October 21, 2012

Nyan Hat: Nice Lasered Things and More

Since the first half of my weekend consisted of

  • Work on projects until 3 AM
  • Rest
  • Repeat
I was able to make significant progress on Nyan Hat.  

First, I modified the motor that moves the Nyan Cat around the outside of the hat.  I started out with a generic hobby servo, and removed the mechanical stop that prevents it from spinning more than 180 degrees.  I also removed all the control circuitry as well, and in its place installed a linear voltage regulator (7805) with heatsink, since the hat's operating voltage will be around 10V, but the motor only operates from 4-6V.  

When I originally conceived the design of the hat, I imagined a gear motor in the center of the hat, with an arm attached the output shaft pointing radially outward and holding the Nyan Cat.  I realized though that if the spinning arm spanned the entire radius of the hat, it would be very difficult to 
  1. Mechanically support the top half of the hat.
  2. Run wires between the two halves of the hat.
To do both of these things, the spinning mechanism needed to have a gap in the center.  To design the mechanism, I used Inventor's handy gear generator to make a large internal gear and a small pinion to mesh with it, as well as a retaining mechanism to hold the gears and servo in place.  The mechanism also slows the output speed to 10 rpm from the ~60 rpm of the servo.  

The parts were then cut out of acrylic on a laser cutter, with the help of Charles and Shane.  While collecting materials, I misidentified some 6mm polycarbonate as 6mm acrylic, resulting in lots of unpleasant (as in poisonous) fumes inside the laser cutter.  Suitable acrylic was found however, and this happened:

The ring gear, which is what drives the cat, is retained by three bearings that sit in a groove around the edge of the gear.

Due to a slight change in my mental design, I also made a matching base plate to fit into the other half of the hat.  I just traced the laser cut piece onto the sheet of polycarbonate that I accidentally lasered, roughed out the shape on the bandsaw, and used a bench grinder to finish it off.  Two holes for wires were cut with with a hole saw.  The second plate is slightly larger, so that it fits snugly into the bottom half of the hat.

To secure the mechanical parts to the hat, I drilled and tapped four holes into the edges of the plates that fit into the hat, and matching holes in the hat its self.

To connect the two halves, I made a large standoff on the lathe.  Also, here's the actual hat:

And here's a clip of the cat circling the hat:

To make the cat's tail, legs, and head move, I made a soft foam track around the polycarbonate plate.  The roller that actuates the cam on the cat rolls along this track.  Originally, I made the roller too short, so I had to extend it.

And here's a clip of the fully animated cat:

On to the electronic bits.  The hat will feature blinking LED stars around its perimeter, so I made a simple two-transistor circuit that will alternately flash two groups of LEDs:

To make the hat play the Nyan Cat song, I tore apart a set of old computer speakers and harvested one of its drivers and amplifier circuit.  Both these parts mount next to the servo, in the top half of the hat.  An old iPod nano given to me by someone on my hall with do the actual MP3 processing.

To power everything, I made a battery pack out of A123 26650 cells.  Originally, I planned to place the battery pack around the corner of the hat, which your head doesn't fill due to its curvature.  However, I decided against this, mostly because I didn't want batteries that, if short circuited, can discharge enough current to melt the wires I used to make the pack close to my head.  Fortunately, I was able to cram them in the top half of the hat, along with the audio bits and servo.



Coming up next:  LED stars, iPod hacking, and a control panel.

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