Hyq robot 2011 frontHyQ is a quadruped robot that was developed at the Advanced Robotics Department of the Istituto Italiano di Tecnologia (IIT) (Semini, 2010 Semini, 2011). The robot weighs 80kg, is about 1 meter long and is constructed in aerospace-grade aluminum alloy and stainless steel. Each of its four legs has 3 joints that are actuated by hydraulic cylinders and motors. High-performance Fomula 1 valves are used to control each joint’s position and force. The force control in the legs enable a smooth interaction between the feet and the ground. Onboard cameras and laser range sensors create 3D maps of the surroundings. These maps are used by the robot control framework to plan its steps and avoid obstacles.

HyQ and HyQ blue
Since 2011, HyQ has been extensively tested in the laboratory on a custom, large-scale treadmill and in an outdoor test site. The robot has demonstrated various gaits and motions ranging from highly dynamic motions like running and jumping to careful walking over rough terrains. The robot uses a trotting gait with reflex and balancing skills on flat or moderately rough terrain. On more difficult terrains, the robot uses a crawling gait that allows to carefully put the foot on suitable spots. HyQ is one of very few robots in the world that have demonstrated such a wide repertoire of behaviors. A copy of HyQ has been sold to ETH Zurich in the summer of 2013. IIT and ETH Zurich have strong research collaborations in the fields of robot modelling, control and machine learning.

Legged robots are vehicles with the potential to replace humans in dangerous and dirty tasks where vehicles with wheels and tracks cannot go. Possible applications are disaster recovery (such as the clean-up of the Fukushima nuclear power plant), search and rescue, forestry technology and construction. 

HyQ is a fully torque-controlled Hydraulically actuated Quadruped robot (pronounced [hai-kju:]) developed in the Department of Advanced Robotics at the IIT. HyQ is designed to move over rough terrain and perform highly dynamic tasks such as jumping and running with different gaits (up to 3-4m/s). To achieve the required high joint speeds and torques, hydraulic actuators are powering the robot’s 12 active joints. For more information on the robot scroll down or refer to (Semini, 2010).

Goals of the project are the design of versatile robots, the investigation of various aspects of quadrupedal locomotion, adjustable compliance, energy efficiency, compact hydraulic actuation and onboard power systems.



  • Walk, trot and run up to 2m/s (video at 0:40)
  • Rear and jump up to 0.5m from squat (video at 1:05)
  • Balance under unstable ground even under disturbance (video at around 1:05)
  • Animal-like step reflex (video
  • Torque and position-controlled joints (video)
  • Indoor and outdoor operation
  • Real-time control system with dynamics simulator

System Overview

The following table lists the key specifications of the robot platform.

Dimensions (fully stretched legs)


Number of active DOF

Actuator Types

Joint range of motion

Maximum torque (hydraulic cylinders)

Maximum torque (rotary actuator)

Onboard sensors

Onboard computer

Control frequency

1.0m x 0.5m x 0.98m (Length x Width x Height)

80kg (external hydraulic power supply), 100kg (onboard hydraulic power supply)

12 hydraulic actuators (8 cylinders in hip and knee flexion/extension joints and 4 rotary actuators in the hip abduction/adduction joint)

Hydraulic cylinders (80mm stroke, 16mm bore) and rotary hydraulic actuators


181Nm (peak torque at 200bar pressure)

120Nm (constant output torque at 200bar pressure)

High-resolution relative+absolute position and torque sensors on each joint, inertial measurement unit (IMU), hydraulic system pressure, stereo camera, LIDAR

PC104 Pentium, real-time Linux (Xenomai) with multi-I/O boards

1 kHz for motor control, 250Hz for motion generation


Hyq robot stage2 cad

Hyq mechanicalstructure front

Hyq mechanicalstructure side

CAD model of HyQ with onboard hydraulic system (left) and pictures of the mechanical skeleton of HyQ (centre and right)

Leg Design

Each leg features three degrees of freedom (DOF), two in the hip (abduction/adduction and flexion/extension) and one in the knee (flexion/extension). The leg is built of a light-weight aerospace-grade aluminium alloy and stainless steel. High resolution encoders and load cells in each joint allow a smooth control of both position and torque. We are currently designing and testing several foot designs with and without adjustable stiffness to soften the impacts at foot touch-down and to store energy from one step to the next.

Hyq legprototype cad

Hyq legprototype picture

Hyq legv2 cad
Hyq legv2

Leg Design Evolution: CAD model and picture of HyQ leg prototype (left) and the improved final leg (right)

In the beginning of 2008, we successfully reached the first milestone of the project: The design and construction of a first 2-DOF leg prototype (Fig. 3, left) with an actuated hip and knee joint in the sagittal plane (Semini et al., 2008). Since then, we have extensively used the leg to test its mechanical structure, the hydraulic actuation system and to evaluate various joint level controllers (Semini et al, 2008; Cunha et al, 2009; Focchi et al, 2010). For the experiments the leg was either mounted to a vertical slider or fixed to a work bench. We studied the behavior of the mechanical structure and hydraulics upon leg impact with varying leg weights up to 25kg. Furthermore, we tested the leg during continuous hopping with different frequencies up to 3Hz, since hopping is a simplified form of running (see video).

The experiments proofed that hydraulic actuation is very suitable for highly dynamic legged robots, due to its high power-to-weight ratio, high torque and speed and ability to cope with torque peaks (Semini, 2010).

Future Applications

  • Search and rescue operations
  • Operations in contaminated and dangerous areas
  • Forestry, construction and firefighting application
  • Inspection and exploration tasks
  • Experimental platform for legged robotics research (e.g. legged locomotion, biomechanics, force control, autonomous navigation)