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[on:]

Hi, Just a quick one.

Would it be safe to power a smallish (I think) servo over Cat5 cable?
I hope that's not too vague.

The max length would be no more than five metres.

The servos are Acoms AS-17. I've tried to find a datasheet for the servos, but with no luck.
They would not be doing anything heavy, just panning and tilting a very small camera about the size of a webcam

I'm a newbie to all this so any help at all will be greatly received.

Thanks
Paul

[Reply #1 on:]

You'd probably be okay. You're not talking amps of current, right?
Cat 5 cable is 26 guage wire?
You can look up current carrying capability of wire & voltage loss over distance online.

[Reply #2 on:]

Cat5 is 24 guage, I am pretty sure that would handle the current for a servo ok.
At worst, you can double up the wires. Wikipedia says
Maximum current per conductor 0.577  A
So if you needed an amp, run 2 wires together.

Check these numbers also
http://en.wikipedia.org/wiki/Power_over_Ethernet

[Reply #3 on:]

I forgot who mentioned this to me on the forum but there is more resistance on the crimped wire like RJ45 than other types of connection, maybe screw terminals, and definitely more resistance than soldered wires.

To reduce contact resistance, you can use multiple wires in the RJ45 cable to pass power and gnd. Say you only need to control one servo motor, then you can chain 3 wires of the RJ45 together to pass power, 3 wires together to pass gnd, and 2 together to pass sensor.

If you plan to run both sensor and power down the same wire, you should put some filter capacitors between the power and gnd, to prevent the power to couple with sensor. In a project I did last weekend, I had to put a 1uF cap for my sonic ranger to work on 12ft of phone cord.

http://liudr.wordpress.com/2011/02/12/arduino-parking-sensor/

[Reply #4 on:]

Thanks guys, really appreciate the help.

It seems like what i need to do should be fine.

Regarding the contact resistence issue, i will probably be soldering the connections.
I am not using leads and sockets, I just have a box of Cat5e that someone gave me.

With the eight cores i can do the following:

3 Cores together to supply common +6V
3 Cores together to supply common Ground
1 Core for Servo 1 Data
1 Core for Servo 2 Data


Lastly ( I promise), will the data line to the servo be ok over this distance, or is it a case of suck it and see?
I suppose as long as i'm not going to set anything on fire, I can just try it.

Thanks again
Paul

[Reply #5 on:]

I've done several projects where I've used cat3 four conductor telephone wire between the servo controller and the servo, and had no issues.

[Reply #6 on:]

Try it  see. At the worst, you give up one power/ground and keep the data lines as a twisted pair combination with signal/ground.
But since you're not sending high frequency signals here, you're probably gonna be okay.

[Reply #7 on:]

If you have the solid conductors in your cat-5 wires, you might be able to solder them ok. Most cat-5 wires are stranded and almost impossible to solder or strip the plastic without breaking them. Just give it a try first. You may end up deciding on using the connectors and jacks.

[Reply #8 on:]

Thanks again guys, much appreciated I can assure you.

Seems like I have plenty of options going forward.

Being on a budget isn't always fun but, at least you use up the things around you.

Thanks again
Paul

[Reply #9 on:]

hi,

accidentaly in the past, i was work with several tests over the use of cat5 cat5 shielded and cat6, using it for transmit usb signal, video signal, audio signal, little voltage currents and more.
and i was found than for like 5mts or more, the voltage input of the cable if is 12v, the output voltage will be more high, like 2~6v high.

why? because the cat cable is twisted and it prevents to loss signal, so it amplifies, for it reason have for more long distance vs a cable than isn't twisted!

so be carefull is your sistem is very sensitive to the voltage, i recommend you to check before the output voltage with a voltimeter.

regards!

[Reply #10 on:]

because the cat cable is twisted and it prevents to loss signal, so it amplifies,

Are you saying that a passive cable amplifies a signal so you get more voltage out than you put in all because the wires are twisted together?

[Reply #11 on:]

because the cat cable is twisted and it prevents to loss signal, so it amplifies,

Are you saying that a passive cable amplifies a signal so you get more voltage out than you put in all because the wires are twisted together?

Maybe his hand-held multimeter is rapidly losing battery power so reading keeps climbing 

Just joking. I don't think there will be increase of voltage from passing DC voltage down a twisted pair, why did Edison not think of that if the passive wire did amplify? He was beat by the problem of DC.

[Reply #12 on:]

Well, sorry for the expression, would not refer to the literal sense, but the twisted cable acts as a kind of coiled but of course with much less spirals.

but if you don't believe me, you can search info in internet or make the test by yours, really i was surprise me when you try by accident