Unexplainable Drift

[Tattoo13]

I have search this forum high and low for a reason of why I have a significant and aggressive drift right and backwards. Of course this occurred after a hard crash and rebuild. I have been through a full set up several times with the same results. And when I say full set up I have done everything I could find on this forum and in the HH videos to be sure I did not miss anything. With everything I have done, this thing should be better set up than out of the factory. If anyone has any other ideas of weird things that could be causing this I would appreciate it.

[butterfingers]

So you have a level swashplate then? Just making sure. Also

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[butterfingers]

Also make sure you don't have any trim in the TX.

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[Jherison]

Is your heli balanced? Mine did the same until I added some weight to the tip of the fame and the left side. There may be a better way to do this, but I lifted the heli by the flybar when parallel and perpendicular to the tail and looked for how the heli would lean. I used about 1/2 ounce total of stick on weights.

Just a though, check it out.

[Fuse Engineering]

Mine did the same thing. I posted a video of it. It was caused by the set up. Swash was not level. Also make sure there are no major vibes. I am still trying to figure out why my tail would always drift right. I replaced the stock gyro with a 780 and no more drift just a wag that would not change with any amount of gain then put on a align 790 and it holds perfect. But back on topic check your swash level first. good luck

[Tattoo13]

Yep, C.G. is right on, the swash is perfectly level. Took out all the radio trim and did the servo setup. pitch has been set, blades are balanced. Really did everything I could find between all the posts and setup scenarios on heli freak. That is what is so strange about what is happening. I did have to replace gears in all but the tail servo but unless there was damage to the servo motor itself I cannot come up with a cause to the problem. And each time after I go through the setup it takes a significant amount of trim to get the heli back to a stable hover.

[Bananaslug]

Make sure that BEFORE you put the servo horns on (as close to 90deg as possible) that you have set all subtims back to zero. Also, I have done this...when I put the servo horns on, I had the collective stick all the way negative, and did the entire set up from there. It made for a really funky set up. Usually when things go wrong, it's something so simple we overlook it.

[Tattoo13]

Yep, subtrims were set to zero, sticks were centered. It's really the craziest thing (well almost) that I have seen. Would it be possible to warp the frame in a crash that could have this effect? Or could have the servo motors have been damage in the crash that would cause this. I would think if it were any of the servos motors I would have all different out of trim situations. Maybe it just needs another good crash...which I am sure will come sooner than later

[Fuse Engineering]

Can you adjust the trim on your radio while your flying to get it to stop?

Also you can use sub trims on the cyclic servos to get them to 90 deg. ( I think) just no sub trim or any trim on the tail. just move the servo.

[Tattoo13]

Yes I can get it to stop for the most part using TX trim but it takes an excessive amount. Servos have been put to exactly 90 degrees each time I re-do the set up. One thing about trimming it out with the TX is that it feel a bit unstable after using that much trim to get it to a close stable hover

[gtrsteele]

Which servos do you have to trim to get it to settle?

[FailureToFly]

I just did two setups on two different 450 3Ds.

I made sure the swash sat flat on the swash tool after I'd leveled and sub trimmed the horns.

At mid stick the swash sits totally flat with exactly the same amount of clearance and even movement (if you shake the gently) between the 3 servo to swash links.

But today, both helis still drifted.

One backward and the other right and backward.

Now this obviously means my setup wasn't corrrect (or the swash tool and top of the heli frame don't provide a perfectly flat reference) but it's about the best I can do at this stage with my current skillset...I really tried to be as careful and precise as I could and did one heli twice (that was the one that only drifted backwards).

The simple solution was trim them and then use the trim settings that keep them pretty balanced in flight to adjust the swash link rods.

I added a turn to shorten the front ele link and bingo, the heli hovers. The other I'll just check my trim settings and add a turn to shorten the appropriate rod by a turn every two trim clicks and it should be pretty much spot on.

I'll get better at it but I'm pretty happy overall with how it's going and how I can pit crew my heli now. There is ALOT to learn with this hobby in a VERY short time period!!

[FailureToFly]

Originally Posted by gtrsteele

Which servos do you have to trim to get it to settle?

Now I'm no expert but as my heli is doing what yours is doing (back and to the right) but more benignly, I'm going to shorten my left (looking from the tail forward) servo to swash link and shorten my front elevator link as well.

Try one full turn of the rod for every two clicks of trim you added. Just centre the trim and count the clicks.

Anyone, if I'm wrong, please set me straight!!

[red420]

check your fly bar is the same length . thats what mine did

[Tattoo13]

It takes about 8-10 clicks of forward elevator and about 6 clicks of left cyclic. My issue with.... well my issue is that this was not the case before the crash. Yes I could adjust the links to take care of the drift, however this places the swash in an out of level situation which mean I have really not solved what the real problem is. The fly bar is perfectly centered as well. While watching the Flyers beat Devils today I will do a tear down and go through the set up again and report back. Should be able to get it done and a test flight in this evening. Thanks for all the suggestions thus far.

[gtrsteele]

Can you post pics of the entire head assembly and swash plate? Maybe myself it somebody else will be able to see something out of the ordinary. Also, when you adjust the trim does swash look visably unlevel?

[Tattoo13]

So after another full setup still have the same problem. Although the swash plate itself is fully intact and seated, I am starting to wonder if one or more of the ball link arms on the swash itself was tweaked just enough in the bad crash to be causing the problem. Just a thought

[jdFin]

Keep in mind that in a hover, you are at 3 or 4 degrees pitch, not at midstick any more (where you leveled the swash).

Assuming you are leveling the swash at midstick (0 degrees pitch), and also leveling it a full up (~10 degrees pitch or so), then maybe it is not perfectly level on the way up between those two positions. Since you have the tripod, it is easy to check - level at midstick, level at full up, then see if it remains level at about 1/3 - 1/2 up from midstick. IIRC, when I had the DS76es on, there was sort of a slight wobble as it moved down. If it is doing something like that, you could try leveling at about +4 degrees and see if the drift is reduced.

I mention "when I had the DS76es on".... I think the hitecs I have on now are a bit more "identical" to each other than the stock ones were, reducing need for travel adjust for one thing. I don't know if that's by chance, or a difference in tendency between the two brands.

[Tattoo13]

Yeah I have adjusted the endpoints and what seems like everything in between. I need to order some spare parts so I think I am going to order a new swash as well and give that a shot. I am also going to upgrade to the hi-tech servos at some point to. I think something a bit more rock solid can only help. Once that's all done I suppose it will be time to take the dive and convert the old bird to FBL

[drdrums]

If your CG is dead on (balances right under the main shaft) and you've leveled with a swash leveling tool, and you still get a backwards drift, I can only think of two reasons why, mechanically speaking:

1) the swash plate itself is out of whack - level to the servo control horns results in a slight backwards tilt to the inner rotating portion. In that case, changing the swash should fix the problem (I'd say the Align 450 swash, if it will fit, or something CNC). Alternatively, adjust the servo links until the drift is gone. You should be able to spot this problem if you put a pitch gauge on the blades with them perpendicular to the craft's long axis (i.e. hanging off each side) - the blade off the left will have more positive pitch than the one off the right (assuming I'm remembering the main disc rotating CW when viewed from the top, otherwise it will be the reverse). Or,

2) The frame is manufactured/damaged in such a way that there's a slight tilt to the main shaft which somehow throws it off, while giving the illusion that the craft is balanced. In this case, the blades will show equal pitch all around the disc.

Otherwise, I can't think of any other way to explain it. Anything out of whack on the head above the swashplate would manifest itself as either poor blade tracking or a vibration, not a drift. Because the head rotates, misalignments would be experienced across the entire disc.

Now, if your radio isn't set up right, that's a different story. For example, if servo travels vary (e.g the swash isn't level at full +\- collective, while level at center), that will manifest itself as an increasing tendency to drift in a particular direction as greater collective is applied.

For some reason, backwards drift sems to be a relatively common problem with the 450. The craft tends to be tail-heavy, which explains much of it. Me, I just dial in trim, about five clicks forward. My lateral drift is negligible.