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I'm totally new to electronicS and do not understand a lot and I've read other posts but people seem to be asking different things to me so apologies in advance if this has been covered but I've typed in what I think are correct terms.

I'm doing an art project installation and require a set up so a DC motor is connected to an axel with lightweight things hanging off it. It needs to winds up 1 way and then change direction and winds down another automatically I.e. Without myself being present to flick a switch to change the polarity. I know it can be done using a dpdt switch.

I have a battery compartment with an on/off switch powered by x4 AA batteries (6v) wired to a 6v DC motor that is already geared to run at 30 rpms which is what I want. I have looked into using micro switches and from what I understand? I can't run 1 switch permanently connected even if I e.g. Hang a weight from the axel that when it is lowered into another switch activating it to change the polarity as if this is done it will short circuit.

Is there a cheap way around having it run in e.g. CW and then change to run in CCW after a switch is activated or after a certain amount of time? If possible I'd like to avoid circuit boards as I don't understand or have the parts for this and time is of the essence.

P.s. I'm based in UK so things may not be as easily available.

Thanks for any help in advance.

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Just a single switch is not enough. Actually, two switches is not enough. You need a memory element, such as a relay, plus a switch at each end of your weight travel.

The following will do what you need. It consists of a relay (double pole, double throw), two limit switches (one normally open, the other normally closed), and a diode.

schematic

simulate this circuit – Schematic created using CircuitLab

The vertical travel of the weight is shown on the left, along with a protruding arm which will contact SW2 at the bottom of its travel, and SW1 at the top. The motor is wired so that with 6 volts on its + lead, the weight rises.

Start by assuming the relay is off. The two sets of contacts are active on the right, so +6 is applied to the - motor lead and the weight is descending. Because the motor + lead is at ground, there is no voltage applied to the diode.

Now let the arm on the weight activate SW2. +6 volts flows through SW2 and SW1 and applies power to the relay. Now the contacts to the left are active and two things happen. First, +6 is applied to the motor + lead, and the weight starts rising. Two, +6 volts flows through the diode, and also tries to drive the relay. So when the weight starts to rise and the arm no longer closes SW2, the relay is still driven and the motor continues to drive the motor to raise the weight.

This continues until the arm contacts SW1 and opens the relay circuit. With no power to the relay, the contacts shift to the right and the motor reverses direction. The weight starts down. Since the motor + lead is now connected to ground, there is no voltage on the diode, so when the weight drops and SW1 closes again, there is still no drive for the relay coil.

The cycle will continue as long as the battery holds out.

Speaking of which, I really recommend either much bigger batteries or a power supply you can plug into a wall. I believe you'll find that you drain AA cells much faster than you think.

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  • \$\begingroup\$ Thanks, is the relay called anything specific i.e. a certain type of relay? and do the switches on the relay return to a specific direction if not powered or is it that every time the relay is powered the relays switch one way and if then not powered they don't move, if powered again do they then change to the opposite position? \$\endgroup\$ – D84 May 17 '15 at 20:07
  • \$\begingroup\$ it doesn't necessarily have to use weights it's just that was a way of determining how long before switches would be pressed. If there is an easier way of having the direction automatically change then I'd be open to hear it, preferably without soldering. Thanks \$\endgroup\$ – D84 May 17 '15 at 20:18
  • \$\begingroup\$ a similar thing I came across was at the following link which is similar, a small delay wouldn't be too bad but it looks awfully complicated to my simple non-electronically-understanding brain. it could run for say 60 seconds minimum at 30 rpms hence 30 turns if that helps? \$\endgroup\$ – D84 May 17 '15 at 20:23
  • \$\begingroup\$ To the first comment. The relay is called a double-pole, double-throw relay. The switches are called momentary action, that is, the close or open the contacts only as long as the button (or lever) is pressed, and spring back when released. They are completely unaffected by the relay operation. SW1 is normally closed: the switch is closed until pressure is applies. SW2 is normally open. It's possible to do without the diode if you use a latching relay, but those cost a good deal more. \$\endgroup\$ – WhatRoughBeast May 17 '15 at 21:02
  • \$\begingroup\$ Second comment. Man up - you're going to have to learn to solder if you want to do anything with electronics. There really isn't a much better/simpler way to do this. If you can find snap-action switches you can connect them by a rod or string on a pulley and do without the relay, but that's a bit tricky. \$\endgroup\$ – WhatRoughBeast May 17 '15 at 21:08

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