Servos

backboiler

While executing one of my previously described aerial manoeuvres (read crashes) it seems I've managed to internally damage one of the aileron servos on my Radian Pro; stripping I believe is the word. There's some teeth missing on the output gear.
See image.



Presuming it's impossible to fix this (it'sin the neutral position so the limit tab makes it impossible to turn it the opposite way), where do you recommend I get a replacement or equivalent. It's a PKZ1081 SV80. Are all servos of that size (what's it called, micro?) the same shape and do they have the same external attachment gear that the arm goes on? If so can you recommend a equivalent from hobbyking or the like?
Another thing: they're held in with what looks like silicone mastic. Is this any specific type or can I use the normal kind you get in the hardware shop?

Bruthal

The limit tab can be removed, it just prevents continous rotation in the event of the servo position sensing failing, i.e. potentiometer failure etc, which would damage control surfaces or linkages. Removing the limit tab might enable the gear to be re fitted with the stripped teeth opposite the pre-final drive gear, with the servo in its central (neutral) position with the radio.

The servo wont turn far enough to reach the stripped teeth then. If you file the stripped teeth into a clean notch, this will then act as a servo stop, preventing the continous rotation in the unlikely event it ever happened.

I often actually converted servos to continous rotation, one was a €100 servo (for steering) i used in the childs tractor project a while back, when back together a gear jammed and burnt out the voltage regulator i was using to power the receiver to test it, i though the servo was ruined, but it was fine when i re fitted the gears, so thats important as you put the servo back together.

The gear may have to be glued to the spindle that goes to the position control potentiometer as it may be keyed onto it, the spindle may have a flat side so the gear might need to be slightly bored out then glued to the spindle to ensure it still turns the pot as the gear turns.

If you do get an equivelent servo, it can be fixed into place with normal silicone.

You could also replace the aileron servo with the rudder one, and fix the rudder in position to continue flying for the moment while you get a replacement servo. It would be no problem flying the pro with no rudder control, as long as its fixed in the central position.

Any micro servo of same dimmensions can then be used to fit on the rudder, it will come with its own servo arms so you wont have to worry about fitting the ones from the damaged servo to the new servo shaft.

backboiler

Good man Robbie, comprehensive as always.
Just after I sent that message last night I decided to try to take off the output gear and cut off the limit tab. Great minds...
There were no indents or flat sides, just friction holding the output gear on so apart from it being a bit delicate to remove without damaging the other gears it was handy enough. Turned it around as you described and when reassembled it seems to work OK. Great days!

Since this will probably happen again I want to get a couple of spare servos (I'm sure I'll find some use for them even if I never use them in a plane). I haven't been able to find the specs for torque and rate for the PKZ1081 so don't know what minimum I need to replace it. Any idea?
Another question is whether they all have the same angular deflection for a given input, so if I replace one with a different model can I get away without putting an identical one in the other wing?

My only remaining problem now is that the plastic bracket the the wing screws into to hold it to the fuselage is broken. Here's an unbroken one:



The impact with the ground pushed on the screw and it broke out of the ring.
Any novel repair ideas for that?

Bruthal

For the servos, the output torque should not matter too much, there would not be much effort needed on the radian control surfaces, but hobbyking does have metal gear micro servos which would be stronger than the plastic ones. All the dimmensions are given so once they are the same size as the originals, they should work well. The different throw would be minimal so that should not be too much of a factor. But you could always replace the aileron ones in pairs anyway.

Im not sure on the radian if the aileron servos are both on opposite sides of the links they control, for servos that both turn the same way, they usually would be, where as for the air brakes they would both have to be installed in the same direction do move both spoilers the same way, or else opposite throw servos would be needed, or a servo reverser.

This is of no concern on a radio with every control surface on a seperate channel, which just made me remember why i have both air brakes on the cularis on seperate channels, because each can be reversed in the radio.
With the ailerons on crow/butterfly braking, the aileron servos have to be on seperate channels as they need mixing to both go the same way on braking, and still work in opposite directions as ailerons. the radian pro seems to slow down very well with just the spoilers alone though, and doesnt really need the crow setup.

Now the broken wing bracket. Is the end of the piece missing, or just split?
For such repairs on plastic items i usually use sewing thread wrapped around any breaks, and soak with superglue, usually braced with carbon fibre strips. So if the end of the hole is just split, you could roughen the area the thread will be on with glasspaper, and wrap the area between the hole and the fuselage with the thread as an anchoring area, and then a few wraps out around the end of the split, with the thread actully going around the curve. There might be no room though if the plastic bit thats broken fits closely inside the area of the wing it gets screwed to.

Put up a photo of the broken one anyway and maybe we can see something.

backboiler

robbie7730 wrote: »

Im not sure on the radian if the aileron servos are both on opposite sides of the links they control, for servos that both turn the same way, they usually would be, where as for the air brakes they would both have to be installed in the same direction do move both spoilers the same way, or else opposite throw servos would be needed, or a servo reverser.

Never thought of that, I must check. From memory they're facing the opposite way but I'll have a look later.

robbie7730 wrote: »

Now the broken wing bracket. Is the end of the piece missing, or just split?

She's clean gone, as if you took a pair of pliers across the screw-hole and snapped downwards. I must get my hands on some fibreglass tape and the like so I can do little repairs like that. Will post a pic of the damage later anyway.

backboiler

Not a great picture but you get the idea.