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Old May 14, 2015, 12:49 AM
Fish99 is offline
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Hey there Paladin,

I have only tested the servo that was suspect for responsiveness. Would be interested in any thoughts on how to make sure there was no damage to the rest during the crash. I can make sure they still respond and are not stripped but you seem to indicate there might be more I can test and am very interested as I am going to buy a new airframe and rebuild.

Marlin
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Old May 14, 2015, 08:14 AM
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it can happen that all the gears look good but the teeth are actually broken and hanging on by a thread. or one of the soldier connections has been compromised. I worked with EE's for years and they told me I have to force the servo to max draw. so to do this I hold the servo in my hand with an output arm on it and I use my thumb to provide resistance to the servo. I don't have the equipment to push to max draw so I give just enough resistance to see the servo is straining. also the hold has a lot to do with limiting your mechanical advantage. I do this both ways with a servo exerciser, push the servo to one end then slowly bring it all the way back while providing resistance. when I reach the other side I reverse and go back providing resistance to that movement.

if you have week gears the servo will stop pushing and just spin in the bad spot. if you have a compromised electrical component or soldier joint that servo will be much weaker than the others when you are providing resistance.

my EE modeling buddy (god bless his soul) used to hook the servo to an oscilloscope and could tell which component was failing by the change in the curve. I'm an ME and that was way to deep for me.

one last thing. the bad servo is a good source of spare parts. most likely the part of the ELE servo that failed was a component on the circuit board. that means the motor, pot, gears, case and lead are all still good parts. these days it is common practice to soldier the motor to the circuit board and glue the motor to the case. I have been in this hobby long enough to have servos like this fail do to one of the motor leads cracking between the CB and motor. the way this failure exhibits is the servo stops working then starts working on and off till the arcing or G's increases the gap to a point where it cant be jumped. sounds a lot like the fail you had.

Joe
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Last edited by paladin-34; May 14, 2015 at 03:04 PM.
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Old May 14, 2015, 08:35 PM
Fish99 is offline
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Quote:
Originally Posted by paladin-34 View Post
it can happen that all the gears look good but the teeth are actually broken and hanging on by a thread. or one of the soldier connections has been compromised. I worked with EE's for years and they told me I have to force the servo to max draw. so to do this I hold the servo in my hand with an output arm on it and I use my thumb to provide resistance to the servo. I don't have the equipment to push to max draw so I give just enough resistance to see the servo is straining. also the hold has a lot to do with limiting your mechanical advantage. I do this both ways with a servo exerciser, push the servo to one end then slowly bring it all the way back while providing resistance. when I reach the other side I reverse and go back providing resistance to that movement.

if you have week gears the servo will stop pushing and just spin in the bad spot. if you have a compromised electrical component or soldier joint that servo will be much weaker than the others when you are providing resistance.

my EE modeling buddy (god bless his soul) used to hook the servo to an oscilloscope and could tell which component was failing by the change in the curve. I'm an ME and that was way to deep for me.

one last thing. the bad servo is a good source of spare parts. most likely the part of the ELE servo that failed was a component on the circuit board. that means the motor, pot, gears, case and lead are all still good parts. these days it is common practice to soldier the motor to the circuit board and glue the motor to the case. I have been in this hobby long enough to have servos like this fail do to one of the motor leads cracking between the CB and motor. the way this failure exhibits is the servo stops working then starts working on and off till the arcing or G's increases the gap to a point where it cant be jumped. sounds a lot like the fail you had.

Joe
Thanks for this info Joe, the failure symptoms you describe sound pretty close. FYI HH got back to me and actually have offered a new servo for replacement. Obviously not a new plane, but to be honest, that is more than I even expected. I think I will take them up on it. Probably just buy a new airframe and re-build as I have SOOO much invested in gear for this plane.

Will check the remaining servos in the manner you describe, much appreciate this.

Take it easy and happy flying.

Marlin
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Old May 15, 2015, 03:36 AM
w1nd6urfa is offline
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I am following your discussion gents and I thought I''d chime in.

Even though I've never lost a plane from servo failure I've had a few close ones (couple of throttle servos and the odd aileron or flap servo).

Ever since I follow a simple rule: 2 independent elevator controls (1 servo and pushrod for each elevator half).
That's cheap insurance for the case where a servo decides to give up mid-flight.

If the kit does not have a tray for 2 servos I build one myself.
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Old May 17, 2015, 05:48 PM
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Quote:
Originally Posted by w1nd6urfa View Post
I am following your discussion gents and I thought I''d chime in.

Even though I've never lost a plane from servo failure I've had a few close ones (couple of throttle servos and the odd aileron or flap servo).

Ever since I follow a simple rule: 2 independent elevator controls (1 servo and pushrod for each elevator half).
That's cheap insurance for the case where a servo decides to give up mid-flight.

If the kit does not have a tray for 2 servos I build one myself.
Neat idea and would likely have worked well on some of the kits I have. Have to do some modding on the tail as the 109 kit has a center, hidden, control horn right in the tail which can not be accessed once the rudder is on, but if a person wanted to re-route a couple control rod guides, probably remove some covering to set it up, create a couple holes and put external horns on each elevator then the only thing would be likely grinding off the control rod that comes out each side to the elevator surfaces. In the end, it was a weird piece of bad luck. ANY other servo failed like that and I am fine, but no ele is death in a warbird. Such is life.

Great pics though, like the clean job you did on the tray.

Marlin
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Old Jul 24, 2015, 12:40 AM
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Denmark, Holstebro
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Just some few pics and video from yesterday flight.
Have not been flying much with this model, maiden flight ended in a crash on takeoff. As you can see in the video, I need to have some right aileron just to fly straight, i did not know this at first = crash on takeoff.

RC Messerschmitt BF 109F-2 .60 ARF (3 min 3 sec)


RC Messerschmitt BF 109F-2 .60 ARF (3 min 22 sec)


But she is flying, so I just have to learn how to control her/get some experience.

Jacob
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