RX battery

[sihinch]

I need some help again, please. RC help, before any of you smart-Alec's give me a hard time!

I am trying to decide whether to use a separate BEC from a 6S 5000mAh lipo or an RX battery. It is for a 90mm EDF, so I think I can afford the weight of an RX lipo/life battery.

How do I decide how many mAh I need for an RX battery?

Thanks,
S

[Bobmic]

How many servos and how big are they?
What about retracts?
I would guess that 3Amp will be enough unless you plan to have some realy heavy duty servos and the plane will pull some major Gs but since it is a foamy I doubt it will be much.
Add the idle current of all servos the servos + let's say stall current for the elevator + some margin above that in case you decide to check how flexible arethe wings.
For reference the Hitech MG82 on the Sundowner when pulling 8g was drawing less then 400mA and idle current per spec was around 220mA so 1.5A should be enough for that plane (I took some extra since I have never measured the current required for the ESC).
As for a sepparate battery you can pick one between 1300 to 2000mAh, and for an EDF even smaller will work with no problem cause your total flight time will not be too long.

[sihinch]

Thanks Bobby.  So if we did say 3A, what size RX lipo would that be?  In mAh?  That is what I am trying to get to.

It will be 5 servos (12g) plus retracts (.46 size.)

[Bobmic]

... I just edited my post... 5 servos and retracts?
How long will you be flying? if we assume even 2Amp draw a 1000mAh will keep you flying safely for 15-20min flight time.
If you are using MG16's send me an SMS tomorrow afternoon and I will measure the current draw on these.

[Ededge2002]

If your going to a separate rx pack then I would highly recommend using a LiFe pack. As they are 6Volts when charged no regulator is required. One less point of failure. Just another option.

[Wingnutz]

Think preceding certainly caught my attention as I'm trying to figure out the requirements for the 90mm EDF I 'm building. Mine will have five servos if it's hand-launched or six servos plus retracts if the retracts are plugged in. The ESC is an opto model and I'm planning to use a separate rx battery.
Same recommendations as for Simon?
I'm familiar with NIMH rx batteries from glow models...do they make good rx batteries in this application?
In terms of "powering up" the model, tx followed by rx followed by motor battery?