[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


I think I have figured out what went wrong here, after staring at the busted motor well past midnight.

This motor does generate quite a bit of vibration as it speeds up - or at least it did in the mounting I created.  Which is to say there was a "zone" in the power band during which I got a lot of noisy vibration.    This "zone" was at about 1/4 to 1/3 power on the variac.  Once past this zone, with the motor running faster (or slower) I didn't sense the vibration, just smooth spinning.

  There are two bushings on the motor case where you can screw in an 8-32.  I'm guessing this is a replacement motor for some household device.  It sounds like a vacuum cleaner or a leaf blower to me, but who knows.

The two brass bushings are located on one side of the motor housing, in line with the shaft.  So the other side of the housing is untouched.  

Not wanting to support the motor from only one side, I opened the case and drilled 2 holes in it allowing me to epoxy in 2 8-32 bolts.   Now I had 4 screws holding the motor, 2 on each side of the housing, in line with the rotating shaft.   I attached an L bracket to each set of 2 screws, and then bolted the 2 L brackets to a piece of G10.

I made the polyetheline hub the same way I have on my other propeller gap.  Friction fit to the motor.  But I used screw-down collars on the rotating tungsten rod as I am forever paranoid the thing is going to come shooting out and impale someone horror-movie-style.

I believe what happened is that as I spun up and down the motor, testing different speeds, and it went through this vibration zone, it actually shook free of the mounting bolts I epoxied (and secured with  nuts).  The plastic housing seems to have cracked around those bolts in inserted, and the two 8-32 bolts themselves are bent.  Of course, I can presume the bending bolts happened when the motor crashed, but I don't know if the cracked housing happened before or after the crash.

With the motor out of alignment, and spinning at a couple thousand RPM, the tungsten rod whacked into something.  I'm presuming it whacked one of the tungsten electrodes, but honestly, all of those are entirely intact.  It may have hit the G10 sheet upon which I mounted the electrodes.

In any case, the force with which the tungsten rod hit was enough to cause it to shatter into at least 5 pieces, including 2 pieces which still had the collars faithfully tightened on.

I would try this experiment again with a different motor and mounting arrangement, or even the same motor and a different mounting arrangement (or perhaps a more liberal use of lock washers and lock nuts).   

In any case, this ARSG setup scares me more than the coil voltage itself, as bullet proofing needs to be erected to protect all onlookers from the sloppy engineering of the builder.



On Jul 31, 2010, at 1:44 PM, Joe Mastroianni wrote:

> As this is becoming the diary of my attempts and failures....
> Let's log another failure.  I built an ARSG around an AMETEK motor number 5409-33  AC/DC.  I think it's a vacuum cleaner accessory motor.  I got the idea from Terry B's web site.
Tesla mailing list