Legged robot systems have been studied in theory and built since the late 1960’s. Their advantage over wheeled vehicles apply when there is a need to isol
ate the moving platform from ground
irregularities and negotiate highly uneven terrain. By using discrete “footholds”, this isolation may result in obtaining straight line motion for their bodies, independent from the terrain irregularities.
Their capacity to negotiate a variety of terrain types make them ideal for applications where prepared surfaces are not available. Such situations may be found in natural environments (forests, desert, etc) as well as in human-made environments ( house interiors with stairs etc).
A key issue for the wide use of such systems relies on their autonomy, which on turn depends on their energetics, ie their ability to operate with low en
ergy requirements during their locomotion. This is difficult to obtain with such multi-dof systems as power losses often occur in oscillatory motion of their limps. HTR has been focusing on energetics of legged platforms during the past years. Energetically efficient legged systems are difficult to design, both from mechanical, electronics and control point of view, as all these three factors play a role in the power requirements of the resulting system. HTR has designed since 1996 several mid-scale quadrupedal systems (1.2m, 20kg) with remarkable energetics. The design of the larger QU1120 platform has been the purpose of a long development based on the experience gained on prior mid scale projects.
Opposite to wheeled vehicles, the energy requirements of legged platforms are not in direct function to their size. This is due to the fact that legged platforms use discrete footholds and therefore do not suffer from wheel friction problems when in contact with dusty, uneven soil, or covered with small stones etc. They can theoretically operate with their centre of gravity moving on a straight line, therefore needing zero energy for the displacement.
This results to the possibility to use a larger legged platform, such qs the QU 1120, which in turn would provide a better ground negotiation capacity, larger area of operation as well as a possibility to transport important payloads during operation.
The choice of the correct actuation and power control units are also of key importance. QU1120 takes advantage of HTR’s long test periods with a wide variety of electrical actuation solutions. Two energy-consuming key areas have to be addressed during operation of legged systems: Actuators working against gravity forces (such as the leg actuators supporting the body weight) and
actuators performing oscillating motion (such as the leg actuators performing the fore-aft motion of the legs).
In both cases an optimised selection of actuation and power control designs provide solutions for best performance. The resulting QU1120 machine has fully acceptable energetics for slow motion (in the range of 140W for slow walking), for its 75kg of weight (of which 8kg battery).
With a length exceeding 2m, the machine can easily carry its own 1m² solar panel and become completely autonomous for outdoor applications.
The QU1120 control is based on the creation of a network of 12 MC300 power cards, each one of which controls a single DOF of the machine, using hybrid (force-position) control strategy.
The network is supervised by another 4 micro-processor based cards, each one of which deals with the following tasks:
– Card 1 : System supervision, communications, start up, shutdown
– Card 2: Gait generation
– Card 3: Stability
– Card 4: Obstacle avoidance
Gait generation comprises walking and trot gaits.
Stability is monitored and controlled through measurements of the force sensor inputs of the machine.
Obstacle avoidance is based on ultra sound obstacle detection.
Overall length : 2130mm
Height : 1257 mm
Battery autonomy: minimum 2 hours
Total number of motors: 12
Height at hip level: 920mm
Width at foot base: 450mm
Net full robot weight without batteries : 67kg=
Battery: 8 kg
Motors as follows:
– 12 basic mobility motors (3 per leg) for fully autonomous walking
Frequency (PWM) : 16KHZ
MAX OPERATING VOLTAGE : 24V
MAX CONTINUE CURRENT : 20A
MAX PULSED CURRENT : 120A (MAX PULSE WIDTH 3ms FOR 24 V )
MAX OUTPUT CONT. POWER : 300W