Trex SE v2 Main Gear Wobble

[nrubens]

Hi,

I am in the process of building my first Trex Heli. I have noticed that the main gear has a bit of wobble. The main shaft looks like it is seated correctly. Could the main gear be defective? or is there something I am missing or should check?

[Ranc68]

I think I know what you mean because I noticed on mine the two gears are not exactly parallel with each other. Is this is what you have noticed? If it is, i have been flying mine with no problem. I'm not an expert but can do mild 3D and I am always impressed at how good this thing flies!

[nrubens]

Yah, thats exactly what I have observed. The main gear, I should have said, is warped (slightly?). This is my second Heli, I am not really at mild 3d yet. So as long as your flying I am good with that too.

[GEARHEAD]

The main gear wobbles, not because it is warped by itself, but because it gets distorted a little when it is assembled with the aluminum flange. The flange is a .004" - .005" on the diametral interference fit in the recess in the center of the gear, which distorts it, and the recess itself is not perfectly flat or parallel with the outer face of the gear. Another problem is that the one-way bearing isn't perfectly round, means the flange won't run true when indicated on it's face or outside diameter. This, plus the fact that the .985" diameter recess for the flange doesn't
run true to the outside diameter of the teeth, means you not only get wooble, but
eccentricity, making it impossible to get consistant backlash all the way around.
The gear by itself is actually flat within .003". I just bought a package of 3 gears, and they were all like this.
The solution requires some machining:
1. Put the gear in a pie collet, and re-machine the recess flat, and no more than .001" smaller than the diameter of the flange. Inspect the parallelism of the recess with a dial indicator, with the gear lying flat against a surface plate, or make a simple spud in the lathe to put the gear on so you can check the out face with an indicator while you turn the spindle.
2. If you don't have access to a cylindrical grinder to put the bearing on a mandrel and true up the O.D., the next best thing in turn a spud .238"-.239" diameter, put
the flange with a new one-way bearing in it, and face a couple thousanths off the flange. The lathe spindle has to be running in reverse (away from you), so the bearing will be in the locked mode, and the top of the bearing should be against a shoulder on the turned spud.
If you were to grind the O.D. of the bearing in a cylindrical grinder to about .392" (from about .396" diameter when new), it would be loose in the flange, and the flange would have to be bored out, sleeved, and re-bored to give you about .0005" - .0007" press fit. The sleeve should be a close fit, with loctite, or a press fit.
3. Flange assembly with a dial indicator, to make sure the O.D. runs true and there is no runout (wobble) on the face.

It's a lot of work, but if you have the equipment, it's worth the effort, to have a true running gear, that you can get a good mesh on, and have less noise and vibration, and longer gear life.

[nrubens]

Great tip. the guys across the street from me have a machine shop. I'll let you know how it goes.

Thanks

[teeson]

youd think align would fix that...

[rufusis]

Just got my V2 kit so this thread drew my attention. As a lathe hand, your post particularly interested me. Have you actually set up these operations yourself? I have no grinding experience but routinely hold better than .0005" run out through multiple machining operations. Sadly, while having access to the machine tools needed, I don't think my boss will let me apply your solution to this project. Do you have your own shop? That would be sweet. Just wear in the new gears slowly until you 'get your mesh on.'