Crunch
Crunch was my third robot, built over winter break of 2003-2004. Though it
was largely inspired by the inherent coolness factor of balancing robots,
balancing robots actually have several neat properties.
Crunch is driven by two Pittman gearmotors from a 24 AA cell NiMH battery
pack. Crunch was originally equipped with an eight channel 40khz sonar
rangefinder which was later augmented with eight Sharp GP2D12 analog infrared
rangefinders. The original main computer, an 8051 with 64k ram + 56k flash,
was also replaced by a spread spectrum radio modem to a pc.
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Bottom view of drive components. The shafts are supported by ball bearings
sandwiched in 1/8" aluminum pieces. The film canisters over the motors enclose
jury rigged encoders.
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The original sonar sensor, controlled by an ATMega32. The inertial sensors,
an ADXL202 and an ADXRS150, are mounted on top of a piece of foam rubber in
the middle of the sonar ring. They are electrically connected to the lower
board, however.
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The lowest board houses the power and balance control subsystems. On the
heat sink are two LMD18200s which drive the motors and an LM2576 switching 5v
power supply. The voltages and currents of the charge circuit and the
batteries and the two motor currents are measured by the avr adc inputs. The
avr also controls a dc-dc converter which is used to charge the batteries from
a 24v power brick.
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Soon crunch learned to build local maps from sonar data. It worked well enough
to make a pretty solid map of my dorm room but that was about as far as the
dead reckoning worked for.
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This is what happens if you drive it a few tens of meters and over several
doorjams.
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Then crunch got infrared sensors which improved map quality significantly.
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Instead of storing all that bitmap data forever, crunch began just storing the
calculated curves where floor-like and wall-like regions meet, as seen from
several locations, as well as the articulated links between them.
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Eventually it tried to adjust the articulations between the observation points
to form a consistent view of the world. That would be like trying to twist the
above broken map back into shape. Here's some of the corridors in the Brown
CIT 4th floor. This is sort of hard given crunch's data quality and it
doesn't always work right.
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Links
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