I have posted this before but using minature servos mounted in high vibration areas can cause servo failure in a very short period of time. Sometimes less than 5 minutes. Apparently something in the motor construction or the circuit board mounting is not up to the task. I failed several before going back to a cheap standard servo. I also watched another fellow fail 2 or 3 trying to get a multi engine ready to fly at a meet last year. If you can use a standard size I would consider it first.
Take a look at the aircraft in my gallery and you can get an idea of the sizes that I am talking about.
ORIGINAL: The Raven
Hi guys, I'm building a 80inch aircraft to be powered by a modified 25cc Homelite "weed whacker" gasoline engine. Work is progressing well but I need to consider my throttle servo.
Due to the position and swing of the throttle arm on the Walbro the options for mounting my servo are limited unless I go to fancy bell cranks and the like.
Looking at the engine mounted to the firewall there is plenty of room between both to fit a normal HS-422 servo. However, it's a little tight so I'm looking for a slightly smaller servo like the HS-81.
This would allow me to mount the servo in a semi-protected position behind most of the engine, with just the servo wheel hanging out into the breeze. With a simple ball jointed linkage can then get a fairly straight push/pull on the throttle.
My concerns are this:
1. While my engine runs smoothly it will vibrate. How bad would the vibrations be on the servo?
2. Which type of gear train is better suited to vibrations: nylon or metal?
3. I could use a HS-55 but will that be able to tolerate throttle control and some vibration (also noting it would live pretty much next to the engines heat - but get lots of airflow)?
Oh, the Walbro will have the return spring removed from it so it won't place any undue load on the servo.
In summary, what servo would you use for a gasoline engine and is it such a bad thing to mount it between the engine and fireall (in the open)?