Stripped gears in front AND back...

[TeroS]

I'm by no means a 3D-flyer, more of a big air-dude.

I've crashed my 800 Xxtreme now 3 times this summer, all of them because of stripped gears. First two with tail-gears, today with stripped gears both in front and back. Thankfully landing was extremely lucky, bladeholders and rear-tube bent, some shaft's need to be replaced just for peace of mind.

This happened in slow, big diameter funnel, blades in, tail up. I know the stress on tail is big on funnel but it was smooth, absolutely nothing special there.

There is no possible way this is caused by too big mesh, I shimmed both front and back. The mesh is done so there is a "free run" with barely noticeable "high spot", so it was not too tight either.

I do have a small difference to original setup. I have the original 5035-380 rewound to 6+6x1.7YY 390KV and it's run with Kosmik 200A and 4400mAh 65C batteries. Pitch is +.11,5 and rpm was 1800.

The thing is, this setup does not bog, in practice no matter what I do it just does not bog, only draws some amperage from batteries. (A lot...)

I'm thinking in this way: Could it be that there simply is "too much" power available and the material gears are made from is surrendering under the pressure?

Opinions? Facts?

I'm thinking of having the gears done in metal. Any interest?

[rcmarty]

I've had the front gears in my 700 and 800 both melt and cause a crash.

I started some threads to try to find out why and didn't get very far.
Apparently it's not an issue and doesn't happen.

After $1800 between the 2 crashes I'm not so sure myself.

Keep in mind I love my logo's and the Mikado product 110% . Heck , just jumped all in on a vbar control last year and some neos this year.

My opinion to the best of my knowledge and a few theory's ...

One theory is gear lifespan - 800 melted at 132 flights , 700 at 116 flights. These are too close together to ignore.

Gear lube , the consensus is to use the ' dry fluids ' gear lube on the gears.
I have been using the dry fluids since the rebuilds.

currently - 82 flights on the 700 , 139 flights on the 800

Gears look good , but I can't say I'm not nervous these days. I have the local heli event coming up in a few weeks so I'm going to leave it alone for now , but if I get board there's a great chance there getting swapped out.

So technically the 800 has surpassed the ' 100 ' flight mark on the gears.
The front tranny gears have been my issue and there all but impossible to inspect when assembled. The tail section I've taken the tooth brush to pull out the old lube and re lubed the gears with dry fluids again. No mention on the lifespan of the dryfluids product so I figured why not.

Another thing to consider is gear mesh..

Going back to the logo 600se days , I had a nice shiny new logo 600se , on the 60th flight the maingear melted on me. I'm a OCD builder and gearmesh can take me quite some time till I'm happy. Noting only 1 gear shimming issue in thousands of flights.

Turns out the mesh was to tight and the day it melted was a hot day. Typically I fly up to 30-32 C , this day was closer to 35 and after 60 flights is was starting to get more aggressive with it.

Now I mesh a little looser than before with the Mikado maingears , the herringbone pattern is ok with a slightly wider mesh.

Moral of the story is that Mikado plastic as hard as it is can expand a bit in the heat.

So the gears that were carefully meshed to perfection (I'm assuming here) in the house at a comfortable 24 C have now expanded a touch in the summers heat (30 ish) , now are too tight and have a high risk of melting.

The mesh scenario for the longest time had me thinking the 800 crash was my fault. Not until the 700 did the same thing so close in flight count that I realized it wasn't me.

My 800 during spooldown with 0 pitch and 0 on tails would make a rattling like noise. I figured the gears were broken in and needed to be re-shimmed. I reshimmed the front gear set by taking one of the thin washers that is on either side of vertical gear and moves it to the bottom to shim up gear and tighten up mesh. Heli was one again quiet on spooldown.

Now I build to book spec and don't reshim and not worry about the rattle on spooldown.

Hope this helps some , I'm assuming not as much as you'd like (I've killed an 800 also) but it hopefully helps some how.

I'd suggest a looser mesh and dry fluids for sure. Call them consumables and replace gears at 100 flights is another good thought.

Martin

[rcmarty]

Also when shimming the gears have a close look at them and the way they mesh.

IMO I think they could be moulded at a slightly different angle to bring the ID section out a touch

I find when the OD mesh is tight the ID mesh is still quite loose.

I set the OD at tight as I dare and make sure to get decent engagement on the ID

If you have more than 1 pack of gears handy , mix and match in hopes of a better fit.

Martin