Hi guys just wanted to know how can I get a DC motor spin clockwise then counter clockwise automatic in a circuit, I need this to be quite simple because I'mm going to use this for a Christmas decoration. is it doable?

 

What is the motor's voltage and current requirements?Do you intend the direction of spin to be changed after a period of time, or by the position of whatever the motor is turning (i.e. limit switches). What is the motor turning? Does it need to stop before changing directions?..as motors don't like suddenly reversing directions under load.

Ken

 

use an H-bridge..
http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/
very easy to implement as there are plenty of designs, even fully integrated ICs that can do it for you! =]

 

I don't think it would be very simple to do, but I would see about using relays to switch the current flow through the motor.

I'm sure those who are more experienced than myself can help you more, but I'll see what I can do.

Sparky

 

hey what do you know..
http://www.allaboutcircuits.com/vol_4/chpt_6/4.html

 

There is a much-simpler way.. you can make the project with a double-pole double-throw switch and not use any relays at all. The only problem is the motor is constantly turning in one direction or the other. The alternative is to use two double-pole push switches or 4 switches as shown in the following diagram. You need to push both of the forward switches at the same time. By pushing the reverse switches very briefly you will get braking when travelling in the forward direction.

 

Depending on the size and current ratings of your motor ( I am assuming this is a small decoration?? maybe a Tree ornament??) It can easily be done with a couple of NPN and a couple of PNP transistors (setup as an H-Bridge), coupled with the all too famous low power NE555 timer IC in an astable setup, you can set the delay (or how long it rotates in either direction) by just using 2 capacitors and 2 resistors.....

Or

You can still use a 555 timer to switch a DPDT (Double pole, double throw) relay via a transistor and just have it swap the leads of the motor to reverse the motors direction...

 

There is a much-simpler way.. you can make the project with a double-pole double-throw switch and not use any relays at all. The only problem is the motor is constantly turning in one direction or the other. The alternative is to use two double-pole push switches or 4 switches as shown in the following diagram. You need to push both of the forward switches at the same time. By pushing the reverse switches very briefly you will get braking when travelling in the forward direction.

It is going to be used as a decoration, meaning it would be kind of tedious to keep having to push a switch or 2 to get it to move....

 

There is a much-simpler way.. you can make the project with a double-pole double-throw switch and not use any relays at all. The only problem is the motor is constantly turning in one direction or the other. The alternative is to use two double-pole push switches or 4 switches as shown in the following diagram. You need to push both of the forward switches at the same time. By pushing the reverse switches very briefly you will get braking when travelling in the forward direction.

only issue is, when your using switches is the cost, its ok, its simple, makes sense, but you dont really want a 10quid/dollar/(insert currency) motor with a 30quid/dollar.. switch?
hence h-bridge, relays etc.

 

What is the motor's voltage and current requirements?Do you intend the direction of spin to be changed after a period of time, or by the position of whatever the motor is turning (i.e. limit switches). What is the motor turning? Does it need to stop before changing directions?..as motors don't like suddenly reversing directions under load.

Ken

Well Im not sure about the motor, its a smnall one used for Toy cars, i wanted the motor to turn a arm on a santa decforation. i need the motor to turn one way for a second or two then stop, pause. then turn the other and then repeat the turns.

 

Well Im not sure about the motor, its a smnall one used for Toy cars, i wanted the motor to turn a arm on a santa decforation. i need the motor to turn one way for a second or two then stop, pause. then turn the other and then repeat the turns.

Well, in this case I would just use some mechanical attachment to move the arm, you can just have the motor turn one way without switching directions..... basically build a cam system that would move the arm back and forth if the motor is just left on, but then couple that with a 555 timer IC and a relay to turn on the motor say every 2 seconds to move for 1 sec, using simple machine techniques to build the arm cam should not be too hard, and you would only require a few components for the circuit to keep it simple....

 

555 slow oscillator? doesnt have to be precision.. could hook up a little transistor circuit or buy an hbridge ic.. should be fairly cheap for that size motor, and then get the 555 to toggle the direction?

 

Instead of a cam like BMorse, it would be easier to use a offset crank pin. Look at how windshield wiper motors work. http://auto.howstuffworks.com/wiper1.htm
Then you just have to slow the motor down to the right speed.

 

Instead of a cam like BMorse, it would be easier to use a offset crank pin. Look at how windshield wiper motors work. http://auto.howstuffworks.com/wiper1.htm
Then you just have to slow the motor down to the right speed.

actually, (as I said) those widshield wipers DO use a cam to actuate

here is a quote from your link:

A short cam is attached to the output shaft of the gear reduction. This cam spins around as the wiper motor turns. The cam is connected to a long rod; as the cam spins, it moves the rod back and forth. The long rod is connected to a short rod that actuates the wiper blade on the driver's side. Another long rod transmits the force from the driver-side to the passenger-side wiper blade.

FYI: Here is what wiki says about CAM's and Cranks:

CAM

The cam can be seen as a device that translates from circular to reciprocating (or sometimes oscillating) motion

CRANK

The opposite operation, translation of reciprocating motion to circular motion, is done by a crank.

 

For display animation take a look at http://www.scary-terry.com/ And even more than you can stand http://www.halloweenmonsterlist.info/

Ken

 

Thank you guys, making a cam for the arm will be my best bet, thanks for all the help.

 

actually, (as I said) those widshield wipers DO use a cam to actuate

here is a quote from your link:



FYI: Here is what wiki says about CAM's and Cranks:

CAM


CRANK

Not to argue with you but look at the animation in the link or the wiper motor in your car and see if it looks like a cam or a crank. The text is some times written by some one that doesn't really know what their talking about.

 

Not to argue with you but look at the animation in the link or the wiper motor in your car and see if it looks like a cam or a crank. The text is some times written by some one that doesn't really know what their talking about.

Not trying to argue either, but to turn a rotary motion to linear you use a cam, and to turn linear /reciprocating motion into a rotating motion, you still use a crank.... and by looking at the picture and my windshield wiper setup, it uses a cam to move my wipers (regardless if it it just a small rod coming off of the motor shaft), anything coming off of a rotating shaft that converts rotary motion into linear is a cam regardless if it looks like a crank..... that is just my understanding of it, and it is the only logical explanation for those terms. If you find a different meaning somewhere else I would be glad to say you I was wrong....

 

Any cam I've ever saw has a follower. Any crank has a connecting rod. A crank also has a pin that changes the rotating motion to another motion by the connecting rod. Since a windshield wiper uses a pin and connecting rod to make the movement and not a follower it where for is a crank mechanism.

 

IMHO...

A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion.

A cam and follower is formed by the direct contact of two specially shaped links. The driving link is called the cam (also see cam shaft) and the link that is driven through the direct contact of their surfaces is called the follower. The shape of the contacting surfaces of the cam and follower determines the movement of the mechanism.

I tend to agree with Shortbus. a cam requires a follower; a crank is used to convert linear to rotary motion or vice versa.

How big is your Santa?