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Motor Reverser

kimbear

Member
I have a really simple elderly model Cable car (rides on a cable strung between 2 points in the air).
It is a really simple contraption, 2-1.5v AA batteries, and a small 3v motor, gears, etc.
The only problem is, that it only goes in one direction.

I would like to try building a circuit that would reverse the direction when it gets to the end of its travel, and the unit would trundle back and forth

Since Im old school, semiconductors, ic's, etc., I would prefer a circuit that doesnt use, Micro-controllers...and yes, I know it would probibly be easier to use them.
Any ideas?
Thanks fin advance.
 

rjenkinsgb

Active Member
The simplest thing is probably a "latching relay" circuit.

Use a four-pole changeover relay, something like this: https://www.ebay.co.uk/itm/Europa-Components-General-Purpose-Relay-6A-4-Pole-Change-Over-14-Pin-Base/323247437963

Wire two poles as a basic reversing switch, ie. supply to the two commons and out from NO and NC contacts, but swapped over between the two. eg. http://www.1728.org/dpdt.gif

Use a normally open push switch or contact of some type at one end of the car travel and a normally closed at the other end.
Use those with the relay coil and another normally open contact to make the relay latch / unlatch, eg. something like this (not showing the reversing contacts).
http://www.reuk.co.uk/OtherImages/make-latching-relay-with-a-dpst-relay.jpg

The relay coil voltage needs to be appropriate for the supply voltage you are using. It can be a totally separate circuit to the motor power that goes through the reversing contacts.


Edit - Or. if you really want to go to basics, just purely a two pole changeover toggle switch to reverse it, with a mechanical rod or cord system to pull it either way when the car gets to a limit point...
 

AnalogKid

Well-Known Member
Most Helpful Member
Because the motor speed is not a perfectly predictable constant speed, using a timer like a 555 or an ebay module to determine when to reverse the motor voltage will not work. Eventually, the car will run into an end stop before the timer changes the directilon. So there needs to be a sensor of some kind on the car to tell the circuit when to change directions. This can be a small plastic vane that interrupts a slotted optocoupler, a magnet that passes near a hall effect sensor, or even just a low-force pushbutton switch that the car bumps into. Whatever, this signal (one from each end of the run) tells the circuit when to change directions.

If 3 V is the max voltage for powering the circuit, then an all-relay approach is out. Next up is either one low-voltage CMOS chip or a discrete, 2-transistor circuit. The circuit is a "toggle" flipflop. With each input, the output alternates between two states, one for each direction.

Really need to know the motor current to determine what the power switching circuit is. Low voltage relay coils can drain a battery pretty fast, and the relay is on half the time. An alternative is an all solid-state voltage reverser called a full H-bridge circuit. Tricky at these low voltages, but doable.

ak
 

ronsimpson

Well-Known Member
Most Helpful Member
What does your cable car look like? I found this one on ebay.com and it climes a string.

The string passes around the wheels around the motor and on. On each end of the string there is a bead that indicates the end of string.
1538174835634.png
Here I added a forward/reverse switch. The switch has a rod and two hoops added. When the hoop hits the end of the string the switch is switched to the other direction.
 

shokjok

Member
There are reversible H-bridge motor speed control circuits online that can be PWM-controlled for preset speeds.
 

NsrMagazin

Member
I have a really simple elderly model Cable car (rides on a cable strung between 2 points in the air).
It is a really simple contraption, 2-1.5v AA batteries, and a small 3v motor, gears, etc.
The only problem is, that it only goes in one direction.

I would like to try building a circuit that would reverse the direction when it gets to the end of its travel, and the unit would trundle back and forth

Since Im old school, semiconductors, ic's, etc., I would prefer a circuit that doesnt use, Micro-controllers...and yes, I know it would probibly be easier to use them.
Any ideas?
Thanks fin advance.
Since you do not have another way to control the motor, you need to control it by suppying the same current and voltage for the same time but on a different pin of the motor. You need a "H-bridge" to control the direction. Just look up a "H-bridge" circuit for DC motor.
 

Pommie

Well-Known Member
Most Helpful Member
This is an old thread, the OP has not been back since Sept last year. Let it die.

Mike.
 

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