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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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12-15-2014, 04:12 PM | #1 (permalink) |
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Replace swash bearing?
Anyone know how to remove the swash bearing? My original and also a new replacement are both far too sloppy for my liking and I'd love to pull it out and replace it with something better. The slop is affecting stability (even with the spring I detailed in another thread).
I see there are two shallow slots on the inside surface of the inner portion of the swash that could be engaged by a special tool.... anyone know if they are used to unscrew that inner portion? I tried using a large screwdriver that fit the slots moderately well but I could not get it to budge. And I don't want to apply heat because the bushing the center ball rides in is plastic. Paul Last edited by pgoelz; 12-15-2014 at 07:19 PM.. |
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12-15-2014, 09:07 PM | #2 (permalink) |
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I have 3 DFC swashplates. They all have this slop. I'd love to find a way to tighten them up. I ordered a SE swash to see if it's any better.
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12-16-2014, 01:24 AM | #3 (permalink) | |
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Quote:
I am also wondering if there is a way to remove that slop? |
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12-16-2014, 05:40 AM | #4 (permalink) |
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The SE swash balls are farther from the mainshaft, right? If so, that would magnify any slop and be counter productive unless there was a LOT less slop.
What might help would be to ditch the DFC head and go to a more conventional setup like the CopterX head, with (I think) the grip arms farther from the mainshaft. Other than that, the only things I can think of are to either replace the bearing or preload the bearing with a spring on the mainshaft like what I detailed HERE. I am currently using the spring. It is a careful balance between enough tension to remove slop under normal conditions and too much tension, which increases servo load. You can try the concept by looping a small rubber band from one arm, over the stopper button to the other arm. It does the same thing. I may sacrifice my old swash and see if I can get it apart without destroying it. A really big screwdriver with some careful shape profiling is about the right tool to fit into the center and engage the slots. That, possibly plus some heat should be able to get it apart. Since they all seem to have slop, I wonder just where they get such consistently awful bearings Paul |
12-16-2014, 01:47 PM | #5 (permalink) |
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I searched the forum a little and saw one post that mentioned using a feeler gauge to fit those slots.
Seems to be the feeling that this slop is inherent due to tolerances relative to the size of the part, but the swashplate in my Gaui X2 is the same size and has no slop whatsoever. It does seem if you could replace that bearing, you could fix it. I may try tackling the disassembly as well. |
12-16-2014, 02:16 PM | #6 (permalink) | |
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Quote:
Would the Gaui X2 swash fit the 250? I believe it is a 3mm shaft so if so, it would not...... Paul |
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12-16-2014, 02:32 PM | #7 (permalink) |
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Correct, because of the shaft it would not.
This is an old thread, but post # 15 is interesting. (I can't figure out how to link to a single post.) Swash Plate rebuild |
12-16-2014, 02:46 PM | #8 (permalink) | |
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Paul |
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12-16-2014, 03:34 PM | #9 (permalink) |
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Indeed. Armed with that knowledge, I custom ground a screwdriver to fit the slots and unscrewed mine. It took a bit of effort to get it started but I got it out. It was a bit harder to get the bearing out but with the upper part of the swash removed, I heated the lower half without worrying about the plastic part and tapped the bearing out. Both the threaded inner sleeve and the bearing were thread locked.
The bearing is 9mm ID X 14mm OD X 3mm thick. I called Boca and the only one they had was the SMR679 for $11.95 each. I ordered two. I'll report back when they arrive if they are any better than the stock bearing. If nothing else, at least the bearing is now serviceable. Paul |
12-17-2014, 01:23 PM | #12 (permalink) |
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OK, I've been looking closely at the swash and the slop as observed at the blade grips. I also took apart my second swash just to make sure I can, before the new bearings arrive. This whole exercise is in response to some wiggle in a hover in non-still air. It got better when I went to the Lynx hard dampers but it never went away completely. It is pretty good, actually. But not rock solid like my little 130X.
I have been pretty certain that the issue is simple mechanical slop, so I have been trying to get rid of whatever slop I can. And I have some observations...... 1. The swash bearing definitely does have some slop and I am hoping the Boca bearings improve it. The slop in both my swash assemblies (one new and one original to the heli) is similar. I tried reducing the slop in one bearing by tapping it down a tapered mandrel to increase the OD of the inner race but I'm not sure it did anything. 2. I have found that the servos are contributing at least as much slop as the swash bearing.... if not more. These are Align DS415s, original to the heli as purchased used. They are the first DS415s I have used so I am not familiar with what is normal slop. I have some HS65HB servos I could try that have zero slop, but they are analog and only capable (I think) of a 50Hz update rate so what I might gain in slop I might also lose in slower updates. 3. Biasing the whole swash / servo system with either a spring on the mainshaft or a small rubber band from one grip arm over the stopper button to the other grip arm helps A LOT in flight. Both tend to preload the entire system so any slop in the swash, linkages or servos is biased to one side. Since this is so effective, I am encouraged and will continue to try to remove slop. 4. The servos and linkages in my 130X are far from slop free, and I am trying to get my head around why it is so much more "locked in" than the 250. My best guess is that the 130X only appears to be locked in because it makes much less rotor wash and the air it flies in is less turbulent. 5. My 250 is a scale ship and has always been a bit tail heavy. This morning I lengthened the battery mount to move the battery as far forward as possible and I think that also helped. Perhaps because the hover thrust is now more vertical because it does not have to compensate for a tail heavy condition? If I ever get this thing flying perfectly, I'll probably get bored with it Paul |
12-17-2014, 01:28 PM | #13 (permalink) | |
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additional info
Quote:
I noticed slop in my servos also. I'm using Eflight ds76. Usually when I strip one, I just replace the stripped gear, it's always the same gear that strips. I found that if I replace all the gears (they come as a set), it got rid of the slop. I did that on all three cyclic servos and got a noticeable improvement in flight. I'm hoping that replacing the swash bearing and going to the new Zeal 210mm blades (when they are available) will help even more. Last edited by Murph_d; 12-17-2014 at 01:41 PM.. Reason: additional info |
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12-19-2014, 12:01 PM | #14 (permalink) |
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Well, now I'm not so sure my mild instability issues are primarily the swashplate slop. Or any slop.
As an experiment (I'm retired and I don't have anything important to do) I replaced the two front servos with HS65HB (very little slop). It flew about the same. OK but not rock solid. So I called that experiment a failure and put the DS415s back in. In the process, I noticed that something had shifted and the swash was no longer level with zero pitch at center sticks. Dunno.... maybe I swapped the servo horns and the teeth are not molded the same. In any case, I set up servo center and swash level all over again on the BeastX. I then did some test hovers and reset the swash neutral point (the cyclic trim in BeastX speak) and whaddya know.... it flies better! Mind you, the servo setup wasn't far off to begin with. But now it is right on. I don't know if it is coincidence or not, but now it really hovers nice and solid in the small space I test hover in the basement. I consider it a good place to test the heli because it is no more than maybe 4' from major obstructions that cause all sorts of turbulence. I also like lifting off from the concrete floor because it reveals any small trim issues. Properly set up, it lifts straight up into a reasonably motionless hover without any right stick intervention. It is also, of course, a good place to test the pilot I have even hovered my 450 there a couple times during testing. Stupid and dangerous, yes. I don't do THAT very often So it will be interesting to see how the new swash bearings work out. And I also discovered I have a sloppy ball link end that needs replacing. Between the two of them, I expect I am getting close to perfection. Paul |
12-20-2014, 02:30 PM | #15 (permalink) |
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I got the swash apart, no problem. I'm eagerly awaiting the new bearings from Boca bearing. My issue with this bird has been that sluggish midstick response mentioned on many other threads. Otherwise it flies smooth as silk, whisper quiet (compared to my other helis), no discernible vibes or tail problems and is the perfect size for my flying area.
I had about 3 or 4 degrees of slop in the blades. Replacing the gears in all the cyclic servos took care of about half of the slop, and the improvement in the midstick collective response as well as general flight was significant. I'm hoping that if I can remove the swash slop, I'll have the perfect little flyer. I'm also considering cutting down some 250mm CF main blades to about 215mm just to see how it flies. |
12-20-2014, 02:47 PM | #16 (permalink) |
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I'll be interested in how those cut down blades fly. But be careful... isn't there a tip weight that might then be free to catapult out of the end of the blade?
Paul |
12-20-2014, 03:01 PM | #17 (permalink) |
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I didn't know that, I'll keep my distance (I always do).
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12-20-2014, 03:12 PM | #18 (permalink) |
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If a blade ejects a tip weight, two things will happen.....
1. The weight will likely come out at the speed of a low speed bullet at blade height. You have a one or two in 360 chance of getting shot unless the rotor disk is above your head height. If hovering at body (or worse, eye) height, distance is only a partial protection. 2. The rotor will suddenly be massively out of balance and the heli may shake itself apart. I actually know someone who was shot with an ejected tip weight from a 30 size. It put hole in his belt and a big bruise on his belly. Paul |
12-20-2014, 08:13 PM | #19 (permalink) |
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Thanks Paul. I'm glad I mentioned it (and glad you responded). I'm always learning stuff on these forums.
I'm not going to be trying this soon, I ordered a pair of 215 main blades (for the SJM 180, a flybarred heli). It will be awhile before they get here, and I'll be trying that first. If fixing the swash slop helps, I might not bother. I saw a post from earlier this year by Luca at Lynx Heli indicating that 215mm blades in CF and plastic were on the agenda. I imagine the Oxy is taking up his time now however. But....I'm wondering if there is a way to seal the tip after cutting the blade. |
12-22-2014, 08:31 PM | #20 (permalink) |
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They are, and anyone who installs an SE swashplate, please remember to dial down cyclic gains. Don't repeat my mistake Had my 250 crash very badly today due to a horrible cyclic wobble that I couldn't recover from. I took off in low RPM, but as soon as I switched to idle 2 I got that wobble that wouldn't go away even after I switched back into idle 1. The heli broke up into multiple pieces right in the air! I didn't even have a chance to hit TH. My worst crash so far, but luckly I have all spare parts (except the belt and the OWB). Man, only after the fact I realize that I should have hit the self-level switch, as I have the cyclic gains set to a lower number on my self-level bank.. Last edited by mba83; 12-23-2014 at 03:36 PM.. |
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