JetPlaneFlyer

Flying on the weekend with my Trex 600Pro DFC and during a fast ascent the front bevel gears driving the torque tube to the tail rotor stripped completely and I lost all tail drive. Probably more by dumb luck than skill I hit throttle kill, which stopped the wild pirouetting, and again probably more by luck I managed to auto-rotate it down for a safe landing. No harm done other than the bevel gears and my underwear

The bevel gears were around ten flights old, they were the new upgraded and supposedly stronger black ones. I've not had any tail rotor strikes in the ten or so flights since fitting the new black gears and there wasn't much slop in the gears. I never had any issues with the old type white ones, I'm thinking of just putting those back

Here's what the gears look like:




Apparently having the governor gain too high may be part of the cause of this. I had the gain on the Castle ESC set to 'medium' which is a value of 25. The advice I've been given is to set it below 15. I've also added some shims to the hears to remove the slight play that was there, which is supposed to help. Hopefully that will avoid the same thing happening again. I'm beginning to understand why many people prefer belt drives!

pizzano

JPF.....yes, seems you've just experienced one of the common reasons many prefer "belt drive" over "direct drive".......lots of torgue in the "rear-end" provides a better amount of response (as you are aware).....but as some cost if not supported by both power management/distribution and very good ($$$) moving parts.......

At least it's not a difficult fix and can be managed.......good job bringing her home in one piece........!

fhhuber

"not much" slop in the gears can be way too much... The general rule is just barely looser than binding.

JetPlaneFlyer

As standard they are non-adjustable, so they just 'fit where they fit' and by design there is nothing you can do about it.

What i did was grab some 0.1mm (0.004") shim washers that were intended for the transmission on RC cars and shimmed the bevel gears so that they were just on the verge of being tight. I also slotted to mounting holes for the gearbox/tail support case so it could slide forward tightening the mash of the straight cut gear that you see in the photo, just in case that might go the same way.

If the wind cooperated I'll test it today.

CHELLIE

Good Save JPF they sell some metal gears for the 550 , 600 & 700 heli, I dont know who sells them, you will have to research it.






http://www.rcheliresource.com/produc...pro600efl-pro/

http://helidaily.com/metal-torque-tu...550600e600efl/

http://www.rcgroups.com/forums/showthread.php?t=674857

JetPlaneFlyer

Good find Chellie. I have heard others mention those metal gears. They used to be sold by Infinity Hobby but are no longer stocked. I found the manufacturer in Taiwan, but cant find anyone who sells them.

Hopefully the changes I made will sort the problem, I flew it three times today and it seems ok.

CHELLIE

The white nylon gears should be good enough if its not pushed to hard, the metal gears would be good for Hi performance use, Take care and have fun, Chellie

JetPlaneFlyer

There are many flying these helis EXTREMELY hard with the standard gears. I think the gain setting on the ESC governor, along with the slight play in the gears was probably the main cause of the problem I had.

With the governor gain in the caste ESC set at 'Medium', which is a value of 25, I could hear a 'chirping' noise when i did hard full power collective manoeuvres like pitch pumps or fast loops. I didn't think anything of it at the time, but according to those in the know this chirping is caused by the gears lashing back and forth due to having the governor gain too high.

I backed the gain off down to a value of 13 and between that and shimming the gears that chirping is totally gone, so I'm quite confident that I wont have the same problem again... (fingers crossed!)

For what it's worth, here's an almost identical heli to mine, with the nylon gears, showing what it can do:

JetPlaneFlyer

So nine months later i've not had any more problems with the bevel gears. I'm sure adjusting governor gain was key but shimming cant have done any harm either.

I've got a couple of newer and 'fancier' helis but the Trex 600 is still a real favourite. I've done few upgrades including putting on a longer tail boom and bigger main and tail blades, it's now a Trex 623 I've also fitted a 'Kbar' flybarless controller which I cant recommend highly enough, they are just fantastic at any price but at $35 for the 'full size' variant they are unbelievable value. Also fitted are KST HV brushless servos.

Anyway here it is flying in cold and breezy conditions earlier today. My mediocre skills are the only limitation now!