[TriEmbed] Running old hard drive motors with a MC: DRV11873 and DRV family ICs

[Collin Ladd]

Thanks for the feedback Pete and Scott! I'll look into the provided
sources. I'm hoping to get anything workable running ASAP.

A little more context on the project: I am trying to build a "disposable"
(and cheap!) spin coater--the kind used to spin photo resist onto an Si
wafer for chip making. Spin coating the liquid metal runs too much risk
with our real equipment.

Hard drive motors just so happen to have the right stuff for the job--high
RPM and near indestructible etc. Most importantly, the center can be
drilled out for a vaccuum line (holds down your wafer whilst spinning) and
they're practically free. Target rpms are  1-5k with a very light (5-30g)
albeit unbalanced load. 11k would be amazing but not necessary.  There's
also the issue of reproducibility, meaning we need decent rpm sensing and
timing control. Despite this being all lab work, I think this is a pretty
cool hobbyist project, as a good craftsman could end up with a thousand
dollar piece of prototyping equipment for a few bucks. Not sure how many in
the group do their own photo masks...BUT this is the only tool I know of
that allows me to make even enough coats to etch super-fine pitch designs
(think <35 micrometers). Pretty crazy capability for garage equipment.
I was hoping the light load and low duty (maybe a minute running full blast
tops) would let me get away with one of these driver ICs... maybe not. Spin
up torque might be an issue, as that is when the load is the most
wobbly--but no more than a cpu fan with a piece of gum on the blade. RC
motor controllers sound beefy enough...


No dice so far with getting datasheets for the spindle control chips that
came with my HDDs (don't have the part numbers on hand, but I looked for a
*very* long time online without success). I could poke around with the
scope and maybe get it eventually, but even if I did I think the x-fer and
rewire without a datasheet might be outside of my skill range. As far as
heat goes, I'm willing to go so far as to chuck the board into a tank of
coolant oil if I have to--as long as it works.

This is an out-of-pocket side job, so I unfortunately don't have the
academic budget on my side--just the awesome tools. I'll take one of those
dip chips if you're offering.  I am going through with ordering a pack of
the DRV chips just out of curiosity... perhaps we can trade.

*FYI to the whole group, from now to December I am full to the brim with
electronics projects for the grad students. Any takers? So far I have:*

*-- This spin coater*

*-- A computer controlled single axis stepper*

*-- A 3 stepper stage leveler using these actuators I have:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G19596
<http://www.goldmine-elec-products.com/prodinfo.asp?number=G19596>*


*-- Induction pump--essentially a 100A+/low volt DC pulse generator, maybe
using a beefy cap bank*


*-- A parallel plate capacitor test rig with little parasitic LC as
possible (just adjustable plates... we have the LC meter)*

*-- Isolation xfmr + rectifier + smoothing to turn a variac into a heavy
duty DC PSU.*

*-- A micro induction heater (40-90W royer variety... hopefully tuneable)*

*--Closed loop temperature control for a metal print head*


*--Some homebrew image processing to gauge the size of drops in real time. *

*-- A LOT of RF transmitters and tune-able inductors. *

*All projects except that last one are more or less free favours and not
required for my job. Anyone who happens to spot something of interest is
more than welcome to join me on Centennial campus any time for a build
session, or, if I ever make it up to Splatspace (I've been trying! But I
work ALOT), that works too.*

I certainly could benefit from having a more seasoned perspective to weigh
in on designs and rigs. It's pretty usual that I have no idea what I'm
doing until a given project is 90% done, haha. Not trying to Tom Sawyer
anyone or beg for help though, these are 100% fun, no pressure projects we
can always solve by throwing lots of lab money at the problem (huge waste).
Oh yeah...I'd be paying for any parts and tools, and while I can't offer
you money for your time, I can say that anyone involved enough stands a
good chance to get their name on an academic paper!

--Collin
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