work on films, but this is a bit beyond me.
But any help would be much appreciated!

[pebe]

Have you decided on the motor type? AC mains, or DC from a suitable power supply?

[MrModelmaker]

Have you decided on the motor type? AC mains, or DC from a suitable power supply?

At this stage it will only need to run on batteries with an AC motor

[pebe]

The problem is reversing an AC motor.
If you could use a DC motor there is a fairly simple solution.

[MrModelmaker]

The problem is reversing an AC motor.
If you could use a DC motor there is a fairly simple solution.

Okay, I can compromise
What's the solution with a DC motor?

[pebe]

Use a DPDT relay run from DC. Wire the motor to the two moving contact. Wire the poles to a DC supply so that when the relay is energised, the motor windings are connected in reverse to when the replay is de-energised. Then switch the relay with an SCR.in series with it.

One of the limit switches is normally closed and wired in series with the SCR and relay. The other limit switch is normally open and closes to switch on the SCR.

In action, imagine relay is energised. The elevator is approaching the bottom. The top limit switch (that switches on the relay) is open. The elevator hits the bottom and opens the limit switch (normally closed). That interrupts the power to the relay and it de-energises. That changes over the polarity of the motor supply and the elevator starts to go up. The bottom switch closes as it goes up, but the SCR is unaffected and stays turned off.

Elevator gets to the top and the top limit closes, turning on the relay again. Elevator starts to go down again. .....Ad infinitum.....

Let me know if you want a circuit.

NOTE: Error. Action amended 6.45pm Relay starts as energised - not de-energised.

[MrModelmaker]

Wow, that is amazing thank you very much, it explains a lot.
A circuit diagram would be much appreciated; but please, only if it's not too much hassle and there's no rush at all.
Again thanks, I'll definitely be mentioning this place to colleagues, you cover a lot of fascinating things over in the other threads.

[pebe]

Hi MrM…..

Here is the circuit. I haven’t tested it but it should work OK. When you have installed it, check the motor windings are the correct way round.

With power off move the elevator to its mid position. Open the bottom limit switch S1 and apply power. The lift should go up. If it goes down, reverse the motor leads.

Best of luck.

[MrModelmaker]

Thank you very much indeed!
I'll let you know how it all goes.