Concept

Overview

This is the structure of the robot in its entirety. To understand the big picture, refer to Figure 4 when reading the sections below.

Figure 4: Schematic of entire robot

Diaphragm actuators

We used diaphragm actuators to produce horizontal motion. A pair of circular (prestrained) DEAs are locked in position by external rigid components. A long, rigid T-shaped component is placed between the centres of the two stretchable actuators (see Figure 5). The length of the T-shaped component is longer than the fixed distance between the two circular actuators, thus, the actuators are held in tension with stress radiating from the centres of the films.

When one actuator from the pair is actuated whilst the other is not, the actuated film will increase in area and there will be a difference in compressive stress provided by the two actuators onto the T-shaped component. Specifically, the activated film will offer less mechanical resistance to the T-shaped component compared to the non-activated film. This results in a net horizonal force pushing the T-shaped component away from the non-activated film and towards the activated film (see Figure 5).

This horizontal motion of the T-shaped component can be utilised to produce the robot's leg movements.

Figure 5: How the diaphragm actuators produce horizontal motion

How actuation translates to leg movement

To couple the horizontal motion of the rigid T-shaped component to the ground on which the robot is resting, a rigid shaft with hemispherical base, which we call the "leg" of the robot, is used to connect the T-shaped component to the ground so that mechanical contact between the two is established. The top of the leg is screwed to the protruding tip of the T-shaped component at A (see Figure 6) and the shaft of the leg is screwed to the edge of the board that offers structural support to all the actuators, at B (see Figure 6). Since both of these screwed points at A and B are pin supports, the leg is free to rotate about the point of connection at B, but not translate with respect to the T-shaped component and the edge of the board.

When the left actuator is activated, the T-shaped component translates horizontally to the left and the top of the leg, which is pinned to the T-shaped component, moves from A to A' (see Figure 6). Since the shaft of the leg is pinned to the board at B, the base of the leg swings from E to E' (see Figure 6). This creates a horizontal leftward displacement of the entire robot with respect to the ground. Note that all this while, the positions of the diaphragm actuators with respect to the board where they are planted, marked C and D on the board, are unchanged (see Figure 6).

Figure 6: Leg movement