capitalB

My Feedback: (36)

I had a servo failure today on my 50cc Yak...I use all Hi-Tec servos and had a HB-5485 on the throttle.The servo is isolated from heat and vibration located behind the wing-tube,connected by Ny-rod.The set-up has 30 or more flights with no problems.The failure occurred at 100' and the engine went to idle and I still had full control of all other functions.I was able to land it with no damage to the plane,but had to take a long walk!!!When I got to the plane I went into "Troubleshoot mode" and did not move it and proceeded to check all the controls.All surfaces operated normally except the throttle.If I manually tried to move the throttle arm the motor would intermittently come to life,but still did not move it correctly.I took the throttle arm off and the servo would work,but you could stop it by just holding the output splines...I let the plane sit for awhile and the servo regained some of it's normal torque.I have had servo failures over the years and have seen this exact type failure on the $10 Futaba servos,so I am sorry to bore you with the long story!!.My question is...What should I have looked for in a pre-flight test that may have indicated the pending failure? I thought using a $25 servo on the throttle was plenty,should I go with the digital version of the 625- mg to replace it? What servo do you suggest? And last but not least,I read on a different thread that there are issues with the Aurora-9's Fail-safe that only effects the throttle servo,and to turn-off fail-safe until they have a software fix for this.(I don't believe this but I had to ask,as fail-safe should effect all the surfaces) I know there are no guarantees in this hobby,but I spend alot of time with redundancy and high-end components,if this failure had occurred literally 15 sec earlier,the plane would have been toast(low level hover)I am just looking for piece of mind on my next flight,any suggestions would be help-full! I don't want to run 2 throttle servos.....(just kidding) Brian

JIMF14D

Make sure the lead/extensions to the servo are clean and good.

capitalB

My Feedback: (36)

The servo lead-extension is new,but I will change it out with the servo,Thanks,Brian

Brendan Lugo

It sounds like the servo is getting over heated. When this happens it looses torque. It may be that the servo/motor is having to work too hard in this application. Is it working against a return spring on the throttle? What voltage are you running the servo at?

capitalB

My Feedback: (36)

6vt.two 2400 mh batteries,no return spring.With the servo arm off,linkage moves freely.I just switched to this throttle servo about 5 flights ago,prior I had a standard,non-digital.I went with the digital for better resolution and consistent idle,it worked great for that.What servo do you recommend,I don't mind a little over-kill!!

mglavin

My Feedback: (31)

Make sure the servo is not binding at any point in the travel arc... Do you have an inline servo volt/amp meter such as Hangar 9 offers, this will indicate the current draw and voltage the servo is working with. If your current draw is excessive due to binding and or load it will be easily identified with the display of the inline meter.

capitalB

My Feedback: (36)

I am open to all suggestions,but I don't see how of all surfaces,a throttle servo could bind...I think you could get away with a mini-servo on this as there is essentially "no load" With no return spring.Unless at small throttle openings and high carb flow velocities that the moving air could be working against the butterfly...I checked my linkage for binding and it is O.K. I am going with a new Hi-Tec high-torque M.G. digital to try it and eliminate the servo as a possible failure point. I could stop the digital HB-5485 servo that caused the problem with no effort on the output arm,It would stall at approx 10 oz. of load...should I warranty it,or throw it away?

mglavin

My Feedback: (31)

Binding can occur at either travel stop peculiar to the linkage and or carburetor end point mechanical stops or; somewhere in the middle too. Simply make sure your not driving the servo past the carb’s end points. An inline servo amp-meter is best for this or reduce end points on the throttle servo throw until you observe some movement.

Generally speaking you want as much resolution as possible with the throttle servos travel arc, most gasser carbs use about 60-80 degrees total throw idle to wide open. Most servos have a travel arc of 120 degrees with 100% travel volume at the TX. As you suggest torque is not an issue with a throttle servo, that said the travel arc is paramount and for best results you need to provide the proper linkage ratio which will allow full servo arm travel (120*) while moving the carb arm 60-80 degrees. Simplest way to get there is to maintain a 50% arm length differential between the two arms, i.e., 1/2” servo arm and 1” carb arm. This allows the servo travel end-point to end-point for the most finite steps or resolution while moving the carb butterfly through its complete travel arc too without over driving the servo into mechanical stops ( if they exist).

If the servo is defective please return it to Hitec Service for warranty repair.