Your robotic problems solved here.
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Q. I’m attempting to “go green” with my solar powered robots, so that means petroleum-free lubricants. I’ve heard that coconut oil is a stable
alternative to regular petroleum grease. Do you have any
experience with coconut (or other organic) oil, in terms of
longevity and protection of the underlying metals?
— Tim Morin
A. What a great question! The main problem with biolubricants is that they oxidize quickly when exposed to air, go solid at low temperatures, and
break down quickly when they get hot. I’ve read articles by
USDA scientists experimenting with an anti-oxidant
compound that they add to biolubricants called zinc
dialkyldithiocarbamate. However, while it is not considered
toxic, they still don’t recommend letting it touch the ground
or getting into water systems. That doesn’t sound like much
improvement to me.
Another USDA project is working with soybean-based
hydraulic fluids that offer excellent lubricating and
biodegradability characteristics. This is apparently a new
niche market, and solutions are not well known yet. If you
want to avoid petroleum-based lubes, I’ve seen several for
sale that are safe for aquarium use, so that means they
can’t be all bad. Google for “non-toxic silicone lubricant” —
you’ll get a lot of stuff that you can buy right off of
Amazon.com. Be careful, though. I’ve found some silicone
lubes that seem even more toxic than the petroleum
versions you’re trying to replace.
When you find something you’re interested in, try to
find the product MSDS paperwork which will tell you all of
the “bad” things about the compound. Good luck!
Q. I need to protect some aluminum tubing walker legs from dings and scratches. Should I go with shrink-wrap tubing or the liquid rubber dipping
— Roger McClure
A. I have been pretty disappointed with the results of protecting rigid structures with shrink-wrap tubing. After several months, I’ve found that most of the
stuff that I’ve used gets brittle and cracks under impact
with other rigid materials. If we add to that the seemingly
crazy expensive heat-guns you need to use to shrink it, you
get a kind of expensive short-term solution. So, you ask,
what about the canned rubber?
This is typically called “Tool Dip,” by the way. There
appear to be a few brands, “Plasti-Dip,” “Liquid Tape,” etc.
I have used this stuff before and it is great for what you are
considering. The Tool Dip and Plasti-Dip are more durable
than Liquid Tape in my experience when dealing with rigid
materials. I have used Liquid Tape to waterproof wiring that
went into wet environments, and it lasted for years with no
trouble. (Note to self, make sure you call for a “Locate”
before digging the next pond ...) I used Tool Dip when
“rubberizing” an entire rigid metal frame. You can either
dip your legs into a can of the stuff, brush it on (not as
good), or even use some Plasti Dip that you can spray on.
I’m not sure how heavy a coat you can get with spray-on
rubber compound, but I had to dip my metal pieces in the
Tool Dip several times to get a really heavy coating, so the
spray-on rubber may be just as good.
Q. I’m starting to design a robotic head that moves with an MP3 recording. I have tested a circuit from an Instructable about a take-away food container.
So, I have a way for the mouth to open and close. Now, I
want to animate the eyes, eyebrows, eyelids, and neck. I
was thinking that a stereo sound file has two channels. One
could be for the sound and the sound-reactive circuit. Could
the other channel carry data on when to open the eyes and
run the other servos? I was thinking that different volume
levels of just white noise could trigger the program (low
volume, medium, high), but that doesn’t tell the program
when to move the servo back. Does any solution pop into
your head? Here’s the URL: www.instructables.com/id/
Thanks. I always enjoy reading your column.
— Charles Ford
A. That is a fun project! I’ve done similar builds. Once, I tried to get one of the cassette tape channels to handle the control timing. However, this requires you
to basically do a very old-school style of data encoding
similar to a 300 baud modem using two different tones to
create a 1 and 0 bit pattern that can be assembled into
instructions — rather like the old 1980’s cassette data
storage tapes. That project quickly got complicated and into
more analog work than I really wanted to do.
I see that you are using audio on an SD card, so that
would mean an even more complex job involving dealing
with different channels on a CODEC. There is an easier way
to do this, and it involves using an ADC channel on your
Arduino. I would sample the output of your audio amplifier,
then rectify it with a simple half-wave rectifier circuit with
an RC integrator for a voltage level storage after it (refer to
Figure 1 on the next page for the following discussion).
Use diodes D2 and D3 to clamp the RC integrator to
+ 5 and ground so you don’t damage your Arduino. Start
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