Trutrak servo growls?

scsmith · #1 10-26-2008, 01:49 AM

Hi,

I just got my Trutrak ADI Pilot I hooked up. I was pretty alarmed by the horribly loud growling noise the roll servo makes, and it kind of resonates in the structure.

I checked the set-up from the factory and they had the 'activity factor' set at 7 rather than the 1 - 2 that the manual recommends. I turned it down to 2, and that did help some, just because the servo doesn't dither as much, nor move as quickly.

But still, every step of the stepper motor makes a pretty loud noise, and when it moves a bunch of steps, its a pretty loud growl.

I did buy the servo second-hand, so now I'm wondering if there is something wrong in the gear reduction that is making so much noise, or if it is normal.

This is in an RV-8, so it is mounted under the floor behind the spar.

Comments?

Steve Sampson · #2 10-26-2008, 03:41 AM

Sounds normal to me. You wont hear it in the air.

DickDe · #3 10-26-2008, 10:27 AM

It probably is normal as mine sounded loud as well. I also started with a low activity level which worked in smooth air but I needed the high activity level when flying in chop so my unit is now set high. I have an RV6 with Digitrak and Altrak VS and it works super!!

Dick DeCramer
Northfield, MN
RV8 fuselage kit
RV6 N500DD flying

Noel Simmons · #4 10-26-2008, 12:41 PM

IF the servo doesn't "hum" when you move the control their could be two things wrong both have to do with wiring .

first step is to remove the d,sub connector from the servo. See if the "noise changes. Most likely yes so CHECK YOUR WIRING

Second after you have checked your wiring apply power to the autopilot and engage the servo. then sometimes the servo will have resumed normal operation and will have a "hum" when the controls are moved. Again if it is not a "HUM" CHECK YOUR WIRING!

Jim P · #5 10-26-2008, 02:48 PM

Had the same thing and as already mentioned, disconnect the D-Sub at the servo and try it again. If it goes away, you have a wiring issue. If that's the case, you're going to have to shoot the wires, starting with the ground and make sure all the pin-outs are correct. It shouldn't make very much noise.

scsmith · #6 10-27-2008, 01:59 AM

Now you guys have me puzzled. Two of you say its normal, two say there's something wrong with the wiring.

well first of all, with the d-sub off the servo, the servo doesn't do
ANYTHING, which is what would be totally expected. the power, ground, and control commands come in there. With it disconnected, its not going to do anything. So I don't know why that would be useful.

The noise that I'm talking about is the servo stepping in response to gyro movement (roll or yaw)

the response of the servo to gyro motion seems correct in every way, its just really noisy.

Can someone break the tie here?

Ironflight · #7 10-27-2008, 07:13 AM

OK, Steve, to answer your question, I have one or two.....

1) When you say "growls", do you mean that it is making a continuous noise any time it is engaged? This sounds anomalous to me.

2) If the airplane is sitting still in the hangar, and you engage the A/P, it should make a little initial noise as it engages (fraction of a second as it engages), then not do anything, If you then command a turn, it should make SOME sounds - but I wouldn't describe it as raising my concern.

3) If you try and move the controls manually with the A/P engaged and the airplane sitting still, then yes, you will hear and feel "pops" as you force-fight the servo.

If it is doing anything other than this, it would concern me if it were mine, and I'd check with Tru Trak, or get another RV'er in your area to listen to it - or post an audio file for us to listen to!

Paul

scsmith · #8 10-27-2008, 12:23 PM

OK, here is how it behaves:

1) when you first engage the autopilot, the servo goes just a step or two then is quiet. Each step makes a 'pop' sound - a discrete noise.

2) If you don't move the gyro, or the controls, it is quiet.

3) if you roll the gyro, or command a turn with the knob, it makes a series of 'pop's that are the servo steps as it moves. If you command a fast enough motion, the sound of the pops blends together to sound like a 'buzz' or 'growl'.

4) if you hold the gyro still and try to move the controls, it fights you, won't let the controls move. But it makes NO noise. If you push hard enough, it breaks a clutch loose inside the servo. One of the comments from above seems to indicate it should hum when it is fighting the control motion, but it makes no sound in this condition

All this seems fairly normal, and the response seems about like what you would expect, its just that the 'pop's and 'buzz' seem really loud to me. The servo seems like it feeds some 'recoil' vibration into the structure that sort of amplifies the sound. I doubt I would hear it in flight over the engine noise, but I think I would feel it in the seat.

Thanks again for the ideas and help

PS I'm a fellow NASA guy, at Ames.

N55CU · #9 10-27-2008, 12:53 PM

Does it make the same sounds when it is disconnected from the aileron push rod?
Randy Utsey
N55CU
Charlotte, N.C.

Jim P · #10 10-27-2008, 12:53 PM

To clear up my previous comment, it wasn't originally clear what you were describing. If the AP is OFF, and you move the control surface, and you hear a grinding or growl, then you probably have a wire problem. When you move the surface with AP off, is this the case? If it's pretty quiet, and only "growls" when the AP is engaged and doing a quick movement of the surface, I'd call the vendor.