Please Help! RE:Servos

[balsa basher]

Hello all,
I have built 30 might mini trainer kits with special needs students in a high school - on my own I mounted the servos (I am an exp. flyer and have done this in ft planes a whole bunch of times) BUT this time more than half of them are bound up and wont move -anyone know what I did? - I really need to get these up in the air soon or the kids will be every disappointed

Thanks!

Dennis

 

[Hai-Lee]

Without inspection I can only guess!
Having said that the main failures I have had in fitting servos to a new plane have been;
1. excessive glue, (glue got into servo and glued gearbox or output shaft solid).
2. Control surface hinge too stiff. (Not cut and prepared properly and too much glue).
3. Linkage stopper unable to rotate freely on the control horn. (poor preparation).
4. Faulty BEC/ESC supplying a voltage to the servos that is too high, (causes lower voltage servos to burn out).
5. Faulty servo, (Rare event).
6. Stripped or broken gears in the servo, (normally caused by 1, 2 or 3).
7. Reusing servo from a crashed plane, (a bad practice without extensive testing).

What I recommend is that you disassemble one of the problem servos and ascertain the problem that way. It is a simple process and should be done with care.

Have fun!

 

[Keno]

Hello all,
I have built 30 might mini trainer kits with special needs students in a high school - on my own I mounted the servos (I am an exp. flyer and have done this in ft planes a whole bunch of times) BUT this time more than half of them are bound up and wont move -anyone know what I did? - I really need to get these up in the air soon or the kids will be every disappointed

Thanks!

Dennis

If they were 9051 servos I got a bad batch. They strip gears very easy. Like what you are doing for special need students A big High five to you.

 

[PsyBorg]

I don't know mate. I have been working on a video system for Rockboys FW 42 project and just killed 4 more servos. Seems the work fine for a while then one time when I power them on the all lurch to one side and lock up never again to respond to a signal. They are not stripped out I can manually move them back to center. The thing is as soon as any power is applied they twitch and that's it. Once in a while if I cycle power a few times one will again jump to max and be done.

I thought it was either my power system or the runs are too long but now I am wondering of its just the cheap crap servos I have been using. Only thing is I am leery about trying good servos in the event I have some other issue working.

 

[quorneng]

Balsa Basher
You really need to get your self a servo tester. Very cheap - about £2 on Ebay) as with a spare ESC and LiPo you can test each servo for normal movement before it is added to the air frame. If when installed it does not work then you know it is something you have done!

 

[PsyBorg]

I have one. the four servos that just croaked are sitting out in the open and not even in a plane.

 

[mrjdstewart]

are you sure they were centered when you started? i had a ED student the other day jumping up and down because his "servo stopped" working. he had rushed as always, and put the horn on w/o being centered. he was now trying to move it past max travel. i took it back off, centered the servo, and it worked just fine.

my next guess would be glue in one manner or another.

good luck, i got 11 more days until summer and they can't come quick enough.

laters,

me

 

[PsyBorg]

Everything was centered multiple times during the build process. I have had the system up and working as I add each part of the design. It just outta the blue decided to peg the servos and that was that. First I set it up to work with sticks. Then I added in head tracking and set the limit for speed and maximum turning to be more realistic of an actual hard point for a gun emplacement. Then I started getting ready to tie the fpv system in and they failed. Had the same thing happen on my Se 5. Still need to dig out that servo and replace it.

 

[Hai-Lee]

Lately I have been investigating ESC/BEC failure modes and the BEC output voltage can vary considerably if there is a great load on the 5V when the ESC/BEC initializes. With some UBECs I have seen voltage spikes well over 6 Volts on 3S setups and over 7 volts on 4S setups. The test load I use is 150% of rated current at switch on.

Mind you I am only testing damaged/crashed or suspect ESC/BECs.

Could your failures be due to an overloaded 5V rail which might include a jammed servo or 2 which will draw much more current at switch on than one that is free to "Twitch"?

It may not be related to the failures mentioned on this thread but overloaded BECs cause a lot of damage!

Have fun!

 

[PsyBorg]

I am pulling 5v from the pdb in the system. Over voltage was the first thing I was checking for. Each pair of servos pulls from its own 5v regulator. Both are outputting 4.8xx volts and I get the same reading at the connections on the servo side. I have the cameras wired to that same 5v but they have not been plugged in yet under power. That was what I was about to test and set up on the three way digital switch when they spiked and suicided themselves.