Mechanism and Structures: Humanoids and Quadrupeds - Bioinspired Approaches for Human-Centric Technologies - page 148

Fig. 5.14 Kinematic
structure of the 16-DOF
robot: each leg consists of
three active joints, hip a/a,
hip f/e and knee f/e. The
fourth DOF is a passive
ankle joint

Table 5.3 Trotting speed
and stride frequencies of
quadrupeds

Quadruped's mass 50 kg 90 kg

Minimum trotting gait 1.57 m/s

1.70 Hz

1.82 m/s
1.61 Hz

Preferred trotting gait 2.6 m/s

2.01 Hz

2.96 m/s
1.87 Hz

Maximum trotting gait 3.56 m/s

2.33 Hz

4.07 m/s
2.13 Hz

We used the above considerations and estimates as a base for the robot compo-
nent sizing and mechanical design.

5.4.2.4 Robot Leg Design

Based on the design and experimental study of a first prototype 2 DOF leg (Semini
et al. 2008 ), an improved version with 3 active DOF ( Leg V2 ) was constructed,
Fig. 5.15 . Table 5.4 lists the most important specifications of the leg.
Due to the cylinder attachment geometry [reported in Semini ( 2010 )], the
hydraulic joints have a non-linear torque vs. stroke length characteristic. An
estimate of the required flow is provided in Semini et al. ( 2011 ).

5.4.2.5 Quadruped Robot Design

In the following sections full quadruped robot with its system components, list the
robot's key specifications, show its mechanical structure and describe the hydraulic
power and sensory systems. Table 5.5 lists the key specifications of the robot.
The total mass of HyQ (stage 1) is 80 kg. The mass of all four legs (including the
cylinders and feet) is 21 kg, which is 23.3 % of the total robot mass. This
corresponds well to animals with a comparable body weight (dogs and small
horses), which have a relative leg mass of 19-26 % (Fedak et al. 1982 ).