running Dragonfly off car battery - RC Groups
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Oct 04, 2003, 08:38 AM
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running Dragonfly off car battery

Gooday, i'm new here. I've got a Dragonfly/Hummingbird,etc.
I'd like to run it off a 12v car battery while i'm learning.
Does anyone know the maximum input voltage a FEDA mixer/speed controller can tolerate without frying? I know it says 8.4v but a fully charged 8.4v/600mAh NiMh reads 10.5v unloaded
and someone was flying his Dragonfly on 10.5v Li-ion .
You can't use a resistor because at 5A plus it decreases the voltage to 4v. A 10A dc regulator costs more than the chopper.
And i've even tried feeding 12v into an ESC throttled down so it gives out 8.45v but at 5A plus the ESC on the chopper cuts out intermitantly.
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Oct 04, 2003, 09:04 AM
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imeins's Avatar
There are example circuits on the National Semiconductors web site for the LM317T regulator where a shunt power transistor is used to increase the output current from 1.5A to ???A. This or a switchmode regulator would be okay. The switchmode will not suffer from the considerable heat problems a linear regulator will have. You are right, a resistor won't cut it ! You will still need ballast in the heli to balance it, since you won't have the battery in place. Also if running for long periods I would not run it at 10+ volts, the motor already runs warm to hot as it is. The LM317T with extras would set you back about $10AU but you will need the electronics knowhow to put it together, or a mate to do so! An ESC won't reduce the voltage, what you would have been seeing is the average voltage appearing to be 8.45v whereas you are really just belting out pulses of 12-13V from the ESC at a lower duty cycle (ratio of off to on pulses). You could buy a couple of 1200mA/H 2s1p etech lipo and get longer flight times like that. Of course that would set you back $130+ charger.

Oct 04, 2003, 07:16 PM
Registered User
Imenes, your a champ. i tried to include everything i'd done.....i forgot to mention the battery is strapped in there for CG purposes. Your right about the ESC belting out square wave pulses. I tried to smooth'em out with 2500mF caps but all that did was interfere with the working of the ESC pot. I've found you can't use any regulated supply because to get an output of 5+A
at 8.4V, the terminal output is always 12+v........only nicads (or car batteries!) with there low internal resistance can show terminal voltages of 9.6v dropping to 8.4v under full load.
I'm going to try my trusted solution of 6x 10A diodes in series.
I used to do this before Esc 's were invented to replace the resistors in Buggies. All the current goes thru but you lose 0.5v per diode. I'm finding just as i'm about to 'click' with this hovering thing, the battery dies!
Oct 04, 2003, 11:46 PM
Registered User
imeins's Avatar
Don't burn your fingers on those diodes.
Here is an example of boosting a normal 3 terminal regulator. They are available in an 9V version (7809) as well.

A lot of heat dissipation though..

Have fun!

(does the telecom bill have anything to do with being (or ex) telecom tech / liney ?, I spent 9+ years in the broadcasting branch).
Oct 05, 2003, 06:10 AM
Registered User
You got it Ingmar , although i've never worked for Telecom/Telstra.
I've got my Austel licence and do all the phone / data/intercom/
fire work . I was taught by a couple of ex-telecom dudes who got there big payout but continued to work to stay sane.
Yes i did burn my fingers so i paralled 2 strings of 4 x6A diodes.
Works perfectly because as the terminal voltage drops i shift to 6 diodes , then 4 ,etc till the battery is dead.
I wish i could fly as well as i know electronics. Do you know how to setup the PG-03 gyro...........setup and gain?
My tails hard to hold steady.
Oct 05, 2003, 07:01 AM
Registered User
imeins's Avatar
Hold everything still, adjust the setup till the led is bicolour. I have the gain set almost all the way up. I understand (could be wrong!) that if the gain is too high the tail may start to wag from side to side as it overshoots.

I left Telecom with a redundancy, could not understand how they justified having a tech, tech officer, supervisor and full time cleaner sitting on a hill all day everyday watching play school for all those years! Then I went off and played computer tech / cabler for several years before going mad and becoming a cop! Albeit a full time programmer/cop.

Told you about those fingers.