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[david48]

Component shop do a voltage dropper ,round about £3 ish it's not very big have a look at the Action part ofthervweb site
David

[PICKETBOAT]

Subculture


I understand completely but I will have to think hard as I don't think I have room for another ESC.
 A bit clumsy but what about a small resistor wired between the switched power and the pump. I know it wastes power but the pump will only be used infrequently.

[Subculture]

What are you using to control the pump? You would only require a very small esc.

A power resistor would limit current, it is more wasteful than chopping the current, which is what an ESC would do, plus putting heat into a cylinder isn't my favourite solution. However, as you correctly point out, you are only likely to run the pump for short periods. Finding the right resistor rating will require a bit of trial and error. You might want to start with a 10 ohm power resistor of 4 watts rating or higher.

[PICKETBOAT]

Subculture


Thanks for this info it's a good starting point.


The pump is being controlled with a 9g mini servo working two very small micro switches. This will run the pump in two directions (fill and empty) when the servo arm moves. When the servo is in the centre point a plastic cam will pinch the silicon feed pipe to the ballast tank. If I don't then the water will slowly leak through the pump and fill the (vented) ballast tank and C1 will keep slowly going into dive mode!
I think I will try the resistor method. I am using the little 1amp ESC from Action (Component Shop) to control the single main motor and I have only just enough room for this. I cant fit another ESC in as well. I will post some more detailed pictures of the WTC internals as they get installed.     

[Subculture]

You can get very small ESC's these days. I have some of these, and these are the large models they produce. They do much smaller versions little more than the size of a servo plug, but with a 5A continuous rating- should be enough for a pump. The one thing I would caution on is not to use the BEC, as they wouldn't be man enough for more than one servo to hang off IMO, especially if you're running higher voltages.

[PICKETBOAT]

Thanks Subculture


This would JUST fit and I might use it. I am also looking into the little voltage  stepper, produced by Action (and kindly flagged up by david 48). I will keep you posted on how it all develops. My first sub is turning into an interesting learning curve.


Thanks again

[hollowhornbear]

Where do you get those esc's Andy?

[Subculture]

Here you go-

http://www.cti-modellbau.de/CTI-Fahrregler/

They have an extensive range. Great little brushed ESC's.