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HomeAircraftHelicopterMain Discussion › Gryo Quick Trim Hard Question - Guru's only
11-20-2006 03:41 PM  11 years agoPost 1
HeliDogIrl

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uk

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Hi there,

I've a question that I have failed to get an answer for.
I've been offered a lot of suggestions but what I'm looking for is hard fact and that's hard to come by.

It's relating to quick trim on a gryo, take the CSM310 for example but gy401 etc also have this quick trim feature.

Ok So I set up my heli's tail mechanically as best i can, but in normal mode it drifts slighly, so I can quick trim it (feature of most gyros i've seen).

This is fine, all makes sence so far, remember we're still talking normal mode.

=== fine... but ===

I don't fly normal mode as most people I fly in heading hold.
So going on my own assumptions I would think that if I get it as close mechanically as I can and then just switch on heading hold and forget about the slight normal mode imprefection then everything is honkey dorey (fine).

But here is the CURVE BALL.
The CSM manual states,
Quick-trim
Note:- Even if you do not wish to fly in mode 0 it is important for optimum performance that you go through the
Quick-trim procedure.

What I would love is someone to finish that sentence with
because . . .

Please someone with the correct answer that is, I've a few guesses myself but they are only guesses, can anyone really tell me why exactly the quick trim makes life better if normal mode is never going to be used?

Thanks in advance

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11-20-2006 03:54 PM  11 years agoPost 2
PaulJC

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Hertfordshire UK

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Because.......

the exact neutral hover point is then stored in the gyro.

With the gyro knowing this more accurate stops can be acheived

Re-entering the atmosphere...

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11-20-2006 04:04 PM  11 years agoPost 3
HeliDogIrl

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uk

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gyro confusion
hi paul,
thanks for your reply,

this looks promising that you know that stops are not going to be as good, but can i venture to ask why?

Why does having the quick trim setup performed cause the tail to have better stops?

Please feel free to go into detail because this has the life tormented out of me.

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11-20-2006 04:21 PM  11 years agoPost 4
Colin Mill

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England

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Hi

It could be worth having a look at some of my replies on the following thread but if they are not quite what you are looking for please let me know:-

http://www.runryder.com/t295477p1

Best regards

Colin (CSM)

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11-20-2006 04:28 PM  11 years agoPost 5
HeliDogIrl

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uk

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I feel an answer coming
Hi Colin,

tnx alot,

i've read your practical theories v.interesting,
i'll have a read of that thread as soon as i get a few free minutes and get back to you.

thanks

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11-20-2006 04:38 PM  11 years agoPost 6
BarracudaHockey

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Jacksonville FL

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The 401 doesn't have a quick trim sequence, you trim it by adjusting the tail linkage for no drift in normal mode. Flipping the switch 3 times just makes it memorize the neutral position again but if you arent messing with radio trims, neutral shouldnt change.

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

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11-20-2006 05:09 PM  11 years agoPost 7
HeliDogIrl

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uk

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Thanks
Hi again, i'm still reading but my question / same question as other thread is already answered.

Thanks alot for your time

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11-20-2006 05:29 PM  11 years agoPost 8
PaulJC

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Hertfordshire UK

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Say for example you have your heli/gyro trimmed to acheive 1 full 360deg piro per second to the right, as a pilot this is not what you want but the heli/gyro doesn't care, it just does what its told.

For a moment forget the gyro has a sensor inside, it now thinks that with no rudder input it should piro as above at all times unless told otherwise.

Now bring the sensor into the equation, for this example we would be in HH, the sensor measures the rotation and overides the trim to hold the tail, remember that its only a sensor so can only tell you where it is at the time.

You now have a trim which gives 360 right rotation per sec which we will give a figure of +100, 360 left rotation would be -100, with tail held in the middle (0).

So the 'Correct' figure according to the gyro/trim is +100, The 'Correct' figure from the sensor gives 0.

Now shoot off into the sky -100 in a left piro, no problem at all then centre the stick, the gyro now thinks that it has to be at +100 to be in the correct place to hold the tail (this is where it has been set in trim/setup)...

The gyro will accelerate up to full speed aiming for +100 as trimmed, in reality it only needs to get to 0 but the only time the gyro will know this is once the sensor gets to 0 to tell it, so it will then try and stop it as quick as possible.

In the time taken to stop it would have travelled past 0 and now has to make its way back which can give a visible bounce, hunting or loss of tail control when demanded.

The smaller the gap between 'Correct' gyro/mechanical trim and the trim required to hold the tail steady the better.

Imagine being a passenger in a sports car, ask them to accel to 100mph ONLY once they hit 50 tell them you may have said 100 but you meant 50, they'll already be doing 75, so then you ask for them to stop! But ONLY as you go past 50 on the way down you again say you meant 50 but your already doing 30....See the problem.....If you said 50 in the first place there wouldn't be one, lol!!!!

Then you move onto the effect of gain on this process but someone else can detail that one.................

Re-entering the atmosphere...

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11-20-2006 05:30 PM  11 years agoPost 9
PaulJC

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Hertfordshire UK

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Wow Obviously spent too long typing that, hope it helps anyway

Re-entering the atmosphere...

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12-05-2006 09:26 AM  11 years agoPost 10
HeliDogIrl

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uk

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thanks again
thanks for that.

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12-05-2006 04:20 PM  11 years agoPost 11
IWonderNow

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NYC

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Why is this not so
Just wondering,

I would assume there has to be logic of some sort built into gryos... obviously there is.. otherwise one may as well tie a lump of plastic to their heli and have the same results.

So In simple terms it seems the logic is as follows

Establish A heading X ....
searching... searching ... searching .... X heading established
check if there is a zero trim offset Y...
new heading is X + Y establish this heading

Why is it not as simple as..
Establish A heading X ....
Add zero trim offset Y (if it is 0 then doesn't make any diff)
searching... searching ... searching .... heading established

?

IWonder...

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12-05-2006 04:32 PM  11 years agoPost 12
brianbruff

rrApprentice

ireland

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pid
I have to admit i'm taking a bit of a guess here, but have a read of
http://en.wikipedia.org/wiki/PID_controller

Then take the example of the water tank,
when the water is low the sensor tells the tap to open
so water is now flowing into the tank.
At a certain level it decides there is enough in the tank and closes the tap.

But I'm guessing that by the time the water has been switched off after the sensor realized that it had eatablished the correct level that a bit more water has flown through the tap.

So it's not as simple as saying
if stop position = x
newstop position z = x + y where y is the offset
Exec Stop at z

again just a guess...

I smile, cause I've no idea what's going on.

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12-05-2006 05:29 PM  11 years agoPost 13
Colin Mill

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England

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Yes, Brian you have it right. There are two things that make life difficult in such situations - the finite speed of response of elements in the system (servo, sensor etc) and noise in the system (mainly the sensor). If everything in the control loop was capable of instant response and there was no noise in the system then you could simply run extremely high gain and all the errors would be reduced to insignificant levels.

You do see signs of this in the tail rotor system. Where very high gains are used the errors in the stop quality with a given trim error drop. With a fast servo its possible to get the 720 gyro up to over 100% gain and at these gain levels 1 degree of heading change gives about 2 degrees of servo movement. With a long servo arm that 2 degrees of servo travel give almost 4 degrees of tail pitch change. So if you have a trim error of say 8 degrees of tail pitch this will cause a post-stop heading change of perhaps 2 to 3 degrees. At a much lower gain the post-stop re-adjustment would involve a bigger swing.

Colin (CSM)

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12-05-2006 06:24 PM  11 years agoPost 14
AlanR8

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Saddleworth near Manchester (UK)

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What I like about this thread is the involvement/commitment of a major player in our market place.

How many times does Mr Average actually get the opportunity to discuss the design of a product with the guy who designed it, and invented it!

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12-05-2006 10:03 PM  11 years agoPost 15
mickeybling

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dudley wmid england UK

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hello i have just finaly tonight fnished seting up the tail on my trex now it takes patience adjusting tail rod until no drift in normal mode at 60%gain then my end stops i have to adjust using quick trim witch also helps the csm giro find center stick. every trany is diferent in acuracy, csm giros work on perfect mechanical set up in normal mode .giro work 50% harder to control the taile and just slaping it into h&h is a lazey way out ,you cant complaine when it doesnt work right .your giro has to pick up centerstick from the electronic pulses etc from the trany . i have achieved 90% gaine.i am not aguru just some who tries to undrstand the poduct i am using

mickeybling

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