What were the chief challenges to designing Crabster?

One of the challenges was to design a hydrodynamically streamlined body. The body shape has to minimize the fluid drag while securing sufficient space for the exploring equipment. The body also has to be lightweight but structurally strong. We decided to adopt composite material to satisfy the competing demands. We designed the frame using carbon fiber reinforced plastic and the skin using glass fiber reinforced plastic.

Another challenge was to design an underwater joint mechanism. The joints of legs have to be powerful, no backlash, no exposure of wiring, watertight and compact. We adopted frameless BLDC motors and harmonic drives for the joint mechanism. More than ten thousands parts were used in a front leg and the leg has more than 60 O-rings for watertight.