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Power to servos but motor not running

#1
I had a crash earlier this year and had not tested things since it was cold (I only have one set motor + esc), I am not sure if this is a motor or esc problem.

Everything was working well but testing today in a new plane, I connect everything as usual, the rx gets power and servos work fine but motor won't turn.

I tried to see how much voltage I am getting out of the esc wires (if that matters):

ESC cable Red, Yellow and Black going to motor:

Legend:
R+ => Red wire to volt meter positive
Y- => Yellow wire to volt meter negative

Results:
R+ B- = -1.1v no throttle, -1.3v full throttle
R- B+ = 1.2v no throttle, 1.4v full throttle
B+ Y- = 1.4v no throttle, 1.4v full throttle
B+ Y- = -1.4v no throttle, -1.4v full throttle
R+ Y- or R- Y+ = 0.0v

Not sure if that tells anything, thinking something on the esc might have melted (see pictures) and so it's not giving full power available or motor took too hard a hit during crash (I checked continuity between motor wires). I don't have another esc to test with sadly. I checked all settings on my TX, tried inverting channels, switching wires, checked throttle curve, even tried using an unused plane model in TX (default).

Any idea? Is this my new glider only ESC? :)
 

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DamoRC

Well-known member
Mentor
#2
Voltages from the motor wires can be difficult to interpret because the ESC generates a pulsed signal to the wires and the signal will vary as the motor turns.

A couple of basic questions.

(1) Does the motor make the usual beeping noises on startup?
(2) When you say it does not turn, does it even try? Does it stutter?

Have you tugged on the motor / esc wires to see if there are loose or broken connections?

The marks on the heat shrink could be just due to heat from the FETs when it was running properly.

DamoRC
 
#3
Voltages from the motor wires can be difficult to interpret because the ESC generates a pulsed signal to the wires and the signal will vary as the motor turns.

A couple of basic questions.

(1) Does the motor make the usual beeping noises on startup?
(2) When you say it does not turn, does it even try? Does it stutter?

Have you tugged on the motor / esc wires to see if there are loose or broken connections?

The marks on the heat shrink could be just due to heat from the FETs when it was running properly.

DamoRC
Yes, I wasn't sure the voltages would help, just figured I'd give any info I can.

(1) Not sure on the beeps, it seems like it makes the same series of beeps as it used to.
(2) No, does not turn or try to, no stuttering when plugging the battery or turning on the TX, no movement.

Yes I tried playing around with the wires at the connections at the motor, esc and in between, nothing worked. I know the wires on the motor are good, same for the esc to motor wires on the esc.

As far as the marks, pretty sure they're actually solder balls, I am wondering if it didn't overheat last time and some of the solder melted while in flight. But also wondering how it could still work if it was solder balls (partly work).
 

quorneng

Active member
#4
My guess is those marks on the heat shrink have been caused by a failed MOSFET. When the go they generate a bit of heat.
This 30A ESC (it no longer works) has had its heat sink removed to show a faint mark on the Mosfet itself and a corresponding 'burn' mark on the heat sink conductive layer.
BlownESC.JPG
A single failed MOSFET normally means the motor will 'twitch' but if two fail, as your appears to have done, then there is no circuit to the motor so it is completely dead.
If I am right then I am afraid the only solution is a new ESC.
I do use this ESC as a power source for one of these simple servo testers
 
#5
Thank you for the reply, I have a new 20A esc in the mail. Hopefully that was it, the motor I usually buy is out of stock from headsuphobby.
It's a EMAX CF 2805, I liked it because it's only 25 grams but give a bit more power than other blue wonder type/size motors.
 
#6
Yup, I smoked my first EsC by using a spare prop that had too much pitch, flew like a monster before it fell out of the air.... it was HOT. Lost the magic smoke. Opened the ESC and parts tumbled out.

Thanks for the post.. just starting to try the power distribution boards to wire the differential thrust mini-twins. I maybe overheated whilst trying to solder.

Is there a “when your kit don’t work after assembly “ thread please?

Many thanks for your share, watching for your solution
Miggy
 
#7
sooo.. I guess I should post this.. I had not flown since before winter, had disconnected everything after my recent flight in spring and just was positive that the esc was meant to go on the last slot (BEC) of the receiver. It does.. if you only want to use it for power.. and no motor...

Everything works hahaha...
 

ElectriSean

Eternal Student
Mentor
#8
sooo.. I guess I should post this.. I had not flown since before winter, had disconnected everything after my recent flight in spring and just was positive that the esc was meant to go on the last slot (BEC) of the receiver. It does.. if you only want to use it for power.. and no motor...

Everything works hahaha...
Thanks for posting your solution. We've all made similar silly mistakes, it's all part of learning and growing. Happy flying :)