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Beginners Corner > how much gain is too much?
 
 
nmrs
Senior Heliman
Location: Austin, TX

I have a new T-Rex 450 se v2 with a 401 and 9257 on the tail (I am using a 5.1v regulator before the 9257). I have delay set to 0 on the 401 and the digital mode switch is set to on. I set it up first in rate mode, but wasn't able to get an exact mechanical set up. Right now in rate mode I am getting a slight counter-clockwise drift. If I shorten the bar one more turn, I get a slight clockwise drift.

In HH mode, no matter how much gain I add, I can't get it to wag and I am getting slight clockwise tail drift. I'm using a DX7 and am using endpoints (rather than gyro sense) to set the gain. I have tried setting the gain everywhere from 50 to 105 and I can't really tell any difference. No matter where I set it at, I get a very slight clockwise drift and no wag. I can keep trying to set it higher but was worried about burning out the tail servo. Is it safe to set it much higher than 100? I've moved it back to 72 for now.
05-28-2008 09:03 PM
 
 
BarracudaHockey
rrMaster
Location: Orange Park FL

Are you sure you're actually adjusting the gain?

Center your tail pitch slider when the servo is centered in rate mode, then adjust the limit pot so you have equal travel and no binding in either direction.

Then set it to heading hold with about half the available gain. If it holds, leave it alone.

The two important questions are, how far from the center of the servo wheel to the center of the ball, and where do you have the limit pot set to?


AMA 77227
http://www.jaxrc.com
05-28-2008 09:09 PM
 
 
nmrs
Senior Heliman
Location: Austin, TX

I think I am adjusting the gain. Gyro gain wire is plugged into the gear channel, and I am raising the endpoint of the gear channel. That's how to increase the gain isn't it?

9mm from center of servo wheel to center of the ball, and the limit pot is set to about 95.

After I set it up in rate mode, slider was no longer centered. Should I recenter it and just let it drift in rate mode?
05-28-2008 09:28 PM
 
 
BarracudaHockey
rrMaster
Location: Orange Park FL

I would, though there is some debate about it, its how I run mine. Don't sweat the rate mode setup, just center it and leave it in heading hold.

Does the gyro boot with a solid light correctly? Thats a lot of gain to not get tail wag.


AMA 77227
http://www.jaxrc.com
05-28-2008 09:30 PM
 
 
nmrs
Senior Heliman
Location: Austin, TX

I recentered it, and yes light is solid when it boots in HH mode. Light goes off if I switch to rate mode, so it seems that the gyro is sensing gain -- at least enough to know that it is in HH or rate mode, but I can't get rid of the drift or get it to wag... I guess I could try pushing it even higher, but a little nervous to push it much over 100...
05-28-2008 10:38 PM
 
 
nmrs
Senior Heliman
Location: Austin, TX

Quote 
though there is some debate about it

Yes, I know. I had originally set it up centered. I reset it up in rate mode to see if that fixed anything after reading the finless bob tail setup thread (http://www.runryder.com/helicopter/t434711p1/). Results were the same: slight clockwise drift and it won't wag... Since setting it up in rate mode didn't seem to change anything, I went back and recentered it.
05-28-2008 10:48 PM
 
 
nmrs
Senior Heliman
Location: Austin, TX

I just tried maxing out gain -- ran it briefly at 150 just to see what would happen... Result was same, still won't wag. I'm just at the hovering stage, so I can't really say how tail will hold in flight, esp backwards flight, but should I send the gyro back as defective?
05-28-2008 11:58 PM
 
 
HeliSmith
Senior Heliman
Location: Canyon Country, CA

Rebinding the DX7
First of all the tail drift in HH mode is usually fixed by rebinding this is because the receiver remembers your gyro center. I have had to do this after months of flying with no problem then all of a sudden.... Make sure you have NO trim on the rudder and rebind. I am not talking about subtrim but some people go to the extent to 0 this out as well. While you are rebinding anyway make dang sure you rebind with throttle at 0. I personally set my throttle curve for normal to all 0 then put my stick in the middle and bind like this. This way if the heli enters failsafe, god forbid, the pitch will go to 0 and the motor will turn off. Don't forget to put your throttle curve back. Again no trim on the rudder for the radio when you are binding.

Gear Endpoints let's make sure:
Since you are using gear endpoints I could just assume you turned off the gyro sense menu but let's double check. I want to setup using gear endpoints so I can flip into rate mode just to setup my tail. I want the gyro sense menu turned off.

1. Get into model select. (Hold Scroll down + Select when turning on radio.)
2. Scroll down to INPUT SELECT and set GEAR = GEAR not GEAR = GYRO. (Bye bye gyro sense menu)
3. Push Scroll down + Select to exit model select menu. Push Scroll Up + Select to get to Function List. Find Travel Adj. Scroll Down + Select will put you in it.
4. Push select until you get to GEAR. Set that top value to 50. Usually you will be around 45 - 60 let's start with 50.
5. Pull the gear switch down to be able to set the L value. Set this lower value to 0. (I don't use rate mode except to setup my gyro so I want no gain.)

So it will be GEAR H: 50 L: 0 or whatever it looks like in the radio. This is by memory.

Start up procedure:
Always start the heli with the gear switch up, HH mode, then move it to rate mode to setup the tail. Otherwise it won't initialize properly. If you ever want to reset your gyro click the gear switch 3 times quickly (within 1 second of each click) ending with it in the up or HH mode position. Again never ever start your heli with that gear switch in rate mode. Also the 3 clicks to reset the gyro is the same as first plug in never move the heli when the gyro is reseting.

Tail Setup:
Now let's talk about tail setup. I want to set my tail pitch slider right in the middle in rate mode. When I push the rudder in both directions I want to be 1 split hair away from the tail case in one direction and the hub in the other. I don't care if my tail blades are flat because HH mode just needs 100% travel.


P.S.

The adjust until tail wag method doesn't always work. Sometimes it just doesn't wag and no two setups are ever the same even using the same parts. Running too much gain can cause your servo to fry from millions of little movements you can't see. Keep it to the norm unless you see a problem.

*** Team HeliHobby.com ***
05-29-2008 01:12 AM
HOMEPAGE  
 
 
nmrs
Senior Heliman
Location: Austin, TX

HeliSmith, thanks for the great post. I'll start from scratch and redo everything per your instructions. One question:

Quote 
Usually you will be around 45 - 60 let's start with 50.

How do I know if/how I need to change this up or down from 50? Lower it if it wags (which mine never has) and raise it if tail won't hold?

Sorry if these are annoying beginner questions, but this is my first heli....
05-29-2008 02:18 AM
 
 
Funky Trex
Key Veteran
Location: Westerville, OH - USA

I would start at 53 using the gear channel (not the gyro menu) and adjust from there. I have set up a lot of 401s on Trex 450s and the majority seem to like this number. I would start there and if it holds, leave it.

Make sure any tail rod guides and all mechanical movement is silky smooth.
05-29-2008 02:22 AM
 
 
Markus87
Senior Heliman
Location: Melbourne, AU

check to see if you have any rudder trim on. I messed around for a while with my gyro trying to get rid of a sidways creep. finialy figgured that i had rudder trim on by 3 points and that was causing the drift. I dont know about the tail way though, what happens when you pump the throttle? any change in the tail?

"Takeoff is optional, landing is not"
05-29-2008 03:10 AM
 
 
Zman9545
Veteran
Location: The Golden STATE

Setup as per Barracuda.
I use same method and it works with no problems. Also note that your endpoints controls your piro rate in this case and don't confuse it as means of trimming your rudder. Use a lazy Susan if you got one during this setup. Another thing to keep in mind during this process is that when in rate mode your tail linkage will follow your stick movement in relation to each other. Hence when at center it will also return to center. In HH mode, the rudder moves with the stick but does not return to center even when the stick returns to neutral. Don't move your heli during this process. Other than that, this is the easiest way to verify what condition your gyro is in prior to setup.


Trex600N Pro
Kinetic 50

-The ONLY way you fail is when you quit.-
05-29-2008 03:33 AM
 
 
HeliSmith
Senior Heliman
Location: Canyon Country, CA

Quote 
How do I know if/how I need to change this up or down from 50? Lower it if it wags (which mine never has) and raise it if tail won't hold?

If I got past 50 and no wag personally I would fly it inverted backwards with some altitude to see if I had a problem. For instance on my Trex 450 SE V2 running 3500RPM head speed if I put it to 55 the tail blows on me in the inverted pull up doing tail first loops. Since this may be a ways off for you just leave it at 50-55 until or unless you see a problem. I have one of my 450 helis at 50 and the other at 55 but no two helis are the same unfortunately even if they use the same setup which doesn't make sense but is true all the same.

*** Team HeliHobby.com ***
05-29-2008 02:16 PM
HOMEPAGE  
 
 
nmrs
Senior Heliman
Location: Austin, TX

For now I'll set it to 53 per Funky Trex's recommendation. Like you said, no 2 helis are the same, even with the same setup, but this number fits conveniently in the middle of your 50 - 55 range so seems a good starting point.

Quote 
For instance on my Trex 450 SE V2 running 3500RPM head speed if I put it to 55 the tail blows on me in the inverted pull up doing tail first loops.

Not that I will see this problem anytime soon, but just in the interest of curiosity, what is the remedy here? Do you run a higher gain so you don't get the tail blowout? As you mentioned, no 2 helis are the same, so I am guessing that some helis would hold fine at that gain, while yours won't.
05-29-2008 02:48 PM
 
 
speeddemon370
Veteran
Location: Spruce Grove, Alberta, Canada

Lots of good advice here but one thing seems to be omitted. Have you tried mounting the slider farther out on your servo horn? I know someone mentioned that at the beginning but I didn't see if you tried it or not.

with 2 ears and 1 mouth you should listen twice as much as you talk
05-29-2008 03:51 PM
HOMEPAGE  
 
 
Skarn
Senior Heliman
Location: Pasadena, MD

Markus87 has great advice there. Make sure you don't have any rudder trim!

Skarn

It's better to burn out than to fade away...
05-29-2008 04:02 PM
 
 
HeliSmith
Senior Heliman
Location: Canyon Country, CA

Quote 
Not that I will see this problem anytime soon, but just in the interest of curiosity, what is the remedy here? Do you run a higher gain so you don't get the tail blowout? As you mentioned, no 2 helis are the same, so I am guessing that some helis would hold fine at that gain, while yours won't.

The remedy for me was to drop it back from 55 to 50. It will still blow if I bog it flying tail first but it holds pretty solid otherwise. We are talking about a perfect 180° blow out too so really a non critical thing.

*** Team HeliHobby.com ***
05-29-2008 04:26 PM
HOMEPAGE  
 
 
HeliSmith
Senior Heliman
Location: Canyon Country, CA

Quote 
Markus87 has great advice there. Make sure you don't have any rudder trim!

Skarn

I said the same thing under the bolded header rebinding. So when Markus says it then it is great advice?

Just messin Skarn!

*** Team HeliHobby.com ***
05-29-2008 04:30 PM
HOMEPAGE  
 
 
nmrs
Senior Heliman
Location: Austin, TX

Thanks all for the great advice. Here is how things stand:

I followed HeliSmith's instructions to the letter (though I used 53 gain, per Funky's recommendation). This included ensuring I had no rudder trim or subtrim (I had neither), rebinding the receiver, initializing the gyro in HH mode, then switching it to rate mode to get slider centered, upping the limit on the gyro a bit to take advantage of full travel without binding.

Result of first test flight: exact same as before! I haven't tried adjusting the gain any, but I am still getting the annoying tail drift.... I know this is probably wrong, but after gyro initialized, I did add one click of trim to see if that would fix the drift. All that resulted in was it slowly drifting the other way... Like I said, its a very slight drift, but annoying none the same. I am just working on tail in hovers, and every 10 - 15 seconds, I have to bring the tail back in line as it has moved out 30 degrees or so.

I will now try changing the servo horn (I am just using the round one now, so can't really go further out) to get the slider a little farther out per speeddemon370's recommendation.
05-29-2008 04:37 PM
 
 
Funky Trex
Key Veteran
Location: Westerville, OH - USA

You are not moving the heli AT ALL during startup until the gyro initializes, right? The heli needs to remain absolutely still until the gyro light goes solid after startup.
05-29-2008 04:43 PM
 
 
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Beginners Corner > how much gain is too much?
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