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Meet Big Bot

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Close-up of  the drive assembly, the sensor package and the arm assemblies

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Close-up of  the arm assembly

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Close-up of  the head assembly

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Big Bot bringing the newspaper!

This robot is named Big Bot. He is our first attempt at making a really big one using only one Lego set. He is conceptually a working robot with the ability to carry odd sized light articles from one location to another using arms with gripping hands. Additional uses might include companionship or entertainment.

This robot was created using mostly the Lego Mindstorms Robotic Invention Set. Several pieces from the Extreme Creatures set were needed to make the gripping portion of the arms. The criteria for this design was to use a minimal number of parts to get the job done since we were sure that pieces would be short near the end. By the time we were done, we  ran out of black connecting pins, several flat piece varieties, and small pulleys.

The first stage of this design was to construct the drive chassis. This model was the first one we have used the treads on. Both motors are used, with each side being independently driven by a motor. The gear ratio is fairly low, but speed and acceleration proved more than adequate. As you can see from the picture at the left, we mounted the RCX brick perpendicular to the drive chassis. This was done to assist in the support of the tall body of the model. The RCX brick is mounted level with the top of the first in a series of connected structural members.

The touch collision sensor was built using a modified design of the "bug" bumper. The large rectangular flat pieces were used to get the entire assembly out in front of the treads. We also considered adding an additional touch or light sensor on or near the head, but we decided not to in the end.

Once the drive chassis and sensor package were completed, it was time to go vertical. The long structural members are linked together with short structural members and pins. Additional support is provided at the joints by using flat pieces on both the front and rear or the body. Additional support is given by two long axles with small pulleys both inside and outside the body structural member.

Two arm assemblies were built based on a design in the Extreme Creatures book. The design was modified by adding additional fingers, and parts that automatically triggered the grasp of the arm were not used. The design as shown will stay open or shut equally well when the robot is in motion. The arms are attached to the body of the robot with connecting pins and do not pivot or rotate.

The final step in the construction process was to give Big Bot a head. Several different designs were tried before the solution was found. The green tubing is held in place at both ends by a large axle that also provides lateral support at this end of the body assembly. If you look carefully at the close-up of the head assembly, you can see how the rotation of the axle is inhibited by the use of two gray right angle connecting pieces (near the rear end of the green tubing). Since several pieces from the Extreme Creatures set had already been used, the small red wings were added to give the appearance of ears.

Big Bot has not gotten his own RCX code program yet. He is currently running off another program already in the RCX brick. Some of the features that will be implemented in the programming stage will be a method to tell him when to start and stop, have him make friendly noises at times, collision avoidance (back up and turn) and general directions to go back and forth along a route autonomously.

What else can be said about this design? Well, don't try this one on rough terrain or uneven surfaces. The small wheelbase and high center of gravity make even small obstacles a big disaster for this robot design. It also would have been fun to add the Scout brick somewhere in the design to perform additional functions such as the head tilt or to control some arm functions. This design did successfully get up to 17 inches high, proving it could be accomplished using only one set (except for the arms of course.)

It seems that the single RCX brick could perform many of the computational functions for a robot this size. The next logical step would be to move some of the components to a larger platform with a fabricated  frame, then use the brick to control the larger model.