Thanks for your input gents looks like a big rethink is on the cards. Dave I think that YouTube video is a bit over the top for my little tug.withall the heavy engineering I am surprised that there were not any metal bracing so between the drivers and driven gears. I will contact the servo shop to see what they recommend.
Havelock there isn't any provision for a pull pull system so I will beef up the control rod by soldering/reinforcing it.
And yes they are the Schottel drives that I will be using. Thanks agaI n
Steve.

sorry it seems the plus doesn't come out in posts even though it does when creating.

http://www.cornwallmodelboats.co.uk/acatalog/CEM040.html

is that the unit your using?

if so you need a beefy servo ( 1/4 scale type) with metal gears. The reason you need high power is that the system tends to self steer and you need to overpower this.

if you can arrange for a pull-pull ( two pushrod) system since a single rod is fine pulling but may well bend pushing.

HI Steve
I can't find the cem040 drive via google but U -tube produced . The steering is continuous on this design but other units suggest 90deg servos scaled up to 180deg. in this case they will need to be metal gear and high tork. I would suggest speaking to some one at Servo Shop in Frodsham as they stock many servos and should be able to offer you advice on the correct servo.
Sorry the ( ) plus sign was omitted from my last post and does refer to positive
dave

HI Dave,thanks for the reply, I Take it that VE means positive ? As Haverlock and yourself use the expression. The drives I am using are the CEM 040 Schottel drive units on a 2ft long tug so I think it will be a (suck it and see) situation.

HI Steve
Servos were originally designed for model planes and in the early days we typically had 4.8v DEACS for batteries with possibly 500Ma of current.
Move on a few years and the position evolved to provide much more powerful power supplies and BEC circuits built into the Rx or Esc. Power was still limited and many rx bec's will only provide about 1000 ma.
There are now several types and size of servo from the minature designed for park flyers to high power digital servos for large scale models.
For most model boat applications we use standard analogue servos so I will confine my comments to this type. Each servo is capable of drawing quite high currents (

Thanks for that Haverlock,what a can of worms,there are at least 2500 different types so where do you start when deciding which ones to use ?

Going back to the feeds for the servo it looks like the three wires are pos,neg and what I call a trigger wire,so as long as they come from the same power source that's fine ?

I am building a harbour tug with azimuth schottel drives with 180 degree steering and using astern for the other 180 if that makes sense both drives independent of each other. is there a gyroscopic reaction that would make it necessary to use heavier servos ?

nominal voltage is 5V

current is dependant upon the particular servo type ( big - small slow -fast)

The current draw is however small enough that a radio receiver can support a number supplying them with voltage ,current , and , signal.

One of the factors is the actual loading upon the servo so current draw is not a fixed value.

http://www.servodatabase.com/servos/hitec

That website should provide some data for you to at least begin with.

if for some reason your expected usage would require very heavy current then one would take the ve lead away from the receiver and connect it to a supply. So long as the negative leads from that supply and the receiver supply are common.