1.1.1 Robot Base
The base will be a Lynxmotion CarpetRover 6" x 6" mobile
robot platform powered by a pair of Hitec HS-300B servos
modified for continuous rotation.
See document: http://www.lynxmotion.com/kits.htm
See document: servos.html
A Lynxmotion "First-Step" Basic Stamp I controller will be used
exclusively to run the drive servos.
See document: lynxbs1.gif
A Parallax Basic Stamp II mounted on a BS2-IC Carrier Board
will be used for reading sensors and navigating the maze.
See document: bs2csche.gif
See document: bs2cb.gif
See document: stamp2.gif
See document: robotwir.txt
1.2.1 IR Object Detector
An Infra-Red Object Detection System was designed and fabricated
on 03-11-99. The IR receiver module (RadioShack #276-137B)
output was too susceptable to false triggering due to ambient
lighting so it's output was integrated and fed into a
comparator with an adjustable threshold reference voltage.
A threshold was picked to eliminate false triggering.
IR attenuation filters (slips,of paper) will be taped over each
of the four receivers in varying thicknesses to equalize the
sensitivity of each module so they all trigger at approximately
5 inches distance from the maze wall.
See document: irsensor.gif
A 74LS156 1 to 4 line Multiplexor was added to route
the 40 KHz clock to 1 of 4 IR LED's using only
2 select lines. A 74LS153 4 to 1 line Demux. was added
to select 1 of 4 IR Receiver Modules and route it's output
to the integrator circuit using the same 2 select lines.
See the Prototype section for a more detailed schematic.
1.2.2 Flame Detector
During a period of indecisiveness over whether to buy a
commercially made flame sensor, such as Acroname's
IR flame sensor or Hammatsu's Ultraviolet flame sensor,
See document: http://www.acroname.com/robotics/parts/R3-PYRO1.html
See document: http://www.hpk.co.jp/products/ETD/UVtronE.htm
I experimented with some IR phototransistors to see if it
would be feasible to design our own. The first tried was
a Radio Shack part. Unfortunately the ambient overhead
flourescent lighting had more effect than a candle flame
on this device. It was evident that both optical filtering
and focusing would be required to make this feasible.
I ordered every photo device in the Electronic Goldmine
catalog along with some mirrored flashlight type reflectors
and some Kodak 87C IR filter material. I also salvaged the
IR lens material out of an old passive IR motion detector.
1.2.3 Wheel Optical Encoders
I purchased some Reflective IR Sensor/Emitter units from
the Electronic Goldmine (cat.# G8669) that looked ideal for
this application. These are an IR phototransistor and
IR LED paired together in a black plastic case, such that
reflected IR light from a close proximity object will cause
the phototransistor to conduct. These can be mounted on
the underside of the Lynxmotion Carpetrover robot base,
facing the inside surface of each tire. Circular paper
disks colored with alternating flat black and flat white
color bands can be glued to each tires inside surface.
Once optimally positioned, the phototransistors should
output pulses marking distance traveled by the spinning
tires. Here is the related calculation:
Tire Diameter = 2.875"
Tire Circumference = PI * D = 3.14159 * 2.875" = 9.03207"
Thus, Distance traveled = 9.03207 inches/revolution.
Resolution of this system is determined by the number of
white color bands on the disk. Thus for a disk with
8 white color bands seperated by 8 non-reflective black
color bands, the resolution is 9.03207" / 8 or
1.129" per pulse. This is provided the Basic Stamp II
controller can count every pulse without missing any.
2.1 Robot Base
A 3 bit bus will be used to direct 5 cardinal motions:
Hold, Forward, Back, Right, and Left.
A flowchart was completed on 02-21-99, and the
PBasic program was written and debugged on 02-22-99.
This would become the basis for motion control of
our robot via the Basic Stamp I controller.
See document: lynxflow.gif
See document: lynx.bas
See the next section "Prototyping" for info. on construction
and further refinements.
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