Throttle and choke servos

[Gobeil]

TazmanianDevil said
Try ball links on both ends of the rod it helps...

try to install the servo NOT on the same surface the engine is.

try to use servo protector mechanism...http://www.anticsonline.co.uk/2039_1_1238831.html

Thanks for the idea TazmanianDevil. I had given up on this thread. This is worth a try.

I have been thinking about a small bicycle cable and sleeve with as little play as possible inside the sleeve. One end attached to the servo arm and servo tray and the other to the throttle arm and the engine mount. A loop in the cable between the servo and engine would be used to "loose" the vibrations.

Just an idea.

 

[stangflyer]

Thanks for the idea TazmanianDevil. I had given up on this thread. This is worth a try.

I have been thinking about a small bicycle cable and sleeve with as little play as possible inside the sleeve. One end attached to the servo arm and servo tray and the other to the throttle arm and the engine mount. A loop in the cable between the servo and engine would be used to "loose" the vibrations.

Just an idea.

I am thinking probably not such a good idea. You will more than likely have too much slop in the complete assembly. Not allowing you good transition, accurate settings and good operation. Have you removed the spring on your carb butterfly? I remove all mine to eliminate any extra stress on the servo. So far, no failed throttle servos.

 

[Gobeil]

I am thinking probably not such a good idea. You will more than likely have too much slop in the complete assembly. Not allowing you good transition, accurate settings and good operation. Have you removed the spring on your carb butterfly? I remove all mine to eliminate any extra stress on the servo. So far, no failed throttle servos.

Being my first gasser and not realising that these motors vibrate so much, I initially set up the servo travel with no play. I should have given these setups some play at full throttle and no choke positions. That is why the servos motors burnt out.

By using powerful servos with metal gear we are just ensuring, by brut FORCE, that the required settings get across to the carburetor. In fact, both butterflies of the carburetor are oscillating like mad as we do it right now. So there is no real precision in their setting. There is just an average setting.

There has to be a way of eliminating the vibrations with some form of shock absorbing device. There are plenty of such devices in cars, boats and fun size planes. Without them everything would vibrate and fall apart quickly.

A monofilament metal cable and teflon sleeve (with little or no play between the cable and the sleeve) looped over itself could eliminate the vibrations between both ends.

The thing is to find such a cable and a way to attach the sleeve at both ends.

 

[Capt.Roll]

You might look at the Sullivan Goldenrod for a throttle setup. It should help eliminate some of the vibration to the throttle servo.

Oh, do not remove the throttle return spring, it's okay to disconnect it but leave it on the shaft. It keeps the throttle butterfly valve from vibrating and wearing the inside bore of the carb throat.

If you leave the spring hooked up it puts very little stress on the servo and does not significantly increase the working load or power draw from your flight packs. There's thread on FG where someone did some testing with several different servos at rest and working against the return spring tension on the throttle. If I recall correctly it something that you shouldn't even be concerned with.

 

[stangflyer]

Being my first gasser and not realising that these motors vibrate so much, I initially set up the servo travel with no play. I should have given these setups some play at full throttle and no choke positions. That is why the servos motors burnt out.

By using powerful servos with metal gear we are just ensuring, by brut FORCE, that the required settings get across to the carburetor. In fact, both butterflies of the carburetor are oscillating like mad as we do it right now. So there is no real precision in their setting. There is just an average setting.

There has to be a way of eliminating the vibrations with some form of shock absorbing device. There are plenty of such devices in cars, boats and fun size planes. Without them everything would vibrate and fall apart quickly.

A monofilament metal cable and teflon sleeve (with little or no play between the cable and the sleeve) looped over itself could eliminate the vibrations between both ends.

The thing is to find such a cable and a way to attach the sleeve at both ends.

All my setups are designed this way: Motor bolted directly to firewall with appropriate hardware. Throttle servo mounted in servo tray as designed by manufacturer or of own design. Typically servo tray is epoxied to the inside of the fuse or servo cut out in motor box somewhere. Dubro ball links on both ends of 4/40 double threaded push rod. Turn buckles work well too. EPA's set at both ends of travel with linear travel through the entire throw of the servo arm. In the past with my glow motors, I did use Sullivan Golden Rod 4/40 cable inside guide tubes. But that really is no longer needed. In excess of over 500 flights this past year. Approximately the same last year. Zero issues and zero servo loss. You have to remember the vibrations you are referring to are typically absorbed by the throttle butterfly and in turn, is floating as the motor is running. There is no restriction on your throttle servo during the motor running. The minute amounts of the butterfly floating will NEVER be noticed during normal flight. I do however remove or release the tension on ALL my throttle butterfly springs.

 

[Mikeq]

You might look at the Sullivan Goldenrod for a throttle setup. It should help eliminate some of the vibration to the throttle servo.

Oh, do not remove the throttle return spring, it's okay to disconnect it but leave it on the shaft. It keeps the throttle butterfly valve from vibrating and wearing the inside bore of the carb throat.

If you leave the spring hooked up it puts very little stress on the servo and does not significantly increase the working load or power draw from your flight packs. There's thread on FG where someone did some testing with several different servos at rest and working against the return spring tension on the throttle. If I recall correctly it something that you shouldn't even be concerned with.

+1...I have been using Sullivan Goldenrod and disconnecting the spring for a long time on many planes and never have had any issues with the throttle servos.