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-   -   RV-9 with Dynon AP servo beta test (https://vansairforce.net/community/showthread.php?t=112807)

Walt 05-07-2014 07:21 PM

Quote:

Originally Posted by N941WR (Post 877984)
OK...

I just returned from the airport. It is as I feared, there is not enough room on the roll servo to move the bearing to the top of the arm. This leaves me with three options:

I've installed a number of wing servos and the bearing is always on top of the arm, you should have enough room (bolt gets inserted from the top).

http://trutrakap.com/wp-content/uplo...0RightWing.pdf

N941WR 05-07-2014 08:01 PM

Quote:

Originally Posted by Walt (Post 877991)
I've installed a number of wing servos and the bearing is always on top of the arm, you should have enough room (bolt gets inserted from the top).

http://trutrakap.com/wp-content/uplo...0RightWing.pdf

Walt,

This is a Dyon servo, not a tru trak. There isn't enough room unless I shave the bolt head and I'm not going to do that.

I guess I could shim the servo with washers but that isn't a desirable solution.

Walt 05-07-2014 08:14 PM

Quote:

Originally Posted by N941WR (Post 878000)
Walt,

This is a Dyon servo, not a tru trak. There isn't enough room unless I shave the bolt head and I'm not going to do that.

I guess I could shim the servo with washers but that isn't a desirable solution.

Oops, my bad, I was thinking TT.

However looking at the servo drawings show:
TT arm height is .768
Dynon arm height .750

Thats not much difference, the TT installs on top with plenty of clearance so maybe the bearing is differnent?

N941WR 05-07-2014 08:29 PM

It is close, very close.

Maybe a thin washer washer will do the trick. Do they make thin versions of those big washers?

Also, I like the idea of the rod dropping away, should the nut come off.

Walt 05-07-2014 08:34 PM

Yes one thin large OD washer is all you need under the head (I get them from Van's), if you're worried about a new lock nut backing off then install a castelated nut/cotter key (but not really necessary).

PS: I always use new nuts and locktite on jesus bolts :D

Toobuilder 05-07-2014 08:37 PM

Quote:

Originally Posted by N941WR (Post 877984)
OK...

I just returned from the airport. It is as I feared, there is not enough room on the roll servo to move the bearing to the top of the arm. This leaves me with three options:

1) Make a push rod that bends up. This could allow flex in the tube.
2) Add a doubler to the existing plate. This will require longer bolts.
3) Make a new plate with tabs bent up to stiffen it. This requires me to buy some 4130 and is probably the route I will go.

Interesting that you can't move the rod end to the other side of the arm... I'm installing a Dynon servo in my Rocket right now and have room to be on that side. My geometry favors "your" side, however. Anyway, based only on your pictures and given the premise the rod end can't be moved to the other side I'd consider the following:

1. Space the servo off the mount with an aluminum sheet spacer (not washers). Move it about a tenth to .125.
2. Fabricate a new mount tab (the bent piece) out of the same material you made the spacer. Nice and thick and stiff.
3. Increase the diameter of the two spacers that hold the tab to the bellcrank as much as you can without overhanging the edge of the tab. This will give you a nice stable base.
4. Fabricate the final spacer with the same large diameter stuff you made the other two spacers from, and make it as short as possible without creating a weird angle and locking up the rod ends anywhere in the travel.
5. Install the travel limiters!

Take it with a grain of salt.

N941WR 05-07-2014 08:58 PM

Quote:

Originally Posted by Toobuilder (Post 878009)
...

1. Space the servo off the mount with an aluminum sheet spacer (not washers). Move it about a tenth to .125.
...
5. Install the travel limiters!

Take it with a grain of salt.

That is good, usefull advice.

Only one problem, the idea of washers to raise the servo won't work because the critical dimension is between the top of the servo arm and the bottom of the servo body. No joy.

As for suggestion #5, as soon as I can find it, it and the one on the pitch servo will be installed!

N941WR 05-07-2014 09:00 PM

This makes me wonder how many other AP servos from all the manufacturers have been installed w/o a limiter.

BillL 05-07-2014 09:10 PM

Quote:

Originally Posted by N941WR (Post 877984)
OK...

I just returned from the airport. It is as I feared, there is not enough room on the roll servo to move the bearing to the top of the arm. This leaves me with three options:

1) Make a push rod that bends up. This could allow flex in the tube.
2) Add a doubler to the existing plate. This will require longer bolts.
3) Make a new plate with tabs bent up to stiffen it. This requires me to buy some 4130 and is probably the route I will go.

Hey Bill,
Can the bolt with spacer be extended through to the second parallel plate to avoid having a bending load on a relatively thin plate? Clearly a spacer would be needed to avoid crushing.

Having said this, I admit to not having a good mental picture of the geometry and if the bolt hole projects in to material or into a lightening hole.

In my head, that would allow the bending on the bolt but a shear load between the bell crank plates to handle the force of the servo.

Just a thought.

RV7A Flyer 05-07-2014 09:26 PM

Quote:

Originally Posted by N941WR (Post 877887)
Are you talking about the 2nd picture I posted? If so, you are correct, and as I stated, that is the position it was in when it jammed, after the AP bent the plate doing a self-test on the ground. Prior to the AP bending the plate, it could not go over center and I flew that way for four or five years without any issues. In fact, I had just inspected that servo two weeks prior during my condition inspection and found nothing amiss.

So I'm confused (not unusual). You say it was originally installed per the instructions, and during a ground test, it went over-center (and ended up in the position it's in in the 2nd picture)?

I can't figure out how that would happen...the only test I know of with the Dynon SV is that it sends the servos to full right/full aft (IIRC), and then to full left/full forward, asking you to confirm that's what it's doing (to avoid reversed servo action). But in the case of the ailerons, they hit the stops long before the servo arm gets anywhere *near* an over-center condition on my -7. Are you saying the servos kept running AND generated enough force to bend that part? If so...YIKES. (FWIW, I have the over-center protection thingie from Dynon installed on both my servos...still, they never get anywhere near even those limits).

I just couldn't imagine them having that much torque...enough to bend the steel bracket...before they would slip. I know I did a quick test on the ground of the pitch servo during installation, and it did, in fact, slip (with quite a loud bang resonating through the skin) when the elevator hit the stop. (Dynon concurred that's normal, btw...scared me enough to email 'em! :) ).


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