Morning Dave, the rudder servo works fine so that's that one out. I do have another motor that came out of an old rc glider, the motor is a simprop Power-Speed 1500-10 12 volt. I'll try this one later today and post the out come. Thanks for your help Dave
Steve.

Yes 2.4 is pretty interference free, but you do need to separate the dirty high current wires from all signal wires. I very old motor may be generating lots of interference and could benefit from some suppression. The ESC is also subject to interference and if this is an old VIPER unit there was a faulty batch sold several years ago but I have had no problems with the several I have used in recent years.
I believe you have ruled out battery and plug problems and the finger is pointing to a motor/interference problem.
I am assuming you can still control the rudder servo at a greater range with the motor not running? Some modern radios have a low power range test mode which may be causing the short range.
Can you try another motor? it could be any motor and not fitted in the boat, if the symptoms disappear you will have found the problem.
Good luck
Dave

Hi Dave, Radio is new 2.4 so am I right in thinking that rules out the interference ?

The 8.4 battery that I also tried is also new and the same was happening with that battery plugged in.
I think I am going to try a New 7.2 volt 3000 mah battery and see how that goes and if I still have the problem the look at perhaps a new motor which has been in the boat for over 10 yrs and sat still for 90 % of that time.

Hi Steve
What radio gear are you using? if it's not 2.4 is the aerial above the deck? is the motor suppressed? Are your heavy current wires remote from any receiver and servo wires?
Your symptoms sound more like radio interference than battery power problems.
The advice given so far should help you solve faulty wiring and batteries.
You do need good connections between the battery and ESC and motor. Electrics deteriorate over time and I have found the Tamiya type connectors to be unreliable at high current. I used to squeeze the female socket together and clean the male plug with fine sandpaper.
Another common problem with older equipment can be corrosion in any of the black wire connections. I recently repaired a 7.2v NiMh that gave correct voltages but failed under load. The problem was corrosion inside the black wire where it had been repeatably bent when being fitted in a boat. I traced it to a thinning of the wire near the battery. Pulling on the wire resulted in the copper parting where it was rotten. There should be little or no give in good wiring. Replacing the wire restored the battery to full working order.
Good hunting and I hope you find a solution.
Dave

No Steve

I don't think you need to replace the ESC with a higher Amp ESC,
I would how ever follow JARVO's recommendation and try the light as a load maybe you have a bad battery.

So are you saying I need 30/ 40 amp esc?

Didn't think of that doh lol ok I'll see if I have a 6 volt and give that a go thanks. it's amazing isn't it put a few heads together!!

Hi Steve, your comment about the battery seeming flat but showing 7.2volts. it could be that the battery capacity is nil or very low, put a 6 volt bulb across the terminals to act as a load, then monitor the ammeter, if the amps drops very quickly the battery is dead. Hope this helps Mark

Steve

The RE380 Motor has a Stall Current of 25.19 Amps at 7.2 volts so if you are using too much volts it will trigger the safety on the ESC.
If anybody degrees with my analogies please interject!

Hi Steve

Why don't you try a 6 volt or 7.2 volt battery instead, I think the motor is being over driven.
so the safety on the ESC is being tripped try this and see if it works.

Ok I have tried to re set the ESC which made no difference, its almost as if the battery is running flat but put the battery on the volt meter and its fine. ???

The solder points seem to be ok. I'll try really setting the esc and see how we do with that. it only seems to happen wwen under load ie in water, out of water is fine.

Hi Steve

Did you check the batteries on the controller itself.
try resetting the ESC, did you look at the solder points on the motor.

Ed