Re: [CAD_CAM_EDM_DRO] Sawyer motor

Anne Ogborn wrote:

> Anybody on this list been sick enough to contemplate
> making a machine based on a sawyer motor?
>
> A Sawyer motor is a sort of 2D linear stepper motor.
> I used to run a giant pen plotter that used one.

These are quite fine, but actually hard to make. There apparently
is a machine tool made with them. We have a roller coaster at Six
Flags amusement part that uses them. They had a $5 million cost
overrun because they ran too hot, and they had to redesign the
whole system to use twice as many feet of armature to keep it
running for a full day of rides.

One problem is that the huge magnets will attract all sorts of metal
chips. They tend to run hot, and draw huge currents at very low
voltages. The attractive forces between the stator and armature
are not balanced (as in round motors) and so the entire design
has to be made with this in mind. The attractive forces can run
to several thousand pounds even in small motors.

If you were designing a machine from the ground up, you could
probably design linear motors into it well. I'm not so sure how well
you could retrofit linear motors into an existing machine tool.

And, if you have a runaway servo, you might have to pick up that
machine table from the other side of a building's wall! These things
can REALLY accelerate!

Jon