help on rc helicopter vibration

[chly3001]

hi everyone, started out on rc helicopter not so long ago. bought a kds 450qs from skyhobbies. i know everyone's going to say it's crap and all but i had to start somewhere i guess

anyway my problem is this: after my first (rather bad) crash (dont worry i got a simulator after that) i went about fixing my heli. however no matter what i do the main shaft just doesnt stay centered when it spools up, causing some vibration. i've already replaced the whole rotor head unit (ordered the whole set and replaced it after just replacing the main shaft failed) and it still vibrates. it's like you know how a car wheel spins smoothly and the center of the hub stays in the center? this one doesnt, it keeps wobbling about

im really lost as to what's the problem and would appreciate any help from anyone here. hope to hear from you guys, thanks!

[perdification]

Check your main bearing blocks and their accompanying bearings. Also, roll the main shaft on a smooth glass surface and make sure it runs true.

Remove the rotor head, leaving the main shaft and spool up, does it wobble?

[perdification]

Oh and I think this thread should be in the RC helicopters discussion section? If any MODS see this, please help. Thanks.

[observer]

Oh and I think this thread should be in the RC helicopters discussion section? If any MODS see this, please help. Thanks.

This IS the RC helicopters discussion section. Is there a dedicated section on troubleshooting for heli here?

[DH_Admin]

This IS the RC helicopters discussion section. Is there a dedicated section on troubleshooting for heli here?

This thread was originally posted in the Newbie SOS section. On request, I moved it to this Helicopters section. At the moment there isn't a section for heli troubleshoorting. Since the question requires the help from experienced heli flyers, this section should get more response.

[feudallordcult]

chly3001, u mentioned a rather bad crash. Depending on yr definition of a bad crash: If yr main blades are busted, main gears stripped, boom bent...I'm afraid a complete teardown would be necessary. In the past when I crash, I would swop out the main & spindle shafts regardless of damage. Check all moving components cos anything can cause unwanted vibes. One thing that I neglected in the past was the tail rotor shaft. If yr schedule does not permit, then pay for repairs at LHS.

When you have repaired the bird and it flies great, that is IMHO the true essence of this hobby. Happy fixing and dun give up.

[perdification]

chly3001, u mentioned a rather bad crash. Depending on yr definition of a bad crash: If yr main blades are busted, main gears stripped, boom bent...I'm afraid a complete teardown would be necessary. In the past when I crash, I would swop out the main & spindle shafts regardless of damage. Check all moving components cos anything can cause unwanted vibes. One thing that I neglected in the past was the tail rotor shaft. If yr schedule does not permit, then pay for repairs at LHS.

When you have repaired the bird and it flies great, that is IMHO the true essence of this hobby. Happy fixing and dun give up.

Good suggestion... Also, you might find it a useful method to take all the parts out and try spooling up, then slowly putting back component by component to determine where the vibes are coming from.

[feudallordcult]

when spooling up to test for vibes & integrity of rebuild, I would first remove the main and tail rotor. mark the top of the shaft with a tamiya red paint marker. If the red dot retains its "size" during spooling, then its good to go. If the dot "enlarges" and there is noticable vibe, change the main shaft. You may also wish to inspect the bearings as it could be damaged after a crash. if the bearings cannot spin freely i.e. notchy, then change it too. dun forget to use bearings retainer (green colour) during installation. I recall having seen a tool gauge in infinity hobby which allows the user to check for integrity of the main & tail shafts. good and inexpensive.

[feudallordcult]

http://www.infinity-hobby.com/main/product_info.php?products_id=9556

shaft gauge

[perdification]

Whoa bro, so high tech ah... I just use the rolling on glass table test, it works good for me. But the OP stated that he already replaced the main shaft, unless the replacement part was also bent...

[feudallordcult]

haha, i dun use it. I just swop out the main & spindle shafts regardless of damage. once a bird has a crash or hard landing, there is just no way of knowing if the steel has "weakened" so the only insurance is to change it.

Bro chly, it may seem pretty daunting initially but hang in there. the rewards will be great...I promise u that.

[hallobaby]

take out all the blades and spool up the helicopter till all the shaft is turning at a comfortable rate.
notice the following:
1. the main shaft remain straight?
2. the swash plate is wobbling?
3. the tail slider is wobbling?
4. hold the heli and feel the vibration?

Note:
Only spool up the heli 1/4 or less throttle.
Not to touch any moving parts.

[FyreSG]

My first CP heli is also a KDS 450QS. I won't say it is crap as it works fine. Without experience, you may not see the problem. Perhaps you could bring to a funfly and ask for some guidance. While I learnt a lot fixing the heli myself, I learnt more when I get my questions answered on the spot by friendly bros.

One advice - if the plastic parts break, buy new ones and not repair with CA (super glue). If the ball links are pulled out of the plastic swashplate in a crash, do not put it back with super glue. I learnt it the hard way.

[chly3001]

hi everyone! wow thanks all for the replies! am really very glad, didnt pop by in a week and so many replies already thank you!

how bad the crash was: it went to about 3-4m high? this was the first time i was flying (previously flew co-ax so i realised the move up was a bad move) when i tried to move it to the left i expected it to auto level itself after i released the sticks. naturally it didnt and it tilted to the left straight down. the field was elevated so it fell onto (thankfully) the grass between the pavement and road which was another 1.5m down. chipped the main blade and bent the tail boom. yup that's the story of my crash

i've already changed the main shaft a couple of times (new ones each time, thought the first time round was bent. rolled them all and they were straight) in fact i have changed the whole rotor head (they sell it as a set, not cheap ) and tried spooling up without the main blades but the thing still vibrates. i'll check out the bearings and other stuff you guys mentioned. one noticeable thing is the large main gear also vibrates (all without the blades on) the vibration does go down somewhat as i increase throttle to around 50% but it's still there

will update you all as i go on, and once again thank you everyone for your help!

[feudallordcult]

Bro chly, think for u to upgrade to goblin liao...