Why is there a magnet sleeve on the armature assembly shaft?

[Alan12345]

I need to purchase a quantity of routers and in inspecting some I noticed that the name brand router has a magnet sleeve on the armature assembly shaft, while some of the cheaper clones do not have the magnet sleeve. What is the purpose of the magnet sleeve? It is only mildly magnetic, and sits inside the plastic motor housings. It's item #18 on the parts blowup. Other pic shows one with and without the magnet sleeve.

 

[waross]

As a guess it may be a tachometer. It looks as though there may be some type of sensor mounted adjacent to the magnet.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Alan12345]

Hello Bill - Part #3 is a speed controller but I figured it was controlled by the speed adjustment pot that connects to it. Maybe the magnet does serve some purpose in regulating the speed. I spoke with tech support and they didn't know the function of that part...

 

[waross]

It is probably a speed feedback device. A crude tacho-generator.
It will help keep the speed steadier under varying loads.
Or it may be something else.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jraef]

There are two ways they do speed control on hand power tools; it’s either a phase angle control using a triac, or PWM. The PWM has some advantages in efficiency, accuracy and quieter sound but needs a speed feedback loop. That’s likely the difference; the more expensive one uses a PWM controller so it has that magnetic sensor as a speed feedback.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Alan12345]

Ok, that makes sense. Thanks everyone!

 

[waross]

Thanks Jeff.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[3DDave]

It is of some interest to see where the poles are.