Sojourner, Spirit, Opportunity and the Mars rovers under development all share a common suspension system known as the ‘rocker-bogie’.
The term “rocker” comes from the rocking aspect of the larger links on each side of the suspension system. These rockers are connected to each other and the vehicle chassis through a differential. Relative to the chassis , when one rocker goes up, the other goes down. The chassis maintains the average pitch angle of both rockers. One end of a rocker is fitted with a drive wheel and the other end is pivoted to a bogie.
The Rocker-Bogie design has no axles or springs, and allows the rover to climb over obstacles, such as rocks, that are up to twice the wheel’s diameter in size while keeping all six wheels on the ground.
Here we see the rather nice rocker-bogie used on Sojourner. Nice drilled arms (as in the SWFRI robot) and a motor on each axle.
The rocker bogie is, in my opinion, one of the most emblematic design features of all the martian rovers; and so it has to be a major feature for Essence and Possibility. Hopefully the DIY rocker bogie (lite) and the flat ‘deck’ will provide enough visual clues as to their design inspirations and functional metaphors.
My own version is a little simpler. 25mm square aluminium tube cut into sections and connected with .5mm copper plate brackets. Each axle is mounted through the tube and a 5mm bearing block which is mounted with sheet brass brackets. The motor is mounted to the rearmost axle using a 5mm to 6mm adaptor. Seeing as these are more of an aesthetic design object rather than a functional design object – even though they’ll have to support the weight of the robot – they will be ‘hard bolted’ to the robot chassis rather than being articulated. Therefore my robots will have no functioning suspension, basically because they won’t need it.
Lessons learned:
Making one of these takes nearly 2 days.
I really need a better, fully equipped workshop to be able to make things quickly and accurately…