Which Dynon Servo For Rans S7S?


Oct 9, 2011
Eastern Iowa
I intend to install Dynon roll and pitch servos on my Rans 2015 S7S.
Have any of you installed Dynon servos in this configuration? Which servo did you choose?
I've seen a Garmin servo installation in the S7S where the the GSA 28 was used. It has 60 lps max torque, but I doubt if it was installed where that much torque was needed.
I'm guessing an SV42 is the right fit but am looking for more info.
Thanks for any experiences you can share.

Bill Putney

Jul 28, 2019
Port Townsend, WA (0S9)
I don't have an S-7S, so I'm just reading the tea leaves and telling you things you might already be aware of.

So long as you don't put the servos where you can't get to them, you can swap out the size pretty easily and Dynon's policy is that they will exchange the servos up or down in torque if you find when you're tuning up the autopilot system that you need to change them. I'll go along with you in guessing that, for the size airplane the S-7S is that the SV42 is a pretty good bet. The Cessna 172 uses SV42C (the capstan version of the SV42 for wire bridle rigging rather than push/pull rod lever) for both pitch and roll. When you're designing the mounting's be aware that the servos with different torque ratings are different sizes. You'll probably want to leave enough space so that you can swap out servos without changing the mountings. The only physical size thing that seems to change is the length of the servo motor. Starting from an SV42, it's about an inch longer or shorter going up to an SV52 or down to an SV32 respectively. See https://dynonavionics.com/downloads/PDF/Customer Drawing - SV32-42-52 STANDARD OUTPUT ARM.PDF

Have you asked over on the RAN'S CLAN forum? Hopefully someone here who has an S-7S will pick this up, but if not I'd forge ahead with SV42's knowing that Dynon will swap them out at no charge if you run into problems.