Voltage versus tether drag. Where is the optimum?

[jacko1]

Hi guys!

I did some experiments with my thrusters.

I used 350 gph thruster with 4,5cm prop in water bucket, powered by 25V lipo battery over 30 meter Cat5 (single wires).
The voltage drop was as expected, thruster got only 6 volts.

If i use thicker cables (i have 4 thrusters), and get.. lets say full 12V, does it pay off as the drag of tether increases?
I would love to have a light tether, but need to move the rov as well. So.. would my rov move if it only gets 6V per thruster? The rov is seafox- design and I am using
2x350gbh for ascent/descent and 2 x 500gph for forward/reverse.

-Jacko1

[jacko1]

I was wondering..

When I got the thruster running in a waterbucket, I got 6 volts in multimeter. When propeller got detatched I got 15V motor still running (30 meter 24awg cable). Is it so, that if I used 12V battery with thick and very short cable, I would see full 12V in my multimeter when submerged thruster running with propeller? Or would i see a voltage drop caused by propeller anyways? How much is the voltage I should be aiming when the thruster actually does work it is supposed to?

Sorry for my poor english and very basic questions. Really appreciate any help

regards,
Jacko1

[fluxno]

the reason for the voltage drop is the amps going trough the cable.
when you put the props on the bilge motor it gives the motor a load(high amps) but without the motor see no load, and the amp draw is very low = less voltage drop in cable.

The thicker cable, the less the amps will affect and give voltage drop.

in my opinion the easiest way of making sure you have enough power for the motors is to have the batteries close to the motors(on the rov)
and use the wires in the cat5 to control relays.

[scubersteve]

It's not just the drag of the tether due to size you have to worry about, it's also the flexibility or lack thereof that hinders maneuverability.

[jacko1]

Thanks guys!
Need to update my knowledge on basic electronics!
Tether mobility and drag seems both to be issues that cannot be escaped.

Some thoughts..
Tether is affected by its physical charachterics (buoyancy, thickenss, stiffness) but also the skill of rov operator and (if there is one) the cable guy. In scuba operations where tether rope is used, it is very important not to give too much rope out, since it will act as an underwater "kite" and will start pulling the diver if there is any current.

-J

[fluxno]

this genius app for android is really nice to check the voltage drop in a cable based on all the different values, it also has load of other nice electronic calculators and reference list.
https://play.google.com/store/apps/deta ... nica&hl=en
highly recommended!