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Old May 16, 2011, 08:11 AM
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Zurich
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Originally Posted by Geir Skjaervik View Post
Hello,

I got a 5888 a couple of days ago. It flew great, but starting yesterday, it will not keep in the air for more than about 2 minutes. There is much more life in the battery, but obviously not enough to keep more than in ground effect , about 5 cm = 2 inches off the floor. I have not had any serious accidents with it, but the blades has hit furniture a few times at low forward speed.

Something that needs adjustment, or do I have a bad battery?

Any comments / ideas?
From my rather extensive experience with 5888s (likely well over 20hrs total flt. time and having to replace defective or me-damaged [from excessive heat, till I learned to tune and also to stop and COOL frequently as needed!], but mostly worn-from-age motors, about 30 motors in total I guess) ..... I have never! encountered a bad LIPO when the heli showed poor performance and would only really fly for a short time and then only in ground-effect.

It was always a bad, tired or dying motor!

First, proper tuning & tracking is very sugnificant in analyzing performance issues (I have posted numerous tips throughout this thread as I discovered "what's [uniquely] what" with the 5888).

A properly tuned & tracked 5888 will show reasonable performance right up to the end of the minimal LIPO charge (of course it is very important to stop flying well before the auto low-voltage cutofff!). During the last minute or 30 sec of flt. it will have difficultly maintaining altitude in fast banked right turns, but do OK with those to the left. At the end of the useful charge it will drop from flying altitude to the ground, despite full throttle, in less than 10 sec.

In contrast, a bad or dying motor will more slowly lower the heli into ground effect.


Here's the trick to find out what is the case with yours >

1. Fly it in ground effect -- continually checking with your lower lip for heating! -- untill the rotors start to have trouble speeding up from standstill, taking almost 2x as long to reach "flying speed". Then STOP!

2. Cool off in the refrigerator for 4 - 5 min, allow a minute to re-warm closer to room temp, and charge.


For me, using the 220v "wall"-charger, a NEW 5888 will take perhaps 70 min for a full charge. An older, much-used LIPO might take maybe 60 min.

If your LIPO, after being flown & charged as in 1. & 2. above, takes at least 50 min for this full charge, the LIPO is OK. Unless you have been seriously abusive charging your LIPO, I'd expect at least a 60 min charge in your case.


Then it's motor-replacement time ....!


Good Luck,
Lee
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Old May 16, 2011, 08:28 AM
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Zurich
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Originally Posted by d4v1d View Post
i've really enjoyed my 5888, however it's developed a fault recently.

Lipo is good, blades are good, swash is good, as far as i can tell... all is good.

but when hovering it rotates in circles. The helicopter points in the same direction but rocks in a steadty circular motion?

can any advise why this might be? I'll try get a video up later
I posted earlier about this oscillation.

The first thing to check is the upper rotor stabilizer/flybar link, Try putting it on the other side of the flybar. If there is still a lot of "play" in the top & bottom ball joint, you must either replace the link or accept the problem.

If the link is very tight, allowing only a few tenths of a mm free movement (half the thickness of a credit card, MAX!), thern the problem is related to inadequate "tuning" and interaction between the upper & lower rotors.

In that case you must be sure that the rotor blades are 180 balanced, which can be tested with a small pile of clear tape on the underside of the tip of one, then the opposite blade to see if vibration stops and tracking improves. Then micro-track the blades (see my earlier posts) on both, now-balanced, rotors.

When I have done all of the above to those of my helis showing this slow circular oscillation .... the problem was totally eliminated!

But the real "problem" is that it is often inobvious which rotor is imbalanced or not precisely-tracked by first eyeball examination ..... when you get it exactly right, THEN, in my experience, do you see the difference between perfect tracking and what seemed very good before!


Lee
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Old May 16, 2011, 09:08 AM
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Joined May 2011
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Thanks Lee, this does make sense. When I put on the throttle and look at the blades, the bottom rotors do seem to 'oscilate' up and down at the same frequency the helicopter rotates. i dont know the best way to balance the blades though. I'll try tape on the tips of one blade to try and blance it and see if that helps, if it doesn't i'll put tape on the other balde and see then.
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Old May 16, 2011, 11:14 AM
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Originally Posted by d4v1d View Post
Thanks Lee, this does make sense. When I put on the throttle and look at the blades, the bottom rotors do seem to 'oscilate' up and down at the same frequency the helicopter rotates. i dont know the best way to balance the blades though. I'll try tape on the tips of one blade to try and blance it and see if that helps, if it doesn't i'll put tape on the other balde and see then.
I've been lucky enough to accumulate a veritable PILE of blades, so I can find pairs with the same weight, etc.

Once you find out how much weight differential is needed for balance, if not much, you can carefully remove material from the heavy tip (and file smoothly curved as it was molded) ..... or add CA gel to the light tip, and then file smooth. If a lot is needed, take one strand of fine copper "wire" of the approx size twisted-cable "wire" used for the motor wires and imbed it in the CA gel.
Or a micro-sliver of solder, etc.

Just to fine-tune your terminoligy, the vertical axis of the heli rotates in a precession-like manner. The axis wobbles, we say ....

Lee
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Old May 16, 2011, 11:32 AM
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d4v1d, I forgot to re-mention what I discovered and posted previously about this rocking/wobbling > the UPPER rotor may be "invisibly" causing the lower rotor to oscillate .... and that could be most likely because the upper rotor flybar-link is way too loose!

Lee
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Old May 16, 2011, 05:58 PM
Joined Dec 2004
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Hello Lee,

Well, the motor can hardly be worn out after about 20 minutes flight. The first day I could fly 6 minutes straight no problemo. The engines does NOT get hot, not need to stop and cool frequently as you state: I touch them with my lip: No heat. My living room temperature is about 20 deg C (68 deg F).

You must spend a LOT of time tuning your equipment: My job is taking most of my time, and I do this for leisure. I am an electrical and software engineer, writing real-time control systems for the industry. I fly rc controlled airplanes or helicopters to unwind when I am not flying my full size Gyro:

http://forums.dpreview.com/galleries...58043/p1300097

Geir Ove
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Old May 17, 2011, 04:57 AM
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i didn't get the chance yesterday, but later i'll check the flay bar, it could well be that!

i'm expecting delivery of a new 5888 today also!
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Old May 17, 2011, 08:29 AM
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Quote:
Originally Posted by Geir Skjaervik View Post
Well, the motor can hardly be worn out after about 20 minutes flight. The first day I could fly 6 minutes straight no problemo. ....Geir Ove
What happens is that more often than you'd expect the tiny and very cheap brushes break! Or get worn down very quickly. Whether a motor was defective from the start or became defective from abuse or over-use, once the brushes are bad, the under-performing motor will not get hot. The reason to keep the motors cool is to try to prevent this from happening, as the shaft will tighten in the "bushing" and overload the motor, causing excessive current to flow through the cheap brushes and thus likely cause premature failure. From my early experience with 5888s, I am highly convinced that 6 minute nonstop flying will quite likely destroy the motors in this manner.

Lee
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Old May 17, 2011, 08:41 AM
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Zurich
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Quote:
Originally Posted by Geir Skjaervik View Post
You must spend a LOT of time tuning your equipment: My job is taking most of my time, and I do this for leisure. I am an electrical and software engineer, writing real-time control systems for the industry. I fly rc controlled airplanes or helicopters to unwind when I am not flying my full size Gyro:

http://forums.dpreview.com/galleries...58043/p1300097

Geir Ove
NICE plane! Years ago I met with Igor Bensen [ http://en.wikipedia.org/wiki/Igor_Bensen ] to consider a joint venture building a man-carrying version of the "Tuned Interactive Autorotative Dynamically-RIGID-Rotor Craft" [so-called "Tandem Giro"] I invented
(or discovered). I backed out, as I feared his approach would get someone killed.

As for "ground-maintenance" for my 5888s, after one to 4 hours initial adjusting, etc., I usually only need to spend a minute or two every 2nd or 3rd flying/charge-cycle. For me, this is enjoyable and relaxing, as I love improving things and unpuzzling puzzles with real-world results. Also, I tend to be a bit of a perfectionist.


Lee
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Old May 19, 2011, 02:55 PM
when is the wind stopping??
markkona's Avatar
Malta, Marsaskala
Joined Apr 2011
1,524 Posts
Hi All. I have been having lots of fun flying my last 5888 and also some crashes as I get more comfortable with my flying skill and try new manouvers |However I noticed a strange whirring sound recently and decided to check it out and to my disbelief I found tthat it was due to a wobbly inner shaft and upon further inspection found that the lower brass bearing or washer had it's hole slightly widened thus causing the inner shaft to wobble excessively! this brass bearing/washer is located between the two lower plastic gears and there's an exact one like it embedded in the plastic holder or sleeve that goes over the top of the main shaft. is there a way to adjust this because I have serious doubts that I'll be able to find a replacement part anywhere on the net or locally.


found it or at least I hope it's included as in picture of this listing on ebay. it's one of the three washers on the left of plastic gear B.
http://cgi.ebay.com/ws/eBayISAPI.dll...tchlink:top:en
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Old May 19, 2011, 03:53 PM
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Cupertino, CA
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are you sure your shaft is not bent, that sounds more probable then a bearing/washer hole widening up all of a sudden.
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Old May 19, 2011, 04:01 PM
when is the wind stopping??
markkona's Avatar
Malta, Marsaskala
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the shaft isn't bent. if it was bent the heli wouldn't be able to hover in the same place!
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Old May 20, 2011, 10:16 AM
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Originally Posted by d4v1d View Post
i didn't get the chance yesterday, but later i'll check the flay bar, it could well be that!

i'm expecting delivery of a new 5888 today also!
Well, one of my older but refurbished 5888-B's started wobbling a LOT today. After swapping out many parts, in the end it was the ball-joint (had to change the inside plastic piece that spaces the two alu plates) & link to the upper rotor flybar that had to be replaced.

Entire adventure took over 4 hours (incl. recharge).

Lee
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Old May 20, 2011, 01:42 PM
when is the wind stopping??
markkona's Avatar
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4hours well spent but seriously I think I spend as much time tinkering with the 5888 as much as charging it lol

Mark
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Old May 21, 2011, 07:52 AM
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Originally Posted by markkona View Post
4hours well spent but seriously I think I spend as much time tinkering with the 5888 as much as charging it lol

Mark
1. Full size helis require ca, 7hrs of very expensive maintenance for every flight-hour!

2. "Ya' get nothin' for nothin" [Physics Law > 0 = 0 ]. I am sure the higher-performance helis costing far more require far less maintenance, but repairs are also far more costly. At any rate, the more I learn (and post here), the less time I spend making mine perfect (which is not necessary, but my personal choice, and I do get a satisfaction from this doing & learning process ....).


Lee
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