Diseño De Control

FEATURE

Low-Cost Magnetic
Levitation Project Kits

©SOTHEBY’S
LONDON/SUPERSTOCK

Using inexpensive experiments to teach analysis
and design in undergraduate feedback courses

A

new magnetic levThe Basic System
itation project
Figures 1 and 2 show assemoption
has
bled magnetic levitation sysbeen develtems. The kit is easy to
oped for the
assemble, but initial perforfinallaboramance of the device is intentory assignment in a juniortionally poor. When assembled
and senior-level control sysas described, the system
tems course (6.302 Feedback
exhibits high sensitivity to iniSystems) offered by the
tial conditions and considerDepartment of Electrical Engiable visible wobble of the
neering and Computer Sciobject. This kit is based on a
ence at the Massachusettslow-cost design developed in
Institute of Technology [1].
[4], which uses proportional
© PHOTODISC AND ARTVILLE, LLC.
The project was made availcontrol and is marginally
able to students in the fall of 2003. The system is similar to
stable. The parts kit includes all of the parts
classroom demonstration systems first described in [2] and listed in Figure 3, while the students are required topro[3], which suspend an object below an electromagnet. In our vide the support stand and the object for levitation.
project, students assemble and modify
The schematic of the basic system is
individual kits to create their own desk- By Kent H. Lundberg, shown in Figure 4. A prewound solenoid
top-sized systems with analog control.
bolt serves as the
Katie A. Lilienkamp, around a soft-steelHall-effect sensor
The unmodified basic system presented
electromagnet. A
and Guy Marsden
to the students is marginally stable, and
mounted at the base of the solenoid
students must analyze and redesign the
senses the proximity of a permanent
system to improve its performance. The main goal of the magnet attached to the levitated object. The output voltproject is to provide a challengingdesign problem that cap- age of the sensor drives the input of a fan-management
tures student interest and allows for open-ended solutions.
chip, which produces a pulse-width modulated (PWM)

October 2004

0272-1708/04/$20.00©2004IEEE
IEEE Control Systems Magazine

65

drive signal to a motor drive chip. This PWM signal adjusts
the average current in the solenoid, which controls themagnetic field.

far from ideal. For the basic system, however, the Halleffect sensor is an inexpensive and adequate solution.

Lab Project

Damping is provided by washers attached to the levitated object. Losses and eddy currents in the ferrous material
help to dampen the vertical wobble of the object [4]. The
system is sensitive to initial conditions and requires a
steady hand. Of course,the measurement of the magnetic
field from the levitated object is corrupted by the field
from the electromagnet, so the position measurement is

After the basic system is demonstrated in a classroom lecture, each student receives an individual kit along
with assembly instructions for building the magnetic levitation device.
The laboratory assignment challenges the students to modify thesystem to improve basic system
stability, transient performance, and
disturbance rejection.
We intentionally present students
with a device that is poorly instrumented and poorly compensated, and we expect the students to analyze sensor performance and perform
compensator design. The project is open-ended, however,
and students are encouraged to explore other areas of
improvement. Modificationscan include sensor selection
and placement; the design of the solenoid actuator; the
magnetic, geometric, and inertial characteristics of the

Figure 1. Student-built system with an aluminum stand. The
system levitates a large metal screw. This industrial-looking
system won the award for lowest power consumption.

Figure 2. Student-built system with a LEGO stand. The system levitates an...