Considering the number of components to be used in the bot, it was necessary to use a light weight material. Ofcourse Aluminum can be used but using plastics will further decrease the bot weight. Hence, we decided to use the material
called Polypropylene (PP) which has good machining properties.Considering the size of the robot, the chassis of the robot will have to be made out of aluminum in order to counter the large bending moments.
The model of legs was initially simple, with the motor-encoder couple at each joint. Worm geared motor was used considering the worm-gear mechanism’s self-locking feature. Each leg consists of 3 articulated joints,
meaning each leg has 3 DOF. The topmost joint at the body will enable the robot to turn all legs instantaneously without having to lift any leg, thus facilitating sharp turns.
The Speciality of the 4 legged Robot that was designed is that it has 3 degrees of freedom in each leg which has allowed us to program the robot to follow any gait pattern that is suitable for a particular condition. This is achieved by
having 3 PW motors on each leg. To control the position optical incremental external encoders (with 1500 PPR (pulse per rotation))are used. The first encoder is placed at the hip joint, the second one at the thigh, and the last at
the knee which may also be referred to as the ankle.
The hip joint can rotate the leg 360ᵒ about a point, clockwise or anticlockwise. The Thigh motor can rotate 180ᵒ about its point of rotation, thus translating to back or front
parallel to the ground. The ankle motor can rotate approximately 270ᵒ max, back and front parallel to the ground. The design is very simple, making the robot flexible.
Moving towards the electronics part each leg has 3 motors, in order to operate each motor individually a separate motor driver is to be used. “Hercules” motor driver of current rating 13A suits best as per the specs of the motor. 3 Arduino due are used as they have ARM cortex processor which supports all pins as interrupt and PWM. Processors in them making them very fast when compared to other Arduinos. Furthermore, all of their digital pins can be used as external interrupts. 2 Arduinos were used for controlling the legs, each controlled 2 diagonal legs. The middle/Central Microcontroller (Arduino due) was used to control and synchronize the functions of the other 2 Arduino Dues. Communication was established between these Arduinos with the help of I2C and Interrupts. Two Arduinos (This was then extended to be operational for the tri-Arduino setup) have been used, the “Wire.h” library and the “PID_v1.h” library to do most of the work.
