3.1. Spring system
Within the spring system, the main challenge is to design it in a way that it is strong enough to keep the robot stable in all positions and generate enough normal force for the traction in the side cylinders, but yet soft enough to open when passing the mast tips. As it can be seen in Figure 2.b, the spring system consists of one pull-spring (1.1) and two rotary springs (1.2). The two rotary springs are pre-stressed. These springs have a no-force angle of 90°. When mounted to the chassis, these springs have an adjustable pre-stress angle. Since these springs are pointing towards each other, the resulting force is zero and the two arms stay within a centre position. The pull spring is installed to fine tune the normal force – required to generate enough grip for a forward motion without wheel slip. When such a pair of cylinders encounters an obstacle such as a mast top, which mostly also implies a change of cable direction; these arms are being rotated out of their centre position. The rotary springs then increasingly add force to the arms for the vertical cylinders (3.2) and therefore take back the arms into a centre position. This effect is also used to increase the normal force in order to generate more traction when passing an obstacle.