tralalala

Gain of your yaw gyro with respect to your roll gyro have nothing to do with each other. Servo speed, control surface size, control moment, axis moment of inertia, etc.. are all variables that will make your gain setting on one axis totally unique to that of another. So saying you had to run a higher gain on your yaw gyro has no bearing (no pun intended) at all.

Guillermo Ibanez

My Feedback: (1)

That is right!.

What I mean is that if I move the rudder/Nose gyro sensor to the yaw axis, maybe I need to reduce gain.

See post No. 25 where I posted part of my gyro manual where it says that this gyro sense rotation around its axis....
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hyperdyne

My Feedback: (6)

ok, I think we all have some misunderstanding between each other. I understand the principle behind the gyro, no dissertation is needed. In fact please re-read my response. I stated that tangential acceleration has no effect on the gyro. That was my entire point!

And while I agree the rotational angle between the entire airframe is the same, the gyro cannot sense this OR angular velocity. So stating things about angular velocity with respect to the gyro is incorrect. For example, imagine the plane rotating with constant velocity - the gyro has no response. It sees zero angular acceleration. Only the start and stop of such an event, where the acceleration is non zero, does the gyro sense this and react.

Also, centripetal acceleration is much greater at the CG than out at the nose. And if the gyro uses this information (along with the Corolis accel) perpendicular to the axis of rotation, then that explains why having the gyro near the CG will make it more sensitive (i.e. work better). I don't know the inner workings of how they measure the accel, but I know it is not a simple thought experiment measurement like we are discussing.

tralalala

No issues except for this statement. If it isn't sensing rotation, what is it sensing?

Angular velocity or angular rate if you prefer, is exactly why a piezo/mems gyro works. To obtain the coriolis force as you have stated, it is derived from F=2m(omega)v, where omega is the angular velocity. In turn, my gyros do work when subjected to constant angular velocity, why doesn't yours?

Also, I think the application of our single axis RATE gyros is not as involved as a full blown IMU you're making it out to be?

Lastly I want to mention that I respect you as an intellectual and I'm not trying to challenge you in anything, but just have an open table discussion.

dcnbear

Bla... Bla... Bla... why must every thread end up in a useless discussion. The guy just wanted to know if the Gyro will help. No need to confuse him with your regurgitation of information. The Gyro will work... Bob

hyperdyne

My Feedback: (6)

The gyro is measuring angular acceleration, nothing more. How it does this is involved, I am still trying to understand all the magic inside.

Try this, take a gyro and rotate it. See how it corrects the rotation, but doesnt keep doing it as you continue to rotate the gyro (smoothly). Only when you have an angular acceleration (the start or stop of the movement) does the gyro do anything. It doesnt detect velocity or position (like a compass would), nor does it respond to tangential acceleration (or linear accel). It is sensitive to the change in velocity (speeding up or slowing down) - i.e. acceleration in the rotational frame (which is usually defined as centripetal or angular acceleration).

I agree with previous statements where the angle of rotation is the same about the plane. That has to be. But the arc length between 2 pts on the plane obviously is not. And the centripetal accel is not the same either (it is greater near the CG pt - inversely related to radius). So these measurements depend on the length of the measured rotation from the CG point.

tralalala

It does not measure angular acceleration. I have edited my previous post, but I will repost here again:

Angular velocity or angular rate if you prefer, is exactly why a piezo/mems gyro works. To obtain the coriolis force as you have stated, it is derived from F=2m(omega)v, where omega is the angular velocity. Add a time integrator and you get your HH/AVCS Futaba gyro.

My gyros do work when subjected to constant angular velocity, why doesn't yours.

Do not confuse gyros with accelerometers.

JackD

My Feedback: (4)

Again, I admit I have no clue about how a heading hold gyro works, or even the logic inside a piezo gyro, but I just don't see what does arc length or centripetal force have to do with measuring angular rate of change. Unless the gyro doesnt measure it, but actually derives it from the other 2 variables, which I would assume not, since then the gyro would have to know how far it is from the center of rotation.

Jack G

highhorse

My Feedback: (2)

I understand your frustration, but the point these gentlemen are admirably and civilly debating IS relevant because it refers to the optimal mounting location for the gyro which is, in turn, central to the original poster's question.

HarryC

My Feedback: (1)

Thank you folks, my questions regarding steering have been answered - yes it works, use in normal and not in HH mode, and a cheap one will do fine. I will be trying some other remedies before resorting to a gyro.
As to the rest of it, a gyro measures a change of angle, not just acceleration in angle and not velocity so where you put it makes no difference to it!
Over and out.
H.

highhorse

My Feedback: (2)

Hyperdyne and Tralala:

As I try to hang on to this discussion and follow your respective lines of logic it all seems to boil down to one primary point as far as I can tell, and I'd like to know if I'm following you guys correctly.

Does it not all boil down to whether, whichever type gyro is used, it's OUTPUT SIGNAL, is BASED UPON:

A) a MOTION, or
B) a CHANGE in motion (accel)

Put another way and : Is the debate, at it's foundation, about whether the gyro, regardless of it's innards, "thinks like" a spinning mass compass gyro ("I have noticed an uncommanded heading change and must send a control input signal and correct the heading to the original course") -VS- whether it "thinks like" an accelerometer (I feel an acceleration in some direction so I will send a control input signal and counter that acceleration)

The reason I am seeking clarification from you guys is because a spinning mass GYRO, which cares ONLY about the positional relationship of it's spinning mass to the case that mass is housed in, or even a device which has no moving parts but mimics a spinning mass GYRO, will not care how far for/aft it is mounted relative to the rotational axis of the aircraft (collatorally renedering moot the debate over whether that axis is a function of CG -vs- tire traction).

On the other hand, a device which senses acceleration WILL be affected by it's distance from the rotational axis....


I'm not trying to take ANY sides here in a personal sense, I promise. I'm just hoping relate your discussions to my own career training/use of gyro's, accelerometers, inertial nav units etc.


Thanks in advance to each of you, Don.

tralalala

highhorse,

The gyros we use, whether it be the old mechanical spinning mass gyros or solid state vibrating member gyro are, in principal, rate gyros. The rate here stands for rate of angular turn (deg/sec, rad/sec, whatever you want). This is the one and only information you get from a rate gyro, what you do with this information next is totally up to you. You can integrate over time and get angular displacement, and bam now you have a HH gyro. Or differentiate to get the angular acceleration, but there is no practical need for this. Leave it as is and you are in 'normal' mode, and through a negative servo feedback loop, will dampen the servo output.

With accelerometers, you can measure rotational motion by using a number of accelerometers at predetermined spacings (or lever arm) on a body. This forms the basis for gyro-free IMUs. It really doesn't matter since our gyros don't work this way. Also, the distance of accelerometers in an IMU to the center of rotation is relevant and this is called size effect, but again for us we are dealing purely with a gyroscope and not accelerometers so it does not apply.

highhorse

My Feedback: (2)

K. If it's angle that's being sensed, as opposed to acceleratation, then (FWIW to anyone who might still be tuned in) it does seem to me that the unit's distance from the CG should not matter.

Whew, my brain hurts !

ajcoholic

My Feedback: (10)

Yes, it does. It will hold the servo in a setting off of neutral as long as the gyro is moving - even at a steady rate - until the gryo stops.

I have 4 or 5 different gyros and they all behave the same. Try my test, hold the gyro in your hand with a servo, and start turning your body at a constant rate. You will see the servo slewed off center and holding there until you stop moving.

Maybe yours is different.. but I doubt it.

AJC

David Gladwin

The distance of the gyro from the C of g IS irrelevant. The gyros used in models are rate gyros, (as opposed to space or earth gyros) which are instruments designed to measure angular rate and direction of rotatation in the appropriate plane, nothing else, and generate a signal to the servo to counter that rotation. In a rigid body, aircraft, the rate of rotation, is the same throughout the structure and regardless of location on that structure the gyro will sense the same rate and direction of rotation. Enough of that, you need proof !

Consider a fullsize aircraft instrument panel. Virtually ALL have turn indicators operated by rate gyros which indicate rate and direction of turn. The principle of operation on flywheel turn indicators and model gyros appears identical (having stripped an early unit, it has the same gimbal system and gimbal restraining spring, in fact a leaf on the model unit ) Where are they located on the real aircraft ? Right up the front about as far away as one can get from the C of G. They all work well and accurately with few errors and no toppling, which is why they are an instrument of last resort for attitude control when all other gyros are lost/toppled/inop.


Modern model gyros have replicated and improved on spinning mass gyros by using piezo type sensors which are far more sensitive accurate and reliable than hitherto. Some have a function, attitude, or heading hold, which integrates rate of rotation with time to produce an error signal. This is "washed out" by the servo being commanded to oppose this error until it is zero. (if I understand that principle correctly, because "heading hold" systems in real aircraft are driven by slaving the compass heading to aileron roll control).

Modern military and civil aircraft have long since replaced spinning mass gyros by taking the turn information from INS, IRS, or INUs. These units are located in the E and E bays usually just behind the nosewheel well , a long way from the C of G. (and often just under the forward galleys where spilling water could get to them !).

I believe lateral acceleration IS being confused with angular rotation.


Regards, David Gladwin.

highhorse

My Feedback: (2)

May I add this please:

In sharp contrast to many threads I have seen, neither of the main contributors to two mutually exclusive theories presented, even while vigorously defending their own beliefs, was particularly antagonistic or rude to the other.

And no one who's theories or views may appear to have been defeated needs to feel or be viewed themselves as vanquished.

IMO this thread has been very educational and because of that ALL parties win. This has been RCU at it's best !

Thanks all, I learned a lot, Don.

BaldEagel

Have to agree with Don this has been a very educational thread, and I have enjoyed reading it, just wish my knowledge was good enough to have been able to contribute.

David

In my days in full size the turn and slip indicator was totally mechanical without gyro's, only the aritificial horizon had gyro's on it, have things changed that much?

Mike

HarryC

My Feedback: (1)

Mike, the indication of turn has always been done by a rate gyro, whether it is the old fashioned turn indicator which had a vertical needle, or the more modern turn co-ordinator which has the little plane-like symbol. Surely you had a Direction Indicator too rather than a compass, that uses a gyro.
H.

Molnar142

My Feedback: (38)

Ok, I’ve keep an open mind here and honestly, I had to go back and read up on Gyroscopic Precession. My initial assumption on gyros was that you wanted them along the axis you wish to control. For example, if you wanted to control roll rate, you would put a gyro anywhere in the airframe (tip to tail) such that the roll axis went directly thru the gyro. Same for pitch and in this case, the YAW axis. But in the end, I just went and grabbed a Futaba GY401 Gyro I had sitting on the shelf and did a little experimenting. I connected the gyro to a servo and held the gyro in my hand and with the label side facing up; I twisted it back and forth as if the axis of rotation was a line straight thru the center of the gyro. Then I held it out (arms stretched) as if it was positioned in the nose of an aircraft and my body was the yaw axis. It is clearly evident that the gyro performed exactly the same. At first it appears the gyro is more sensitive when simply rotated (along the axis example) but if you move the same degree of sweep the servo moved the same amount. My conclusion, the Gyro can go at the center of rotation or the nose…it still works effectively.

Mike
wanna be Mythbuster!

BobH

My Feedback: (2)

You are correct, it works the same regardless of where it's placed .

I think these gyros have a voltage change depending on the rate of angular change of the gyro. This technology is also used in strain gages and acceleormeters. We start out a Zero volts at the reference point or zero angular state. Once the sensor moves to the side, right or left, there's a change in voltage that translates to how much the rate of change has occured. The gyro sends this information via a signal to our servo giving it a counter active movement. How much movement can depend on the gain we select on the gyro. Some tweaking is sometimes necessary to get the gyro controled servo excactly the way we want.

When I fly my heli's this is not as critical (for me anyway) because A: my heli flying skills aren't that great and B: I can normally correct before disaster strikes.

Now I may have some electronic assertioins that aren't exactly correct in my Gyro model but in essence I think its pretty accurate.

BaldEagel

Nope sorry, a gyro requires some kind of power and the turn and slip indicator in my ASW17 had no power to the panel, just a vertical needle on a pendulum weight and bubble level, Altimeter, ASI, VSI and a compass, and the most accurate instrument was your own back side and the piece of wool on the canopy.

Mike

David Gladwin

Then you did not have a proper turn indicator in your glider ! In a balanced turn a needle on a pendulum would show zero turn. (Even Tiger Moths had a venturi to generate suction to drive the gyro in the turn and slip, or so I was told when I last flew Tigers)

So far as the distance from C G argument goes, I could draw the RAF schematic, used by all QFIs and IREs on just how a rate gyro works as a TURN indicator showing the layout of the instrument and the forces acting on it. This is the same as the original model gyro I dis -assembled, principles are the same.

I could superimpose on that diagram the forces generated as a result of LATERAL motion, (as a result of the instrument being remote from the C of g or rotation axis) steady state or accelerating. It will be sen that these forces cancel each other and so have NO nett effect of the gyro system. The gyro reacts ONLY to rotational forces. (although increasing G forces can cause overreading).

You could put a rate gyro on a wingtip, top of the fin right in the tail or nose, it would still experience the same rate of rotation and give the same reading.

I will do it if there is any interest.

Regards,

David.

BobH

My Feedback: (2)

I think its fairly well established by now.. or at least should be.. that the gyro works regardless of where its positioned in the plane. For those who are still non believers there should be sufficient information rendered here to convince them otherwise.. if not.. then no amount will suffice

Xairflyer

My Feedback: (1)

I have a PG-03 fitted to my bobcat, stuck on the side of the fuselage and it works great.

BaldEagel

Your right David, I forgot about the venturi, its a long time ago now, I only remembered that there was no power i.e. battery connected to the panel, silly boy.

Mike