FYI to builders...pondering servo size (strength) when installing their autopilot system. I have a STOL 750 with two axis autopilot ( Dynon SV-32 servos.)   During my 40 hr test phase I was having problems getting the autopilot pitch servo to not slip - esp. in turbulence.  Went thru the whole setup routine per Dynon, but no joy, airloads were too much for the servo as the A/P worked to maintain selected altitude in anything but smooth air.  Even then, in smooth air, during prolonged turns, the slipping would occasionally occur as the A/P worked to hold altitude.  Finally decided to step up the pitch servo to the next size servo (SV-42) which has a bit more torque.  Installed it today and it seems to have taken care of the problem.  Kudos to Dynon for allowing a swap of the servo I bought 3 years ago for the new servo.  Evidently it was no big deal, they would rather it work right and they make it easy to resolve issues. 

So, my advice for those outfitting their CH750 with servos from Dynon, install the SV42 servo (at least for the pitch servo) which should work fine for our aircraft.  HTH someone...


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Thanks for the info David.  Do you have the Y-stick or dual stick option?

Y stick...

Good info Dave. When you swapped servers, did you need to re-do the connections to the controls? It looks like the motors are identical except the bigger versions are longer in the back, making me think the swap should be pretty painless. I have the 32 in the airplane I am currently building and fear I might run into the same problem.

Ken, relatively painless affair.  No change of the physical setup to flight controls or servo mounting. Have the correct connector and shell (DSUB 9 pin male) for the new servo wires, dsub male pins to crimp and your done with electrical!  The SV software detected the new servo and did a software update to the servo.  I then had to run the servo calibration and test.  Ground and flight check and done!  Only downside to the 42 is it indeed physically larger (just a bit) and approx one pound heavier with slightly more current draw (which is really not an issue for our wire size and C/B's)  I would suggest doing the swap earlier (unused servo) might get you a new servo versus a re-manufactured servo like I received.  Just a note regarding physical setup.  In  an attempt to get more torque from the SV32 servo during my testing I had gradually moved the relay rod from the outermost hole of the servo arm to the middle and finally the innermost hole.  At the innermost connection, I was able to jam the flight controls (on the ground) for the elevator while checking range of motion, etc. due to overcenter geometry.  The torque output of the SV32 at the innermost connection point is the same as the SV42 at the outermost point of connection to the servo arm.  That's when I elected to swap servos. The angular deflection at the outermost points of the servo arm is much less then when connected at the innermost point for same control deflections and makes setup of the physical connection geometry a bit easier.  Hope that makes sense, the Dynon literature is very good and emphasizes all the above "take-aways" I experienced.  Good luck with the build!!  Glad to take questions if you got any later on.


Thanks Dave. 


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