n4t

I have noticed that my Trex 450SE V2 makes high pitch noises during flight. It seems to quite down when I hover. Wondering if it could be bearings wearing out but which one? Could it be the bearings in the Align motor or the two bearings on the main shaft or maybe some other bearing...? is there a way to locate/identify the bearing that needs replacement or do I just replace all of them (think there is a bearing kit one can buy).

Thanks guys

Trexcopter

My Feedback: (4)

You just need to replace all to them.  I have  a Trex 450 pro. just made a same noise. After I replaced gears and bearing. Smooth operator.

mnemennth

You can tell a lot about the source of a noise or vibration by feeling the chassis while the drivetrain is spinning. When I'm hunting a noise or vibration first I'll remove the main blades, clamp the heli down to my bench and spin it up slowly, observing, then feeling for vibration. You'd be amazed how often that resolves the issue; time to inspect & balance my blades again.


BE VERY CAREFUL! The front side of the tail rotor (DUH!) WILLBITEYOU! SOWILLTHE FLYBAR! Always be mindful of exactly where your extremeties are in regards to moving parts; I cannot stress this enough. It is too easy to take these little machines for granted; they WILLmake you pay the price. If you're lucky, it'll just be a few love nips from tail blades or friction burns from a spur gear; but even just the flybar paddles have enough mass to break or amputate a finger and the tail rotor can cut to the bone. Goggles are also a VERYgood idea.


Tail rotor bearings are a common failure, and a slightly bent tail rotor shaft can cause bearing noise as well. In my experience, either will often manifest in waggling of the vertical fin. This can usually be verified by feeling for vibration at the back side of the tail rotor assembly. If you can feel a vibration in the center of the tailboom that doesn't seem to be concentrated at either end, it could be a worn belt or cogs in the belt drive. Inspect tail rotor cog and belt drive cog; if there's bits of rubber dust or lots of fuzz, or the cogs appear worn, replace the belt and any suspect drive cogs. If this happens with relatively little flying time on the airframe, you may be tensioning your belt too tight. Don't forget to inspect the bearings in the belt idler pulley in the tail assembly! They can make SUCH a screech as you wouldn't believe!

After that, try isolating the drivetrain bit by bit. Loosen the tailboom, unwrap the belt from the drive cog. If your noise or vibration goes away, you've eliminated the tail spur gear, autorotation gear, belt drive gear and motor. Check all the bearings in your tail rotor assembly very carefully. If the noise persists, then you can start taking things apart at the mainshaft. You can disassemble the mainshaft and reassemble the autorotation (upper) gear and hub to the shaft without the tail spur (lower) gear; just assemble it with a spare bearing sleeve for the one-way clutch (This is the metal sleeve that's pressed into the lower gear that you always have to be careful to get aligned with the screw holes in the lower gear when you accidentally spin it while assembling the gear cluster).

If your noise goes away, then probably the bearings in the belt drive countershaft. If not, then probably main bearings or motor bearings or some internal fault in the motor (like a loose magnet or metallic junk rattling around; I had one motor pick up a rusty staple from the ground, made it wail like a banshee but no harm once removed). Again, feel around the mainshaft bearing blocks (CAREFULLY!) or disassemble the mainshaft and feel the bearings as you turn a bare shaft by rolling it against the inside of a finger while the shaft is inserted into one bearing at a time. If they aren't smooth, or feel even a bit crunchy or gritty, time to replace 'em.

Things to look for before you tear it all apart:

Make sure your belt is tensioned properly; it can make a heluva racket if it starts to skip teeth when the tail is loading up. Again, look for lots of black dust or fuzz; this is evidence of a worn belt.

On your bench, check that both main gears turn true. Even a 0.5mm wobble can translate into a lot of vibration and noise. When you assemble the lower gear, be very careful not to overtighten the main screw. This deforms the plastic of the lower gear and it can also deform the one-way bearing sleeve, causing the upper gear to wobble. LOTSof noise &vibration when this happens.

Loosen the motor and slide it away from the spur gear and tighten it down so the pinion doesn't contact the spur gear. Spin up the motor and feel around for your vibration. Anything more than just noticeable is an indication of a motor out of balance or maybe a bad motor bearing. Both of these are so common you wouldn't believe it, even with new, name brand motors. I won't get into motor balancing here; it's an art form I'm still trying to master after 20 years. I've seen brand new, name brand motors vibrate so badly they make a 450 heli walk off the bench on its skids!

Last ditch tests, if you have the tools & know-how:

Balance the motor spindle.

Make sure your one-way bearing & gears run true by spinning on a prop balancer or new mainshaft. Spin the main gear backwards (the way it spins freely) and see that it continues to run true. If not, remove the gear from the hub and check the hub for trueness the same way. You would not believe the number of crap one-way bearings I've seen in the wild; a good prop balancer and the Align one-way bearing press tool are tools I recommend every 450 owner have, whether you run genuine Align or not. If you don't have the means or inclination to press the bearings yourself, do yourself a favor & buy a couple of genuine Align main gear hubs with the one-way bearing installed, and maybe a couple of new one-way bearing sleeves from them at the same time. $16 each for the hubs, $6 for a pair of sleeves. Especially with the T-Rex clones, you will not believe how much truer the gears run, and how much smoother your whole heli runs with them.

Test your main shaft and tail rotor shaft and, where possible, your motor shaft for trueness using a Dial Indicator. You can get a serviceable one and the required base at Harbor Freight for about $28. You will not regret this expenditure. Catch a sale on their Digital Calipers when you can; get one with .001" scale accuracy and inch/mm scales. Typically on sale for $9.99-14.99. Again, you will not regret this expenditure.

In case you didn't guess, I'm an Engineer. Not exactly a good pilot yet, but LOTS of experience tearing these little machines apart & putting them back together after I crash...err, fly them.

Good luck and good hunting,

mnem
This is real life. of course there will be a test.

Rafael23cc

My Feedback: (6)

NEVER, NEVER, NEVER Clamp a helicopter down to anything! Or spin a helicopter without it's blades securely fastened.

Here are a few videos that will show you why:
[link]http://rc.runryder.com/helicopter/t704752p1/[/link]
And please, do not say that you do it slowly, carefully, or what not. By you suggesting it, is enough to perpetrate the extremely dangerous activity. Newbies do not know better. I did not read the entire post. You might have great info there, and it looks like you do, from a fast scan of the content. It is just the strapping down part.


to n4t:

I know it is tedious, but disassembling the helicopter and carefully looking at all the parts is your best bet. Sometimes you don't even have to disassemble it. Just carefully looking at the areas where rotating parts meet non-rotating parts, you can get a pretty good idea of what is going on. If you have to disassemble, take the bearings and spin them carefully with your fingers feeling for rough spots or what not. They should be silky smooth, if they are not, you need a new one.

Rafael

n4t

Thanks a lot for all the info guys.  I have decided to replace all the bearings as I do not have the technical knowhow. I will keep you posted as to the outcome as soon as I have done so.  Once again, thank you so much!