Current draw, anyone have any figures ?? - RCCanada - Canada Radio Controlled Hobby Forum
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Old 05-02-2008, 02:59 PM   #1
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Current draw, anyone have any figures ??

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How many amps would different setups draw?

1) 40 size trainer- with 4 standard Futaba servos ( 1 elevator, 1 rudder, 1 aileron and 1 throttle )

2) Biplane with 4 aileron servos ( ds821 digital ), 2x analog hitec 625 mg on elevator, 2 x hitec 625 mg on rudder. and 1 hitec standard servo on throttle.

Thanks for an info.
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Old 05-05-2008, 08:09 AM   #2
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Re: Current draw, anyone have any figures ??

[QUOTE=Bdegan;525239]How many amps would different setups draw?QUOTE]

This is not an easy question to answer. The receiver alone, would draw a constant and measureable current, but servo current draw varies from very low (uA) when idle to hundreds if not thousands of mA when moving and even more if it stalls (Depends on servo size and application). Add to this that even using the same servos, you will get different values depending on the setup of your linkages (due to load on the servo to drive the surfaces) - and this will change in flight due to surface loading caused by the airflow over / under the surface....)

Very difficult to be specific....

Even trying to measure the value with an ammeter is difficult because with a digital meter the reading is too erratic to get a true figure and with an analog meter the needle may not respond fast enough to give a true reading.

You didn't say why you need to know, so I'm assuming that you're trying to determine how long certain setups will last in the air (i.e., flight time). If so, then one way I use to come up with a decent figure is to charge my plane fully and then hook up a voltmeter to one of the receiver ports (a Y connector works if there are no ports open) and monitor the voltage. For a 4 cell receiver pack, I use a lower figure of 4.4V (1.1 V/cell) as my cutoff. My radio has a function called "Servo" where it moves all the servos from end stop to end stop at a constant rate. I turn on this function and then time how long it takes for the voltage to drop to 4.4V. I then use 70% of this value (Personal preference) as my flight time. In the air, the servos don't move all the time so this value is probably very conservative, but still gives me about 6-8 fifteen minute flights on a charge (4 servo setup = Throttle, Rudder, Elevator and Ailerons). Better to be conservative and charge when you get home than to push it and have to rebuild... Just as extra insurance, I have a volt monitor in each plane that turns off a high intensity green LED when the battery drops below about 4.5V - No green = No fly.
Regards, John.
MAAC 33776.
My planes gotta be up there somewhere....
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