For a complete overview of the 2.007 course and the 2.70 contest, check out the home page.
Definition
- Strategy
My strategy is basically offensive and was to design a vehicle that could quickly climb the back shelf and gather the balls into a bag.
I would then drive off of the shelf and remove the balls thus reducing my score.
I would do this by building big wheels to give high speed, ball clearance and an easy means of driving onto the 2" back shelf.
Also, I would put a spinning reel on the front of the machine to feed the balls under the chassis and into a bag.
There are a couple of reasons I decided to use a bag:
- A rigid container can only have a volume that will fit in the size constraint where as a bag can be folded up until it is needed and thus can have a larger overall volume.
- If I put the balls in the bag then not only can I remove them from the shelf but I can also take them with me to the other side if time allows me to add more to my strategy.
- Functional Requirements
In order for my machine to function, some requirements must be met.
These requirements can be divided up into two categories, strong and weak.
- Strong
- Wheels must be large enough so that balls can pass underneath the chassis.
- The opening of the bag must be large enough for balls to pass into it.
- The frame for the bag opening must not interfere with the machines maneuverability.
- The real must provide enough force so as to accelerate the balls to a velocity where they will not have any problem rolling into the acquisition bag.
- Weak
- Machines ability to climb over center barrier.
- Ease of construction.
- Defense against opponent.
- Look Cool.
- Strong
- Dominant Physics How much energy is required to get the machine onto the back shelf? (Mass of Machine)*(Height of Shelf)*(Gravity) + (Force to move machine translationally) * (Distance the Machine moves) = Total Energy Required to get onto Back Shelf. How much energy is required to get one ball over the frame and into the bag? (Mass of Ball)*(Thickness of Frame)*(Gravity) = Energy to get Ball into Bag. The energy that the balls use to get into the back comes from their velocity relative to the frame. If, for example the machine as a whole is not moving, all of this energy must come from the spinning reel. The reel may also have to handle more than one ball at a time so let's find the energy required at an instant in time. (Energy to get Ball into Bag) = (.5)*(Mass of Ball)*(Velocity of Ball) (Energy to get Ball into Bag)*(Number of Balls in contact with Reel) = (Total Energy Reel must be able to Supply) How much energy is required to get the machine off the back shelf? (Force to move machine translationally)*(Distance the Machine moves) - (Mass of Machine)*(Height of Shelf)*(Gravity) + (Mass of Balls)*(Number of Balls in Bag)*(Gravity)*(Coefficient of Friction between bag and table) = Total Energy Required to get off of Back Shelf.
- Schedule
It is important to develop a schedule for production and testing of your machine. Here is my schedule:
March 18th Make Wheels 19th Mount Bosch Motors Mount Front Wheels Start Making Rear Wheel Mounts 20th Finish Rear Wheel Mounts Mount Rear Wheels Test Clearance 21st Begin making Reel April 1st Finish Making Reel Make Reel Mounts and Bushings 2nd Make Net Frame Make Pneumatic Mount 3rd Mount Frame and Pneumatic Test Pneumatic Assembly Make Pulley for DC Motor Mount DC Motor 4th Make Drive Belt for Reel Make Net for Balls Final Assembly 8th Wire Motors Hose Pneumatics Put Wires into Quick Attachment Harness Wires and Hoses
Of course, this was an ideal schedule and if everything would have gone as planned, I would have had almost a full month to practice driving and add components to my strategy. However, things take longer than you think and MIT wears you down and messes with your schedule so, I did not add anything to my strategy and I ended up with only about a weeks worth of practice time. - Resources
There were many resources available to me for this contest.
- Machines and machinists in the shop.
- Professors and UA's to answer questions.
- Computer programs to analyze and design.
- Instructional lectures and handouts.
- My peers
Development, Prototypes and Testing
- Concept Drawings
I made many drawings and sketches of my ideas.
Here are some pictures of drawings I made for earlier ideas and for my final one.
- Sketch Models I also made a sketch model of my first design which quickly helped me realize that this was not a good design. After that I turned to this design but I did not have time to make a sketch model.
- Bench Level Prototypes (BLPs)/Concept Selection
In order to further develop my concept I made a working bench level prototype using plywood as my chassis. I tested the machines ability to climb the back shelf and found that I must put the power wheels on the back of the machine (rear wheel drive). I also found ways to save space and by using the plywood first I did not make any mistakes on, or have any extra holes in my Lexan sheet. Here is a picture of my final chassis (Lexan) against my original, BLP chassis (plywood).
- Hardware and Manufacturing Assessment/Schedule Update
At this point in the process, I took a look and the hardware and I had to work with and made sure that my concept was feasible.
I also tried to take a look at how long it would take to make each of the required parts and from there I updated my schedule.
Here is a table showing a list of parts as well as an estimated time to make each one.
Part Time (Hours) Wheels 3 Rear Wheel Mounts 1 Reel 4 Net Frame 1 Pneumatic Mount 1 DC Pulley .5 Reel Drive Belt .5 Net for Balls 1
Embodiment and Detail
- Detailed Layout Drawings I then drew final isometric drawings of my machine and it's parts. From these drawings I manufactured all of my parts and assembled my machine.
- Hardware and Manufacturing Assessment/Schedule Update Again, I took a look at the hardware I had to work with and reassured myself of the concept. I then updated my parts list and time estimation and from that I again updated my schedule.
