RunRyder RC
 9  Topic Subscribe
WATCH
 6 pages [ <<    <     1     ( 2 )     3      4     NEXT    >> ] 4106 views
HelicopterRadio - Servo - Gyro - Gov - Batt › Gyro with the most amount of gain?
01-13-2011 02:21 AM  7 years agoPost 21
dkshema

rrMaster

Cedar Rapids, IA

My Posts: All  Forum  Topic

A long servo arm coupled with very high gain is a recipe for disaster.

First of all, the long servo arm equates to very small movements of the servo translating to very large movements of the control surface, and that leads oscillation in flight. The servo will be working continuously, moving very short distances back and forth, and will most likely overheat the output transistors of the servo amp, causing early failure of the servo and loss of the aircraft. A lot of heli fliers have found that out the hard way, and to this day blame the servo for burning up on them. It just got worked to death and fried.

If you run a very long control arm, you need a very small gain number for the system to work properly.

Shorter arms allow larger gains, higher control surface resolution, and much much better, more accurate control.

Second, does your jet actually require LARGE amounts of control surface travel to control it. If so, perhaps you have a more basic problem with the airframe, the design, and/or the CG location. Have you ever seen how much aileron deflection is actually needed (and the actual size of the aileron itself) on a large transport aircraft to control it while flying at 40,000 feet? Very small surface, very small control movements.

And gain controls how fast the gyro will react to rotational movement, not how far it moves the servo. If your gyro has a TRAVEL LIMIT function, you need to properly set that up so that the servo you are using is allowed to travel something on the order of +/- 45 degrees from neutral without binding up the control surface at either end of its travel. This allows you to run lower gains, get much much higher precision control out of the servo, and will make a whale of a difference in how the control surfaces and aircraft behave in flight.

As mentioned, your servo may just be way too slow for the task at hand.

The Yaw rate, Roll Rate, Pitch rate (how fast the gyro will allow movement in each of those axes) is determined by the ENDPOINT setting of the associated control, not by gain.

If you need to increase the roll rate, for instance, increase the end-point/ATV setting of your transmitter for the aileron channel. If the roll rate is too fast for you, then make the end-point/ATV number smaller.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

PM  EMAIL  GALLERY  Attn:RR  Quote
01-13-2011 03:48 PM  7 years agoPost 22
Eddy

rrNovice

La Ca

My Posts: All  Forum  Topic

Can we all try a little experiment? Set your gyro to 0 then grab the tail of the heli and wiggle it back and forth say 1/2" both sides, while doing this slowly turn the gain up and tell me what you see the servo do.

PM  EMAIL  Attn:RR  Quote
01-13-2011 05:25 PM  7 years agoPost 23
Ace4

rrApprentice

Chandler, AZ

My Posts: All  Forum  Topic

That isn't really a valid test, since there is zero effectiveness on the control output so the error will integrate up until the servo hits maximum throw. In flight, the gyro commands the motion and the heli responds to this, but when the heli is not running the tail will have zero effectiveness.

Anyway, there is little difference (depending on the controller structure, obviously) between gain in the gyro controller and mechanical gain in the tail system. For simplicity's sake, you can think of it this way (purely as a proportional controller).

Sensed error = x
Tail reaction force = u*m, where u is the commanded servo travel and m is the mechanical advantage in the tail
u = x*k, where k is the gain in the gyro controller

So you can see that the tail reaction force = x*k*m, and that you have a "total system gain" that is the real gain, such that if you have a very high controller gain you would likely offset that with a smaller mechanical gain. The total system gain has a range that will produce the desired response, if you get that too high the system will oscillate.

That is why you cannot simply say "I can set the gyro gain on my model X heli to Y", because the mechanical gain is different for various models of helis, as well as head speeds and tail blades. Servo arm length also plays a huge role.

You are looking for a gyro to stabilize a Harrier (in roll axis only, or pitch as well?). Helis have a huge amount of control authority in the tail, whereas I'm guessing your Harrier does not while hovering using small ducted jets like the real one. The Harrier in a hover is going to be significantly less reponsive than the yaw axis of a heli, so if I were you, I would go with a gyro that allows the most tweaking of settings. You'll likely need to mess around with delays in the gyro to get a good response.

PM  EMAIL  GALLERY  Attn:RR  Quote
01-13-2011 05:36 PM  7 years agoPost 24
Eddy

rrNovice

La Ca

My Posts: All  Forum  Topic

That's a perfectly valid test that shows the more you increase gain the more servo travel you have, that's just how gyros work.

If you are hovering and a light gust come along and swings your tail a few degrees you add just a tiny bit of input on the stick to straighten it out, if its a large gust and it swings your tail 90 degrees you add very large input, no different than what the gyro does. So gain = servo throw, that's all there to it.

My puffers are very small air ducts, there is almost no power needed to move them, unfortunately there is not enough room in the wing for 3 inch long arms so more gain would equal smaller arms. No to mention you lose resolution due to play in the gear train with long servo arms.
This puffer system is a completely separate system than what operates the flying surfaces.

PM  EMAIL  Attn:RR  Quote
01-14-2011 02:26 AM  7 years agoPost 25
AWittleWabbit

rrElite Veteran

O.C., CA

My Posts: All  Forum  Topic

Sounds like you need more force from the puffers themselves. I think you're trying to make up for that by looking for bandwidth everywhere else in your system. Would it be easier getting more maf through your puffers?

If you are after actuation like this

Watch at YouTube

you're going to need more than servos.......

Heli-itis sufferer.

PM  EMAIL  GALLERY  BLOGAttn:RR  Quote
01-14-2011 02:46 AM  7 years agoPost 26
ncostes

rrVeteran

Va, US

My Posts: All  Forum  Topic

http://en.wikipedia.org/wiki/PID_co...oportional_term

Gain controls how FAST the proportional term gets big. How fast the controller reacts. Too high a gain and you go unstable or have large transients (wag).

For your analogy, how fast I move my stick to compensate is more about the gain, how far I can move it is the extent (or ATV).

If my extent is small, doesn't matter how fast I move to full deflection, since I can only move the actuator a little I can't do anything.

I can crank the gain up high, all it will do is move the actuator there faster and then clamp as the error just keeps increasing.

If your controller is lacking authority, as others have said, you have to look elsewhere.

You can also increase the sampling frequency (get a faster gyro + servo combination - I assume you are already using a very fast digital servo (not all digital servos can move equally fast)) which may help (again you can crank the gain up higher if you have a faster actuator).

Ultimately for us with a heli, if our control system is responding quickly but just doesn't have enough authority, as others have said we go to larger tail blades (which slows down the servo and puts more load on it etc.) It's all about tuning.

I hope that helps clear up why saying "gain = travel" isn't quite right and why you may have to look somewhere other than for a gyro with a "higher gain" to solve your problem.

PM  EMAIL  Attn:RR  Quote
01-14-2011 06:13 AM  7 years agoPost 27
Eddy

rrNovice

La Ca

My Posts: All  Forum  Topic

What I have works, and thrust is all divided up the best its going to get. More thrust out of the puffers = less out of the nozzles. I had a 3 axis IMU and computer built just for this thing and it worked great, however, we decided on a new more powerful board, and since then the guy doing it has problems finishing it. I don't want to change things now, if he finishes I can bolt it right in. I really just need a gyro with more gain, this will get me going until my friend has the new computer done. I have a total of 22 years in 3 attempts of making a Harriers, I am almost done I just need the right gyros to get me by, any other ideas would really be appreciated!

PM  EMAIL  Attn:RR  Quote
01-14-2011 06:40 AM  7 years agoPost 28
AWittleWabbit

rrElite Veteran

O.C., CA

My Posts: All  Forum  Topic

What exact futaba gyro are you using now? Newer gyros max out servo throw with less displacement e.g., gy401 vs gp750 all else being the same. I don't know what's different in the control loop between the two. You may want to consider a gyro that has more than just gain control like the Spartan mentioned earlier.

Heli-itis sufferer.

PM  EMAIL  GALLERY  BLOGAttn:RR  Quote
01-14-2011 09:10 AM  7 years agoPost 29
jgunpilot

rrKey Veteran

Pollock, LA

My Posts: All  Forum  Topic

My gyro doesn't just go from, 1-10 on its gain setting. It goes to 11, baby!

PM  EMAIL  GALLERY  Attn:RR  Quote
01-14-2011 11:55 AM  7 years agoPost 30
Andypants

rrApprentice

Sydney

My Posts: All  Forum  Topic

Some pictures would be super-helpful. I guess you're into fixed-wing and I think it's cool you've come to a heli forum to ask for advice on gyros. We're the guys to ask! You'll find our gurus thrive on technical information - pics, dimensions, specs. Video, so much the better. Which radio do you use? How big is the aircraft? Many of us fly fixed-wing too so it'd be awesome if we could help solve your problem!

So the more info the better, but consensus seems to be your servo isn't up to scratch. What are you using at the moment?

Lots/Very high/Ridiculously hard/No you can't

I HEART BLADE FARTS

PM  EMAIL  Attn:RR  Quote
01-14-2011 12:02 PM  7 years agoPost 31
ChristianM

rrVeteran

Oslo, Norway

My Posts: All  Forum  Topic

Maybe you should try the CSM SL720 gyro. Those gyros allow you to change all the PID parameters which will allow you to optimize it for your application. Most of the gyros out there are optimized for the heli tail rotor application which may be a reason why they do not work well in your application. As an example using regular tail gyro in a FBL application does not work well at all since the behavior / response is very different on the cyclic vs. the tail.

I believe AirWolf previously has done some testing on this and has a link to a writeup on this in his gallery.

Best of luck on your project.

Christian

Burn fuel, be happy

PM  EMAIL  GALLERY  Attn:RR  Quote
01-14-2011 01:53 PM  7 years agoPost 32
BlakeMcBrayer

rrElite Veteran

Georgetown, Ky

My Posts: All  Forum  Topic

OK, The single most important piece of info needed here is still missing. EXACTLY WHAT GYRO MODEL ARE YOU USING?

Most all gyro have some sort of means to set travel limits. These travel limits control how far the servo can travel in each direction. If these setting are not correct, then no matter how high you turn up the gain, you won't get enough travel.

And YES, higher gain will make it appear to have more servo travel.

Blake McBrayer
Fromeco Factory Rep

Don't come off the throttle untill you see your GOD!

PM  EMAIL  GALLERY  Attn:RR  Quote
01-14-2011 02:07 PM  7 years agoPost 33
BarracudaHockey

rrMaster

Jacksonville FL

My Posts: All  Forum  Topic

The GYA 352 I believe. He said it in an earlier post

Andy
AMA 77227
http://www.jaxrc.com

PM  EMAIL  GALLERY  Attn:RR  Quote
01-14-2011 02:15 PM  7 years agoPost 34
fenderstrat

rrProfessor

Aston,Pa

My Posts: All  Forum  Topic

So gain = servo throw, that's all there to it.
if this were true,they would not be able to be adjusted independently.You are working with an assumtion that is not correct.I can put a gyro on my 450 heli and have high gain with short travel and then move this same gyro to my 50 and need much longer travel and lower gain

also the tail wiggle test does not indicate anything because you are moving the tail by hand. The gyro is seeing movement and commanding a response.But it is not getting the response it is commanding because you are moving the tail independant,so it continues to try to overcome a situation that is being manipulated by outside unnatural forces....basically you are freaking out the gyro

so lets just try to get back on track.As said, what is the exact gyro model?Is there any posibilty of a damaged gyro(i.e. recent crash).Is there a possibility you are just asking for too much throw from a micro servo?What is you ATV for the gyro channel.lets get some facts and sort this out

Compass helis Support Team
PerformancePlusRC field rep
Mini Titan/SE
TEAM KBDD

PM  EMAIL  GALLERY  Attn:RR  Quote
01-14-2011 02:39 PM  7 years agoPost 35
Eddy

rrNovice

La Ca

My Posts: All  Forum  Topic

I have tried a g501 which to date has worked the best, it has more gain than most by almost 2. I have tried a ms composite gyro I think it was, a gws, a futaba 401, some jr gyro and a old mechanical gyro from a Kalt whisper electric heli from 20 years ago, so far the mechanical gyro and the 501 so far have the most gain. The 352 is a 2 axis gyro, that would be good due to it being one nice compact package, not that it has to be that.
The aircraft is 1/6th scale, all my hover tests are done indoor with an electric version sucking 11kw in hover, my ultimate version has a
1/6 th scale Pegasus style turbo fan in it.
here's my website although it has not been updated in 6 years or so.
http://cpl.usc.edu/eschuste/

Due to how well the Harrier is coming along I had to test fly the engine, to do this in the harrier was to high risk so I built a test bed with a nice big wing to test the turbo fan in, here is the video of this aircraft

http://www.youtube.com/watch?v=OJl7Dig1gLQ

This engine does not use nozzles but is the same in every other way

PM  EMAIL  Attn:RR  Quote
01-14-2011 02:47 PM  7 years agoPost 36
fenderstrat

rrProfessor

Aston,Pa

My Posts: All  Forum  Topic

ok,so basically,no matter what the gyro,the issue is servo travel?correct?
I have tried a g501 which to date has worked the best, it has more gain than most by almost 2
can you explain this more,what exactly do you mean by more gain by 2? Are you refering to actual travel it allows a servo.I do not understand how or what you are measuring "gain" with

Compass helis Support Team
PerformancePlusRC field rep
Mini Titan/SE
TEAM KBDD

PM  EMAIL  GALLERY  Attn:RR  Quote
01-14-2011 02:54 PM  7 years agoPost 37
Eddy

rrNovice

La Ca

My Posts: All  Forum  Topic

I have hooked up 4 of these gyros and taped them together and held 4 servos together, I moved all the gyros and the futaba gave me twice the servo throw than the rest

PM  EMAIL  Attn:RR  Quote
01-14-2011 03:02 PM  7 years agoPost 38
fenderstrat

rrProfessor

Aston,Pa

My Posts: All  Forum  Topic

ok so have you considered a servo that has 180deg rotation instead of the nornal 60deg?it seems the basic issue is you cannot get the travel you need with a normal servo no matter what the gyro.

Did all gyros have their travel settings maxed out?if so, we are back to mechanical travel,or a servo that has more rotation.

No gyro is going to ADD travel to a servo.once the servo has reached its mechanical limit of rotation,thats it

Compass helis Support Team
PerformancePlusRC field rep
Mini Titan/SE
TEAM KBDD

PM  EMAIL  GALLERY  Attn:RR  Quote
01-14-2011 03:15 PM  7 years agoPost 39
Eddy

rrNovice

La Ca

My Posts: All  Forum  Topic

That's an interesting idea,this is the input I am looking for. However now you have the problem that the manual input is also more not just the gyro out put, plus I don't think they make micro servos that have that range, although it would get things going short term. I am talking to a fellow now that can change the pot values in the servos, so I am considering this just so I can go try the first transition from hover to forward flight. Do they make micro servos that have 180 degree movement?

PM  EMAIL  Attn:RR  Quote
01-14-2011 03:17 PM  7 years agoPost 40
Eddy

rrNovice

La Ca

My Posts: All  Forum  Topic

Yes I did max everything out

PM  EMAIL  Attn:RR  Quote
WATCH
 6 pages [ <<    <     1     ( 2 )     3      4     NEXT    >> ] 4106 views
HelicopterRadio - Servo - Gyro - Gov - Batt › Gyro with the most amount of gain?
 Print TOPIC  Make Suggestion 

 9  Topic Subscribe

Tuesday, January 16 - 9:25 pm - Copyright © 2000-2017 RunRyder   EMAILEnable Cookies

Login Here
 New Subscriptions 
 Buddies Online