Final Project

As it was reported in the mechanical design assignment, the final project has switched to a hexapod robot. The intent of the robot is to be able to walk through various terrains or surfaces by having six legs, each one with two degrees of freedom: one to move it up or down, and one to move it forward or backwards.

 

Actuators and sensors selected

The first selection was the type of actuator to use. Multiple alternatives were considered but looking for ease of driving and compactness the pico-servos were selected. Driving them with a micro controller was shown in the output devices homework (see image below). Similarly it was important to select some way to sense the environment in order to facilitate navigation. Infrared sensors were selected based on the range they covered (10-80 cm) and the direct output of 0-5V making it easy to interface with a micro controller. One was also tested in the input devices and output devices homework (see image below).

First Attempt

The first attempt achieved the simplicity and compactness but the motors were inadequate for the load that the robot required. All the pieces that made the body of the hexapod, the legs, and the structure to connect two servos in place were made in acrylic cut with the laser cutter. A photo of the early design can be seen below next to the model in Solid works. The main flaw was not to consider the weight of batteries which ended up being significant.

 

 

Second Attempt

Despite having a fairly simple and compact design, the motors had a lot of problems maintaining the standing position, and it was noted that most of the range of motion of each servo was being wasted because each articulation of the leg did not move the 180 degrees which is roughly the range of motion of the servo. Gears were used to provide more force in each leg while maintaining an acceptable range of motion.

This new version was done similarly, in acrylic cut with the laser cutter, small pieces to mount the sensors were cut separately and glued into the base with crazy-glue.  An exploded view of the final assembly can be seen below.

Electronics Design

Part of the intent of the electronics was to have a single board as compact as possible. Single layer designs resulted in too many bridges and connections so a 2 layer design was done which allowed for a much compact PCB. The design of the board was made and then it was sent to a local shop that had more experience with multiple layer PCBs.

As you may notice in the printout of the board the design was made jointly with my friend Fabian A. Salazar who is not participating of the FabAcademy.

To control the movement of the legs there is a master microcontroller basic stamp BX-24 that is programmed in basic and an Atmel AT89C52 that was programmed in assembler to generate the PWM for the servos. The two microcontrollers are connected through serial communication in which the master indicates which step to take: forward, backwards, turn left, or turn right, and the slave does the generation of PWMs to produce the step.