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Old Jan 02, 2006, 06:16 PM
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Blade CP2 - Tx Probs, servo probs

OK, it's been a week of practice for 3 of us on one Blade. Hovering in the garage, learned to slow down bigtime w/the learning curve.

Here's what we notice...

Barely touch the "elevator" stick and the servo jumps and jitters up and down. Applied slight pressure on the PC board attached to the "elevator" pot on the TX and it disappears, for a few flights.

Applying full up "elevator" there is a jump in the throw as if there is a gear binding in the servo (in normal flight we never go there...yet).

Sorry for the lack of knowledge in terminology of the surfaces, hope you get the idea.

Anyone else experiencing this???

I'm 99% convinced this needs to go in for service.

AARRRRGGG. Just about the time we figure out all kinds of wonderful stuff (balance, throws, tweaking here there and everywhere), we spot disturbing problems.

Thanks for your input.
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Old Jan 03, 2006, 12:12 AM
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Fort Worth, Texas
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Old Jan 03, 2006, 12:41 AM
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San Carlos, California, United States
Joined May 2002
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I don't have a Blade CP, but this sounds like a potentiometer problem.

If you look at a transmitter joystick, there are two electronic devices mounted in the gimbals of the joystick, with either two or three wires going to each device. These devices are called potentiometers, or sometimes rheosats.

These are basically sensors that detect the rotational position of the gimbal. They are basically variable resistors where the resistance of the device is equal to the rotational position of the gimbal.

There are basically two types of construction used for potentiometers.

The first type of potentiometer is a wirewound potentiometer. In this type of device, there is a torus with many turns of high-resistance wire wound through the center of the torus. (Not the way women wrap hair around a hair curler...but through the center of the torus for each turn of wire). There is a rotating wiper arm which touches the wire, and the insulation is scraped bare at the touch point so electricity can be conducted. The resistance of the unit is directly proportional to the rotational position of the shaft attached to the wiper arm because the wiper arm makes contact at the wire at a farther distance depending on the shaft rotation.

This type of wirewound potentiometer is of good quality and is very reliable.

The other type of potentiometer is a carbon composite potentiometer. Instead of using a torus with loops of wire wrapped around it, this type of potentiometer uses a partial torus of high-resistance carbon composite material. The wiper arm rotates along the carbon composite material and the resistance is directly proportional to the shaft position, as in the wirewound potentiometer.

The carbon composite type potentiometer is of lower qualtiy and less reliable than the wirewound potentiometer for the following reason: as the wiper arm rotates along the carbon composite material, it scrapes off material and builds up "gunk" which makes the potentiometer jittery and unreliable.

Since the Blade CP is rather a cheap helicopter, I suspect the transmitter uses low-quality carbon composite potentiometers rather than high-quality wirewound potentiometers. If this is true, then there are at least three solutions to this problem which I can think of offhand:

1. The cheap solution is to squirt contact cleaner into the potentiometer periodically to clean out the gunk. Contact cleaner is available at most electronics shops such as Radio Shack:

http://www.radioshack.com/product/in...entPage=search

The contact cleaner can should have directions printed on it, but if it doesn't, you should squirt a quick burst of contact cleaner into the potentiometer, then move the joystick back and forth several times to clean off the wiper. You may need to repeat this process a few times for best effect.

2. A better but more expensive solution is to replace the carbon composite potentiometers in the joystick gimbals with wirewound equivalents. This would require sourcing a wirewound potentiometer with the equivalent resistance range and physical dimensions of the stock potentiometers. Electronics supply houses such as Digi-key would be the best source for such replacements.

3. Probably the best solution is to replace the transmitter with somethiing decent, such as a JR/Futaba/Hitec/Multiplex transmitter. As far as I know, all these transmitter manufacturers use good quality potentiometers that do not have jitter problems.

Toshi
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Last edited by TMorita; Jan 03, 2006 at 12:52 AM.
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Old Jan 03, 2006, 01:09 AM
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I forgot to mention the wirewound potentiometers generally cost more becuase the manufacturing process is more complicated.

For a carbon composite potentiometer, the resistance element is molded in a machine, which is very simple, very fast, and very cheap.

For a wirewound potentiometer, the reistance element requires a few hundred or more turns of wire be wrapped very neatly and precisely around a torus. This is a more complicated process which results in a more expensive product, albeit of much higher quality.

Toshi
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Old Jan 03, 2006, 07:12 AM
Vintage Flyer
Treasure Island, FL
Joined Jan 2002
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As all early Kraft and Heathkit RC owners know, wirewound pots in RC transmitters were abandoned about 30 years ago... why? if it fails, it's catastrophic.... the channel goes to the extreme throw.... if a composition potentiometer fails, it's usually a case of "noise", as noted above, and one can "usually" still get the model down....

PS.... I work for a company that makes both kinds... one of the few survivors
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Old Jan 03, 2006, 06:01 PM
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Quote:
Originally Posted by FenceMagnet
As all early Kraft and Heathkit RC owners know, wirewound pots in RC transmitters were abandoned about 30 years ago... why? if it fails, it's catastrophic.... the channel goes to the extreme throw.... if a composition potentiometer fails, it's usually a case of "noise", as noted above, and one can "usually" still get the model down....

PS.... I work for a company that makes both kinds... one of the few survivors
Then I guess the better-quality transmitters just use better-quality composite potentiometers where the material doesn't gunk up the wiper?

Toshi
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Old Jan 03, 2006, 06:42 PM
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Toshi, sometimes you impress the hell out of me. Thanks for the wisdom, its' nice to know how things work. Regards, Crewdogg
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Old Jan 03, 2006, 07:35 PM
Team Compass/KBDD Team Pilot
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Joined Mar 2005
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Fatboy,

I would contact EFlite and let them know about the problems with your transmitter. Although I have not had to use it yet, their support is known to be excellent.
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Old Jan 04, 2006, 08:10 AM
Vintage Flyer
Treasure Island, FL
Joined Jan 2002
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"Then I guess the better-quality transmitters just use better-quality composite potentiometers where the material doesn't gunk up the wiper?"

yes.... the cheapy Noble pots are screened carbon material, and a bit soft... the better pots, like CTS or Spectrol or Bourns (all mid-quality BTW) are molded carbon... quite a bit harder and more durable...

wiper design is a whole 'nother ballgame...

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