RV-4 Autopilot

[Scott Hersha]

Nice job Scott! Looks good to me. I used 3 #8 screws on the bracket (overkill probably) and made my bracket out off mild steel from Menards, but the setup is very similar. Your setup which is further up towards the stick will give you more torque, which is probably a good thing. This configuration works very well, and is easy to check and service. Seems like a preferred location for RV4 roll servos.

[Freemasm]

Originally Posted by Scott Hersha

.....very similar. Your setup which is further up towards the stick will give you more torque, which is probably a good thing....

First off, make no mistake assuming I have any experience with autopilots; however, in my experience with designing (mostly industrial gas turbine) systems, it is most always better to take advantage of the full range of motion of an actuator whenever possible. Regardless of how finite the feedback, doing the aforementioned reduces the chances of the system acting overdamped/hunting/etc. Who knows what issues I'll encounter trying to validate everything but hopefully that issue won't be one of them.

On other related second thoughts, I'm probably going to forgo a bushing and thicken the attach bracket to match that of the actuator arm. I'm fine with the strength aspect as installed but unsure of any linkage fastener hole wear. I'm assuming Garmin's analysis and experience have validated their material choice from that perspective so I'll probably copy that in time.

Much thanks to all.

[Peter Grylls]

Originally Posted by FinnFlyer

Used 4130 1/16" plate. Beefier than needed.
Really the only point I wanted to strengthen was around the 3/16" hole for the link to the servo arm. Should probably have made it with 1/16" alu and enlarged and put a small bushing in that hole.

I'll update this post with more pictures later when re-installed.

Added link to pdf file with dimensions for servo mount bracket. Shows up a a black square below. Click on it to open or download.

Do not take my dimensions as gospel. Mock something up with cardboard or thin alum. Make sure you get the servo throw you want. That link doesn't bind on bend nor servo arm. That you have room for nuts underneath screws (or bolts).

Finn

Thanks for posting that stuff. You have simplified my research enormously.

[jull_under]

Anyone install TruTrak servos for roll & pitch.
Pictures would be greatly appreciated.
Also, what hardware was used to fabricate pushrods, rod end bearings etc.
I can't find an "install kit" like the other manufacturers.

Thanks.

[Freemasm]

Originally Posted by jull_under

Anyone install TruTrak servos for roll & pitch.
Pictures would be greatly appreciated.
Also, what hardware was used to fabricate pushrods, rod end bearings etc.
I can't find an "install kit" like the other manufacturers.

Thanks.

I installed Garmin but I pulled the TT drawings/models from their website when looking for ideas. IIRC, both pitch servos attach almost identically to the elevator bell crank. That should be the easy one.

Unlike TT, there is no Garmin RV-4 release for roll servo installation. TT attaches a band to the control column for actuator attachment. While it would have been an easy thing to replicate, the mechanical advantage/leverage is fairly limited thus requiring more actuator force. Mr. Hersha's and FinnFlyer's approach made better use of the available kinematics. Since anything I did would have required custom fabrication/application, I decided to stand on their shoulders.

If I were installing TT, I would have followed their kit instructions and not thought twice about it.