Design & Manufacturing

Bot DESIGN

The bot was designed with a 2-story chassis with enough space to hold all the components of the bot in a 12 inch cube space. This includes -

Two NiMH batteries
One Arduino Mega
Two Ultrasonic sensors
One Phototransistor sensor and breadboard with circuit
Sensor Electronics
Power Electronics
Ingredient Holder & Gate servo
Ignition & Arm servo

Chassis DESIGN

The chassis was designed to be modular and easily iterable. Initially, we made a chassis for the maximum dimensions (12" x 12") because we wanted a moving bot as soon as possible. At this stage, the bot would be a test bench for checking the functionality of the motors, line following setup and the software used to achieve these smaller tasks. We manufactured the chassis using 5mm Duron wood laser cut using the Laser Cutters in AMPS.

However, we soon realized that the large size of the bot would become a constraint during turning and entering tight space during the run. Using the approximate dimensions of the components, we redesigned the size of the chassis and that resulted in the chassis you see above. Although initially we planned to switch to acrylic for added stiffness, Duron was able to handle the weight of the bot and the impacts that it would face well. Hence the final bot was also manufactured usign Duron.

First Iteration

Final Chassis

Motor Selection

To select the appropriate motor for the bot, we started by determining the key operational parameters required for movement. Our goal was to achieve a maximum speed of 1 m/s while carrying a maximum load of 5 N. Given these constraints, we calculated the required power, torque, and RPM values needed for optimal performance.

Using the available wheel radius of 0.04 m, the following values were determined:

RPM at maximum power: 238.73
Torque at maximum power: 0.2 Nm (approximately 2.04 kgf.cm)
Maximum power per motor: 2.5 W

With these requirements in mind, we selected the Geartisan 12V motor, which provided an appropriate balance of speed, torque, and power while remaining within our design constraints. The specifications of the selected motor are:

Rated Voltage: 12V
Speed: 550 RPM
Rated Torque: 0.7 kg.cm
Power: 2 W

The motor’s electrical characteristics were also taken into account:

Motor constant (k): 0.137 Nm/A
Internal resistance: 12 Ω
Peak torque (T_pmax): 0.0981 Nm
Peak current (I_pmax): 0.716 A

Although the selected motor's maximum power rating (2 W) is slightly lower than our calculated requirement (2.5 W), it was deemed sufficient due to the overall efficiency of the drivetrain and additional factors such as the reduced size of the chassis. Furthermore, during testing, the motor was able to meet the bot’s movement and manoeuvrability requirements effectively.

Motors attached using mounts to the chassis

Assembled bot without ball holder

Ball Holder

The initial design of the ball holder was a simple tower structure mounted on top of the chassis. This tower was designed to hold a single ball, with a gate controlled by a stepper motor that would open to release the ball at the right moment. However, this design presented several challenges:

Dimensional Constraints – The bot had a strict 12-inch height limit, while the chassis itself was already around 11 inches high. This left a narrow 1-inch margin to fit a functional ball release mechanism and ensure smooth ball movement.
Stability Issues – In early test runs, the ball often fell out of the holder prematurely due to vibrations and sudden movements of the bot.
Lack of Controlled Release – The ball would sometimes drop out of alignment when the gate opened, leading to inconsistent performance.

Iteration & Redesign

To address these issues, we redesigned the holder to accommodate six balls instead of one. This new design incorporated the following improvements:

Larger Storage Capacity – Instead of a single-ball holder, we created a multi-ball magazine that could hold up to six balls, improving efficiency.
Guided Release Mechanism – The stepper-motor-driven gate was widened and integrated with a ramp to guide the balls smoothly as they were released.
Enhanced Stability – To prevent balls from being ejected unexpectedly due to vibrations, we enclosed the holder with side barriers and refined the ramp’s angle to keep the balls contained until the gate was activated.
Space Optimization – The new design was carefully adjusted to stay within the 12-inch height limit, using vertical space while maintaining a compact footprint.

This final design significantly improved reliability, ensuring that the balls were held securely in place during movement and were released only when required. We fine-tuned the gate mechanism and ramp angle through multiple test iterations to achieve consistent and controlled ball deployment.

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