TomBot (the GOAT)

The task of this assignment was to create a robot using the LEGO MINDSTORMS EV3 set that moved forward/backwards without requiring wheels. In other words, we were to create a walking robot.


Various YouTube videos were watched to get an idea of how this task is generally accomplished, but none were explicitly used for inspiration. Most of the idea came from ME42 knowledge of four-bar linkages and more than a few failed attempts to design Tom.


Tom is a four-legged walker driven by one motor that rotates 4 gears. The motor is connected to the output port D as shown in the header image.


Each front leg is driven by what is essentially a four-bar linkage mechanism. The first link is ground (Tom's motor and brain), the second is the top gear connected to the motor axle (which can be modeled as a short beam that completes a full rotation), the third member is the one with wings on it (translates motion from the motor region to the front region), and the fourth member is the front leg and foot. This can be seen below. The front leg is on the left.


The hind legs instead, are entirely driven by gears.  Each hind leg relies on the rotation of two gears, one of the motor axle gears and the auxiliary gear on one side of Tom. This can be seen above. The hind legs are to the right.

The driving mechanisms are entirely symmetrical, but set 180° out of phase. This is critical because it allows Tom to balance on three legs at a time and drive himself forward.

Tom also has striking blue eyes, a cute little mouth and fangs, two large horns, and wings that move.

Additionally, Tom's is very easy to feed as you can get to the battery pack but removing one LEGO connection and rotating the EV3 brain around a pivot in the rear. Tom remains entirely intact during this procedure.


The Code

Tom was designed to be able to walk both forwards and backwards at a variety of speeds ranging from 1050 (in our case full speed backwards) to 0 (which is not moving at all) to -1050 (full speed forwards). During testing it was noted that Tom was able to proficiently move in both directions; this makes sense because all of his linkages were fully constrained and the assembly was limited to one degree of freedom. It was also noted that there was a maximum optimal speed around 500. Any slower and the bot was limited by how slow the motor could turn, any faster and Tom would actually tear himself apart at the joints.