Mukhlisakhon Fazliddin

Design of Four Legged Robots:

Leg Locomotion, Sensors, Etc.

Introduction

A four-legged robot is designed like an animal. It can navigate through rough terrain and climb steep hills. Several companies have succeeded in designing and making four legged autonomous robots. So how are these robots designed so they can walk like a real-life animal? There are three considerations:

• “supporting the bo  dy with a vertical bouncing motion,
• controlling the attitude of the body by servoing [a servomechanism, or servo for short, is a device that uses negative feedback to correct the action of a mechanism] the body through hip torques during each leg’s stance phase,
• and by placing the feet in key locations on each step using symmetry principles to keep the robots balanced as they moved about” (Railbert, 2008).

 

As shown in Figure 1, the four-legged robot has legs like a dog or horse and can move about in the same way. Where the head should be in a real-life animal, there is a metallic sensor head in the robot, which it uses to scan the terrain ahead. With the three functions mentioned above, the robots can hop, jog, pace, leap, climb stairways, and jump over obstacles. Figure 2 shows an example of parts for a four-legged robot. The robot is called Big Dog and is designed to carry heavy loads on rough uncertain surfaces. An actuator is a device that gives machine movement, it converts energy from a control signal, received from the computer, to mechanical movement.

The legs are designed based on the anatomy of legs of real life animals. For example, the HADE leg in Figure 3 is designed based on a horse’s leg. A horse’s leg is chosen, according to Garcia, Arevalo, Muñoz, and Gonzalez-De-Santos, because it can carry a lot of weight while being light enough to move about easily and quickly. The leg is made of a metal alloy that has a high payload to weight ratio, meaning it can carry heavyweights while being lightweight itself. It has three joints, hip, knee, and ankle. The structure of the links and a high strength aluminum alloy contribute to a high payload to weight ratio (Garcia, et al). 

A rubber pad is attached to the bottom of the foot to absorb shocks and to increase friction with the ground. The leg has two actuators, one between hip and knee, and another between knee and ankle.

 

Conclusion

Design of a quadruped autonomous robot is an ongoing research.  It has many parts to it, such as material used, the number of joints, and the actuation system used. Robotics is an amazing field with many applications in real life. The quadruped robots will be beneficial for many people, especially for those who live outside the city. However, even those living in the city can benefit from the robots because they can be made smaller and designed to handle different obstacles.

 

References

Garcia, E., Arevalo, J., Muñoz, G., & Gonzalez-De-Santos, P. (2011). Combining series elastic actuation and magneto-rheological damping for the control of agile locomotion. Robotics and Autonomous Systems,59(10), 827-839. doi:10.1016/j.robot.2011.06.006

Raibert, M., Blankespoor, K., Nelson, G., & Playter, R. (2008). Big Dog, the Rough-Terrain Quadruped Robot. IFAC Proceedings Volumes,41(2), 10822-10825. doi:10.3182/20080706-5-kr-1001.01833