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Servo Failure

Jerry_C

Junior Member
#1
Hey Guys. I recently built the FT Corsair and installed Tower Pro metal gear servos. Twice now, I've plugged the battery to the plane before turning on the radio. I know. Anyway, the servos all moved to their extremes and I unplugged it. When I turned it back on, radio first, They did not respond. I removed power, moved them to neutral by hand and still nothing. I removed the servos and tested them out of the plane and nothing. They do not work at all. I've made this mistake with numerous servos in the past and simply turning on the radio re-centered everything. But for some reason, these "Higher quality" servos died. Any ideas? Can they be saved, reset or anything? Thanks for any help.

Jerry
 

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Jerry_C

Junior Member
#3
Are you sure the Rx is bound to the Tx?
When you took the servos out & tested them. How did you test them? With a servo tester?
Thanks Merv. But yea. I had been operating them previously checking throws and retract functions. I've done this sort of thing for many years. Turn the plane on and the servos would spaz but as soon as the radio went on, thery'd all center out. These, apparently just break.
 
#4
Fundamentally that's not a servo problem as the root cause. Sure it's a mistake connecting the battery first, and something you need to watch for as it's a really bad habit as you get into larger models (instant fail on your BMFA exams over here). But mistakes are human, we've all done it and as you say, usually you get away with it.

But if your receiver is commanding the servos to go to full travel if it's powered on without a transmitter that's a problem. It may be a bad failsafe setting in the receiver, or just a badly designed receiver, but it's the receiver that's the root problem here. Any servo that's commanded to go to full travel, or push against its stops can burn out. The problem isn't the servos, it's the receiver that's commanding them to do something that can break them.

You should see if there's a setting in that receiver that can be adjusted, and should also check your failsafe settings. If the receiver loses radio contact you want the servos to stay how they are, and given it's commanding full deflection here that's definitely something I'd want to check.
 

quorneng

Well-known member
#6
I wonder if your servo linkage installation is also a factor.
None of my servos have a problem being tested out of the plane using a servo tester at maximum movement which is notionally 125% travel.
I try to ensure the linkage when in the plane accepts the same 125% travel, then I know any 'switch on' effect will not cause the servo to stall.

I fear the quest for high speed servos requires such power that results in stall currents that can instantaneously 'blow' the servo circuits.
 

Jerry_C

Junior Member
#7
Fundamentally that's not a servo problem as the root cause. Sure it's a mistake connecting the battery first, and something you need to watch for as it's a really bad habit as you get into larger models (instant fail on your BMFA exams over here). But mistakes are human, we've all done it and as you say, usually you get away with it.

But if your receiver is commanding the servos to go to full travel if it's powered on without a transmitter that's a problem. It may be a bad failsafe setting in the receiver, or just a badly designed receiver, but it's the receiver that's the root problem here. Any servo that's commanded to go to full travel, or push against its stops can burn out. The problem isn't the servos, it's the receiver that's commanding them to do something that can break them.

You should see if there's a setting in that receiver that can be adjusted, and should also check your failsafe settings. If the receiver loses radio contact you want the servos to stay how they are, and given it's commanding full deflection here that's definitely something I'd want to check.
Thanks Myxiplx. That makes a lot of sense. The reciver is an FrSky V8FR-II I never thought about the signal loss but ifit happened or even glitched, That would become unrecoverable right now. I'll get the paperwork out and set the fail safes. Excellent advice. Thank you.

Thanks for the paint job compliments. I have a vinyl plotter/cutter and wanted to do Pappy Boyingtons brid. I used a watewrslide paper from Papila to print the kill stickers. Spray htem with 3 coats of clear lacquer to seal them and they slide off like a model car.
 

Jerry_C

Junior Member
#8
I wonder if your servo linkage installation is also a factor.
None of my servos have a problem being tested out of the plane using a servo tester at maximum movement which is notionally 125% travel.
I try to ensure the linkage when in the plane accepts the same 125% travel, then I know any 'switch on' effect will not cause the servo to stall.

I fear the quest for high speed servos requires such power that results in stall currents that can instantaneously 'blow' the servo circuits.
Thanks Quorneng. Unfortunately that wasn't the problem. When the servos went full throw, the linkages went right along with them. No binding what so ever.