Shake After Servo Upgrade?!?!

[micccain]

I have a T-Rex 700 with DFC head. I also have the CGY750 running v1.4. I have used Align DS610 servos since I have had the heli. A couple weeks ago I had a servo go bad some I got some Futaba 451's. I was using Rail Blades but I just switched the Cyclone blades. I've never had any kind of shakes at all. Tonight when I flew it (first time with new blades and servo upgrades) it had some shakes. My engine is running pretty rich because I was going to tune it when the servo failed. In normal mode it was bad, I was running 1750 head speed. It really did it the most when I was in Idle Up 1, which I had set up for trim (50% gain in normal mode). In Idle Up 2 which was 65% gain and 1860 head speed I didn't really see it shaking. I just thought this was weird because it had never shuck. Would it be more likely to do it in normal mode? Any help is appreciated.

[Ah Clem]

Was it a vibration or an actual shake?

Assuming that it is a shake (or high frequency nod)...

Best guess (at least my best guess) is that you put faster, more powerful servos on the machine, and will need to decrease the gain on the FBL unit.

If this is the case, the lower the RPM, the more you will encounter the shaking (usually the remedies for the shake is to lower the gyro gain and/or increase the RPM).

This will tend to happen more with firmer dampers than with softer ones (but you didn't change the dampers in this situation).

There is some chance that it could be a blade balance issue, but that is extremely remote with Cyclone main blades.

[micccain]

I'm not sure...It looked like a fast shake coming from the servos not really a vibration. I thought the engine being rich might cause some vibrations. I just thought it was weird it was really noticeable in normal mode at 50% and not at AVCS at 65%.

I have the KBDD hard dampeners in it.

[micccain]

Yea, I have never balanced any of the blades I have used on it. (Radix, Scott Grey, Rail, Cyclone).

I just wondered if the upgrade to Futaba's had something to do with it.

[Ah Clem]

"It looked like a fast shake coming from the servos not really a vibration."

"I just wondered if the upgrade to Futaba's had something to do with it."

Yes, I suspect it did.

You put faster, stronger, better servos in it.

Again, I would look at turning the gain down a bit in the FBL unit.

Also, make sure that the KBDD Dampers are coated inside and out with silicon grease.

Please keep us posted as to your results, sir!

[micccain]

Ok, I'll lower the normal mode gain down so that I can finish trimming it, because that's all I would use it for anyway...

[Rob43]

FWIW, I concur with Ah Clem. I like to use Dow Corning EM33 Light grease for the dampers. It's very good stuff and does the trick. Several times now, I've cured some head wobbles by greasing it.

Best wishes!