I am adding a geared motor to a turntable on a model railroad module. I would like to control the motor direction and planed to use 2p2t switches on each side of the module using a circuit like this:
Is there an easy way to be able to route power to one switch or the other to avoid a short that would happen if two people tried to operate the motor at the same time?

 

Three position switch. Center if off.

 

View attachment 210379
Three position switch. Center if off.
View attachment 210380
View attachment 210381

How does this solve the problem of multiple reversing switches to the same motor?

 

You could have the 2 switches controlling a couple of SPDT relays that do the motor switching.
That would solve your problem.

 

 

View attachment 210396

This will work, even for multiple DPDT switches connected in the same manner.

But, and this may not be a limitation, the position of each switch won’t indicate the direction that the motor will move. To move in the direction opposite to the last direction the motor moved, just requires flipping one switch to the opposite position.

 

If you use the 3 position switch; any switch set to off (center) will stop the project. All switches must be in run.
If you use the 2 position switch; there will not be a off. All switches, don't touch the switch = run this direction. Flip the switch reverses the direction.

 

You could have the 2 switches controlling a couple of SPDT relays that do the motor switching.
That would solve your problem.

Could you expand on this? How would this eliminate a short situation if both of the switches are activated at the same time?

 

View attachment 210396

Thought you might have had it here, but I need to use momentary contact switches so that I can control the stop position of the turntable. I am using a 2rpm geared motor. MC

 

Could you expand on this? How would this eliminate a short situation if both of the switches are activated at the same time?

If both relays are operated, it is just the same an neither operated.
Both ends of the motor are connected to the same polarity, and the circuit is open.

 

You can build an n-way switch. e.g. https://en.wikipedia.org/wiki/Multiway_switching using SPDT and DPDT switches, but first you would need a single signal to open/close the rotary turnstyle.

Don't know if you need limits or just have to reverse the polarity or what.

Motors such as door lock motors are controlled with two SPDT relays. The advantage is you get dynamic braking. You can add limit switches as long as the switches can handle the coil current.

Here (motor_limits.pdf) https://forum.allaboutcircuits.com/...house-roof-window-control.134958/post-1131056 is a comprehensive method of control.

You do end up with two relays with.
On On - this also brakes the motor
On OFF - one direction
Off ON - the other direction
OFF OFF - brakes the motor

You can add another relay that could give you (position 1)/(position 2) type of control.

You would have state info, so you can wire that next to the switch. Put the state info to the right or left of the switch. Flipping the switch the other way would reverse the state.

So, you can potentially have n-station control with indication.

You could use 3-lead bi-color LED and say indicate moving with yellow and the state with RED.

 

Sounds like two SPDT relays with two momentary push-buttons (or a momentary SPDT switch with center off) for each control point is what you want.
That would not have a shorting problem with more than one person trying to control it at the same time.

Note that to minimize relay and switch contact arcing you will need to add diodes for inductive spike suppression, one on each relay coil, and four on the relay outputs (below).

 

Sounds like two SPDT relays with two momentary push-buttons (or a momentary SPDT switch with center off) for each control point is what you want.
That would not have a shorting problem with more than one person trying to control it at the same time.

Note that to minimize relay and switch contact arcing you will need to add diodes for inductive spike suppression, one on each relay coil, and four on the relay outputs (below).

View attachment 210450

So adding another SPDT center off at the bottom of the diagram (one on each side of the module) would not cause a short? what happens if the two switches are set in opposite directions at the same time?

 

Like I said earlier, the motor stops, The relays will connect both sides of the motor to V+ instead of ground.
The switch is momentary, so you have to wait until the turnstyle completely changes state.

 

If both motor leads are returned to ground or V supply = motor stopped, no problem.

 

what happens if the two switches are set in opposite directions at the same time?

Follow the current for all positions of the switch and relays.
You will see there is no combination that can cause a short.

 

Like I said earlier, the motor stops, The relays will connect both sides of the motor to V+ instead of ground.
The switch is momentary, so you have to wait until the turnstyle completely changes state.

OK thanks, I thought that was what I was seeing.

 

If both motor leads are returned to ground or V supply = motor stopped, no problem.

Thanks.

 

Follow the current for all positions of the switch and relays.
You will see there is no combination that can cause a short.

Thanks. Sorry I am soooo dense.