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automatic forward reverse motor with limit switch and relay

Crafts4Me

Feb 10, 2022
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i am a serious hobbyist. i want to create construction scene with a crane about 18 inches tall, to lift a simulated load of brick,s rise till the top, hit a limit switch pause and reverse to the ground hit a ilmit switch and go back up.
i do not want any manual swiches involved. i need this to turn on and off with a time clock to run for about 6-8 hours at a time. i'd like to use a 12v small motor and 3A 12v plug wiring.
is this possible?
 

crutschow

May 7, 2021
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Here's my take on doing that:

It uses two SPDT relays in a bridge configuration and connected as a FF latch.

In operation, one relay will always be ON and the other OFF, with alternating action.

To understand its operation, assume U2 is ON, U1 is OFF (12V on both sides of the U1 relay coil) and the motor is going up, with neither limit switch (U3 and U4) tripped (both closed).

When the Up Limit switch opens, U2 turns OFF. This grounds the (-) input of U1 and turns it ON, reversing the motor.
As soon as the Up Limit switch closes again after the motor moves, 12V is applied to U2's coil, which keeps it OFF.
This continues until the Down Limit switch opens and the cycle repeats.

R1-C1 is to set U1 ON when power is applied otherwise it could possibly oscillate without settling into one state.

upload_2022-2-10_14-2-55.png
 

Bluejets

Oct 5, 2014
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Yes, but the size of the power supply will depend on the load requirement.
If you don't want any mechanical switches for the limits, you can use optical slot sensors.
Possible to do with relays or microcontroller, the latter would remove the need for a separate timer.
 

Kabelsalat

Jul 5, 2011
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It's very possible. You should getting to know how to set up relay logic, latter diagrams.
e.g.



 

Bluejets

Oct 5, 2014
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I'm curious just where the negative of the 12v is supposed to go.
Drawing error??
If it's the little down arrows then one had better hope the relays are break-before-make type.
 
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Tha fios agaibh

Aug 11, 2014
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I'm curious just where the negative of the 12v is supposed to go.
Drawing error??
If it's the little down arrows then one had better hope the relays are break-before-make type.
Yes, the 5 little down arrows.
Why? I see no issues with it.

The only thing I see left out is a delay timer the op wanted.
 

crutschow

May 7, 2021
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I'm curious just where the negative of the 12v is supposed to go.
Drawing error??
If it's the little down arrows then one had better hope the relays are break-before-make type.
No error.
Yes, the "little down arrows" are standard schematic common/ground symbols, which is the negative connection for the 12V supply.

Virtually all mechanical relays are break-before-make due to the way the contact mechanism works.
There is a movable contact (the wiper) which moves between two fixed contacts, so it can't make contact with both at the same time.
 
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crutschow

May 7, 2021
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The only thing I see left out is a delay timer the op wanted.
I assumed that would be a standard plug-in timer operating from the mains to power the supply.
I see no reason to do anything custom.
 
Last edited:

Tha fios agaibh

Aug 11, 2014
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.... rise till the top, hit a limit switch pause and reverse to the ground....

An on delay timer consisting or a transistor, a few resistors and a cap could easily be added to accomplish the requested pause.

Nice circuit Crutschow.
 

Bluejets

Oct 5, 2014
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One of the side effects of using hardware only, change something, major works revamp.
Microcontroller, add a software change.
 

Crafts4Me

Feb 10, 2022
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i am more lost then before. i know a few words to explain what i am looking for. please explain in "baby language" what do i need to do
the picture looks good but i dont understand fully understand what is D or U or R or C
i want my magnetic train (magnorail) to use a reed switch to activate your diagram to have my crane go up and down
i do not want an arduino
12v plug
 

crutschow

May 7, 2021
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i dont understand fully understand what is D or U or R or C
D - Diode/Rectifier
U - Label for an active component (here the relays and limit switches)
R - Resistor
C - Capacitor

If you don't know what those components are, then look up their description.
 

CircutScoper

Mar 29, 2022
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Here's my take on doing that:

It uses two SPDT relays in a bridge configuration and connected as a FF latch.

In operation, one relay will always be ON and the other OFF, with alternating action.

To understand its operation, assume U2 is ON, U1 is OFF (12V on both sides of the U1 relay coil) and the motor is going up, with neither limit switch (U3 and U4) tripped (both closed).

When the Up Limit switch opens, U2 turns OFF. This grounds the (-) input of U1 and turns it ON, reversing the motor.
As soon as the Up Limit switch closes again after the motor moves, 12V is applied to U2's coil, which keeps it OFF.
This continues until the Down Limit switch opens and the cycle repeats.

R1-C1 is to set U1 ON when power is applied otherwise it could possibly oscillate without settling into one state.

View attachment 54202
A somewhat simpler solution from another thread.

https://www.electronicspoint.com/fo...-from-mouse-switch.293361/page-2#post-1829782
 
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