On 04/29/2018 06:13 AM, Dave Malham wrote:
Excellent - this is exactly the method I was about to suggest - steppers,
related hardware and motor control boards have been driven down in price so
much by the 3-d printing/cnc/maker revolution that it makes almost no sense
to do anything else.
Yes, I like that too... I was planning on adding a stepper and gear
drive to my test rig (I turn it manually, not too hard).
This would have been fine for tetrahedral microphones and horizontal
plane only measurements. The problem for me surfaced when I went to
second order microphones and needed measurements above and below the
horizontal plane. I built a "better" test rig that can tilt, added a
small xy table to be able to "calibrate" the center of rotation (and of
course 3d printed a fixture to attach the mic!), but I need to
physically reposition the rig between each layer being measured. Not the
best.
I was going for a different approach when it was suggested to me (both
by my boss and a phd student here, thanks Chris & Elliot) that a robotic
arm would be better and more general purpose. I was reluctant because of
the cost...
(a bit off topic but maybe of interest anyway)
I was actually going to use a telescope mount (_not_ an equatorial mount
which are the most common, apparently), I found one that would do what I
needed, was not expensive, and I could control azimuth and elevation
through rs232 (SkyWatcher AllView). I designed (on paper :-) a
pantograph that would keep the microphone away from the mount, and
replicate the movements. But again, lots of mechanical parts and tricky
design. Better to spend time on the microphones.
So I bought a robotic arm. Len (from Core Sound) asked off-list about
it, so I'm including some information here. I got the WidowXL from
Trossen Robotics. Anything better (as far as I could find, not an
expert!) would have driven the price up exponentially - this one is not
cheap anyway. I just spent two full days assembling it (lots of pieces,
lots of screws). Beware, ask before you buy as to delivery times - mine
was delayed several times and they were not very upfront about it (or
just did not know).
Anyway, I just did some preliminary tests today and it seems to be able
to hold my microphone and move all the joints so as to point it in the
right directions and rotate it accurately. Lots to do, but it is a start
(to get better data).
-- Fernando
I would use the esp8266 arduino compatible wifi module
which costs about the same as a decent cappuccino - I paid about 4 euros
for one at the end of last year - which has a reasonably powerful 16 bit
processor and is quite capable of acting as a web server, so I'm doing that
and controlling my steppers from a web based interface on my mobile or
laptop. Note, however, that I've confined it to just my home network for
security sake - don't want people using it to influence the elections :-)
Dave
PS Sorry once again I'm not currently doing this for audio - maybe one of
these days I'll get back to that.
On 24 April 2018 at 02:58, umashankar manthravadi <umasha...@hotmail.com>
wrote:
I have been using a stepper motor (of the kind used in 3d printer ) driven
by a low cost Arduino and motor control board. I 3d print a snug fitting
fixture for the microphone with the motor shaft aligned to the array
centre. ....
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