Circuit question

[Madman]

I want to set up a cable car or arial tram. It will be very simple, with a single gondola moving back and forth along a cable. I was sketching some circuits with two DPDT switches that the gondola would trip as it reached the end. However, on paper it does not work, since the switches, once tripped, will remain in that position.
Then I thought of using a relay, controlled by two SPDT switches. But alas, the same situation. Once the gondola reaches the end and trips a switch, that switch can never be switched back to it's original postion. Below is the sketched circuit for the relay. But I don't see how this circuit would work. The relay has a DPDT switch that can change the polarity of the cable car motor.
http://1stclass.mylargescale.com/madman/HOW TO/relay.png

 

[Tim Brien]

Dan,
in a recent thread 'Tramcar Trev' discussed something similar but with tram direction. Perhaps have a look in this section of the forum. Follow the link to the thread. It may be of some help.

http://www.gscalecentral.net/m180584

 

[tramcar trev]

Yes this would have worked... However I did not go down that road because of other factors. However reed switches top and bottom and a DIL latching relay would work. Another consideration is that you may find a delay at top and bottom station necessary...

 

[minimans]

LGB and others make a circuit just for this scenario which will include a delay at top and bottom stations although it is designed for operating through the rails I'm sure it could be adapted for this application. or just use a couple of reed switches operating a 1200 solenoid for the same thing without the delay.

 

[Neil Robinson]

I want to set up a cable car or arial tram. It will be very simple, with a single gondola moving back and forth along a cable. I was sketching some circuits with two DPDT switches that the gondola would trip as it reached the end. However, on paper it does not work, since the switches, once tripped, will remain in that position.
Then I thought of using a relay, controlled by two SPDT switches. But alas, the same situation. Once the gondola reaches the end and trips a switch, that switch can never be switched back to it's original postion. Below is the sketched circuit for the relay. But I don't see how this circuit would work. The relay has a DPDT switch that can change the polarity of the cable car motor.

I chose to solve this by using an additional set of "hold on" contacts on the relay with one reed switch normally open and the other normally closed.
In practise 3PDP relays may be a bit rarer/more expensive than 4PDT, if so use a four pole with a redundant set of contacts. Again if normally closed reeds are a problem to source use the normally closed pair of a changeover reed.
As previously mentioned the problem may also be solved by using a "latching relay" but I've not explored this alternative.

In the following diagram the sequence is started by driving the car towards reed 1, once this is triggered the cycle repeats until power is switched off.

 

[Philbahn]

Think a latching relay is the easiest Maplins sell them. http://www.maplin.co.uk/2a-miniature-dpdt-latchingrelay-37529

 

[Madman]

Excellent! That's what I didn't think of, a latching relay. Thanks to all.

 

[Madman]

Found a latching relay. However I am having some difficulty figuring out the wiring diagram for it. I know it must be simple, but my mind just can't get around it for some reason. Here is the relay schematic. It is a DPDT switch controlled by a relay.
http://1stclass.mylargescale.com/madman/HOW TO/Relay_Spec DPDT.jpg
Pins 4 & 13 are the center poles on the switch. 6 &11 are one one side and 8 & 9 on the other. I presume that poles 4 & 13 would be wired to the load or motor in this case. But where would the power come in? Would it be 8 & 9?

 

[Neil Robinson]

Pins 4 & 13 are the center poles on the switch. 6 &11 are one one side and 8 & 9 on the other. I presume that poles 4 & 13 would be wired to the load or motor in this case. But where would the power come in? Would it be 8 & 9?

Wire 6 to 9 and 8 to 11. You then effectively have two pairs of terminals, one pair is 4 and 13 the other 6(or9) and 8 (or11). Connect the input power to one of these pairs, it doesn't matter which, and the motor to the other pair.

 

[Madman]

Thanks Neil. It works perfectly.