2 Mechanical description

The current version of the prototype is a chain of 8 similar linked modules called Y1. In figure , a CAD rendering is showed. They have just one degree of freedom, actuated by a Futaba 3003 RC servo. The design is based on generation G1 Polybot modules[4]. In this first version, no sensors are included. Our main interest was focused on the study of locomotion, and its implementation on FPGA.

Figure: CAD rendering of two Y1 modules. On the left, Two isolate modules In the middle, connection in phase. On the right, they are connected out of phase.

Y1 modules are simple and cheap: it is very easy to build prototypes of worm-like robots with them. These modules can be connected in two different ways, as shown in figure . One way is the connection in phase, in which two adjacent modules have the same orientation. Robots constructed using this link have all the articulations in the same plane, perpendicular to the ground (figure ). Cube comprises 8 Y1 modules, connected in phase, so that it can only move along a line, forward or backwards.

Figure: Two schemes of worm-like robots. On the left, all the articulations are connected in phase so that they all are on the same plane. On the right, the connection is out of phase. With this configuration, the modules can be on different planes.

The other way of connecting the modules is out of phase. Two adjacent modules are rotated 90 degrees one to each other, obtaining two degrees of freedom. One articulation moves on the ground plane (yaw) and the other does perpendicularly (pitch). The right image of figure shows a worm with this kind of links. Black circles represent articulations that moves on the ground plane and grey circles represents articulations that moves perpendicular. This kind of robot can turn and move on different directions, not just in straight line.

The dimensions of each module, in its initial position (0 degrees angle), are 52 x 52 x 72mm, and the weight is 50gr. They are made out of PVC. The rotations range is between -90 and 90 degrees. The robot is 576mm in length and 400gr in weight. The electronic and power supply are located off-board.

The consumption depends on the gaits, but typically it is 200mA per servo, giving a total of 1.6A. All the locomotion experiment at this first stage are realized using an off-board power supply.