Computer Control of Viscosity

[Ron Horowitz <RonHorowitz@domain.elided>]

>>The latest in technology it controlling the viscosity with electricity.
>Then you can use a computer to control the degree of slip.  VERY cool
>stuff.<<
>
>So when can we have clutches and brakes made using this stuff?

I may have missed part of this thread, but if you're refering to
Ferrofluids, I know a fair amount about them.

Ferrofluid brakes probably aren't a great idea, since even in the
"unexcited" state, the fluid has viscous drag. (Damping effects are
routinely used to flatten the response of acoustical transducers, for
instance.)

This is just off the top of my head, so don't take it to the bank, but
Ferrofluid-variable viscosity requires electro-magnetics, and residual
magnetism could be a problem in a DC circuit. You'd probably need AC, and
the system might have to go through a de-Gaussing cycle every time. Don't
really know, but I imagine there would be inductive roll-off at too-high
frequencies, and maybe enough of a time constant at too-low frequencies to
be an annoyance. Might be a bitch getting it sorted, but if the circuit
were tuned OK, you could probably do it with a pretty simple circuit, maybe
just the decay after cutting power to the oscillator.

BTW, this wouldn't be regenerative braking, you'd have to dissipate the
heat elsewhere

Ferrofluids have been tried in computer controlled shocks, but last I heard
they weren't terribly successful, or at least not yet. I may be behind the
times, as this was probably three or four years ago, but one of my
race-junkie buddies tried them (barely has money to feed himself, but his
race cars are amazing!) His comments were simple: "Great idea, but they
don't work." Don't really know the details.

BTW,  since Ferrofluids are a colloidal suspension of magnetite in oil, you
have to be pretty carefull about the stability of the oil used as a base.
You can use synthetics, but even some of these seem to suffer from volatile
fractions and "un-polymerizing." Not really sure why, but there it is.

RON
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