I lost a shaft on my Platt. 20-12 today , does anybody know how the shaft is held in? there is no lock ring on shaft, and no set screw!  looks like a press fit...

Larry,
That happened to me last week. I was going to do a post on it and never got around to it. I was flying my SV11 and it pulled right out the front,while I was doing squares. I was able to recover inverted and landed with very little damage to the plane. Back to the shaft, they are press fit. What I did to fix it, was to scratch up the shaft at the point it sits in the motor with a dremil cutting wheel. Then i scratched up inside the motor,where the shaft sits with like a 1/32 drill bit on a slight angle. Then I mixed up some JB weld and put it in the motor hole and on the scratches or grooves that I put on the shaft. I then presses the shaft back in. I used an arbor press but it wasn't that hard. I cleaned up the excess JB weld and let it dry over night then reassembled the motor. Since this was a 15-18 I had some excess shaft out the back. I put a 5mm collar on the back for extra insurance. So far I haven't gotten to fly it. I feel that this is a weak point in the pletts. One option,besides ordering a new shaft, might be to order some 5mm steal rod from McMaster Carr or some other supplier and make a new longer shaft that will allow you to put a collar on the back. I believe the 20 sized pletts are flush with the back of the motor. Make sure that you take the part that the shaft presses into off the motor before you work on it.

Wow.  When I read Larry's original post I wondered two things.  One, how in heck does Plettenberg achieve the necessary precision to make these things assemble well, yet still hold in normal 3-D service?  And two, can an ordinary user replace the shaft?

I guess both questions are answered...

There's a Locktite bearing glue that I'd use instead of JB weld, so I wouldn't feel that I had to degrade the fit by roughing up the shaft and bell.  It's just like ordinary CA, only it's insanely strong for metal-metal contacts.

McMaster should have hardened 5mm shaft material.  Hopefully.  You want something sold as "shaft" -- 5mm hardened drill blanks will shatter on impact, 5mm drill rod is fairly soft and would need to be heat treated (and may warp during heat treat).  The cool way to do this if you had a machine shop would be to turn a groove in the end of the shaft and use an 'E' clip, or otherwise machine a feature into the shaft so that you can clip, snap or screw something on positively.  But that's gilding the lily.  The collar idea is going to work just as well if you can get enough of a grip on the shaft.

They're German, and they manufacture technical equipment.  Not all German manufacturers of technical equipment are this way, but when I was working in aerospace, the only times that a vendor would come in the door and dent the conference room ceilings with their noses, it was when it was Germans or Swiss selling stuff to us unwashed 'mericans.  They had this notion that the only competent engineer is one who has a Dipl. Eng. (the equivalent of a Doctorate) and who learned German on his mother's knee.  As a US engineer with a Master's degree I had to have iron-clad evidence that a problem was theirs before they'd actually look at it, and heaven forbid that they would accept the testimony of someone with a mere Bachelor's degree (this was a challenge for them, because one of our smartest and most capable guys never even finished his BSEE).

They may well be better than AXI, but the whole pressed-in shaft thing is odd -- I would expect that the 3D RC guys have the same problems with sudden turns that we do, so it's not like we're flogging these things outside of their expected loading.

There's a company out there that you could just buy a shaft from, with or without retaining rings (or screw threads, or a threaded hole, or a bazillion different other options), if you want to get a couple of dozen and share with friends: http://us.misumi-ec.com/us/ItemDetail/10300087010.html.

can you do a pictorial on how you re-pressed the shaft - I might do this as preventative maintenance .....just got a Plett into a yatsenko and dont want it to come up short!!

Tim, will the Loctite stuff seep into the joint while the motor is assembled?  How do you get it unstuck?  Heat it?

Tim, will the Loctite stuff seep into the joint while the motor is assembled?  How do you get it unstuck?  Heat it?

I'm a systems engineer on this one (i.e., I don't know the answer, but I do know who to ask).  I suggested it because when I used to do controls for electro-mechanical systems, whenever there was a shaft-retaining problem someone would suggest 609 or 648, and all the mechanical guys would go "Ooooh -- that'll hold it!".  Then they'd all get happy and excited until someone said "how's service going to take this apart?" and then they'd get glum again.

According to the folks I asked, trying to wick it into an assembled motor is probably a no-go.  Press fits, if they're done correctly, don't allow much room for wicking.  Someone did suggest 209, which has very low viscosity -- but that's intended as an after-the-fact threadlocker, and threads generally give you much more space for stuff to wick in.  Someone else suggested that 7452 accelerator might wick in, and pull glue in after it.  Perhaps you should try it, and then test the joint to see how much force it takes to press the shaft out.  Then, when you put it back together you can glue it up correctly .

I believe that heat is the way to go for disassembly on this.

According to my mechanically-inclined buddies, Locktite 609 or 648 is probably best.  Regardless, I think that Locktite is going to be barely sufficient at best.

To a man, they all referred me to Locktite's excellent product selection page:
http://useloctite.com/products/index.html

This quickly lead me to their "press fit shaft" page:
http://useloctite.com/products/product_details_retainingb76c.php

You can also try calling or emailing their apps engineers -- Locktite is famous for being accessible and helpful.

We also have to remember that the only purpose of the collar,c-clip or anything else we can devise to put on the  back of the shaft is only there to keep the shaft from pulling through should whatever method we use to secure it in the front fails.

Looking at the cutaway picture, I think that with the shaft in the position shown it's the end bell bearing against the inner race of the bearing, and the shaft pressed into that.  So if you retained the shaft to the end bell there'd be clearly defined support for both end bell and shaft.  If that's not the case then the only thing retaining the shaft at the mounting flange end is the press fit into the bearing.  Again, we're left with a press fit trying to hold everything together...

To know more I'd have to take apart a few motors.

Safety and reliability at its best! I mean worst.........

Derek

I'll put this in the win column for IC!

Shaft ejection: another first for electric 

Close. I personally saw quite a few shaft ejections in rat race.. Those (ground out front rotor) G21 and Max H  cranks were famous heart breakers... Always broke 5 laps from the end in the 140.... I have to say that a pressed in shaft is a curious choice on Platt's part.

how many motors has this happened to?  seems there are 10000s of pletts out there - so what is the REAL risk that this will happen?