Bot Building Day!

   Finally!  A beautiful, sunny weekend with time to work on my new robot.  I cut the acryllic boards for the first layout today, using a Dremel.  I put way more holes in it than planned, and learned alot about how to lay out a chassis.  I built 3 proto boards for the bot's main systems: a carrier board for the brains, a motor driver breakout, and a power regulator board.  When I tested these with the motors, I realized that a single power source of 4 AA batteries was not going to be enough.  I would need a separate power supply for the chips.  I thought it would kill the design I had in mind.  The whole bot was designed to be as small as I could make it.  After some jigsaw puzzle like work, I came up with a new arrangement.  I managed to get all three boards on the bottom layer with the motors.  The top now has the AA battery pack as well as a 9 Volt battery.  It looks a little less pretty, but it will work.  I mounted the 9V at the very back, but this made the bot do wheelies.  I moved it on top of the 6V AA battery.
   The bottom chassis is just 8cm wide by 9 cm long.  The top is 8cm by 10cm.  The extra centimeter allows for the brackets for the servo.  In later bots, the extra centimeter will be on the bottom for the sensor boards.
   I am planning to use all the same basic gear for 3 robots.  The first will have a tiny servo with a Sharp IR sensor on it.  The second will swap these out for a line sensor array on the bottom.  The last will swap this out for 5 IR Led/Phototransistors to sense walls.
  The basic equipment is:

• 2 Pololu 30:1 Micro Metal Gear Motors - $15.95 USD ea.
• 2 Pololu Wheel Encoders - $14.95 USD ea.
• 2 42mm Pololu Wheels ( That work with the encoders ) - $6.95 USD for 2
• 2 Pololu Extended Motor Brackets - $4.95 USD pair
• 1 TI SN754410 - a "drop-in" replacement for the L293D - $2.35 USD 
• 1 5V Voltage Regulator - $1.25 USD
• 1 Pic 18F2455  - $5.95 USD
• 1 Pololu Ball Caster - $2.95 USD
• 1 4 AA batter holder ( The one I'll use has a power switch; not the one shown below ) - $1.99 USD
• 1 9V battery & 4 1.5 AA batteries

   The mini servo was $8.95 USD and the Sharp IR sensor with pigtail was $14.95 USD.  I haven't put together the other sensor arrays yet.  The proto boards were the little cheap ones from Radio Shack.  They cost a dollar and change.  I used a thin 0.083 sheet of acryllic from Home Depot.  The was about 2 feet by 3 and cost about $7.95 USD.  All of the female pins on the boards are Swiss machine pins ( round holes instead of square ) except for the ICSP header.  The ceramic resonator uses pins, so I can swap out different value.  With this Pic, I can put in a 4MHz crystal and crank it up to 48MHz with PLL.  The total cost of the robot is in the $130-$140 dollar range, adding in the pins, wire, caps, resonator, standoffs, screws, solder, etc.  It weighs in at 137 grams.


   Here are some pictures of the basic assembly.  It's pretty rough, but I'll get better.

   One of the downsides of my hasty layout change is that it is really hard to reach the power switch.  It was supposed to go on the top of the robot.  I bought a new battery holder for the motor's batteries.  It has a built in power switch.  That way, I can catch the bot and kill the motion.  Then I can power down the TTL chips at my leisure.  

   Note the "awesome" soldering job!  I designed boards in Eagle.  I sent the carrier board for the Pic off to batchpcb.com.  If it comes back as a working board, I'll swap out the proto board.  I'll send off the other designs and replace them as well.  More than likely, I'll just get a really little coaster.  We'll see.

   All the junk wire in there are from a quick power and motor driver test.  I plan on taking my time, fitting the wires in tightly.  The exception will probably be the servo wires.  I'll just tie them in a bunch and stuff'em.  Well, that's all for now!