Chassis and Shoulders of Polar Lunar Robot

Polaris is a rover specialized for drilling lunar ice. The chassis (Pic1) is an ‘H’ shaped carbon fiber structure to which aluminum radiator, baseplate and torque tube are mounted.
Four rocker arms provide a passive suspension via chains, sprockets and transverse torque tube. To test this setup, the torque tube, all four shoulder assemblies, and chains were fitted and tested for motion.

Each main shaft has a large sprocket which is used to link the rotation of the two shoulders on that side of the rover. The two larger shoulders have additional shafts and sprockets for chain tensioning and the differencing mechanism.

The two shafts located towards the bottom relate to the passive averaging suspension. The larger one, known as the differencing shaft, contains a sprocket and is connected to the torque tube. The other shaft is an idler that redirects the chain loop to increase tooth engagement on the differencing shaft sprocket. The differencing shafts on opposing shoulders are connected through a carbon fiber torque tube which completes the system. The differencing effect is achieved by routing the chain “over” one of the differencing shaft sprockets, and “under” the sprocket on the opposing shoulder. The result is that rocker arms on either side of the chassis rotate together and opposite to the other side. This is illustrated in the appended video where one chain loop is rotated in one direction, and the other side rotates the opposite way.

This assembly provides a simple and compact implementation of passive averaging suspension, which is stiff and exhibits low backlash. With its completion, assembly will move onto preparing the swing arms and electronics for final installation.

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