Corsair013

Why is my rc airplanes motor vibrating uncontrollably at high throttle? I am running a 1500kv Turnigy SK3 spinning a 8x6 prop.
Motor runs offa 30amp esc, and i use a 2200 3cell 25c lipo.

it runs fine up to just above half throttle, then it vibrates uncontrollably and once even broke the mount!

Prop is balanced, nothing is bent.

What is going on!!!!??

BTW, I am using the motor in this plane:

Thanks

All Day Dan

My Feedback: (5)

Post an image of the motor mount with and without the motor attached. Dan.

BarracudaHockey

My Feedback: (11)

You say the prop is balanced and nothing is bent but it really sounds as if something is bent or out of balance

Corsair013

Here you go, pictures of it with and without the motor:

Corsair013

Brand new prop, checked it was balanced. Also tried the motor with different props and same result. Runs fine without any though.

No evidence of shaft bending, all straight as far as I can see.

Propworn

My Feedback: (3)

Try it with just the hub and spinner. Sometimes over tightening mashes things out of place.

Dennis

Corsair013

Thank you, will try now.

Corsair013

Just tried it now, works just fine all the way up to full throttle.

Would a too small prop do this? (vibrate on a too large motor?)

Propworn

My Feedback: (3)

Don't think so ducted fans are even smaller and rev higher without problems. A prop can be balanced statically but be out of balance dynamically. First try a different prop preferably different brand. We had problems with hobby king props vibrating right off the motors on our indoor.

Try taking the motor out of the airframe and mount to a solid block of wood and run it up with the prop and spinner. If there is no vibration then I would suspect what they call soft foot which is a soft, flexible or weak motor mount structure on the airframe. Try re gluing and some re-enforcement in places you suspect may be weak.

Dennis

All Day Dan

My Feedback: (5)

That's one long cantilever you have there. All those lightening holes, lite plywood and no gussets add up to a weak structure. Add the weight of the motor and torque from the prop it's no surprise you experienced your problem. As a last resort you may want to consider beefing up the structure with some aircraft plywood, hard wood triangular stock and plenty of epoxy. Dan.

Corsair013

Ok, will do. The mount seemed to be a bit weak looking.

Corsair013

Yup, structural reinforcement seems to be the answer.

Thanks!

ron_van_sommeren

No, not possible. It is impossible for motor to run faster than Kv × voltage.

Construction is strong enough, it can handle the vibrating, but it is not stiff enough.
Motor mound is already strengthened at bottom, I would strenghten the motor mount on top as well, close the box as it were, with horizontal piece of ply.
Glue outside the gap is useless, adds only weight. Remove excess glue before it sets.

Vriendelijke groeten Ron

Corsair013

ok, thanks

Quorneng

Your prop may be balanced but is it running centered & true on the motor shaft?
With the prop running slowly and looking directly from the side do both prop tips pass in exactly the same place?
If they do not then the motor will 'feel' an out of balance force that gets worse with speed and any 'give' in the motor mount will likely make it even worse..
.

Corsair013

ok, will try that.