User:Medelen8/ENES100/APW Design D

Problem Statement
Design subsystems in order to make the power wheel autonomous. It is obvious that these subsystems be have to able to work together with ease. In doing so, we anticipate that at some stage, the vehicle will be able to drive autonomously without any operator instructions. However, as it stands now, several subsystems must first be designed in order to replace the interactions a human driver would have. These subsystems must be both simple to build, simple to repair and improve upon. At this, stage an improved steering subsystem needs to be designed and a mechanism and subsystem for depressing the accelerator must be constructed.

Requirements for each element or component derived from system level goals and requirements
The goal of the project is to materials, designs, and data gathered by past groups to create a design for steering controls, pedal controls, and to have them controlled and powered by an Arduino and a Monster Motor Sheild.

Steering:

•	needs to use a Firgelli Miniture Linear Actuator L16 Series with 140mm stroke and 150:1 gear ratio

•	steering controls cannot modify the Power Wheel strucually

•	must be controled by an Arduino and a Monster Motor Sheild

•	capable of turing the steering wheel 40° in either direction

•	must be reomveable

Pedal:

•	must use 12VDC, 78RPM Motor with Right Angle Leadscrew

•	must be able to depress the pedal with 3 N of force

•	be able to mount to the power wheel with only the use of the 4 wing nuts on mounting platform

•	must be removable

Arduino and Monster Motor Sheild

Alternatives in design
Steering There were three initial designs for the steering mechanism: linear actuator pulling and pushing a chain, linear actuator attached to steering wheel, and a lever with the liniear actuator.

Steering Concept #1 The chain concept is to have a bycicle chain along a track around the perimiter of the steering wheel and haing the linear actuator push and pull the chain to turn the steering wheel.

Steering Concept #2 To mount the linear actuator onto the steering wheel and attach it to the base of the mounting platform. As the actuator extendes it will turn the steering wheel in one direction and as the actuator retracts it will turn the steering wheel in a counter diretion.

Steering Concept #3 A lever will be attached to the steering wheel and extend out to the side of the steering wheel. At the end of the lever the steering wheel will be attached to the linear actuator and that will be the pivot point inwhich the steering will be turned. As the actuator extendes it will turn the steering wheel in one direction and as the actuator retracts it will turn the steering wheel in a counter diretion.

Pedal There was the original design of the pedal pusher, form past groups, utilizing a pedal pusher with side brackets attached. An alternative design was made using a retengular pedal piston and a square bracket.

Pedal Concept #1 The oringal design was a pedal pusher with side brackets built on to the pusher. The brackets were on either side of the pedal pusher and was made to go on each side of the pedal. The pedal pusher will have hollow center to allow the screw from the motor to fit inside the pusher. There will also be a cut out on the side to allow access for a nut that will attach to the screw mechanism of the motor. As the motor turns the screw, the nut wiThe initial designll extend and move the pedal pusher. The brackets were used as a way to stop the pedal pusher from spinning.

Pedal Concept #2 The second design was to use a retangular piston to depress the pedal and a square reciving bracket. The piston will have hollow center to allow the screw from the motor to fit inside the piston. There will also be a cut out on the side to allow access for a nut that will attach to the screw mechanism of the motor. As the motor turns the screw, the nut will extend and move the piston. The bracket will riecive the piston and prevent the piston from spinning and causing it to not extend. The Initial Design As described above these were the initial design concepts of the steering and pedal controls. Due to the limitations, in money, time, and constraints of the engineering work shop, the chain concept for the steering controls could not be built or tested. The other designs were feasible and could be tested or built with the limitations that were presented. Experimental Prototype Testing Conducted During Design

Steering Concept #1 This concept would use a track built around the perimeter of the Power Wheel's steering wheel. Inside the track will be a bicycle chain that was attached at one end to the steering wheel and to the other end the linear actuator. As the linear actuator would extend the chain would move forward in the track and push on the steering wheel and cause the steering wheel to turn. As the actuator retracts it would pull on the chain and that would turn the steering wheel in the opposite direction. This concept would provide the greatest movement of the steering wheel and have the tightest turning radius. The design would also be compact and not add much bulk to the overall design. The fault with the design was the complexity of the construction, the complexity of instillation and removal, and overall cost. To make a track and use the chain, there needs to be metal work done, which the engineering workshop is not equipped. The design would be hard to install and remove, and one of the criteria be it could easily be removed from the Power Wheel. Since the workshop is not equipped with the equipment or materials for a prototype to be built, the cost was more than what our budget allowed.

The initial design
The initial design was to simply attach the linear actuator with a nut that can pivot, so that the linear actuator can move without difficulty. Our initial design for the gas pedal actuator was the same as the previous groups, which was to have a piston attached to a screw with a nut, which was operated by a DC stepper motor. The difference between the previous design of the actuator and the newer design is the piston.

The Initial design for the bracket that holds the piston in place was originally designed to hold the piston in place with no specific mounting points to the platform.

Experimental prototypes and testing conducted during design

 * Steering Wheel Prototype

Appropriate optimization in the presence of constraints
1. With steering Concept #3, the lever arm needs to be at an adequate length to allow for enough torque to turn the steering wheel, but not long enough to impede on the movements and function of linear actuator

Iteration until convergence
In addition to the testing described above, there were one area in which iterative design was required.

1. The material to construct the lever arm

The final design
Steering

The finalized design will be used for the steering will be Steering Concept #3. It is more complicated than Steering Concept #2, but is not complicated. It will use only three parts: the lever, mounting brackets, and the linear actuator. The use of the lever will allow for adequate torque as the angle changes between the lever and the linear actuator.

Mock Steering Wheel

Technical and scientific knowledge
The steering controls will need to use the Firgelli Miniature Linear Actuator and must fall within the contracts of the linear actuator. The stroke length of the actuator is 140 mm and to steer i both directions with restrict the actuator to using half the stroke length in each direction, 70 mm. The steering wheel itself in the power wheel, measured by the past groups, is 86.6 N at 8.3 cm to turn the steering wheel. Using the equation τ = F x r Torque = Force x Length of Lever The amount of torque can be calculated to find the actuator was capable of pulling back the steering wheel at that length. But further research into the design and the options how to mount the actuator on the steering wheel we need to have two pivot points, one at the base of the actuator and one at the point where the actuator and the lever connect. With that the actuator will not be always perpendicular with the lever to apply the force. We need to account for the loss of torque at different angles as the steering wheel is turned by the actuator. To find the correct length of the lever and the angles that the lever will be with the actuator I will use the equation: τ = F x r x Sin θ Torque = Force x Radius x Sin θ θ will be the angle which the force is being applied. Doing this we can see much force is lost in changing the angle in which the force is applied. When the force is applied at 90° the full amount of the force is applied to the lever, but when the force is being applied at an angle, the force that is applied in the direction in which you want the lever to go is a fraction of the overall force being applied. To find that new force we need to find the component vectors and to do that we need the force times Sin θ to get the amount of force being applied perpendicular to the lever. It is now know that there will be less force applied as the angle in which the force is being applied gets bigger, calculations are needed to find what is the largest angle, when the steering wheel is fully turned, to figure out the minimum length needed for the lever for the actuator to still have enough force to turn the wheel. To find that calculations are needed to find the angle of attachment point to the platform, so the midway point for the actuator going in a straight line and is perpendicular to the lever. When the next group has that angle the length needed for the lever can be found.

Creativity, problem solving, and group decision-making
There was one problem we had to solve,which was to figure out what type of lever we should use to operate the steering wheel. To determine which design to go with, we created a design matrix for steering wheel actuator. For this, we determined that the most critical characteristics we needed to evaluate are how complexity of construction, ease of installation, adjust-ability, and strength of the design. Complexity of construction refers to how simple the lever design is using the specific material. Ease of installation is how difficult or easy it is to build the lever. Adjust-ability is how hard or easy it is to adjust the lever if the setting isn't righ tor something went wrong. And strength is how much effort can the linear actuator can use to pull the lever. The results are outlined below:

Prior work in the field, standardization and reuse of designs (including reverse engineering and redesign)
The previous group worked on the code used to operate both motors. But after testing it, we realized it needed modifications, which are included below. We has faced a problem with the gas pedal pusher that the previous group built and this is because the pusher didn't exactly do what to was designed to do, which is to push the gas pedal. So, we designed a new pusher using Sketchup (which is also included below). After testing, we saw that the code and the gas pedal pusher proved better than the previous design. Although the code works, the only modification it needs is to fix the timings of the motors so it drives as instructed.

Code:

CAD Drawings:

Modeling and/or Simulation
Gas Pedal Presser Test Video http://youtu.be/gIV6zhy3gRI

Performance, life cycle cost and value
Because we are still in the design phase, there were no tests done to evaluate the performance of the power wheel. At the same time, the cost is very low because hardly and money was used. This is also because the prototype was built using wood and the 3D printer

Aesthetics and human factors
Human factors are not a part of this project since the project is about removing them. Because we are in the design phase, we only built a prototype. And since we only worked on the prototype, aesthetics was not a requirement we focused on.

Implementation, verification, test and environmental sustainability
After testing performance of each sub-system, the implement phase can begin. First, a new platform will have to be measured and built to fit the power wheel. The linear actuator should be the next thing mounted on the platform because it is the most initial part of the power wheel. It is also going to be the hardest part to install. Then the gas pedal actuator can be installed because it is the easiest; it only needs to be screwed onto the platform after it position has been decided. Once everything is lined up properly, it can be tightened down to ensure it doesn't move around during operation. Finally the Arduino and the batteries can be installed along with the wires that run to the two actuators. This should be the last part installed because the Arduino and the battery positions are determined according to where the actuators are placed. After everything is checked, the testing can begin. During the testing phase, monitoring the steering performance is the most important. Environmental sustainability isn't a concern for us since we aren't using any pollutants.

Maintainability, reliability, and safety
Because the subsystem is not complex, the subsystem is reliable because the parts should not war out easily. Also, maintenance is not an issue because the only thing that needs to be maintained are the batteries. The batteries should be replaced and charged when the voltage of the battery runs low.

Robustness, evolution, product improvement and retirement
Many of the parts were built by previous groups, but they didn't work according to our needs. So, we redesigned a few parts of the system to work better and more efficient. Although this design is in the design phase (as sensors need to be added to improve the navigation of the power wheel), the power wheel might start driving autonomously to test the efficiency of the system we created. Also, because a lot of attention is paid toward the function of the car, the final product is anticipated to be reliable and efficient.