I'm flying an RD1 electric with an Eflite 15 motor.  Its front mounted, as you can see in the picture.  The mount is made from stainless steel (the original was aluminum, but I felt I needed more strength).  The problem I had was with vibration.  I think I hit a resonant frequency with the rpm I wanted to run (10,000-10,500) and the nose shook violently in that range.  I decided to add a rear bearing to it, which you can see in the 2nd photo.  Its a real simple addition, just a piece of basswood with a 5mm bearing pressed fit into it.  I had to move the shaft back 1/8" to engage the bearing, but it works perfectly.  No noticeable vibrations at any rpm.  I would be a lot happier with a longer motor shaft, so I could get full engagement into the bearing.  I was wondering if a shaft from an Eflite 25 (which is about 1/4" longer) could be used in an Eflght 15?
Thanks,
Rick

If you are getting a vibration , there is most likely something wrong. either your shaft is bent from the crash, or you have a bad or damaged bearing. You should not need a third bearing to stop vibration. Also your prop or spinner may be out of balance or alignment. Read this http://www.apcprop.com/v/html/tech_support_notice.html#holealign and this http://www.apcprop.com/v/html/balancing.html  both are very important. As far as using a longer shaft I don't see why you cant as long as the diameter is the same.. I've even made my own shafts fro 5mm music wire. Most people feel that the extra bearing may not be needed. Most people that I know that are using this motor are not using a support.

William,
Thanks for your thoughts.  I believe I balanced the prop correctly, but I did try another prop with the same results.  I removed the spinner and tried it with just the prop: same results.  The crash was pretty violent.  The lines caught on the grass in takeoff, it came at me, then went straight up, then straight down into the ground.  The spinner, motor and 1/3 of the battery were buried.  I was totally surprised that the shaft appeared straight.  I suppose it doesn't have to be off much to cause vibrations at 10,000 rpm.  I'll order another shaft and try it.
Thanks,
Rick

Rick,
Here is my solution to a rear bearing.  This was done back in 2009 and still going strong.  If you have vibration like you describe, then look elsewhere.

Dean,
I received the E-Flight 25 shaft and installed it in the E-Flight 15.  It fit perfectly and the shaft extends 0.200" behind the motor, which is perfect engagement into the rear bearing.  I'm pretty sure the motor mount was not stiff enough, but the rear bearing takes care of the problem.  Thanks to all for your help.
Rick