Project title:  Solenoids for locomotion

Proposed by:  David Baird

Date: 2002 Aug 29

Description:  Build and evaluate solenoids to use in our robotics
applications.  The idea is to wrap a hollow core with wire and put and
wrap a ferromagnetic material around the wire.  This will create a device
that sucks iron right into its center.

Initial plans:

1. Testing:

Use iron filings to observe the magnetic field around magnets and
various types of metals.  We can probably let the iron filings float
in an oil mixture in a closed shallow container (like a pitre dish).
This allows us to investigate what materials influence magnetic fields
and how to control the shape of magnetic fields.

Use PIC16C871 microcontrollers to setup controlled tests and record data.
The tests will collect data about resistance of coils, how much force they
can lift for certain given objects at certain distances and electrical
currents, etc..

2. Building:

Wrap 1/4" diameter copper tube with wire.  Try using scrap IDE/ribbon
cable with each circumference of wire hooked up in parallel.  Also try the
"more traditional" method of wrapping enameled wire.  Make sure there is
some slack of wire to attach it to control circuitry.  Place the wrapped
copper tube inside of steel conduit.  Now you have a solenoid that
will attract iron to its center.  For convenience, it may be possible
to solder the wire to the copper tube it is wrapped around and use the
copper tube as a low resistance source/return path for current.

For the control circuitry, a capacitor can be placed in parallel with the
solenoid to allow it to operate in switched mode at a resonance frequency.
Back to back zener diodes should be placed as a backup protection.
We may want to reverse the direction of current in order to keep things
demagnetized (ie. magnetism only comes from the current, and not from
other things we accidentally magnetize).  For simplicity, an H-bridge
can be used in an initial switching control circuit.  A current source
would also be useful for non-switched use of the solenoid.  This may be
better than the H-bridge if we can use switching techniques to generate
a constant DC current.

3. Demonstration

Levitate a steel ball (ball bering).  Mount a solenoid in a stand.
Use optics and/or hall effect sensors to locate the ball and a pic
microcontroller or analog circuitry to implement a control system.
Use either an H-bridge or controlled current source to control the
solenoid.  This setup may also be useful for testing the solenoids.

Produce a useful part for robot motion.  Make a leg, or hand, or
something =)

Initial parts list:

1. About (however much we can get for $10) 1/4" diameter copper tube,
$10, Lowe's Hardware in Albuquerque

2. Steel conduit (however much we can get for $10), $10, Lowe's Hardware

3. Threaded rod, about 10ft, $10, Lowe's Hardware

4. Enameled wire, $5?, Radio Shack

5. Pic microcontrollers, hopefully these can be obtained in another
project

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