Project Overview

 

The climber consists of three main parts: the right and left arms (constructed of Legos), the weight shifter, and a tail.  The motion of the climber is designed to climb the ladder using its attached pulley system.  The right and left arms are each attached to a servo motor.  These two servos are then connected via a crossing Lego bar.  This design allows the one arm to move vertically, while the other hangs on the ladder rung.  The third servo sits on the connecting Lego piece while controlling a flat piece of wood used to balance the creature as it climbs.  A long, narrow stick is also connected onto the connecting Lego piece to assist in balancing.

 

The Lego arms are designed so that it has artificial limbs which would retract when the claw touches a ladder rung.  We attached a piece of exposed wire to the surfaces to create a manual switch.  These switches would be activated when the arm retracts, indicating that a rung was reached.  The switches trigger an external interrupt, which sets the climber into the next stage of its climbing motion.  The process by which it climbs is as follows: shift weight, raise first arm, arm hits rung, latch arm over the rung, and repeat.  The motions of the arms are controlled by two timers.  One for the two servos attached to the arms and one for the servo attached to the weight shifter.  Each timer is used to control the servos through pulse width modulation.  This allows the servos to rotate to the desired position, at the desired speed.

 

A critical aspect of our design to create a weight balance in the motion of the arms using a piece of string which ties around the tail of the climber on one end and connects to a weight on the other, via the weight shifter and pulley system.  The algorithm used to control the weight shifter begins by keeping the arms stationary and moving only the shifter to the opposite side.  As the shifter approaches the center position, the free arm begins to move upwards, using the shifter to assist it to its desired location.

 

In addition, we use two pushbuttons (S1 and S2) on the 373 board as external interrupts to control switching the climber on and off (S1) and to manually move the arms (S2). 

 

The bulk of our external circuit was designed solely to allow for our manual arm switches to work properly.  The switches were designed using two wires: one connected to ground, while the other was sent to the output signal via an additional filtering circuit.  This circuit consists of a low-pass RC filter which feeds into a Schmidt Trigger.