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Old Oct 01, 2008, 09:11 PM
Ted M
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Ann Arbor, MI, USA
Joined Feb 2007
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Quote:
Originally Posted by Prof100
Gandalf Sr.

Wow, I need to digest this. I am short one mixer. Prices range from $3 (UH/HC/HK plus shipping) to $30 with Tower having a couple in the $12 to $15 range plus shipping. My plan currently has the battery mounted on CG so we can only mount left and right.

Like I said, I need to think it through.

Bill
(Go Blue)
Yeah, what about the Wolverines last Saturday eh?

I haven't used a mixer before but I know what it does, I wonder if there are mixers that allow you to reverse the channel inputs? The elevon configuration is really a pain to deal with. You could always add a canard and have an extra gyro-controlled channel that just works the canard; that is my setup.

Did some more testing on the 0704A today; I was suprised to find that, with the extra gyro channel (single wire) connected to a spare channel set up with a tranmitter control, that I could not only switch between HH and rate mode (which I expected) but the gain seemed to be changed by the control too. The O704A is notorious for creeping when in headhold mode and I spent a while tweaking the sub trim for the elevator (canard) and it seems OK but you have to let it warm up. Anyway I'm ready to test and here's what I expect...

In rate mode the gyro controls the canard to try and maintain a rate of pitch change that is proportional to the amount of stick movement. I also played with HH mode, I'm pretty sure that what it will do is lock the direction of the plane (in pitch axis) and when I move the stick, it will work to move the plane onto a different pitch heading and hold it there. I say this because, when I tweaked the elevator control, the canards moved to a new position but when I rotated the plane in the direction the canard movement would take it, the canards came back to center again - COOL! Obviously the gain may need to be adjusted but I can do that from the gyro control.

I'll let you know how I go on. If rate mode works OK, then the $12 EK2-0704 from Hobby City will be the obvious way to go, however, I've got a sneaking feeling that I'm going to like HH mode more
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Old Oct 02, 2008, 02:28 AM
Registered User
Sverige, Västra Götalands Län, Trollhättan
Joined Oct 2006
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Gandalf:
Heading hold is the way to go, at least for me. I have tried it a while back with an AP-ship and it was just great! However, I managed to destroy the gyro after just a couple of flights (rough landing, or one might eaven call it a crash ) and I havn't had the possibillity to get a new one.

One thing to think of with heading hold is that you have to really "fly" the plane. For example if you are doing high alpha and the motor cuts out for some reason. With a regular plane, the nose drops and you gain speed so you can glide it down. With heading hold gyros, the gyros will try to keep your plane in the high alpha position all the way to the ground, which may result in a flat leaf-like fall, unless you give it down elevator to point the nose down and gain speed.

As long as you are aware of these effects there is no problem! Gyros are cool and why should we only let the heli guys have them?
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Old Oct 02, 2008, 03:36 AM
Just one more flight...
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Pasadena Cal-i-Forn-I-AY!
Joined Sep 2005
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Quote:
Originally Posted by kalleman
Gandalf:
"...Gyros are cool and why should we only let the heli guys have them?"
Best quote of the thread right there.
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Old Oct 02, 2008, 04:03 AM
Build, fly, learn!
Versailles, France
Joined Jul 2008
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Quote:
Originally Posted by RCSuperPowers
To kinda summarise how my gyros are helping with the SU-35:
...
Dave
Dave,
Thanks for the explanation of how the gyros work in your SU-35 design. This is really a sophisticated flying machine and hats off to you for your successful R&D work.
I am sure more people will follow in your steps using gyros for their RC models but you sure paved the way!
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Old Oct 02, 2008, 04:28 AM
Winging it Ò>
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Joined May 2006
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Dave,

Do the gyros have to be mounted in any particular orientation to the axis they are controlling?

I love watching the video of this jet flying, so cool.
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Old Oct 02, 2008, 05:55 AM
Ted M
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Ann Arbor, MI, USA
Joined Feb 2007
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Quote:
Originally Posted by RCSuperPowers
Best quote of the thread right there.
Actually, I'M a heil guy too. That's why I have a couple of gyros just lying around

Kalleman, thanks for the comment about HH being best. The weather seems to be improving so I hope to re-maiden my X-42.1h soon.

I'd love to make something like the SU-35 or the F15 active

I was giving this some thought and went looking for a mixer and found a cool one called the Digimix II
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Old Oct 02, 2008, 11:43 AM
Ted M
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Ann Arbor, MI, USA
Joined Feb 2007
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I have flown my X-42 with the gyro...

The gyro-stabilized canard (pitch) is a resounding success

If you're interested, you can read all about it here

Ted
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Old Oct 03, 2008, 06:24 AM
Ted M
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Ann Arbor, MI, USA
Joined Feb 2007
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Quote:
Originally Posted by RCSuperPowers
...I'm real short on time these days but I do plan to do a schematic of my set up when I pull it all apart to install it in the new final plane (which is being built).
Well, I've got to build one of these here SU35s! In the absense of a pdf plan, any chance of a shot from above with a 36inch ruler in the picture? I could probably figure it out from there. A BIG advantage would be if you could mark your CofG on the plane (or picture).

I will post build pictures here which may help others of they want to follow along.

[EDIT] Also, please can I get info on the motors you're using?
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Old Oct 03, 2008, 11:50 AM
everything with RC
Brest..."grand ouest"
Joined Nov 2004
156 Posts
nano gyro

Hi,
Ahter seiing the vid, I immediatly bought the nano gyro (hobby lobby) to try it at home on my "profil raptor"...quite funny to see how fast the servo is reacting.
The problem is that I am using only to servos (elevon) like a delta wing setting.
So my question is: "do I have to use two gyros for this radio setting? if yes, how to be sure that the two gyros will show the same gain and will act in the same way with the servos at the same rate?...doing the testflight can be disastrous
Thanks for the help
Eric
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Old Oct 03, 2008, 12:25 PM
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I think this was discussed, perhaps in another thread. for an elevon setup, the mixing has to be done onboard (not on the radio). The signal flow diagram would be as follows:

The reciever puts out independent PWM signals for the elevator and the ailerons. Those signals will flow through their gyros (one or two, depending on how many axis you wish to stabilize) then the modified PWM signal will go into a v-tail mixer. The mixer will output the signal to the two servos that you have.

There is no way (that i am aware of) to put a combined signal through a gyro and have any logical output, hence, no mixing my be performed on your radio.

rick
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Old Oct 03, 2008, 12:37 PM
everything with RC
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thanks Rick
I think I understand.
I will try that on another plane already equipped with a Vtail mixer and an older Tx
Eric
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Old Oct 03, 2008, 01:01 PM
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Alright, perhaps I have been thinking about this too much.

Center of Gravity.

Dave mentioned that he has it much farther aft than the model could easily fly with if you were not using gyros. I think I follow this, please correct me if I am wrong. Center of gravity is not that important anymore as the gryo will correct for any tendencies. If the CG is aft it wants to push the nose up, the gyro corrects that and pushes it down. so it flies as if the cg was correct, right?

Now, what effect does that have on general flight characteristics? If the cg is off the gyro will keep the servos at some defection off of center. So you now are limited in total throw of the control surfaces, as the "steady state center" is not at the actual "center". Also since you are using aerodynamics to produce level flight, as opposed to a "properly" balanced plane, it requires airflow to do this. So you are loosing some efficiencies.

So the result of having a off center CoG on a gyro stabilized axis are:
1) reduced, or at least, uneven total control surface throws
2) reduced airframe efficiency (hence lower top speed)
3) different moment of inertia, so rolls may be slightly different than properly balanced
thats all I can think of.

While those three points are likely soooo small that they are not measurable while in flight, is my logic here right?? I am totally new to these gyros (sort of) my mechanical engineering senior design progect was a gyro stabilized rocket. However I was not in on the electrical design, just the mechanical. But this isnt the forum to discuss that.

Please correct/confirm my thinking....

Thanks,
Rick
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Old Oct 03, 2008, 01:26 PM
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Temecula
Joined Jul 2004
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CG is still important because a plane with a CG that is too far back and compensated with down elevon throw and augmented with a Gyro to correct stability problems will have much higher drag than a plane with a correct CG.

At speed the roll characteristics should not be drastically affected as the center of lift is the same and the moment along the roll axis is unchanged.

The plane will be very touchy to positive pitch and sluggish in negative. As a matter of fact you may stall the wing before you can nose it over.
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Old Oct 03, 2008, 01:32 PM
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Sounds like all my thinking was correct on all points. Thanks for confirming that. I will still try to hit the CG, but wont worry too much if it moves around (and I am not sure where it truely needs to be for my model anyways).

I have a feeling that this gyro thread should be turned to a sticky at some point (if it fleshes out). pretty great data here. will post data when I get soem testing in.

Rick
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Old Oct 03, 2008, 02:14 PM
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I'm thinking that the best Cg would be when all surfaces are completely neutral. Should give very symmetrical behavior in orientations of flight! Flying inverted with no down elevator for example.
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