Biped Robot

Introduction:

A Biped Robot is basically a 2-leg walking robot which mimics human walking. We made this robot mainly to understand the mechanics of walking and as a start to our dream of making a complete humanoid. Here is a step wise description of the project:-

Step1: Finding out the Functional Requirements

In the first step we studied the kinematic requirements for the robot and hence decided the degrees of freedom required. Further we decided the approx. dimensions of the robo. The lower limit of the dimensions was controlled by the size of actuators and electrical components whereas the upper limit is controlled by the torque rating of the motor.

Step2: Making the CAD Model of the Robot

Once we have the kinematic requirement, we designed the parts and made a CAD model of the robot in solidworks. This helped us understand the limitations in various designs and also helped us to make suitable changes.

Step3: Calculations for the Stability of the robot

Refer to the equation showing xcm1 and xcm2(ignore other text)

 The  Balancing is done using the concept that if the Center Of Mass of the robot, lies within the foot of the robot  which is in contact with the ground, then the other foot can be lifted without toppling the robot. Hence at each position the robot must satisfy this condition. However when both the feet are on the ground the center of mass of the robot can lie between the feet.

Step4: Generation of trajectory of walking

To learn generate the trajectory we experimented a lot on how humans walk and tried to incorporate the exact same steps into our robot; making sure that at all the time the robot satisfies the condition for stability of the center of mass.

The figure(Pardon me for uploading just a rough sketch made on my wall) below shows the Sketch of the robot in each position in its path

Front view at the top and side view at the bottom in each position

Left leg is shown in Hatched line and right one in Solid line

The leg in contact with the ground(FIXED) is shown with black

The leg not in contact with the ground(IN AIR) is shown in blue

                          The positions 4 to 11 are repeated to generate continuous motion.

Step5: Fabrication of the parts

Now that we were ready with the entire Trajectory, CAD model and Required Components, we started with fabrication. The parts were fabricated using aluminium sheets of around 1.5mm thickness. The picture below shows the fabricated parts:-

Step6: Assembly of the robot

After fabrication of the parts we assembled the robot. The picture below shows the robot after assembly of the robot:-

Step7: Programming the robot

After the assembly of the entire robot we programmed the microcontroller ATMega8535 using the 16bit Timer to control the 6 servo motors and incorporated the trajectory that we generated considering the stability of center of mass. We took the weight of each Sub-Assembly of the robot and used those values in the equation to calculate the center of mass. Hence found the joint angles to generate the required trajectory.

Step8: Testing the Algorithm

We took many trial runs to test the algorithm and made the required changes in the program to generate a stable walk

Step9: Mounting the Microcontroller On-Board

Once everything was working as expected we mounted the microcontroller on the robot and fixed all the wiring to the robot as below:-

After doing this we had to re-calculate and change the values of the joint angles to compensate for the weight of the microcontroller.

Step10: Adding Balancing Weights

After re-testing the robot we noticed that the robot tends to fall backward and hence we added standard 9V radio batteries as balancing weights and here is how the final robot looks:-