How To Make Almost Anything Class
Lassiter's WEEK #9 Assignment
Assignment: Fabricate a metal mold for the injection molder, make a plastic object with the
injection molder. Also try vacuum molding an object. Last but not least, present your final project
in fine detail.
This was a short week for us, Thanksgiving week, and so not much time was available to compelete the
project. None-the-less, for my mold I combined two ideas that fit into the 2" X 4" capacity of
the injection molder. In my case, I made two nested hearts, both made for hanging from a string in a
window. Additionally I tried to make some heart gik.
This activity required a lot of John's time to teach and supervise us through the process. The machines
were large, dangerous, and required more learning time than any of us were able to devote to the process.
I made the file in OpenOffice, transferred it to OmaxLayout, and then made a dxf file for the Haas. Again
the cleaning ofthe file was not simple, and I don't think I can repeat the steps John took to prepare
it for cutting. Also, I forgot to make the mold depth dimension to be 1/4" and instead created something
that was 1/8th inch at best, which made the finished product approximately 1/16th of an inch thick. So the
injection molding was somewhat of a disaster. Also, my heart gik was a failure. The shape is undistinguishable
at this scale, once you put tabs and indents in the heart shape. I think with three basic shapes, one that
features a perfect rounded top, one that features a perfectly pointed bottom, and one that is just a central
holder (having indents on all 4 sides) -- this might have worked better, but I didn't think it through
Then I tried vacuum molding my digital camera. Kids, don't try this at home. Because the shape is not
flat and has lots of buttons and knobs and curves that stick out and indent, the plastic was impossible
to remove as one piece. Rather I had to cut and tear away at the edges to extract the camera. Also
learned that plastic molding on plastic is very very efficient, and probably isn't a good idea for
expensive objects like digital cameras. The camera was succedssfully extracted, a little worse for wear,
but still fully operational.
As we enter the last month of class, I have identified and been working on the three major challenges
for my Heart Throb project:
1. Shape and form for functionality
2. Motor actuation
3. Sensing proximity.
I have made progress on all three fronts, but do not yet have a operational heart prototype.
SHAPE and FORM:
I did create a digital design for Heart Throb which I am in the process of cutting now. There is a
base box that holds the electronics, batteries, and telescoping parts. There is a set of 4 nested
hearts-- each attached at three points to the preceding heart using a telescoping pole. It's critical
that the telescope be strong enough and stable enough to permit fast linear motion without catching
on edges. It also needs to support some weight. I have determined that a metal heart is probably
going to be too heavy for the telescopinbg mechanism I've so far incorporated. So I'm planing to make
the hearts from 1/2" acrylic instead.
Did not make much progress this week, other than to design a spool that will accommodate a moving 3/4"
diameter magnet. Will finish the spools and test the full size linear motor design this week. The magnet
will push up for 40 pounds, so this magnet should do the trick if the linear motor idea tryly works.
The spools need to move with the magnet-- such that they expand when the magnet moves forward, and
contract when the magnet moves backward. I think I can accomplish this by sequentially timing the
power connection to each spool. Anyway, a prototype will be very helpful determining whether or not
the linear motor will work, or if I have to change strategies to use another type of motor.
This week I was able to more formally test my 40kHz transducer/receiver pairs using the oscilloscope
and the function generator. Matt Reynolds and I spend an evening testing both the 40kHz and the 25kHz
transducers. Based on our results, we have determined that the 40kHz has a clearer signal-- less noise.
We also concluded that the 2 foot proximity sensing is a relatively simple threshold to establish.
However the 6 foot proximity sensing is more difficult. The receiver signals won't be able
to distinguish between a wall, a bulletin board, a pole and a person at 6 feet away-- not without some
heavy duty computer number crunching on a live basis, and I've ruled that out as I don't want to
be tethered to anything. We did discover that if we bump up the voltage from 5 Volts to 9 Volts that
the signals at 6 feet become better and more distinguishable, but the ATTiny microcontrollers we use can only
handle 5.5 volts-- and all the connections on the receiver side are to ATTiny pins. Amon mentioned that one
of the groups working on the lab bench testing equipment is looking at reprogramming on of the ADC
pins to accommodate 9 Volts. Must look into this.
(Pictures-- oscilloscope and table of results)
I also milled a new single circuit board for the transducer pair-- where they sit side by side.
Have figured out the programming code for the transmitter, but now need to add the receiver code to
the program. This will require some significant study and help over the next two weeks.