Sleeve on Fisher Price

[sanddrag]

What is the purpose of the thin metal "sleeve" on the fisher price motor? Should this be taken off if we use a heatsink?

[ahecht]

It is a flux yoke (as Joe Johnson calls it), and provides an additional magnetic path between the field poles. It should not be removed unless you want to reduce the torque of the motor. Like the fan blades you broke earlier, it wouldn't be there if it weren't important.

[sanddrag]

Originally Posted by ahecht

It is a flux yoke (as Joe Johnson calls it), and should not be removed unless you want to reduce the torque of the motor.

Could you explain this a little more? Yoru saying it alters the magnetic field?

[jgannon]

Originally Posted by sanddrag

Could you explain this a little more? Yoru saying it alters the magnetic field?

http://www.chiefdelphi.com/forums/sh...8&postcount=27

See this post for an explanation. Basically, more metal means more magnetic field. Since F = q v B sin(theta), more magnetic field (B) means more force (F).

[ahecht]

I don't want to get too much into motor theory, as it's been a while since I've done this stuff, but basically the job of the yoke is to provide a path for the magnetic flux. As I remember it, having a steel path between the magnets instead of air increases the flux density, and therefore the efficiency of the motor (someone correct me if I've got this backwards or plain wrong). The more steel the better, up to a point when things become saturated.