HTR has developed legged robot systems since 1998 with focus on energy efficiency and autonomy. Our recent developments in variable flexibility wheels for Martian and Lunar rovers enable a new approach to high mobility and optimal efficiency vehicles: The wheel / leg hybrid concept. High efficiency wheels are used for high speed / moderate terrain while leg mobility ensures obstacle negotiation, staircases and steep slopes. The result is a versatile, extreme mobility system that can respond to the most demanding terrain and obstacle negotiation requirements, while preserving record setting efficiency as set by HTR’s variable stiffness wheel concept.
Hybrid QUAD on steep, loose stone pebble slope
The large payload capacity of these vehicles (80 kg) and their efficiency (8h – 60km range) make them ideal for logistics support in a number of 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).
The 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 energy 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 25 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 long, 20kg mass) with remarkable energetics. The design of the Hybrid QUAD platform has been the culmination of a long development based on the experience gained on prior mid scale projects.
Hybrid QUAD takes the advantages of all terrain wheeled vehicles, when terrain conditions permit it. It uses its adaptive leg suspension system when wheels are not able to overcome obstacles or develop enough traction to move the vehicle forward. Legs also regulate the posture of the vehicle as a function of terrain condition.
Posture regulation as function of terrain condition
The choice of the correct actuation and power control units are also of key importance. Hybrid QUAD 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).
Hybrid QUAD on soft ground
Overall length : 2130mm
Height : 1257 mm
Battery autonomy: minimum 8 hours
Total number of motors: 12
Height at hip level: 920mm
Width at foot base: 450mm
Net full robot weight without batteries : 67kg
Battery: 12 kg
Speed : 10km/h
Hybrid QUAD and HTR factory