How do I stop a full-throttle screech?

[Frank v B]

Calling any and all Techies:

I tried to fly the DeNight Special twice and twice at full throttle just after breaking ground the motor screeched and stopped working.  It would then power up fine afterwards in the pits  This happened twice to me on two separate days this summer.

The motor is a Turnigy PropDrive approx. .50 size on 5 cells swinging a 13.5 x8 Graupner prop with a 70 amp Opto ESC and a separate 4.8 volt RX battery pack.

The sound is not bearing related but appears to be timing.  How do I fix it?... pretty please.

Frank

[bweaver]

Calling any and all Techies:

I tried to fly the DeNight Special twice and twice at full throttle just after breaking ground the motor screeched and stopped working.  It would then power up fine afterwards in the pits  This happened twice to me on two separate days this summer.

The motor is a Turnigy PropDrive approx. .50 size on 5 cells swinging a 13.5 x8 Graupner prop with a 70 amp Opto ESC and a separate 4.8 volt RX battery pack.

The sound is not bearing related but appears to be timing.  How do I fix it?... pretty please.

Frank

While not being a techie, I have two comments. 

1) Sounds like many situations I experienced when flying glow fuel airplanes.  This is why I switched to electric.

2) Sounds like it's broken.  In my technical view, I would replace something. 

Maybe a true techie will have some real advice.   

[battlestu]

had this problem some time ago... you'll need to change the timing on the ESC (assuming you have a programmer for it)

[Frank v B]

Bruce: re  In my technical view, I would replace something.  ...like the pilot?? 

Greg:If it works fine up to 3/4 throttle and screeches only at full throttle, does that mean the ESC needs to be programmed to a higher frequency?

Maybe I should just replace the ESC or increase the size of the prop to reduce the RPM on the motor.

Frank

[pmackenzie]

Screeching is usually caused by the ESC losing "sync" with the motor.

Try a smaller prop, or adjust the timing on the ESC.

ESC frequency does not usually affect this.
This frequency has to do with how fast the current is "chopped" at part throttle. At full throttle there is no chopping going on, only commutation.

Pat MacKenzie

[Frank v B]

Pat,

Thank you.  I was hoping you would weigh in on this.  Will do all this next spring knowing what to do now.

The electric guru has spoken.... and I have listened.

Frank

[davidk]

Is it possible that there are wires in the mix that are either not the same length... or too long?

I've been reading lately (dangerous pastime) and it's been suggested that motor wires of difference length could cause a timing issue... and that too long a wire length between the battery and ESC could cause a timing issue.  Even that too short a wire from battery to ESC will cause problems.

Since you're seeing odd behaviour at full throttle, when more juice is used, maybe something electrical (spikes) is happening.

[Frank v B]

The leads are the same length.  The only thing "short" is me on technical experience.

Frank

[davidk]

Me too! 

[Frank v B]

...a year and a half later........

Followed the posted advice:
Bruce's "I would replace something"
Pat's  "Screeching is usually caused by the ESC losing "sync" with the motor.  Try a smaller prop".

Went to a smaller prop to get a higher RPM and it worked. So it was a timing issue as Pat suggested.

The old prop was a 12.5 x 6 Graupner (heavy, wide blade).  The new one was a 12" x 8" Master Airscrew E (a lot lighter, narrower blade).

Have repaired the model.  Glued the fin's broken leading edge, glued the cockpit.  The plane flipped over and pushed the cockpit and cracked it most of the way around. 
Also replaced a wing retainer lug.  When Rob D. donated the airplane, he gave two old smoke damaged wing halves.  I cut out the lug from the corresponding smoke-damaged wing and replaced the one in the damaged good wing.  It was 1/4" plywood about 4" long and straddled the first two plywood ribs at the root.

The plane is ready to go....again.

Thanks for the help.


Frank

[Andy Hoffer]

Good job @Frank v B .

Looking forward to a photo-op - with fill flash! 

Andy

[Andy Hoffer]

hi @Frank v B ,

Just reflecting on this whole thread.  To quote our resident master of pearls of wisdom, I think you have been over-thinking this.

Clearly, the screeching noises were in fact screams of terror from a helpless aircraft in fear for its life.  If you listen closely, and slow down the playback speed, you will hear, "O.M.G.  He's going to kill me!!  Somebody save me!!!"

Andy