Pig loose from Pin

[Jumna]

My Protos, a bit of a pig at 1850g, was getting stressed out with tight funnels and bad piroflips, gave out a squeal and yawed out of control and took out the grips, blades & frame bottom. The cnc tail gear slipped away from the pin. I thought I had it in there pretty good and even added a little CA.

Is there a trick to getting it to stay? Is the plastic tail gear better?

Really liking the protos, except for the sneaky pin......

[alexf1852]

I use the CNC tail gear and never had an issue with it. Even with 500g batteries flying hard. Did you have your shims on each side of the gear? Are you using the stock tail case? Are you using the right size bearings in the tail case? The reason I ask is because you should not have any room for that pin to come out because the shim and bearing keep it in there.

[DoubleCH]

While my 1st CNC 20T tail gear last a long long time (maybe 1500 flights, properly shimmed, rotor perfectly balanced), I had to finally replace it (I have close to 2000 flights on my Protos) from normal wear-and-tear accelerated by the flawed design that has the pin NOT sitting on the blade-side of the tail gear. If you don't CA the tail gear to the tail shaft like I do, the normal anti-torque tail thrust will push the pin against the shim on the bearing, causing the shim to crush and may eventually break. The pin should've been designed to sit on the other side of the tail gear so that the anti-torque tail thrust (the reaction force to it, to be specific) can push pin against the tail gear and let the tail gear press against the bearing so as to even out the pressure with a much bigger area than the pin.

[Jumna]

alexf1852, I have all the standard shims and parts. Tho I just noticed that the pin side shim looks concave, so I'll replace that. And I'll clean the oil away and also ca the gear in addition to the pin, maybe that'll do it...
Thanks.

[DoubleCH]

Before and while CA'ing the gear to the tail shaft spin it to make sure the gear doesn't wobble on the shaft.

[alexf1852]

Not sure what's different, but I've never CA'd the gear to the shaft or pin to the gear/shaft. You might have some strong vibes causing your issues.

[DoubleCH]

Like I said my tail has been meticulously balanced and there's zero vibes. My tail case bearings last over 1000 flights. The key is lots of flights (~2000) and after running my double-idler and solid steel pinion mods hundreds of flights ago I started flying harder doing things like full aileron/elevator mobius transition with responsive 470 blades and fast cyclic servos. This maneuver barks the main blades crazy and would've slipped stock belt/pinion/OWB setup for sure. And then there's stuff like full rudder vertical piro and then sudden stop in between tic-tocs that's not just hard on the tail but sudden impacts on the pin. This is like going full collective descend while piroing and then hard-stop both he piro AND descend at the same time. And then there's the high-speed pie-dish (port-side) that spans almost the entire flying field that I love to do since day 1 with my Protos. This maneuver runs almost full 45 degrees tail pitch constantly and presses the pin against the shim and bearing.

[alexf1852]

I'm not saying the shim doesn't wear out after many flights. It does and it needs replacing. Since I change belts often enough, I probably change the shims often enough before it completely fails and allows the pin to come out. I wonder if using 2 shims (or 1 thicker on that side) would last longer and help with that.

[DoubleCH]

At one point I had 2 shims on the pin-side of the tail gear but if the CA holding the gear to the shaft broke, the pin would still crush the shims. If anything 2 shims were worse than 1 because the flawed design still has the pin pushing on the shim(s) if tail gear is not CA'ed to the shaft, regardless of how many shims are used.

After my solid steel pinion and double-idler mods, belt replacement is about 5-600 instead of 150-200 so it's easy for me to forget to check if the CA is holding the gear to the shaft.