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250 Class Electric Helicopters 250 Class Electric Helicopters manufactured by Align, Tarot, SYMA, Airhog, Chaos, HK and similar. |
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06-24-2014, 06:55 AM | #1 (permalink) |
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Join Date: Apr 2014
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250 vibration or tail wag sever, wind induced, not sure
I've heard people talk about a 250 tail wag. In general I think mine is at a minimum and it doesn't bother me if I notice it at all.
However, yesterday in pretty high wind, high bank turn into our out of wind, can't remember, a pretty heavy vibration started. It sort of reminded me of a tail wag, but really it was the entire heli. Almost lost control, but did my best to level and sort of wait and let the load off the blades etc, anything to let it calm down. And it did. I kept going, and had the same occur twice more but minor. I loosened blades a little and tried different things. Laster in evening I flew again and it was pretty smooth as wind had died down. Several flight and no issues. I have an align 250 dfc. Just wondering if anyone else with 250 has had this happen and what it might be caused from. Straight up wind is not always so bad for my 250, but gusty wind can often be challenging with sudden pitch loss. But I don't think I have every had wind induced vibrations. Not even sure that was related, but it seemed to be.
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Marc Norman, OK - Synergy N7, TREX 700N DFC, TSA 700N, TSA 600N, Trex 550, Trex 500 ESP (FBL), 450L, RCHN - 700 |
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06-24-2014, 08:15 AM | #2 (permalink) |
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Join Date: May 2013
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I'm no expert,others here know much more. Having said that, in my limited experience (I have 2 T-Rex 250 DFCs, with >500 "flights"), ..
- I have to run a lower gyro gain on "windy days". About 5 points lower than on calm. I think this is normal, but I'm interested in what those that know more have to say. - I have 3 gain settings on one of my Tx switches. --- pos 0 - highest gain, for calm mornings, and really most of the time. --- pos 1 - Slightly lower gain, I use this on windy flights. Also nice to have available in case "something" starts to go wrong (slop developing in tail, wind picks up, ...) during flight. --- pos 2 - rate mode. Good for final setup, and as an emergency measure. I also always flip the switch to rate mode then back right before takeoff as that causes my gyro to go to center on swash and tail. If its actual "wag" on the collective (which I call "bobble", but don't know the correct term, maybe "porpoising"?), you may need to lower gain on the collective. Once I had collective servos that were getting near end of life (slop in gears) and I had to reduce gain on collective quite a bit until I got replacements. Otherwise I would get "bobble" at times, but always on windy flights. |
06-24-2014, 10:24 AM | #3 (permalink) | |
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Join Date: Jul 2013
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Quote:
Do you loose the ability to auto-change the gain when switching between flight modes this way? Or do you have the switch somehow "mix in" with your standard gain values? Thanks. Oh and BTW, my 250 also has more tail wag on windy days. Wagging starts when I fly sideways into the wind (such as when doing funnels). |
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06-24-2014, 11:40 AM | #4 (permalink) |
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Join Date: May 2013
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mba83 - I use a 3 position switch just for gain. I use same selection of gains for normal, IU1 and IU2 (which is on a different 3 position switch). I have a Taranis Tx, so switches work however I want them to. I could have the flight mode (normal, IU1, IU2 is flight mode right? or am I misunderstanding?) modify or set the gain, but have never had a need.
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06-24-2014, 03:04 PM | #5 (permalink) |
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Join Date: Jul 2013
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Yeah that's what I meant as flight mode: IU1 vs IU2. Thanks
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06-24-2014, 05:29 PM | #6 (permalink) | |
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Thread Starter
Join Date: Apr 2014
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Quote:
Thanks for the reply. It helps to have another pilot's perspective with the same heli.
__________________
Marc Norman, OK - Synergy N7, TREX 700N DFC, TSA 700N, TSA 600N, Trex 550, Trex 500 ESP (FBL), 450L, RCHN - 700 |
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06-25-2014, 03:19 AM | #7 (permalink) | |
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Join Date: Jan 2011
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Quote:
Dr. M's CopterX/ZYX tuning thread has a lot of good general tuning information that applies to all flybarless controllers (e.g., watching for oscillations when you unload the disk in a gentle descent). Check it out: https://www.helifreak.com/showthread.php?t=485789 |
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06-25-2014, 07:10 AM | #8 (permalink) | |
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Join Date: Apr 2014
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Quote:
__________________
Marc Norman, OK - Synergy N7, TREX 700N DFC, TSA 700N, TSA 600N, Trex 550, Trex 500 ESP (FBL), 450L, RCHN - 700 |
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06-29-2014, 10:27 AM | #9 (permalink) |
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Join Date: Dec 2012
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I've got the same problem as the OP. Hovering and flying in no wind it flies great. As soon as there's a gust or moderate wind, hard banking turns into the wind and FFF the heli bogs and gets really choppy, almost like it's skipping through the air. I almost lost control a few times. My gain is set to 70 on my DX7, I'll try to turn it down and see if it fixes the issue.
Setup.. Trex250FL - Scorpion motor - Phoenix ESC/BEC - 3G Gyro - Align servos Bry
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06-29-2014, 02:19 PM | #10 (permalink) | |
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Join Date: Apr 2014
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Quote:
__________________
Marc Norman, OK - Synergy N7, TREX 700N DFC, TSA 700N, TSA 600N, Trex 550, Trex 500 ESP (FBL), 450L, RCHN - 700 |
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06-29-2014, 02:42 PM | #11 (permalink) |
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Join Date: Jan 2011
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Getting the three gains on the three axes set right is the most important part of a flybarless setup, IMHO (assuming everything's right mechanically). It's worth some study... "PID controllers" is the engineering lingo. There are individual proportional ("P"), integral ("I"), and differential ("D") gains on all three axes (though your controller may not let you adjust them all), and there's also usually one or two higher level master gain settings (on the TX, for example), that multiply all of those at the same time. The VBar is the only flybarless I've used that was pretty much plug and play, with only minor gain adjustments necessary. At the other end of the spectrum, the CopterX took months of fiddling with about 20 settings to get it right...
As a simple rule of thumb, if it's acting kind of drunken and sloppy, gains are too low on that axis. If it starts dancing/hopping/shuddering/whatever, gains are too high. And "too high" gains often don't show themselves until you do something that stresses the controller--unloading the disk in gentle descent and FFF for example. I also often see bad behavior after quickly flipping the heli inverted (especially with bad collective management--my specialty ). I thought I had my 400 perfectly tuned until I came out at the bottom of a big loop going really fast and pulling back hard on the elevator--that set off a really interesting and loud oscillation. Again, just dialing the gain back a little fixed it. |
06-29-2014, 10:45 PM | #12 (permalink) | |
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Marc Norman, OK - Synergy N7, TREX 700N DFC, TSA 700N, TSA 600N, Trex 550, Trex 500 ESP (FBL), 450L, RCHN - 700 |
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08-21-2014, 09:18 PM | #13 (permalink) |
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Join Date: Oct 2010
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Did lowering the gains fix it? I have a similar issue on a newer align 250 - started as a 250 Plus, but after a crash I replaced a bunch of stuff with metal, including the new metal tail slider - and a ds76t with carbon tail blades. Running a robird on the 250 - so no PID settings.
The tail is silky smooth on the bench. Tail blade holders are a touch loose, but I have new bearings (thinking it might help). No wind, banking climb out to nose right at about 2/3s of a battery pack and the it just starts shaking violently, but the cyclic is still responsive and it seems to come from the tail. Most times it it stops after a bit. Today though it didn't. So, I pitch pumped and it stopped. Next flight, fresh pack I didn't have the issue. The vibe doesn't seem to cause the robird to lose control (but it's pretty violent), so I can't tell what to play with. I put the gain on a 3-way and raised the gain, since I already have it pretty low, but that doesn't help. It just seems like a mechanical issue, but I can't figure it out. Also, I though about the tail shaft and mesh, but nose right would seem to help the gear mesh. Last edited by nflanagin; 08-21-2014 at 09:20 PM.. Reason: clarity |
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