The SILO-6 and DYLEMA Projects'
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PROJECT:
Walking Robot

Department of Automatic Control
Industrial Automation Institute
Spanish National Research Council - CSIC

 

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Sensor Head

Manipulator

Locator

  -Leg Design
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Body Design
-Robot Features
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Pictures
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Videos

Controller

 

The SILO-6 Walking Robot

Walking robots are intrinsically slow machines, and machine speed is well known to depend theoretically on the number of legs the machine has.  Therefore, a hexapod can achieve higher speed than a quadruped, and a hexapod achieves its highest speed when using a wave gait with a duty factor of β = 1/2, that is, using alternating tripods.  Although stability is not optimum when using alternating tripods, a hexapod configuration has been chosen just to try to increase the machine’s speed.  The walking-robot development is based on certain subsystems developed for the SILO-4 walking robot.  The SILO4 is a quadruped robot developed for basic research activities and educational purposes.  For this reason, this new walking robot is named SILO-6, referring to its six legs.

Walking Robot: Body Design

The main tasks of a walking robot’s body are to support legs and to accommodate subsystems.  Therefore, the body must be big enough to contain the required subsystems, such as an onboard computer, electronics, drivers, a DGPS and batteries.  The preliminary volumes of these subsystems define the volume of the body (see Table 1).

“Alternating tripods” means that two non-adjacent legs on one side and the central leg on the opposite side alternate in supporting the robot (see videos).  That means that, for a given foot position, the central leg in its support phase is carrying about half the robot’s weight, whilst the two collateral legs in their support phase are carrying about one-fourth of the robot’s weight.  This is especially significant in traditional hexapod configurations, where legs are placed at the same distance from the longitudinal axis of the body.  If the robot has similar legs, then the non-central legs will be over-sized, and to optimise the mechanism the central leg’s design should differ from that of the rest of the legs.  However, using just one leg design has many advantages in terms of design cost, replacements, modularity and so on.

Satisfactory force distribution and system homogenisation can be achieved by shifting the central leg slightly from the body’s longitudinal axis so that the central legs support less weight and the corner legs increase their contribution to supporting the body. 

The solution chosen was to select equal legs and situate the central legs in a forward position with reference to the body’s longitudinal axis. A distance of about 156 mm was finally selected, because it produces an adequate body shape and reduces the required torques by about 15.06% (see Figures 1 and 2).

 

Figure 1. Main structure of the SILO-6 walking robot

 

 

 

SILO6 body

Figure 2. Body structure of the SILO-6 walking robot

Walking Robot: Leg Design

 

Figure 3. Drawing of the leg

Figure 4. Leg prototype

Walking robots need leg configurations that provide just contact points with the ground, so a 3-DOF device suffice to accomplish motion.  Legs have to be designed to be lightweight mechanisms and have to support the robot's weight.  Therefore, the load carried by each leg is very heavy and must be supported with the leg in different configurations.  A mammal configuration is the most efficient leg configuration from the energy point of view (lower torques are required).  However, it is not very efficient in terms of stability.  Insect-like legs seem to be more efficient stability-wise, but power consumption increases extraordinarily in an insect-like configuration.  The idea is to provide a leg configuration that can accomplish its job with both stability and energy efficiency (a very important factor for outdoor mobile robots).  Development is therefore underway on a leg that can be used in both the mammal and the insect configuration (see pictures).  The starting point is to consider the torques the robot has to endure in the worst-case scenario, an insect configuration.  These torques, for the selected body configuration, have been computed through simulation. One good way to reduce motor size is to use actuators working in parallel, that is, actuators placed so that two actuators work at the same time to accomplish motion in a single joint.  Simultaneous motions in two joints are also allowed.  This configuration gives the benefit of using small motors.  Therefore, a differential driving mechanism will be used for joints 2 and 3.  Figure 3 shows a preliminary design for the leg, and Figure 4 presents the leg prototype. Table 1 presents the leg’s main features.

Feet can be designed in two basic configurations, a ball fixed to the ankle or a flat sole with articulated passive joints.  The first design is the simplest and can work for applications in loose terrain if the radius of the ball is big enough.

 
Walking Robot: Features

Table 1. Main walking robot features

Body

Dimensions (m)

Length

0.88

Width

Front/rear

0.2

Middle

0.45

Height

0.26

Moments of inertia (kgm2)

Ixx

0.99

Iyy

3.11

Izz

0.99

Mass (kg)

44.34

Speed (mm/s)

50

Leg

Link

1

2

3

Length (mm)

94

250

250

Moments of inertia (kgm2)

Ixx

0.016

0.0027

0.0031

Iyy

0.016

0.0027

0.0031

Izz

0.018

0.0001

3 10-5

Mass (kg)

1

0.5

0.6

Foot speed  (mm/s)

Transfer phase

140

Support phase

50

 

Walking Robot: Pictures
SILO6_pic1 The SILO-6 in insect configuration carrying the first version of the scanning manipulator.
The SILO-6 in pseudo-mammal configuration
SILO-6_pic2
silo6

 

 

 

The SILO-6 on soft terrain

 

 

 

The SILO-6 with the newest version of the manipulator

Walking Robot: Videos
SILO6 video
SILO-6 on flat and hard terrain
SILO6SILO6 video
SILO-6 on natural terrain
SILO6 video
SILO-6 carrying the manipulator and sensor head
SILO6 on irregular terrain
  SILO-6 on irregular terrain

SILO6 video

  SILO-6 following a trajectory to sweep an area
(speedx10)

 

SILO-6 walking over forbidden areas

(speedx4)

SILO6 video
DYLEMA system working on irregular terrain (speedx10)  

 

 

 

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PROJECT: Walking Robot
Department of Automatic Control :: Industrial Automation Institute :: Spanish National Research Council - CSIC