next topic »

[on:]

Hi all,

I am building...let me re-phrase, I am trying to build a little ROV to play around in the pool up until this afternoon I thought everything was done but then added 20 meters of telephone cable to use as the umbilical ( 2 wires for PWM and the other 2 wires for + and - terminals) but for some reason the servos will not take power through this cable any ideas as to why not. I hooked the far ends up to a multimeter and get the required 5v and the PWM signal works great through this cable even at this length.

I am using an arduino uno and 4 core telephone wire.

thanks in advance for any insight.

[Reply #1 on:]

You might get the voltage with no load (the meter), but with a load (the servos) - things might be much different. Likely, with a load attached, your voltage drops (maybe to almost nothing).

I would abandon this approach; put a power source on the ROV itself for the servos/motors - then just send your signals for the servos down the line (remember to connect the grounds).

[Reply #2 on:]

Well, 20m of AWG24 cable -- 40m for round trip -- does have a significant resistance.  If the load at the far end exceeds a few 100 mA, you will be getting a pretty substantial voltage drop.  Maybe enough to put you outside the operating voltage range of the servos.  This would most likely show up as the servos acting weird when they are working hard though, rather than as a not work at all situation.

It's not clear why you have a PAIR for the servo control.  Shouldn't the servo control signal share the power ground?

If the power and control grounds are separate, have you connected them somewhere?  Ideally at BOTH ends of your long run?

Some sort of failure to connect the grounds is my bet.

[Reply #3 on:]

I've operated a servo over ~12' of cat3 phone wire. What is your power supply to the servos? Servos actually operate only so-so on 5v (4.8v is the usual minimum value). Operate the servos at near their max spec voltage of 6v. You might put a UBEC on the ROV to supply power to the servo, and run the max voltage for the UBEC on the phone wire.

[Reply #4 on:]

Thanks cr0sh and everyone else,

As it turns out it was just a voltage drop, upped it to 10volts now running fine. 

thanks