User:Medelen8/ENES100/APW Design C

Problem Statement
Google has developed full-sized self-driving vehicles that are street-legal in Nevada. Stanford's autonomous vehicle won the DARPA Grand Challenge in 2005. Project Goal: Design and implement the electro-mechanical systems and software required to control a Power Wheel. The autonomous vehicle should be able to travel outdoor on specified paths while avoiding obstacles.

Requirements for each element or component derived from system level goals and requirements

 * The autonomous system must be independent of the car system in terms of power and functions;
 * The car operating system cannot be altered;
 * The autonomous system can be installed and removed without damaging the operation of the car;
 * As the project moved along a new requirement: motors must be programmed off the same Arduino;

Alternatives in design
Two design were considered:
 * Use a gear motor for the pedal and a linear actuator for the steering wheel (This was a previous team design);
 * Use a wheelchair motor to control the steering wheel; It was abandoned because it was not following the requirement of having the autonomous system independent of the car system.

The initial design

 * The steering wheel:

linear actuator data sheet


 * The pedal

A 12VDC, 78RPM Motor with Right Angle Lead-screw motor was purchased and the following pivot was printed:

Experimental prototypes and testing conducted during design

 * The steering wheel: See this page for design on how to operate the linear actuator.
 * The pedal:

This video shows that the previous pivot needed to be revised because nothing is keeping it from spinning. So this new model was drawn:

Appropriate optimization in the presence of constraints

 * The steering wheel:

The linear actuatorcan operate up to 200 N. The design should help obtaining the maximum torque. The sequence of the code used to operate the actuator should match it.


 * The pedal:

The pedal pusher should not spin, otherwise it won't slide. It should also be able to lift 5 pounds (22.2 N, value to depress the pedal).


 * The battery:

The autonomous system cannot use the car battery. The gear motor and the linear actuator operate on 12 V but the gear motor requires more current. The battery should be able to power both motors. This website can help you find the right battery with the right size.


 * Wires, Arduino, battery and other should be able to fit in the back of the car, which is why this frame is considered.

Iteration until convergence
Each subsystem will require iteration but for the most part the pedal pusher and the code were improved during testing. The final design is the last design before further testing.

The final design
This website will provide connectors for the gear motor for a proper installation instead of using alligator clips. We also found out that we can use the same charger use to recharge the car battery since it is also operating at 12V.
 * pedal pusher:


 * linear actuator and frame design are still under work.


 * This code operates both motors. It still needs some adjustments. So far, the delays were adjusted (the code shown is the original code).

Technical and scientific knowledge

 * Physics: The torque formula was used to determine the force needed to operate the actuator. Ohm's law was also used to understand why voltage was dropping when testing gear motor with ammeter. Circuits in parallel theory was used to determine what battery to use.


 * C programming knowledge: was necessary to troubleshoot issues when operating both actuator and gear motor together and to program Arduino ans motor shield


 * CAD : used to design pedal pusher and determine how to save file so 3D printer can print correct model.


 * Electronics: Arduino and motor shield wiring and mode of operation.

Creativity, problem solving, and group decision-making
For each step, brainstorming was required for this project, which is why each main subsystem (pedal and steering wheel) was assigned to two different members. In the end, A group effort was made to solve each problem that each test brought.

Prior work in the field, standardization and reuse of designs (including reverse engineering and redesign)
The manual instructions of the power wheel was consulted. The previous team work was reviewed, measurements were done ( pedal pusher, force to steer the wheel) and the data sheet for gear motor, linear actuator, sparkfun monster moto shield, Arduino duomilanove were consulted.

The pedal pusher design from the previous team was used and improved and the code for the motor shield was reverse-engineered during testing.

Performance, life cycle cost and value
The system as for now (with correct code) can move according to a certain sequence. Because this system is independent of the car system, it will last as long as the parts are working. The battery is rechargeable so, its life is not an issue. The overall cost of the project is estimated at less than $150 (autonomous system).

Aesthetics and human factors
Aesthetics were not very important but it was incorporated on some design. The pedal was printed in green PLA so it would match the power wheel that happens to be black and green.

Implementation, verification, test and environmental sustainability
Both actuator and gear motor were tested to work together. Even though the sequence of their operations will require more testing, it is clear that this can be implemented. Sustainability was not an issue.

Maintainability, reliability, and safety
The system is easy to maintain because of its simplicity and the fact that it is a kit that can be unmounted. The power wheel physical appearance and its operation are not altered so it is safe. However, there is no sensor, which means it can only move on a straight path, with no obstacle and according to the code sequence defined by the programmer.

Robustness, evolution, product improvement and retirement
According to their data sheet, both motors are powerful enough. Mounting them properly (following all calculations) is critical to guarantee they can handle the operations they will be programmed for. Because it is kit running with its own rule, it can be easily unmounted for improvement and repairs. Eventually, sensors can added to improve navigation of the power wheel.