Packaging the Sub-systems"
One of the primary design criteria for the "GP-Bot" was to be reconfigurable making it easy for anyone to add experimental payloads or different control packages. To this end I wanted to design a simple yet inexpensive packaging scheme that anyone of our club members could build with just simple hand tools and using supplies easily obtainable from the local hardware store.
The design I decided upon was the following. A rectangular frame made of 3/4-inch angle aluminum, bolted at the corners. This made for a simple framework to which circuit boards, prototype boards, terminal strips, plugs, connector, indicators, LCD's, and barrier strips could be mounted. Holes are drilled in the bottom of the frame facilitating easy mounting to the GP's plywood platform using wood screws.
Since this robot platform is intended to be used to test various experimental packages, it was
important that it be easy to modify and rearrange. This meant that power had to be easy to
control and be connected to. Packages needed to be individually protected. It was important to me
that each sub-system could be turned on and off seperatly. This way when I wanted to experiment
with a new device, be it a controller, GPS navigation, or whatnot, it could be powered up without
having to activate the entire robot. Consider it to be similar to powering a sub-system that is
under development on the workbench. A bot this size is nearly a workbench in itself!
One lucky day I was frequenting the local TV/Radio Repair and Electronics store here in
Ann Arbor (Purchase Radio) when I spotted a box full of D.C. circuit breakers! Now if
you've ever priced DC breakers you'll know they are rather costly. This box had an assortment
of 12 Amp, 8 Amp, and 3 Amp breakers. They even have N.O./N.C. trip switches for remote sensing
the position of the switch. Great, someday my future bot will be able to inform me when it pops
a breaker. Luck would have it that Purchase was only asking $1 each! I bought the entire box...
The Power Distribution Panel is constructed of 1-3/4" aluminum angle. The
breakers were mounted to 3/4" aluminum angle forming a rack unit that can be bolted to the front
of the big frame. The remaining open space in the big frame will be used for future 5-volt
regulators and power filtering.
The white breaker is the 55-Amp MAIN followed by three 12-Amp, an 8-Amp, and finished
out with 3-Amp breakers. The first two 12-Amp breakers are used to power the drive motors and
steering subsystem, respectively. One of the 3-Amp breakers is used to power the Basic Stamp.
All the breakers are pre-wired to a barrier stip in front of the big frame. Grounds are all
brought to a common ground window before going to the battery's Negative terminal.
All wiring is done with 12-gauge stranded.
Power Distribution
I mounted a 12 Volt Lead-Acid Garden Tractor battery on the rear of the chassis. Now lots of
people suggested putting the weight in the middle of the bot, that way it won't pop a wheelie
when the front wheels hit a bump. Well, I figure there will eventually be enough hardware far
enough forward on the moment arm to offset the weight of the battery sitting just behind the rear
axel. Besides, I want to keep corrosive acid as far away from the electronics as possible.
The battery will eventually be contained in a plastic-lined box for added protection.
Emergency STOP
The MC6 Motor Controller
The CPU/Stamp package
Second "task" - Try to avoid hitting stuff