Cole-Parmer makes an immersion stirrer that has no moving parts and
is incased in a block of epoxy. I used them almost 17 years ago. One
way to maintain constant etch rates is to use a large bath of heated
oil, and set your flask (beaker, etc.) in the oil. If you need a
stirrer, then you set the flask on top of the immersion stirrer, and
place a magnetic bar inside the flask. Going over the top, add a
reflux condenser on top of the flask to keep your etchant from
evaporating off. The immersion stirrers never seemed to last that
long, because the oil took a long time to heat (only an hour, but
that's too long for some). I will guess that some of the students
left the heated bath on 24/7. The oil and spilled etchant would eat
right through where the wiring entered the block of epoxy.
Older than immersion stirrers were the DC brushless motor drivers
that Dan Orange designed at Sprague Semiconductors.
The judges should be impressed because so few kids enter areas of
math and science. The ones that have an interest get discouraged for
any number of reasons. I help my daughter any way I can.