The Cyprus peanut scale twin engine F104

BB, I think Simon was teasing - we all know he's a skinflint! [badass]

No it's by far not the first time

[badass]
Quite right BB

BB
My apologies.
The comment was not intended to be any sort of criticism. I simply can't afford to build such a model - I only wish I could!
I will be following with interest!

A question, on a model that has 7v power supply like my jets that go's through a power box switch that converts it 6v to the receiver, could a high voltage servo :ie 7v be used if the power red wire was connected direct to the servo through a separate switch
I think it would be OK, but then I know nowt

Without knowing much about turbines (other than I can't afford them!) I'd say yes.
BUT - where is the 7v coming from? It's an odd voltage! A 5-cell nimh gives 6v, and a 2 cell lipo gives nearly 9v when freshly charged, and drops to 6.4 at the end of a charge.
So - it depends on how 'clean' and stable the 7v is - no electronic noise sneaking in via the power line, to corrupt the digital output signal of the receiver.
Perhaps someone more turbine-wise can answer.

Hi Eric, the high voltage servos are designed to run off 2 S lipos which is where the power would be coming from, normally the power gos through a high voltage receiver
As I will be using a normal Futaba receiver I wondered if I could run the power line, red wire, direct from lipos to servo through a switch, with the black and signal wires going into the receiver
The reason for asking is the servos I was going to use and what I built for were normal voltage but if I use the high voltage version of the same servo I get twice the power from it with no increase in weight
or sized
It has nothing to do with the turbine as it has its own life battery

BB
What you are proposing is used in RC trucks where big digital servo are used. The receiver takes only its own power directly from the battery and just provides the signal to the servos.

Thanks for that info Simon, pleased I had it right, so for just £3 extra per servo I can double the power
Just what I need

I see, You run the receiver from a BEC, and the servos from the high voltage.
A bit like electric flight backwards, where the motor gets the high volts, and the rx and servos run from the BEC. [badass]
So, yes, disconnect the red wires from the rx plugs, and take them to the 7v battery, and a BEC from the 7v to the receiver, but don't forget you need a neg (black or brown) wire to BOTH rx and battery, or nothing will work.

Hi Eric, I was thinking the black wire would run with the signal wire through the receiver to the battery

BB
Just make sure your black wire return path is as 'sufficient' as the red. It is after all carrying the same current and you don't want the rx in particular not see the exactly the same "0" volts as anything else.

In that case Simon I should run the black wire straight back to the battery bypassing the receiver
Thanks for that, don't want to kill the expensive Futaba receiver

THE BLACKBIRD wrote: Hi Eric, the high voltage servos are designed to run off 2 S lipos which is where the power would be coming from, normally the power gos through a high voltage receiver
As I will be using a normal Futaba receiver I wondered if I could run the power line, red wire, direct from lipos to servo through a switch, with the black and signal wires going into the receiver
The reason for asking is the servos I was going to use and what I built for were normal voltage but if I use the high voltage version of the same servo I get twice the power from it with no increase in weight
or sized
It has nothing to do with the turbine as it has its own life battery

If your 2S LiPo is only giving 7V they are dead and you're about to crash, or probably just did because you're now measuring them.

2S should measure up to 8.4V when charged and we stop using them for flying at about 3.7V each or 7.4V. But assuming the servos are designed for use with 2S, these voltages will have been taken into account, unless the correct Rx has a 7V BEC designed in, which is a completely non-standard voltage for electronic devices, so I doubt it.

I would design a 2S + GND bus system around your airframe to carry the power (sufficient current) to the servos with a BEC set for 5V powering the Rx, as others have suggested. The Rx ground should be common with the 7V power supply ground and the servo signal wires are the only link from Rx to servo. This sort of system is available and properly designed from SM Services(sp?) who supply systems to the LMA boys in the UK, including dual Rx redundancy. I think that sort of thing is mandated for LMA models to be allowed to fly under FAA exemptions. I'm not sure how heavy your auw is expected to be, but it might be worth a chat with the guys there.

Hmmm, the forums suggest SM ceased trading due to retirement. Mainlink is another name. However, the LMA must have a supplier so I'd go there first. Just my two pence worth, good luck.

HTH, Nigel

Thanks Nigel, it. Is for my A10 I have 4 servos in the tail, 2 for rudders and 2 for elevators it was the 2 elevator ones I was looking to power up from 4 kg to 8 kg without adding more weight to the rear end