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HelicopterScale Model RC Helicopters › First Hover tests - 4 blade head - UPDATED
11-23-2006 03:09 AM  11 years agoPost 21
Dr.Tim

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Mojave Desert

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High Headspeed will blow the head up!! Multiblade heads should run around 900 to 1350 tops depending on blade length.

From Simple minds come simple ideas! Approach Engineering

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11-23-2006 03:12 AM  11 years agoPost 22
racer944

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Greely, Ontario - Canada

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OK, I will try dropping the head speed down to around 1350 and see if that helps... It will be at the low end of the power band but should still be OK for the motor as its a pretty strong unit. I'm also going to try a set of 550mm blades which should help that too...

Cheers;
Eric

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11-23-2006 06:22 AM  11 years agoPost 23
Gearhead

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Vt

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""Multiblade heads should run around 900 to 1350 tops depending on blade length"",, well that the info you needed..

oscillation,, I would think you could get an oscillation if you had 1 blade with to much or to little lift ??

Jim

Jim
Buzz Buzz Buzz

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11-23-2006 02:24 PM  11 years agoPost 24
Dr.Tim

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Mojave Desert

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There are many Factors ... Headspeed is just One. Mechanics not mounted properly is another. Blades out of Balance .. Taking Off from a Hard surface ... and so on ..

From Simple minds come simple ideas! Approach Engineering

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11-23-2006 02:34 PM  11 years agoPost 25
rcadd1ct

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Richardson, Texas

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He is still test flying pod and boom, so fuse mounting should not be an issue.

-RCA .......... Making Cuisinarts Fly!!!!!!!

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11-23-2006 04:19 PM  11 years agoPost 26
AirWolfRC

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If the oscilation goes away when the gyros are removed, I think you have the answer.

Since nothing else is working, I'll ask the obvious,
is the pitch gyro mounted in the correct orientation ?

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11-23-2006 09:47 PM  11 years agoPost 27
racer944

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Greely, Ontario - Canada

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Yep, elevator gyro is indeed mounted correctly (triple checked). About the ony thing I have to go on now (for the gyro side of things) is to perhaps try a softer gyro tape (CSM type) under the assumption that vibrations are interfering...

For those that missed it, I have tried harder (Futaba type) with no success.

Thoughts?

Cheers;
Eric

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11-24-2006 02:57 AM  11 years agoPost 28
AirWolfRC

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I doubt that your low frequency oscilations are any where near the frequency of anything that might be related to the natural frequency of any gyro mounting tape.

The reason I askec about the gyro mounting is if it's off axis, it might be inducing some oscilation.

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11-24-2006 03:18 AM  11 years agoPost 29
rcadd1ct

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Richardson, Texas

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I would look at the gain setting.

It reall does not take much to make a big difference.

-RCA .......... Making Cuisinarts Fly!!!!!!!

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11-24-2006 03:42 AM  11 years agoPost 30
racer944

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Greely, Ontario - Canada

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Hi Guys;

The oscillations occurred regardless of where the gain setting was set. I turned the gain on the elevator gyro all the way down to minimum and the heli still bobbed around in a circular manner(maybe slightly less).

The only way to stop all oscillations and get steady hover was to disconnect the gyro completely from the mixer...

Cheers;
Eric

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11-24-2006 04:04 AM  11 years agoPost 31
AirWolfRC

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I'm inclined to suspect a bad gyro, a bad mixer or incompatibility between the two.

I'd still like confirmation of just exactly what your setup is.

I am suspecting that you have standard servo swash setup and are using the mixer because the multi blade head has caused your phasing to be something other than 90º ?

How about a close up of your head linkage ?

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11-24-2006 04:31 AM  11 years agoPost 32
racer944

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Greely, Ontario - Canada

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Hi AirwofRC;

I'm using Century Raven Pod/Boom mechanics with an OS .50 Hyper engine. These mechanics are 120 degree CCPM controlled by 3 Hitec digital HS6965 servos connected directly to the swash. I'm running a Futaba 9CHPS radio, a helitronix mixer, and a pair of CSM 180 Gyros (only one on the elevator at this point, aileron one was removed).

At this point the mixer is controlling the head phasing and the CCPM mixing (radio is set to standard swash). My pitch links (swash to grip) are 100% vertical and parallel to the main mast and timing/phasing is spot on using the standard blade over boom technique.

Does this give you more info to go on?

This thing hovers decently, it just oscillates with the gyro in the circuit, and its generally not overly responsive (although that was getting better with tweaks to the Expo settings (positive), and some additional cyclic pitch (6 degrees).

Cheers;
Eric

P.S. Can post pics of the head links once they are back together... as mentioned earlier had a boom strike on the last test flight.

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11-24-2006 04:37 AM  11 years agoPost 33
rcadd1ct

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Richardson, Texas

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If you plug one servo in the gyro does it act correctly.

Does the oscillation only happen when the engine is running?

What batteries are you running?

-RCA .......... Making Cuisinarts Fly!!!!!!!

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11-24-2006 04:37 AM  11 years agoPost 34
AirWolfRC

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Assumption;
Your head needs 30º phasing and there is a compatibility problem with the mixer/gyro.

Trial;
Loose the mixer and make another anti-rotation bracket so the swash guide pin is 10º off to one side. Move the phasing ring above the swash around to make up for the other 20º.

The links will no longer be vertical but you now have 30º phasing that the mixer was giving you. You can now connect the gyro to the Elevator servo directly.

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11-24-2006 04:46 AM  11 years agoPost 35
rcadd1ct

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Richardson, Texas

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But he said it flew correctly with the mixer without the gyro.

With the gyro it oscillated.

IMHO I think the gyro is whacked or the gain is too high.

-RCA .......... Making Cuisinarts Fly!!!!!!!

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11-24-2006 04:47 AM  11 years agoPost 36
rcadd1ct

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Richardson, Texas

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Are you resetting the system after adjusting the gain?

-RCA .......... Making Cuisinarts Fly!!!!!!!

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11-24-2006 04:49 AM  11 years agoPost 37
AirWolfRC

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42½ N, 83½ W

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Hard to make firm conclusions without specific details.

What is the frequency of the oscilation ?
- - - If it's real low, it's not the gain setting.
Is the oscilation about one axis or is the heli wobling ?
Has a different gyro been tried, like a GY240 or GY401 ?

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11-24-2006 04:00 PM  11 years agoPost 38
AirWolfRC

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42½ N, 83½ W

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I missed the part where you said you have ECCPM with 3 servos connected directly to the swash. My mechanical method won't accomplish anything there.

If you had standard mechanics, adding the gyro would be easier and straight forward and not need the mixer.

Can you better describe the oscillations you are getting ?

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11-25-2006 01:15 AM  11 years agoPost 39
racer944

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Greely, Ontario - Canada

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Hi Guys;

I really do appreciate you giving this some thought and trying to give me some advice... I know its extremely difficult to try to diagnose the cause of something without actually seeing it happen for yourself...

To answer the latest questions:

- The oscillations begin as a slow tail bob up and down and then the heli begins to move in a circular manner similar to what a coin would look like in its final stages of spinning on a table top. As I lift off into a hover, the oscillations/wobble motion gradually increase over the space of about 10 seconds to the point where I have to set the helicopter down or it would become uncontrollable. This occurs regardless of gain setting, but it does occur faster and stronger if I increase the gain up from 0. Only way to get rid of it completely so far, has been to unplug the gyro and run only with the mixer.

- I have not tried a different gyro yet, although I do have a new CSM 180 gyro on order and will swap that one in when I begin retesting.

- Yep, I am resetting the power switch after adjusting gain settings...

One again, I really sincerely appreciate the help you guys are trying to give me.

Cheers;
Eric

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11-25-2006 01:56 AM  11 years agoPost 40
AirWolfRC

rrProfessor

42½ N, 83½ W

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The oscillations begin as a slow tail bob up and down and then the heli begins to move in a circular manner similar to what a coin would look like in its final stages of spinning on a table top. As I lift off into a hover, the oscillations/wobble motion gradually increase over the space of about 10 seconds to the point where I have to set the helicopter down or it would become uncontrollable. This occurs regardless of gain setting, but it does occur faster and stronger if I increase the gain up from 0. Only way to get rid of it completely so far, has been to unplug the gyro and run only with the mixer.
To me, this sounds like the gyro is NOT lined up with the control axis. It sounds like the gyro thinks it's tilting one way and the corrective action is given a number of degrees off from the gyro axis causing the "woble".

Is the gyro on the proper input to the mixer ?

As No. 5 would say "Need more input".

Show us a picture of your gyro mounting for your pitch axis.

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HelicopterScale Model RC Helicopters › First Hover tests - 4 blade head - UPDATED
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