Hello Forum Users!

My brain is melting trying to sort this, so I thought I would reach out to your good selves.

I’m trying to control two linear actuators.
by using 3x 3 position DPDT switches (momentary On - OFF - momentary On).

The intension is for an operator to use the front switch to move the front actuator in and out, a rear switch to move the rear in and out. And a middle switch to move both front and rear actuators in and out simultaneously.

I’m hoping to archive this with switches and diodes or alikewith out the need for a microcontroller.

Any help is very much appreciated.

here is a incomplete schematic to help explain where I’m at so far.



kind regard

 

Apologies I can’t edit my post above.
For clarity I should have

“And a middle switch to move both the front and rear actuators in or out simultaneously.”

 

Welcome to AAC, @Qwik234
You can do this with diodes (x8) but it would short the supply if the middle switch was operated in one direction while one of the other swaitches was operated in the opposite direction at the same time.

 

It would be simpler to understand if you use two relays (one for each actuator) and the switches set logic levels for a few logic gates to control the relays.

Bob

 

I should have said 2 relays and 3 switches. The 3 switches produce logic levels that go through some logic gates to control the 2 relays.

Edited: Oh, I see what you are saying. There would need to be two more relays, so forget it.

Bob

 

I should have said 2 relays and 3 switches. The 3 switches produce logic levels that go through some logic gates to control the 2 relays.

Bob

how will you get to the center "off" position on the relays? You'll need more than some signal switches, you'll need some power Mosfets or other to get the relay to an OFF status or the actuators will always be moving. Partial answers of essentially, "use some relays and logic gates" is not helpful at all.

 

What happens to an actuator when a momentary switch is released? Does it continue to its destination, or simply stop moving?
When the centre switch is used, must both actuators move in the same direction?
Do the actuators have built-in limit switches?

 

Apologies I can’t edit my post above.
For clarity I should have

“And a middle switch to move both the front and rear actuators in or out simultaneously.”

What type of actuator and what is the operating current and voltage of the actuators?

 

Apologies to BobTPH.
I inadvertently deleted my previous post about dealing with center-off when using two relays.

So below is the diagram for using two DPDT relays, and three DPDT center-off switches, that solves the problem (I think all the wiring is correct):

The center switch position is OFF.

When the "Both" switch is actuated in either direction, it powers the relay coils to remove the individual switches, and connects the "Both" switch to both actuators.
(It shows polarized coil relays, but the relays would need to be non-polarized, as most are).

Edit: To avoid possible confusion I blocked the coil polarity symbols.

 

That is not what I imagined. It is much better.

Bob

 

If you use the front switch to move that actuator out, then when you next hit the center switch, one actuator will be in and one will be out. What do you want the circuit to do in this case?

Expanding on that, there are four possible actuator conditions:

In - In
In - Out
Out - In
Out - Out

And 27 possible switch position combinations when you walk up to change something,

And twelve possible switch actions to do something.

That's a lot.

Are there some disallowed combinations, or anything else to reduce the size of the truth table?

For example, are the switches spring-loaded, so they cannot stay in either On positions without operator presence? In your text you say the switches are momentary, but in the drawing you say they can be "left on".

ak

 

This circuit uses ((on)-off-(on)) DPDT switches and non-polar relays.
SW3 activates both actuators.

 

Do the linear actuators have limit switches and diodes at the endpoints?

ak

 

What are the Actuators controlling ?
( a picture is worth a thousand words ).
.
.
.

 

It would be simpler to understand if you use two relays (one for each actuator) and the switches set logic levels for a few logic gates to control the relays.

Bob

It would be very simple to do IF you used two realays for each motor, one for in and one for out. Then the logic to control relays would be simple. The problem with the switches is that any connection to both relays removes the chance for single relay operation. You would need four single throw two pole relays

 

Hi Qwik234,

Here's how.

The schematic is in two parts:

1. Actuator Selection

Three momentary push button switches, magnetic latch relays and indicators are used.

Fly-back diodes, for the relay coils, are not shown.



2. Actuator Control



Only one common 'momentary DPDT switch with centre off' is used to control the actuators.

Actuator 'end-of-travel' limit switches stop the actuators at their end limits.

Nandu.

 

YES!! I did not think clearly. It can be done with three relays. One two reverse the polarity and two to enable the motors. BUT then both motors at once will always be in the same direction. Is that what is wanted??

 

YES!! I did not think clearly. It can be done with three relays. One two reverse the polarity and two to enable the motors. BUT then both motors at once will always be in the same direction. Is that what is wanted??

Did you see post #12?
Just change the two paralleled relays to one 4PDT relay.

 

Just change the two paralleled relays to one 4PDT relay.

The could also be done with the circuit in my post #9.

 

The could also be done with the circuit in my post #9.

Yes...but requires polarized relays.