QU 1120       


Introduction

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 isolate 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 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 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.

Detailed Specifications

Robot code name:   QU 1120 / 25 

QU: Quadruped
25: Nominal power of dc motors

Physical dimensions

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

Mass

Net full robot weight without batteries : 67kg
Battery: 8 kg

Motors as follows:
 
-  12 basic mobility motors (3 per leg) for fully autonomous walking

Power control servo card and micro-controller unit

MC300  MOTORCARD  SPECIFICATIONS
 
A.  FUNCTIONAL DESCRIPTION

      The card is composed from:

       1. Central processing unit   80C592.
       2. CAN-BUS TRANCEIVER PCA 82C250.
       3. Analogue processing unit
       4. Parameter modification unit.
       5. PWM power DRIVER unit .

B. SPECIFICATIONS

       1. CENTRAL UNIT.

            There are  7  CONTROL MODES available for the dc motor control
      
            1.1  P      FOR POSITION FEEDBACK
            1.2  PI                         “
            1.3  PD                        “
            1.4  PID                       “
            1.5  POSITION &  FORCE FEEDBACK
            1.6  POSITION  & VELOCITY FEEDBACK
            1.7  POSITION, FORCE, VELOCITY FEEDBACK

The card communicates with similar units through CAN (Control Area Network) protocol and exchanges a frame of 2 variables and 6  control parameters with a rate of 1Mbaud

                - MAX PROCESSING TIME FOR A FULL OP. CYCLE  (WITHOUT  COMMUNICATIONS  DELAY TIME):   LESS THAN 1ms.

      2.  CAN-BUS  TRANCEIVER

            - FULLY COMPATIBLE  WITH  “ISO/DIS 11898”  STANDARD.
            - UP TO 1 MBAUD
            - BUS LINES PROTECTED AGAINST TRANSIENTS
            - SLOPE CONTROL TO REDUCE RADIO FREQ. INTRFERENCES
            - THERMAL PROTECTION
            - SHORT CIRCUIT PROOF.
            - 110 NODES CAN BE CONNECTED.

Other communication: RS232 9pin

      3. UNIT OF ANALOGUE PROCESSING
           - GAIN ADJ.
           - OFFSET  ADJ.
           - FILTERING

UNIT of  PWM POWER DRIVER

  •     Frequency (PWM)                :   15KHZ
  •     MAX OPERATING  VOLTAGE    :   24V
  •     MAX CONTINUE CURRENT      : 20A
  •     MAX  PULSED CURRENT         : 120A    (MAX  PULSE  WIDTH 3ms  FOR  24 V )
  •     MAX OUTPUT CONT. POWER  :  300W


Onboard Sensors

The machine is equipped with analogue position sensors for all axis as well as force sensors built in the mechanical structure of the system (HTR patents pending).

Plans


Assembled Chassis of QU1120 with legs

Photos from integrated system

Completed prototype during tests

Detail of motor for lateral motion of leg during tests

Control architecture

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


Communications with a remote control centre are made over wireless RS-232 for general type commands (direction of motion etc).

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.