These were only used
in 1 quake3 level but I'll show you how to create
them.
In your
level create the object that you want to be
swinging.
Next load the 'common' texture set and find the
texture called origin, next create a small brush an
place it at the top of our object or the area that
you want it to swing from as shown here.

Now
select the origin brush and the objects that will be
swinging and press N to get the entity info up, find
the func_pendulum and double click.
you can
leave the settings as default but if you need to
alter things here are a few bits for you
Key:
speed
Value: 30 (default)
Key: dmg
Value: 2 (default) 200 should kill :)
Use the
angle buttons to set the angle you want it to swing
at.
Here's a
map
file for you.