Page 104 - Robot Design Handbook ROBOCON Malaysia 2019

2.2 Mechanial Design of MR2

The MR2 is tasked to walk in the Gobi Area to reach Mountain Urtuu and it has to
overcome two challenges which are the Sand Dune and Tussock ropes. Therefore, the MR2

must have at least three Degrees of Freedom (DOF) in order to walk along the Gobi Area.
The three DOFs are forward and backward, left and right, and up and down.

An attempt to replicate the SpotMini with guidance from Androtics [4] was
performed. The SpotMini quadrupedal robot has a hip and knee joints with elbow

configuration style and it uses linear actuator to control the knee joint and high torque motor
to control the hip joint. ‘Webots’ simulation software was used to simulate the robot with

motor controlling each joint, replacing the linear actuator for a simple simulation. The

simulated robot was using the fastest locomotion with two legs contacting the ground at half
walking cycle but failed to walk straight because the centre of gravity of the robot is behind

the centre of the body so it was difficult to balance on two legs while walking forward unless

the robot is able to move faster than it falls. Moreover, the torque on the knee joint must be
greater than the torque on the hip joint. Hence, the hip-knee elbow configuration style robot

was not chosen due to difficulty in achieving balance, and high speed linear actuator is heavy
and difficult to obtain.

Another design was studied and it was inspired by MIT Super Mini Cheetah [5] and

one of the Vietnam’s ROBOCON robots [6] due to its speed as shown in Figure 5. This

design of the robot has two hips joints, two knee joints, and one ankle joint for each leg.
Each hip joint on one leg is control with at least 1 motor while the knee joints and ankle

joint are free rotating joints. A forward kinematic was identified for the leg structure so that

it can be used to control angular rotation of the motors to provide linear motion for the robot.
The leg structure was simplified into a diamond shape as shown in Figure 6 and Eq. (1) was

obtained via forward kinematic where the angular position of the second motor depends on
the angular position of the first motor when performing linear motion for the leg.

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