Mission Statement
The SphereWalker Project's goal is to create a hexapod that can walk stably using only 3 motors. It must be able to support and carry large loads on the surface of the moon, as well as operate autonomously or via remote control.
The SphereWalker Project's goal is to create a hexapod that can walk stably using only 3 motors. It must be able to support and carry large loads on the surface of the moon, as well as operate autonomously or via remote control.
The SphereWalker robots motion is based on the spherical four bar mechanism. The inspiration for the creation of the mechanism came from the hope to replicate the front foot motion of the African Spurred Tortoise. It uses 4 links that create a spherical motion through the rotation of one motor. The mechanism was then implemented with two feet on the coupler link to propel it forward via the circular motion.
Prior to my arrival, the robot was assembled into the three link assembly with rigid joints and spiked feet. The first change was creating and implementing hinged joints. The next step was using these joints to allow the robot to turn via a series of coded steps. The final change made to the robot was a re-work of the feet used and a more stable holding for the electronics(brain stem).
The hinged joints allowed for turning via a combination of movements making up the turning method. The robot would turn from the home position via a half rotation(one step) of the front leg, then a half rotation with all three legs and then another half rotation with the front leg followed by one more half rotation of all three legs. This turns the robot to the right and then straightens out due to the spherical motion of the legs returning it to the home position. In order to turn left, one half rotation of all three legs would be added to the beginning and the end to return to the home position.
The original foot design was a stiff rubber ball with spikes for traction similar to soccer cleats. The design did not perform well on any surface other than dirt and needed improvement on dirt as well. The next idea was inspired by other walking robots, the wide and curved body allowed for easy mounting and provided a large surface area for striking on various surfaces. The curve in the design was also essential for adhering to the spherical path of the walking motion, but the design still struggled with impact damping and sinking in granulated surfaces. To combat these issues foam pellets were placed in between the foot and an outer layer of bike treads. The foam cushions helped reduce the shock from impact and the treads increased the traction, but the robot still was sinking and had non ideal motion.
The final design was modeled after a prosthetic leg. The shape of a prosthetic leg adds natural damping through the allowed flexion. The design also solved our sinking problem due to the surface area we added to the end of the design. The curve of the foot was also made to perfectly fit the sphericial motion of the steps and the bottom was texturized to add the proper traction for the robot to walk on all surfaces.