LINEAR MOTOR FOR MAGLEV TRAIN
__________________________ electromagnet | | _____ n |drive circuit & batteries | | | |__________________________| | | |_____| hall sensor force <----- |_| s === ___________________________________________________________ | S | N | S | N | S | N | S | N | S | N | |_____|_____|_____|_____|_____|_____|_____|_____|_____|_____|Fig. 1 Central thrust track, coil, and sensor
In figure 1 above, we've built a "stator" track out of permanent magnets.
Hovering over the magnet strip is an electromagnet coil, a hall sensor,
and the rest of the 3-transistor "magnet cradle" circuit discussed
elsewhere. (see magschem.gif) The position of the hall sensor chip and
the tip of the magnet is important. The hall sensor is next to an "S" pole
of the magnet track. It turns the coil on, and the coil is oriented so
its bottom pole becomes "S". The tip of the iron core of the coil is
between an "N" and an "S" pole of the permanent the magnet track, so it is
attracted/repelled from right to left.
Since the coil, sensor, and battery circuitry is all riding on the
levitated cart, the entire cart moves forward. As the cart moves forward,
the hall sensor moves away from the "S" pole of the track, and approaches
the "N" pole. This turns the coil off, then turns it back on again with
its poles reversed. But now the tip of the coil's iron core is between
opposite poles of the magnet track, so the fields still force the coil to
move from right to left. The cart keeps moving, the sensor keeps
switching the coil polarity, and the fields always force the cart from
right to left.
When placed on the maglev track, the cart should take off fast,
accelerating as it goes. At some point the speed should level off because
of air friction or switching speed of the coil circuit. Battery voltage
should control the acceleration (reduce voltage to reduce the coil current
and the magnetic force.) Rather than the two separate 24V power supplies
used for the cradle device, I bet that a pair of 9v batteries would work
It might help things if you first develop your linear motor on a wheeled
cart. Once it is all working, you can move to the levitated car.
Note that the linear motor's magnet strip is not part of the main
levitation system. Figure 2 below shows where it should be positioned in
my "train.txt" permanent magnet levitation project.
I don't know if the attraction between the drive coil and the NSNS magnet
track will cause troubles. It might attract the drive coil so that it
drags along the magnets. You'll have to experiment. If the drive coil and
the NSNS magnets are fairly weak, then their downward pull should not
overpower the main levitator magnets. If they do, you might need to
change the linear motor so the central magnet track sticks up, and two
drive coils face it from the sides, with one coil on either side. This
would eliminate any vertical forces (but add some horizontal forces, as
well as adding complexity.) Or instead you could try removing the iron
rod from the coil, and perhaps use a coil which is as large in diameter as
one of the magnets in the NSNS strip.
side ____ (end view) ____ side rail | | | | rail | | levitated cart | | | | __________________________________ | | | ||__________________________________|| | | | |_____| |_____| | | | | _____ __ _____ | | __|____|____|_____|_____|__|_____|_____|____|____|__ |____________________________________________________| /\ central NSNS thrust trackFig. 2 Maglev train with central thrust track
If all of this is a bit too much to contemplate, then here's a hint:
Propellor and rubber band from a toy balsa wood airplane!
> Date: Tue, 7 Jun 2005 14:14:36 -0400 (EDT)