First post here.

I've got a small linear actuator that is controlled by a servo. The actuator's displacement is monitored through wipers connected to an Arduino. I want to have the actuator extend for x distance then retract to its original position.

The circuit shown is basically how I wanted to do it at first, just to keep it simple. Through a NPN transistor the Arduino activates the coil. While in normally closed position the actuator moves forward, but when the coil activates it stops moving until it returns to normally closed position and after a few cycles the contacts on the relay go kaput. Any ideas or advice on what I can do to get this setup working, or a similar setup to replace it.

Thanks!


Ignore the values in the schem. it's only a visual representation

 

circuit with relay contacts servo etc (part you think it is not working) is correct. if the contacts are welding or blowign up, it is because your relay is not rated correctly OR because you did not wire it according to circuit. I suspect that actual wiring is wrong and you get short circuit so relay contacts weld.

 

Well that's good to hear, I recheck everything and see if I have any luck.

Thanks

 

are you sure V1 and V4 are isolated from each other?

 

100% positive

 

Could you post specs on the servo ?

 

Try reversed diodes across the contacts. The inductance of the servo windings is rather high. This is the same type of protection afforded by a reverse diode across a relay coil.

 

What kind of relay will working on 1V?

The below is the general connection, transistor and arduino need a common ground.

 

@Tubeguy

Here are the actuators I'm using: http://www.firgelli.com/products.php?id=42

@Kermit2

That was going to be my next idea

@ScottWang

I mentioned that the values were not representative, the Arduino ouputs 5v to the relay coil and operates it properly. If I replace the servo with two leds they properly toggle on/off, I think the issue may be the relay: http://www.radioshack.com/product/index.jsp?productId=12477120&filterName=Type&filterValue=DPDT

 

The actuator's displacement is monitored through wipers connected to an Arduino. I want to have the actuator extend for x distance then retract to its original position.

Are you using the actuator with the limit switch option or the pot option?

Your circuit should work with the limit switch option, but if you are using the pot option then it appears power will be continuously applied to the servo in the N/C position. Not good for the servo according to the data sheet.

 

Hey guys, first off thanks for all the replies! Secondly I've got the circuit working properly, instead of flopping the outputs I'm flopping the input from the battery and that seems to be working correctly. I'm not sure why I didn't think to try that sooner, but I'm still slightly puzzled as to why the previous setup wasn't working right. I've included and updated diagram with proper voltages on the sources, so take a look if you want.

Again,
Thanks!