Preliminary Detailed Design
Table of Contents
Team Vision for Preliminary Detailed Design Phase
- The objective of this phase to was finalize many open questions that remained for the fish.
- Questions such as, "How many pumps?", or, "How will the fish catch the object?"
- What was significant for this phase was the selection of the pump.
- With the new pump purchased and delivered to our team, we were able to successfully run the pump and gather data.
- With these conclusions, we were able to select how many pumps would be needed, which we have determined as only 1 will be required to complete all the Customer Requirements for both teams.
- Note, these were not the only questions asked, or answered.
- The Design Review should mimic the flow of how the Robofish will complete the task.
System Flow Chart
- The Flow Chart above details the process the Robofish will make to intercept the object.
- There are a few key assumptions made in this chart for simplicity.
- If the fish does not catch the object, it will assume that it has hit the bottom of the environment and will return back to home.
- The dive stick will be standing straight on the bottom of the pool, not laying on the bottom of the pool.
In this phase we started looking into the different options for cameras that could be implemented for the image processing, the two primary options were either a regular webcam, or one with a fisheye lens. In order to get a better idea of which camera is better for our system, the field of view of both were calculated. Further discussion is needed, but in terms of cost effectiveness and ease of implementation, the regular webcam appears to be the better option.
Utilizing the input from last review, the algorithm for detecting the object was modified to now identify it using color versus "teaching" the program what the diving stick looks like. The use of tracking the color allows for greater versatility of the program, because now it can track any object as long as it has been set for the appropriate color.
To determine the distance to the of the object, it was chosen to use the relative size of the known object at known distances to create an equation that when inputted the pixel width will give the relative distance of the object. This was tested with measuring the size of the object every two inches until the object was three feet away, and the given data for the current setup resulted in the equation in the graph below. When the equation was put into the program it outputted distances within two inches of the correct distance.
- Video of the program outputting distance can be seen here, and of the Raspberry Pi communicating with an Arduino can be found here
We have changed our hydraulic system to a simpler design. Instead of using a compressed air tank to force water back out of our ballast tank, we will use a series of valves that can redirect the flow from the pump. This lets us draw water from the environment to fill the ballast tank, or draw water from the ballast tank and push it back into the environment.
We ordered a pump that provides 5 L/min of flow and a max pressure of 100 psi. We were unable to create an experimental pump performance chart due to the difficulties of measuring the pressure of a diaphragm pump. However, we did measure the flow rate through one of our valves to be 2.6 L/min, which corresponds to 48 psi of pressure on the theoretical pump performance graph.
Using this initial pressure and the slope of the pump performance graph, we modelled how the ballast tank would fill over time as the air inside it was compressed. From there, we estimated velocity, depth, and the time to intercept a sinking object.
By changing the size of the ballast in the calculations above, a chart of the time needed to intercept a sinking object at two different speeds was generated. Based on this chart, we were able to determine an appropriate size for the ballast tank.
- gears not included on CAD design
Why did we choose this design?
- Easily attachable to the body of the fish
- Easy grabbing of objects
- Light weight, with intentions of 3D printing the parts
- Low drag force
- Able to pinch objects of multiple shapes
- Easy attachment of McKibbon muscles on back of jaw
RSSI was monitored for 450ms then histogram was generated.
Simulation of approaching "Home" was conducted by moving cell phone towards the beacon in constant speed. It indicates that "Home" location can be approached by using RSSI of a single Bluetooth beacon within 5 meter radius.
Bill of Material (BOM)Confirm that all expenses and contingencies are afforded by the project financial allocation.
Fish CAD Model Design
A rough CAD model was assembled to give us an idea of how big the fish body would need to be. The current design is 12" tall, 8" wide, and 20" long.
- With current testing and purchases made, these are the updated risks.
- A concern that has not been brought up as much, which will be more of a risk for MSD II, is the programming behind the scenes for the Robofish.
- Click here to view P16029 Complete Risk Sheet.
Plans for next phase
- Finalize the Bill of Materials
- Continue Pump Testing
- Order Hydraulic Connections
- Reach out to Triline for 3/8'' Valves
- Finalize the 3D Model of the Fish
- Test Buoyancy System
- 3D Print Claw Design