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Old Apr 21, 2004, 12:11 PM
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blueprints's Avatar
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Johnson, Like 90 & 2 cell 3 Inch hover

Need some help here. Im flying a FEDA DragonFLy these r some of e parts i hv on my heli,

Like 90 blades
Johnson motor
Stock speed controller
10T Pinion
2cell Kokam 1500
stock tail (await mttb dual tail setup)

I cant see to fly any higher than 3 inches off the ground. Im at full trottle n it juz hangs at that level. Wad could be e problem? could someone suggest on this. Would changing a pinion help? bigger or smaller pinion, how many T? Would hving 3 cell be better, e only thing i worry is dat my speeed controller can't take e voltage. Anyone here using 3 cell on ure stock DF speed controller? Can u guys tell me wad i could do. Anyone knows of where to get kokam 1500 cell? thanx


Jem
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Old Apr 21, 2004, 02:17 PM
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well it sounds like a problem i had with my piccolo pro... Check the gear on the motor to ensure that its not slipping... if it is then use a little crazy glue.
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Old Apr 21, 2004, 02:59 PM
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Halfmoon Bay, BC, Canada
Joined Feb 2002
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Hello blueprints.
This is exactly the same setup I run on my bird except for the tail and I have no problems at all.
First things to check are the main gear mesh. Make sure there is some play in there or you are losing power and drawing too much current.
Second, check that your battery is fully charged. I get over 15 minutes with that setup of lively flying.
Also, what connectors are you using? Go with the deans ultra for best performance. Deans micro are good too.
Your electronics should be OK on 3 cells, but you should be able to run on 2 cells no problem. Perhaps try a different motor. I have heard of some of the johnsons not working well from the start. They are super cheap remember.
co
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Old Apr 21, 2004, 03:44 PM
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Rumson, NJ
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try a higher voltage battery. i prefer 3c, lots more power.
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Old Apr 21, 2004, 04:13 PM
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United States, WA, Olympia
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I used to be a big 3s advocate, but given the extra heat and wear on the batteries, I'm happier with 2s packs now.

All johnsons aren't created equal (or so I've heard). Could be you're just $0.50 away from a fix!
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Old Apr 21, 2004, 04:31 PM
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I have had a problem with one of my Johnson motors as well. But for .50 cents who cares, unless it is your last one.
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Old Apr 21, 2004, 07:21 PM
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Palm Beach, FL
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I'd check to see if pinion is slipping as sunny suggested. If it's not then a 3 cell would get you airborne for sure with plenty of power, less amp draw and a tad heavier. The hummingboard should take 3 cells fine.


www.b-p-p.com sells the Kokam 1500 cells seperate I believe.
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Old Apr 21, 2004, 08:00 PM
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[QUOTE=ChrisT88]I'd check to see if pinion is slipping as sunny suggested. If it's not then a 3 cell would get you airborne for sure with plenty of power, less amp draw and a tad heavier. The hummingboard should take 3 cells fine.


Just curious - How do you figure it will have less current draw with added cell?

Thanks,
Mark
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Old Apr 21, 2004, 08:05 PM
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More voltage = less amp draw.
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Old Apr 21, 2004, 08:28 PM
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United States, IN, Martinsville
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>>>>>>>>>>>>>>If it's not then a 3 cell would get you airborne for sure with plenty of power, less amp draw and a tad heavier.<<<<<<<<<<<<<<

Uhhhhhhhh...........the last time I checked Ohms Law applied to helicopters the same as the rest of the world.....

I think what you ment to infer is that the watts would increase because the voltage increased and the current remained the same.

Remember current in a series circuit is constant.....voltage changes.....

Rick
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Old Apr 21, 2004, 08:29 PM
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Quote:
Originally Posted by ChrisT88
More voltage = less amp draw.
Ohm's Law would not aggree with that.

Resistance of the motor is constant. If voltage increases, current will increase as well. (This does not incluse the added weight of an additional cell.)

Mark
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Old Apr 21, 2004, 11:08 PM
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SO u guys suggesting going 3 cell. im hving a FEDA DragonFly so im not sure if 3 cell would burn the board. also adding another cell would be more work cos i made my own charger n solder e cells together... but i guess im still more concerned wit bruning my bard. would anyone hv any suggestions? think i really hv to go 3 cell. How bout going with higher pinion. Would that help? hows e relation of power n stuff wit higher n lower pinion? thanx for all ure help really appreciate it.

Jem
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Old Apr 21, 2004, 11:28 PM
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Quote:
Originally Posted by ChrisT88
More voltage = less amp draw.
That equation is wrong for non-pulsing DC voltage through non-induction resistor load (Ohm's Law). However, the helicopter controller produces pulsing DC voltage and the motors are inductors, thus Ohm's Law doesn't apply correctly anymore (not without considering the frequency). The whole circuit behaves somewhat like a Pulse Width Modulator (PWM) DC-DC converter (not that efficient though). Thus if the motors are to consume the same power level then more voltage to the controller does mean less input current to the controller in order to maintain the constant power consumption (the current and voltage at the motors are still the same - same power). Of course if you keep the throtle level the same then the circuit would draw more current at higher voltage, but then the motor would have more power (more voltage, current), i.e. more lift. I agree with Christ88, but that equation cannot go without description.

Now with all that saying, I don't know the specification of the controller, thus don't know if it could handle 11.1+V (3 cells). So I don't recommend it. However, people are having success, so go at your own risk.
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Old Apr 21, 2004, 11:39 PM
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Quote:
Originally Posted by mpj220
Ohm's Law would not aggree with that.

Resistance of the motor is constant. If voltage increases, current will increase as well. (This does not incluse the added weight of an additional cell.)

Mark
The motor resistance is constant for non-pulsing DC voltage, but the controller produce pulses. The controller actually produces short pulses at low throtle level, longer pulses at higher throtle, and straight DC at full throtle. The motor is actually an inductor. The resistance of an inductor is depending on the frequency of the input voltage (the rate and width of the input pulses).
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Old Apr 21, 2004, 11:39 PM
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i may be wrong, but I think ChrisT88 was speaking more in a practical sense

ie The higher the voltage of your packs (11.1 vs 7.4), then the less amps you need to draw to get the same power Watts.

I have no idea about ohms law and electronics, but this is how I understand the differences b/w 2 and 3 cell packs.

Is this correct ?
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