James,
Actually, sailplanes can draw quite a bit of power, especially 6ch planes with digital servos. I have long been convinced that the reason for many crashes is due to catastrophic voltage drop-offs caused by high current loads.
FWIW I have calculated that my average current draw in a 6 digital TD ship (both an Artemis and a NYX) works out to around 325 mA. Compare that to my giant scale 40% aerobatic planes with 10 LARGE high torque digitals where I have an average draw of 2 amps. This was done based on calculating the amount of capacity consumed for a certain amount of flying time.
A similar set up with 14 digitals recorded an in flight average of 3 amps with a single 5 ms peak of 10 amps during a series of consecutive snap rolls.
This of course assumes that you are not stalling servos. And by stall I do not mean fully deflected under load. I mean mechanically stalled, which should not happen in a good installation anyhow.
I have never experienced a plow voltage lock out under any flight condition in either a glider or my large aerobatic planes. I know this for a fact since the Futaba radios have a low voltage lock out feature that moves everything to a preset condition and then releases it when you move a predesignated control (like the throttle/flap stick). This activates at either 3.6 or 3.2 volts. A I said, I have never had it engage under even extreme flight conditions. I am running a 2100 AA pack in my NYX right now. 4.8 volts and everything, seems to be just fine. Even in the aerobatic plane I have with high internal impedance NiMH I have never seen this happen, even when getting close to the end of the useful charge.
However, how many people think to check their packs under load?
As far as I know this is the only useful way to check packs. Of course the voltage tells you nothing about remaining capacity, but it does tell you what the pack is delivering under a certain load at that instant in time.
I have measured loads as high as 6amps on an Icon fitted with 3 DS3421s and 3 DS368s.
How did you measure this?? Seems unreasonable high to me. That is near full stall current on those servos, which I believe is around 1 to 1.2 amps. 6 amps means you stalled ALL of them.
> can easily cause a high impedance AA pack to
suffer a voltage drop long before they are fully depleted.
True enough, which is why it is a good idea to get the lowest impedance cells possible. In my big plane I run 3300 Sub-C cells with an internal impedance of 5 mohms. Under a 1.5 amp loaded check they drop only 0.24 volts. Compare that to a 2700 pack ("A" cells) with an internal impedance of 25 mohms. That drops off .85 volts under the same 1.5 amp load.
But the point remains unchanged, put the biggest capacity, lowest impedance cells in your plane that you can fit.
RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
