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[Captain Flack]

Have just completed a powered "Duck" running a very small motor, MTronics Speed Controller , Radio Gear RX, micro rudder servo. 4.8v rechargeable battery.  Since its first outing it hasn't performed at all, with the thing coming to a complete stop after about 15 seconds on the water.
I have changed the speed controller, motor, battery and the wiring still to no avail.  I haven't changed the RX or the rudder servo.  Is it possible that either one of these is causing a dead short and draining the battery in 15seconds.
For such a small and simple  project it's causing all sorts of problems!!

[barriew]

Are you using the ESC to power the RX? If so, you need more  than 4.8 volts. Try 4 x alkaline batteries and it may last a little longer, or provide a separate power source for the Rx.

Barrie

[Captain Flack]

Thanks, but I can't see the motor draining the battery that fast, it's barely moving(as you would expect a duck to move)  Howeve,r I will give your idea a try, but I want something that is going to last a while not just half a minute or so.

[john s 2]

The battery voltage may be dropping under load.John.

[barriew]

Thanks, but I can't see the motor draining the battery that fast, it's barely moving(as you would expect a duck to move)  Howeve,r I will give your idea a try, but I want something that is going to last a while not just half a minute or so.

Sorry - should have given a fuller explanation of my answer. The BEC in the ESC needs a minimum voltage input in order to output sufficient voltage for the Rx. I think that this is around 5.5v (don't have Mtroniks specs to hand) so starting with 4.8volts you're already struggling, then the motor starts and this will drop the voltage further.

Hope this helps,

Barrie

[cuppa]

Barrie's advice is very sound.

Mtronics state a minimum cell count of 5 1.2v cells so the minimum supply voltage should be 6 volts for the Viper 15: http://www.mtroniks.net/details1.asp/ProductID/591/sid/2/Viper-Marine15-Plug-and-Play.htm

The Viper 10 has a minimum cell count of 4 1.2v cells so the minimum for that controller is 4.8 volts:
http://www.mtroniks.net/details1.asp/ProductID/185/sid/2/MicroViper-marine10.htm

Personally I would be a little wary of operating a speed controller at the minimum supply voltage because, as Barrie says, cell voltage will drop under load.

Cheers
          Jon

[malcolmfrary]

If it performed to expectations the first time, but not since, it might be that the loading has changed - i.e. the prop shaft might be binding.  This would have the effect of increasing the load on the battery, and if its max voltage was marginal in the first place, might just tip it rather rapidly.