Biped – Two legged walking robot

V.V.Sri Harsha-J08109

G.Venkata Ramana-J08045About biped:

A biped is a two legged walking robot which imitates human gait. It is used in places where wheels cannot go easily for example stairs, terrains, etc.

Aim: To build a biped robot (prototype) which can balance and walk autonomously so that we can know the errors that we will be facing while building a human sized biped.

Specifications of apparatus used:

Hardware:

• Servo motors: High Torque Servo motors Link

• Micro controller: Arduino Mega Link

• Power hardware: Used for distributing the power to the servos.

Software:

• Solid works: For Designing of bot.

• Arduino: For coding the Micro controller.

Development of the Project1 st model:

We built our first model without any design just using servomotors and raw aluminium holdings.

Failures:

This was a failure as we hadn’t considered the moment of the ankles. The model proved to be a structural failure.

Modifications:

We modified this by building a “Solidworks” model and analysing all the required spacing for the motion of all the ankles.

Failure:

Though the model was structurally stable, it had the problem of misbalancing due to change in the position of the centre of mass while walking.

Modification:

We then used the battery pack as a moving torso, so that the centre of mass would align vertically above the foot which remains on the ground, so that there is no toppling due to external torque. Hence the misbalancing can be addressed.

Final Bot:

After testing the robot with the torso, we understood that the problem was not with the torso but was due to the reaction at the foot. So we removed the torso and built our final working bot.

Working of the robotHow our bot works:

When controlling manually we use Serial communication using the Serial monitor of the Arduino IDE to send commands to the Arduino board. We are using the PWM pins of the Arduino board to control the servomotors at the power board.

Example: In the test code when we press the 'q' key in the keyboard mortor-1 will be rotated by 1degree clockwise. So for six motors we assign 12 keys clockwise and anti-clock wise.

When controlling automatically we record all the keys that we

are using when we are controlling manually and code them on Arduino board so that we don't have to give any input.

About power hardware:

First we gave the power supply to the Servomotors from a battery of 3A current rating. It was not enough for running the serovs so we made a small circuit where we can give external power and all the Servomotors are connected in parallel to the power and each of the signals is connected to different PWM pins of the Arduino board.

C ode:

As we don’t have a control system built into the prototype, it is difficult to move the bot to unknown positions as it cannot balance itself. So, we wrote a code for manually controlling the bot and know the balanced positions for taking two steps and we can run it in a loop for continuous walking.

Codes are available in the folder.

Human Sized biped:

We are going to solve the kinematic problem in the big biped by using D-H parameters and the balancing problem by ZPM.

Analysis can be found in the document named “Knematics,

Dynamics, Motion Analysis, Control and Fabrication of Biped.pdf”