250 plus with dx7 question.....

[blueleagueflyers]

Hi guys im a newb with the 3gx mrs and its driving me crazy! Any help will be appreciated. Its on a 250 and im using a old school dx7. Once i set everything up and triple checked everything i took it out for a maiden hover.

I first noticed the heli was trying to spin left once it got light on its skids.

2nd hover attempt i gave its some right stick just to get it in the air. Once i let go it violently spinned to the left.

The gyro gains on my dx7 are both 40 the gyro is on f. Mode and not set to rudder. I noticed when i set the gains to 40 the status light on the 3gx mrs is red. When i raise the gain on normal to 53 the status light goes green but when set at 53 its hardly any movement in the tail when i go left and right on the rudder.

Today i noticed i dont have any gyro in the tail with the status light red or green. Im wagging the tail left and right, its not counter acting with the movements at all.

So now i have decided to turn off the gyro to see how it flies without. Now it hovers and i can fully control the tail but the tail wag is some what violent.

I cant keep flying it without the gyro and im sure the crazy tail wag is coming from the gain. Please help me! I heard its been problems with these in the past but i think this problem is all me.

[bazsound]

gyro correction wrong direction. You really need to check everything is moving int he right direction before attempting to test fly.

This means physically moving the heli like its yawing and watching the tail blades/slider to make sure the gyro is giving the right correction. If not it will spin like a top.

I dont have a 3gx but it could be set to the wrong installation direction, or the servo needs reversed, or theres an option to reverse rudder correction direction.

[blueleagueflyers]

Thanks for the response. I checked direction of the rudder and its correct. Ill take the tail apart tonight and inspect for any binding. I also heard gettting a better tail servo fixes the problem so thats my next option.

If anyone is out there that can help me with the gyro setup with a dx7 i would appreciate it.

Im not sure if i sould have the gyro sens set to RUDD D/R or Auto F.MODE

[bzlytbeer]

I believe it should be F.MODE. This may help:
[ame="https://www.youtube.com/watch?v=ikbmEpOx6QI"]Setting gyro with DX7 - YouTube[/ame]

That vid is a little blurry and not the easiest to understand.

Finless has a really good one, and explains DRs really well:
https://www.helifreak.com/showthread.php?t=28681

[nflanagin]

I believe the old dx7 used a 0 to 100 scale rather than a plus/minus scale. So, 50% on the gyro menu = 0% gain, above 50% is heading hold mode and less than 50% is rate mode. Align calls heading hold mode AVCS. The 3gx mrs manual says to start at 55% or 5% gain which is pretty low. At 40% gain, your basically in rate mode, meaning the tail will not hold heading,

Now, rate mode is not a bad thing, When I set up new heli's after getting my tail servo and tail levers both at 90 degrees, I use rate mode to fine tune dead center in flight. Flip the gain to rate mode and check it in a hover - it will piro one way or the other at mid stick. I adjust the pitch link to get as close to holding the tail dead center in hover - it's never perfect and there is always a slight move left or right even when screwing in or out the pitch link 1/2 turn. Once I get as close as I can in hover, I land, set the gyro back to heading lock mode with the recommend gain and also change the tail travel so I don't get any binding either left or right. For a 3gx mrs you do that with the servo end points in the radio, other FBL units do it in the unit's software. By doing this the tail will have a slight pitch at dead center to fight the torque in hover and you will be able to maximize your tail throws left and right.

[nflanagin]

I was wrong on the rudder travel limits. In the 3gx mrs, you use the set button on flash 5 and then flash 6 to set the tail travel limits. Page 30 of the manual covers it.

[bazsound]

Originally Posted by blueleagueflyers

Thanks for the response. I checked direction of the rudder and its correct. Ill take the tail apart tonight and inspect for any binding. I also heard gettting a better tail servo fixes the problem so thats my next option.

If anyone is out there that can help me with the gyro setup with a dx7 i would appreciate it.

Im not sure if i sould have the gyro sens set to RUDD D/R or Auto F.MODE

a better tail servo is not going to solve your problems. You can mask binding by brute forcing with a really strong/fast servo but spinning like a top is not a servo issue.

you need to get your tail correcting in the right direction and your gyro setup with enough gain to hold the tail and not wag

[blueleagueflyers]

Wow thanks for all the help guys. When i get home i will post back results.

[nflanagin]

If you were watching the Align Fassbinder video on 3gx mrs setup, he was using a DX8. The gains are different, e.g. 0%-100% on old DX7 and -50%.+50% on dx8. So, I would probably start on an old DX7 at around 75% although he started at 40% which would equal 90% on an old DX7.

[blueleagueflyers]

Originally Posted by nflanagin

If you were watching the Align Fassbinder video on 3gx mrs setup, he was using a DX8. The gains are different, e.g. 0%-100% on old DX7 and -50%.+50% on dx8. So, I would probably start on an old DX7 at around 75% although he started at 40% which would equal 90% on an old DX7.

It worked! Set the gains to 75 and bam tail is holding like a charm. Thanks to everybody for the help. Happy flying