A go at a Foamie

Q's doppelganger and others have used the LE2204 on their FX707's.
forums.modelflying.co.uk/index.php?/topi...ons/page/2/#comments

The internal motor winding has been pulled out & twisted beyond use.
 
Note I have removed the circlip on the end of the shaft to see If I could dismantle the motor but the bearing must be pressed in.
 
 

I've taken some photos of the folding prop.

This is the back view of one of the 7.5 x 4 props straight out of the packet. The blade pivots are a reasonably close fit in the plastic housing.
 
This is a back view of the 6 x 4 prop in use when the motor failed, there is a gap at the side of the blade pivot
 
This is the prop dismantled. Note that the pivot screws are bent.
 
 
It looks to me that the cause of the vibration was too much side play on the blades.
I assume the bent pivot screw was the result of the vibration.

I had bought two 6 x 4 and two 7.5  x 4, that being what was available.
Both the 7.5's are a reasonable fit, the other 6 x 4 also has alot of side play. It suggests that the 6 x 4's were from the same batch, possibly assembled by the same person,
The pivots on the 6" blades are 4.9mm thick, those on the 7.5" blades are 5.9mm.
Should different plastic housings have been used on the different sized blades?

They were all got from Aliexpress. I'll try complaining but I'm not optimistic.

 


 

I would have thought the last thing you need for the hub of a folding prop assembly is plastic, should it not be ally 

I cannot see a missing chunk or a crack. I think maybe the camera angle & lighting is creating some illusion so I have scanned all four of the props.
The top one is the one that had been on the motor when it failed, I have put some washers in as spacers (more on that later). The next one is the other 6" prop & the other two are the 7.5".
 
 

I added some washers to the 6" prop that had been on when the motor failed & mounted it on an A2212 motor on my test rig using a 3.17mm collet to match the motor shaft.
I didn't get the roaring vibration but I did not push it too far.
I then tried the other 6" prop without any washers.
I couldn't hear any difference between the two but my hearing is not of the best.
I have ordered a sound level meter. I will have to drive the ESC from my Raspberry Pi so I know I'm running the two props at the same speed.

I am now wondering whether the LE2204 motor is acting like a tuning fork (or the Tay Bridge).

If you really bent those blade retaining screws simply from just the vibration then I am not surprised the motor back plate failed!
I would suggest that any noticeable vibration at 1/4 throttle means stop and cure the balance.
Out of balance forces increase by the square of the RPM. 1/4 to full throttle means at least 16 times the forces.
A really rigid test mount doesn't help.
Note on the full power run of the rotary although the test stand was loaded down with a big lead weight it was also sitting on a 5mm thick foam pad to allow it to move about a bit to absorb any vibration.
www.youtube.com/shorts/kOjTkcVH5x8

I don't know what the pivot screws are made of but they are magnetic.
They could only bend if there was a gap (which there is) between the blade & the side walls.
The vibration started at just over 50% ish.
The motors are mounted on the 2x1 arm using screws through it into T-nuts.
Maybe if I mounted a piece of ply on short stand-offs on top of the arm & fastened the motor to that it would reduce the resonance.
The whole thing stands on a car floor mat to help quieten it.


 

I cannot see what you mean.
Can you see the missing piece on the slots on the scanned image?

Remember the motor is a write-off. I've got to wait for a replacement before I can do much more.

Apart from being short of clevices I've got the wings assembled. I've got a problem though managing all the servo cables. I've got ready-made extensions & a Y-lead but its going to be a struggle getting them all into the space under the wings in the fuselage. Jamming them in will run the risk of them getting entangled with the tail & fin servos so I'm thinking of cutting & soldering them. I've done alot of soldering in my time but these wires are very thin for my eyesight & dexterity.
The replacement motors should arrive this week so that means some very carefull testing on my rig. I've bought a cheap sound level meter, I can't think of any other way to monitor the vibration.

There isn't enough headroom over the servo arms, I'd had to lower the servos so as they didn't foul the wings. I've used the shortest leads I could get, the connectors are quite large, about 35mm joined up & rigid.
I'll do as you suggest but put in a thin vertical barrier which will reach right up to the wing lower surface.

My replacement motors should come in the next day or two then I can see whereabouts under the canopy the battery has to go to get the CG in the right place. That will determine where the receiver can go (under the wing or under the canopy) & hence what space there is for the wiring.

On small light planes I hate using servo extensions both for the space the connectors require and their weight.
Soldering 32 AWG servo wire is also a bit of a fiddly chore but it is worth the effort so every lead including the motor and ESC has just a single plug on it and is exactly the right length.
Even better if you can get the servos out the way as well 
 
Loads of room!