393 motor output sockets not centered


Over the last three months or so, I have bought a dozen or so 393 motors, and several (most?) of them have output sockets (that you insert an axle into) that are significantly off center.

I say significantly because:
[INDENT]The offset is easily visible (some more than others) when the motors are operating (spinning a shaft),
They slow down during each revolution as the axle they are turning binds against other parts of the robot, and
They cause axles to rub against the square holes in the metal pieces they are mounted upon (I am using bearings, just not at every single place where the axle passes through a piece of metal).[/INDENT]

Do you think I have just been unlucky enough to get a handful of motors that slipped past quality checks at the manufacturer? or can you think of something I might be doing wrong when using them?

As you know I have building VEX bots for quite a while, so I don’t think I am doing anything wrong.

What’s our next step?


Hi Blake,
This is not a known issue. Please contact our support department so we can get more information and see about sending you replacements. I’d love for you to work with our support folks to put those bad motors in my hand.



Will do.

I’m separating them into naughty and nice piles for you today.

Instead of the socket mouth being off center; the problem could be that the mouths of the sockets are centered, but that the socket well isn’t parallel to the axis of rotation.


An update:

The motor that was causing an irritating squeak each revolution, is the motor I thought was causing its axle to to rub against the metal it was mounted in. Seeing a grove cut/eroded into a nearly brand-new axle, combined with the squeak, made me think that.

However, today I see that having the the axle fully seated in the shaft coupler on the motor, would have put the groove inside the coupler. so now I am uncertain whether that axle was rubbing against the robot’s structure.

I might have had the axle partially seated in the coupler (but held firmly at that position by shaft collars); and it might have been rubbing. Or the groove might have been worn into the axle during an earlier use (but the axle is very nearly brand new).

Regardless of the info above, some of our several motors’ problem symptoms are still easily repeated; and I’ll work with the Support team to get them returned.