Holonomic cross drive with Omni wheels is selected for its capability to move to any coordinate in the X-Y plane by calculating the instantaneous resultants of all 4 wheels, while also providing control over the rotation about
the Z-axis. Thus, the Holonomic Omni cross drive has an advantage in terms of maneuverability and traction. Four Planetary geared motors are used for locomotion. Sensor data from the Arduino Due is transmitted to Raspberry
Pi, the main processor of the system. Odometry is achieved through sensor fusion of encoders and IMU using ROS. Here PS2 controller is used for maneuvering. Additionally, rollers are also fixed on the sides of the TR’s chassis
to assist the wall following with baffles
The throwing mechanism is made up of many layers of Thera-band that are coupled to the rack and the sector gear, which is powered by a worm geared motor. When the Thera-band is stretched, it produces a certain amount
of elastic resistance. The elastic feature of the Thera-band with Y = 2.75MPa makes it an excellent choice for storing the energy required to propel an arrow.
When the motor drives the sector gear along the rack, it pulls the Thera-band, thereby storing potential energy in the band. This stored energy is released when the gear reaches its slip point. Thus, providing enough energy to launch the arrow through the guide. To achieve the required launching speed of the arrow, the band has to be stretched to a specified distance. This is done using a sector gear with teeth present along 240mm of its circumference. This ensures that the band is stretched only up to a distance till the sector gear reaches its slip point.
To land the arrow in the desired pot, Image processing is implemented and the pot is detected using the color detection algorithm on the image captured by the camera, while the accurate distance to the pot is determined using a LiDAR sensor. A
laser pointer is used to estimate the exact incidence of LiDAR on the pot for the operator’s assistance.
Picking arrows from the rack is done by a mechanism with 2 degrees of freedom. The end effector of this mechanism consists of 3 grabber clips. Each clip has a “V” notch with friction padding for enhanced grip. The clip is made up of two segments,
one of which is fixed, while the other is movable. The movable part of each of the grabber clips is connected via a common axis. This common axis is actuated using a pneumatic piston (25mm stroke length), which is responsible for holding
an arrow in the “V” notch. These grabbers are mounted on a frame that is held with a pivot joint attached to a servo motor.
To pick and load arrows from the arrow rack, the angular displacement of the grabber mechanism is needed.
This requires high torque which is achieved by using a cycloidal reducer mounted onto each of 2 NEMA-17 stepper motors (Stall torque: 5.5 kg-cm). These motors are operated via a single high current driver to ensure synchronized movement.
In order to reach the furthermost arrows on the rack, the grabbers can slide laterally to align themselves with the arrows by using a pneumatic actuator (200mm stroke length). After grabbing the arrows, they are then aligned back to the
launcher to complete the loading.