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ESC/Motor interference with 401 Gyro

Old 03-22-2009, 03:29 PM
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jdhughen
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Default ESC/Motor interference with 401 Gyro

I have a 60 size H9 spitfire converted to electric. (e-flite Power 60, Phoenix 80A, 5000mah 2x3cells). Using Futaba CAP10C, 2.4ghz. I use a separate 2700mah batt with switch circuit for the servos/receiver, the center wire from the BEC is disconnect as I'm not using lipo power for the rec/servos. The plane flies great once you get it in the air but have had problems with ground handling so decided to add a gyro on the rudder to assist in more scale like ground handling and take-offs. I have used futaba 401 gyros on squirrelly tail draggers and a twin with rock solid success but they were all nitro models. This is my first electric convert. After I installed the gyro I did some test and noticed some very strange and disturbing behaviors.

1. Anytime the esc/motor "chirps" or "beeps" the rudder has short but violent flutters in sync with each "chirp, beep"

2. Once the motor rotates, after RPMs get over approx 2500 you can see the rudder to start behaving erratically. With the gyro in "rate" mode, the rudder will flutter and as the RPMs increase the flutter becomes more violent and throws become larger, by full rev (approx 7500, with 15x10E) , it's shaking the tail and deflecting 3/4" in ea direction. If in "heading Hold" mode the rudder will vibrate slightly but then start to drift to the left as the rpms increase eventually reaching/holding full left deflection. With the gyro in OFF mode the rudder is rock solid at all RPMs.

There is obviously some interference being induced some place. The gyro is mounted in the fuse at the CG point and is approx 8" from the ESC and 11" from the motor, and directly behind the Lipo location. I have included a diagram of the layout, the power wiring, and a pic of the gyro mounting. The Gyro is mounted using the foam tape provided by futaba on a small platform attached to the main battery board.

I've read about twisting the wires and using ferrite chokes. Other than that are there any other ideas on how to cure this problem ??

thanks

Joel Hughen
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Old 04-10-2009, 12:12 AM
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freeair
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Default RE: ESC/Motor interference with 401 Gyro

Joel, most of your radio set up looks to be ok except for maybe the Gyro is too close to both the lipo and rx batteries. all i can think of is you should test this by removing the Gyro from the tape and hold it out as far as possible then see how things go.
Old 04-10-2009, 01:24 PM
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otrcman
 
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Default RE: ESC/Motor interference with 401 Gyro

Joel,

I'm not a rate gyro expert but do have quite a bit of user experience with them in full scale planes and in two models. First off, what you are seeing is the gyro getting some unwanted outside signal and amplifying it. The outside signal can be either structural vibration or electrical noise. Either one can drive the gyro crazy.

As freeair suggested, a good starting point would be to remove the unit from the plane and hold it in your hand. If your problem was structural vibration, the fluttering should stop as soon as you mechanically isolate the gyro from the plane. If it is electrical interference, you will probably find that the fluttering will increase as you move the gyro close to the offending motor component.

Since you mentioned that the rudder flutters even when the motor chirps, I'm inclined to think that your interference is electrical rather than structural. Also, you mentioned that your previous experience with the Futaba 401 was in nitro models. Perhaps that particular gyro is unduly sensitive to electrical noise. I've used a Hobby Lobby Icarus micro gyro in an electric model with no difficulty, and of course gyros are used almost universally installed in electric helicopters. Is the 401 advertised as being usable in electric helicopters ?

Please let us know what you learn. We'll all be wiser from you experience.

Dick
Old 04-10-2009, 02:05 PM
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Default RE: ESC/Motor interference with 401 Gyro

We ue those gyros all the time in electric helicopters with the components a lot closer together than that.

They can be sensitive to outside interference though if you have a bad component. Try mounting the gyro farther back, away from the ESC. Nothing says it has to be at the CG
Old 04-10-2009, 03:14 PM
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jdhughen
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Default RE: ESC/Motor interference with 401 Gyro

Thanks for all the replys.

The 401 is designed for helicopters and I know several guys in our area that use it in electric chopers. It has a carbon housing that is suppose to help shield it according to futaba. I think its electrical interference being introduced into the rec and being amplified by the gyro thru it's input directly from the recever. I hooked a scope up to the lead going to the gyro and can see the noise on it so I really don't think it's a mechcanical vibration problem as it's mounted on foam on a platform that mounted on foam and the vibration in the fuse is a lot less than any of my nitro models to start with. I decided to try several things before I move it's location. I had a lot of extra wire my ESC signal line was flowing thru (see original pics), y's / switch / etc , and a matchbox being used for aileron diff, all to try to get the most out of a 7 ch rec (2.4), and I had the esc control line bundeled with a lot of that extra wire and near (2") the gyro. Soooo... first I dumped the 7ch swaped it out for a 14ch (I already had a spare) so now I have 10 channels and extra slots for batt input and a cap filter (I use a CAP10c 2.4). I dumped the matchbox (will do aileron diff in the radio now), dumped the y's and shorten the leads on the gyro. (See pic below for old/new layout). Then I "Twisted" all the servo, esc and gyro leads and put Ferite RF chokes on the esc lead and the gyro input. I also am re-routing all the cabling so the the esc lead is on the oposite side of the fuse as everything else and crosses at 90 then it has to and goes directly to the throttle input on the rec (batt takes a totally seperate path now), and added a capacitor filter to the esc/rec input for extra overkill. As soon as I get this all done I'll let you know how it goes, I going to finnish it up tonight or tomorrow, I had set it aside while I waited for the ferite rings to come in and I got them today.

Thanks

Joel
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Old 04-10-2009, 05:00 PM
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Default RE: ESC/Motor interference with 401 Gyro

Twisting servo wires is useless.

Just so you know
Old 04-11-2009, 04:08 AM
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jdhughen
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Default RE: ESC/Motor interference with 401 Gyro

Well all that got rid of the majority of it but I was still getting the Flutters "shakes" with the "chrips" for the esc. So I moved the gyro back to the other side of the Receiver (see pic). It's rock solid now. I'll give it some time and see if the gyro makes it behave on the ground like it should and I might try switching back to a 7ch receiver, I have another plane where I really need the 14ch and I really don't want to buy another if I can get a 7 ch to work here. I've heard that it will not OK not being at CG but you would think that there would have to be some deg of accurcy loss by it being off the main rotational Axis ??

Thanks for all the replys.

BarracudaHockey, I've allways heard the twisted wire are less prone to picking up RF interference, is that just a myth ??

Thanks

Joel
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Old 04-11-2009, 07:48 AM
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Default RE: ESC/Motor interference with 401 Gyro

As long as its flat to the yaw axis it will work fine, whether you stick it in the wing tip or the tail. Flat, and isolated by vibration are keys to good gyro performance. Think about it, if the nose rotates 10 degrees, everything on the airframe rotates 10 degrees at the same rate. If you've ever seen a helicopter do 3D you will know that any other movent that doesn't effect the yaw axis is ignored by the gyro.

As for wire twisting its an awesome thing, it prevents a phenomenon called cross talk which occurs when pairs of wires next to each other are carrying a signal such as voice or network data. Since there's no pairs of wires carrying voice or data involved, and twisting doesn't do anything for lines carrying dc current (the black and red), and theres only one signal wire, twisting doesn't do anything for servo wires.

It does look pretty though.

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