T-Rex 450 DFC - Wobbles on Collective - HeliFreak
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Old 04-30-2012, 05:02 PM   #1 (permalink)
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Default T-Rex 450 DFC - Wobbles on Collective

I've read a few threads about wobbles, and I've been dealing with it on my 450 for a while now, thinking it was a side-effect of the head (Tarot FBL).

So I finally got my DFC head installed and the issue is still there, I've played with Pot 1 (nearly all the way down) and it is still present. It's very noticeable with pot1 in the factory position, so lowering it does help a bit, but not enough.

So going down the list of potential issues:
1) Headspeed - I'm running Scorpion-6 Motor (4400kv) w/ 11t pinion and 40C 2.2A lipos, my headspeed is easily 3200+ at all times.
2) Dampers - Brand new DFC head, hard plastic dampers, brand new grip bearings, etc.
3) Mounting Tape - Hard 3M grey tape, sitting on the anti-rotation bracket tray. I have not tried relocating the BeastX yet.
4) Servo strength - I purposely went with slower, very strong servos, the Savox SH-0255MG, running them at 6V.
Speed(@4.8V sec/60): .16
Torque(@4.8V oz-in): 43.1
Speed(@6.0V sec/60): .13
Torque(@6.0V oz-in): 54.2
5) Swash is perfectly level (using a leveling tool)

Other noteable - I am still running flybar blades, and cheap carbon's at that. I did, very briefly have a set of Edge Flybarless blades before I trashed them, and they blades made no noticeable difference in flight characteristics for me.

Vibrations are minimal with the blades removed. I can spool up to 100% on the bench and the servo's don't twitch.

So in detail, what I experience is, upon collective changes, mainly noticeable when flipping to hover inverted, the heli seems to wobble a bit and almost appear to have to catch itself before leveling out. Once hovering, it is rock solid, floating like a dream. Pitch pumps also exhibit the behavior of making the heli roll a little to one side, but not a significant amount.

Any ideas here?
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Old 05-01-2012, 08:39 AM   #2 (permalink)
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5) Swash is perfectly level (using a leveling tool)
But are the servo arms 90 when the swash is level and zero pitch?

what you describe sounds like they are not.
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Old 05-01-2012, 09:24 AM   #3 (permalink)
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But are the servo arms 90 when the swash is level and zero pitch?

what you describe sounds like they are not.
They are as close as I can get them by eyeballing them. It may be worth taking them out and double checking it again, I can see where that would cause issues.
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Old 05-02-2012, 05:52 PM   #4 (permalink)
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it might be the servos, very slow servos dont seem to like fbl. .09 seems to be a sweet spot and any faster is always better.
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Old 05-03-2012, 06:14 AM   #5 (permalink)
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I was thinking the same. 0.16 does sound a little slow to me.
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Old 05-03-2012, 08:35 AM   #6 (permalink)
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servo speed has to do with how locked in you can get because of their ability to react faster, slow speed servos don't cause bobble unless they have too low a torque and/or poor centering ability and the Savox do not in a 450 application.
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Old 05-04-2012, 07:54 PM   #7 (permalink)
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I was thinking the same. 0.16 does sound a little slow to me.
I'm running at 6V, so 0.13

I went back and re-checked all the mechanical setup. The servo arms are at 90, the swash is level.

I did get some replacement blades, the 325 3G Blemish blades, it seemed to soften out a tiny bit, but there is still a significant amount of wobble with large collective changes.
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Old 05-04-2012, 08:30 PM   #8 (permalink)
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I tried to capture it on video the best I can. It's not really noticeable, but here it is anyways.

[ame]http://www.youtube.com/watch?v=QwSUG40jSes[/ame]
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Old 05-04-2012, 08:35 PM   #9 (permalink)
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How is the CG?
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Old 05-04-2012, 09:36 PM   #10 (permalink)
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How is the CG?
It's a bit nose heavy, running turnigy 2.2a 40c packs. I don't really have a way to change the battery mounting unless there is a trick I don't know about.
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Old 05-05-2012, 06:57 PM   #11 (permalink)
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Originally Posted by jaofos View Post
They are as close as I can get them by eyeballing them. It may be worth taking them out and double checking it again, I can see where that would cause issues.
Sounds like you need to spend the $10 and get a swash levelling tool.

Re: wrecked blades...are you 100% sure your feathering shaft is 100% straight? I rolled mine and had no noticeable wobble, but 3500RPM turns small wobbles into big ones.

I'd also say check your blade tracking, and remove the blade grip links and rotate the blade grips and watch the tip of the blade. If it wobbles around -- feathering shaft.
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Old 05-05-2012, 10:12 PM   #12 (permalink)
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Quote:
Originally Posted by seanp2k View Post
Sounds like you need to spend the $10 and get a swash levelling tool.

Re: wrecked blades...are you 100% sure your feathering shaft is 100% straight? I rolled mine and had no noticeable wobble, but 3500RPM turns small wobbles into big ones.

I'd also say check your blade tracking, and remove the blade grip links and rotate the blade grips and watch the tip of the blade. If it wobbles around -- feathering shaft.
I do have the swash leveling tool. That's why I am sure that the swash is level with the arms at 90.

I went ahead and replaced the feathering shaft. I took it out and rolled it across my glass desk and didn't see any obvious wobble, but I had a brand new pack of feathering shafts so I replaced it. I'll see tomorrow if that made a difference.

I really should have captured some rainbows or tic-toc's on the video, that's where the issue is the most noticeable.
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Old 05-06-2012, 11:07 AM   #13 (permalink)
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Quote:
Originally Posted by seanp2k View Post
Sounds like you need to spend the $10 and get a swash levelling tool.

Re: wrecked blades...are you 100% sure your feathering shaft is 100% straight? I rolled mine and had no noticeable wobble, but 3500RPM turns small wobbles into big ones.

I'd also say check your blade tracking, and remove the blade grip links and rotate the blade grips and watch the tip of the blade. If it wobbles around -- feathering shaft.
You were exactly right, it was the feathering shaft. Thank you so much! I did a few tic toc's this morning and the stops were very crisp and she finally flies the way she should!
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