The Chimichanga was mainly designed by Tanner Smith and Sunny Gupta. Officially (as TIMS saw it), the robot was still named "Logan Rover" from 2009, though it was named the "Chimichanga" at the 2010 Palmetto Regional.
Four wheels drove the Chimichanga: Two Plaction and two omni-wheels. The wheels were put on triangular stilts in able for the robot to drive over the bump. Two CIMs geared through a Toughbox provided a 1:1 reduction to the wheels on each side.
The kicking system consisted of the 80/20 kicker, the winch, and the sail clutch. Each performed a role in making sure the robot successively executed a kick.
The actual kicking part of the kicking system was basically a square frame of 80/20 with a attachment so that it looks like the shape of a "L" from the side. In terms of how it was mounted, the kicker was mounted so that the lower part of the "L" shape was the highest point. This point was also where the surgical tubing was attached.
At the bottom of the kicker (the top part of the "L", continuing the metaphor) was a toe to kick the ball. The toe design has changed many times over the build season, though the final design at the Palmetto Regional was using several 80/20 triangular brackets.[Citation Needed] Along with the toes, at the bottom of the kicker was also the attachment point for the winch rope.
The winch mechanism consisted of a Fisher Price motor that was attached to a AndyMark Super Shifter with an encoder. Early in the build season it was thought that the shifter might be needed to let the kicker actually kick, but the tension proved to be too much for the small pneumatic piston supposed to shift in/out of gear. The output shaft of the shifter consisted of a circular plate to keep wound rope on the spool.
The sail clutch was positioned in between the kicker and the winch. The purpose of the clutch was to allow rope to slide in both directions in one mode, but only allow it to slide in one direction in another mode. This allowed the kicker to stay in position easily until the desired time to kick came.
The clutch was operated by one small diameter pneumatic piston mounted to the back of the frame.
The ball holder's design was changed throughout the build season and even after the first competition (Peachtree Regional).
Before the Peachtree Regional, the ball holder consisted of one Makita vacuum cleaner driven by a Fischer Price motor. The vacuum was connected to two AndyMark suction cups positioned in the front of the robot to grasp the ball.[Citation Needed] However, the design proved to be hard to get a good seal on the ball thus losing controllability, and also the kicker would interfere with the positioning of the two suction cups.
After the Peachtree Regional and during the Palmetto Regional, work was done to convert the suction system into a roller system that was pursued early in the build season, but conclusions came that the design would not work. Work by Sunny Gupta and Logan Su on the roller pinching system made the roller system what it was during the Palmetto Regional. The roller system consisted of one roll of unobtainium powered by a Window Motor.[Citation Needed] The soccer ball was pinched by a bottom bar positioned beneath the roller along the bottom of the robot. The bottom bar was a quarter piece of 80/20 coated in a plastic material for hand tools.
The robot was controlled using two XBox 360 controllers - one for driving and one for manipulation.
Driving was an arcade-like mode using the two independent joysticks on the XBox 360 controller. The left joystick's Y-axis was used for the robot's forward speed, while the right joystick's X-axis was used for the robot's rotational speed. A press on either of the controller's thumb/index finger potentiometers limited the drive speed to a percentage of the full power.
Manipulation control was quite simple and could've been done using some other control device other than the XBox 360 controller. Only two buttons were used along with one of the thumb/index finger potentiometers.
The green "A" button controlled when the kicker would arm or fire and the blue "X" button to set the kicker to the armed position in the case that the kicker failed to arm for any reason.
The potentiometer controlled the power setting of the kicker. When the potentiometer was fully out (i.e. - no finger on it) the kicker was set to full power, while when the potentiometer was fully down (i.e. - finger fully pushed onto the potentiometer) the kicker was set to low power. When the potentiometer was in between these two values, kicker power was extrapolated out and correspondingly set. This allowed for freedom of control instead of being strapped to a fixed number of fixed power settings.
With the small, effective manipulator design of the Chimichanga, the robot weighed way under the maximum weight requirement set by FIRST of 120 pounds.
The Chimichanga was programmed using LabVIEW. The arming and variable kick setting of the kicker was all automated using encoder values and a limit switch. The rest of the robot was pretty basic.
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