3.  Proposed locomotion mechanism
We set  basic  requirements  for our  experimental
mobile robot as follows.
1)  On  flat terrain, fast and efficient  locomotion  is realized with simple control.
The  robot  can move  in the  discontinuous contact
locomotion environment.
For, the movement  on  steep slope, traction  is
generated at the all contact points between  the robot
and terrain.
In  order  to  increase the reliability  and  decrease  the
cost, the robot  has  less number  of  actuators than
normal legged robot.
satisfy  above  requirements,  we  propose a  new
configuration  as  shown in Fig.1. Many mobile robots
developed earlier have an active wheel  at the  tip of  their
leg. Though such a mechanism shows high adaptability
to the environment, it requires large number of  actuators.
In our proposed scheme, different kinds of mechanism are
employed  at  the front end  and  rear end in order  to
decrease the number  of  actuators.  The  robot  has  two
front legs and two rear legs. Front leg has a serial link
structure, and  has three  rotational  joints.  A relatively
small lockable passive wheel is attached at the tip of each
front leg.  The  first joint, that links  the  bcdy  and the
thigh,  has vertical axis  and  the second  and  third  joints
have horizontal axis.  End  of  the front leg (passive
wheel)  can  be  positioned arbitrarily in its  work  space.
Rear  leg has a rotational joint, and also has  a relatively
large active wheel at the tip of the leg.  The  joint axis is
horizontal, and its  movable  range  is  over one
round.  Accordingly,  the active wheel moves on a
circular trajectory  in  the  lateral plane.  Totally,
this configuration has ten degrees of  freedom, and
it  is  smaller  number  than  that  of  a  normal
quadruped robot, twelve. On a  flat  terrain, four
wheels are used for locomotion.  Wheels contribute fast and efficient locomotion. When front passive wheel  is
positioned  at just  bellow  the first joint  axis,  steering
action is performed by controlling the first joint only.  In
addition, legs can function as active suspensions. In  the
case of  rough terrain, the front passive wheels are locked,
and front two legs are used to walk.  Rear active wheels
are still  used  for  locomotion.  The  robot  can  generate
traction at the all the contact points between the robot and
the ground.  When the robot encounters a large step where rear  wheel  can  not  climb, the rear leg is moved
from the rear  side to the front side through the air by  leg
joint motion.
Fig.2 shows a photograph of constructed mobile robot,
and  it is called ‘Walk’n Roll”. Basic  specifications are
also shown in Table 1.  The robot  is separated from the
power  source, motor  amplifiers, and a control computer,
and they  are connected by  the cables.  DC  servo motors
are used  to drive the joints and rear wheels. Solenoids
are  used  to  lock  the front  wheels.  Rotary  encoder  is
attached at each joint and active wheel. In order to detect 轮足复合式移动机器人英文文献和中文翻译(3):http://www.751com.cn/fanyi/lunwen_9943.html