Excuse
Since space is
very limited,
the smallest mouse that could be found was used. The mouse was the
Atek Super Mini Optical Mouse which
measured 2.36” by .925”. This mouse featured an
Agilent H2000 optical chip that was PS2
compatible. The mouse interface to the BS2SX was handled by the
PAK VIa from AWC Electronics. Note:
a 10K ohm pull up resister is required on the clock or data pin of the
mouse to ensure that the mouse is in PS2 mode. Without the
resistor, the mouse thinks that it is in USB mode and the PAK can't pick
up anything.The technique to read data from the mouse was to A) clear the PAK VIa registers, B) wait 5 milliseconds, and C) read the PAK VIa buffers. The results were two byte sized variables for the X and Y velocity.
For test purposes, the mouse was read and the results were stored in
EEProm for later recovery and examination. The actual results were
repeatable, reliable velocity readings up to 12 inches per second (the
maximum speed of the mouse). Unfortunately, no useful information could
be gained at normal sumo speeds of 20 to 30 inches per second. Since
this robot was blind at normal speeds, it became a poor Excuse for a
real robot. This experiment will have to wait until faster optical
mouse chips are available.
The original motors in Excuse were
Lynxmotion 7.2 Volt, 30:1 gear
motors. Two motors (one axle) were epoxied to an “H” shaped piece
of carbon fiber laminate which held the two mounting grommets that
provided the pivoting axle movement. An additional strip of carbon fiber
laminate was epoxied to the top of the two motors to add
strength.
The
five IR sensors are mounted very low in the extruded aluminum front
bumper.
Each sensor covers
approximately 15 degrees width, so the five sensor pairs cover about 75
degrees. Panasonic PNA4602M detectors and Fairchild QEC113 IR LEDs
were used. An adjustable Voltage regulator provides power to the
LEDs and is used as a sensor distance adjustment. No line sensors are used.
The
control was exactly the same as Expendable with a Parallax BS2SX
processor, driving a
Pololu PIC and driver chip, controlling two H bridges. Twelve
AAA Nickel Metal Hydride batteries powered the robot. The first speed
test resulted in 62 inches per second! Since this is way too fast for a
five foot sumo ring, the gears in the motors were replaced with a 50:1
ratio. Ten AA Nickel Metal Hydride batteries were used to keep the
total weight of the robot under 3 pounds. The 2 pound 15.4 ounce Excuse
could push 8 pounds 7 ounces to 8 pounds 12 ounces. That is 2.85 to
2.95 times the robots weight in push. Also, the speed was down to a
much more manageable 32.8 inches per second.
For the Winter
2004
NEIRG, Excuse was entered in the 3 Kilogram sumo class to test the
motors driven by 14.4 volts and the survivability of the epoxied motor mounts. It was
hoped that Excuse would last a few rounds so that the tests were
worthwhile. Twelve AA Nickel Metal Hydride batteries were installed to
assure that Excuse was too heavy for the 3 pound sumo class. The result
was a 3 pound 4.2 ounce Excuse that could push between 10 pounds 14
ounces to 11 pounds 0 ounces and had a top speed of 36.4 inches per
second.
A week before the Winter Games, Excuse developed an intermittent reset
problem. While looking for the problem, the control was shorted to full
battery voltage that destroyed all of the electronics. A new,
experimental control
was fitted using IPS0551 and IPS5551 MOSFETs which provided drivers
included within the FETs. These MOSFETs can be turned on and off directly from
microprocessor pins. The new control was less than 1.75” square, has a
drive current capacity of 16 to 18 amperes per side, and can be run with
up to 40 volt batteries. The large device in the photo is a switching
voltage regulator which is required due to heat generation from standard
voltage regulators at the higher voltage drop. The switching voltage
regulator partially covers the BS2SX and completely covers the Pololu
PIC and the PAK VIa.