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# Preliminary Detailed Design

Overview:

## Team Vision for Preliminary Detailed Design Phase

The objective of the Preliminary Detailed Design Phase was to take the narrowed concept selection from the Problem Definition Phase and refine it even further to a specific design we want to pursue. During this phase, subsystems were identified and group members were assigned to each based on their expertise (mechanical, electrical and design).

Items that were accomplished:

• Developed proof of concept for designs (Ex. lead screw mechanism and Bluetooth communication)
• Established contacts with sailors with disabilities and other accessible sailing programs
• Developed test plans and set an agenda for prototyping and testing during the Detailed Design Phase
• Created drawings, CAD and took video of working components
• Pitched our SailBot project in Tiger Tank and sent financial proposals to additional prospective sponsors
• Visited Rochester Yacht Club to measure their boats and see the facilities we may use for testing

## Feasibility, Proof of Concept and Analysis

In depth analysis was performed through proof of concept and feasibility calculations in order to refine and ultimately decide on a system design that will function and meet all engineering and customer requirements. These calculations have been, and will continue to be referenced when purchasing materials in order to ensure its specifications match our needs. Feasibility was done through prototyping, and calculations. Most of the electrical sections required proof of concept, and therefore was completed through prototypes. Mechanical was done mostly through calculations to determine the best numerical concepts.

Mechanical Feasibility:

The two mechanical options to choose from were Lead Screw and Gear option.

Concept Sketch of Gear and Lead Screw Option

The deciding factors would be based on how fast each system could move the tiller, how expensive the system would be to make, and how much space would it take on the boat. To numerically ran these options, the following steps had to be done:

1. Calculate gear ratios to satisfy required torque on tiller
1. Calculate torque on tiller
2. Calculate speed of tiller to turn from fully starboard to fully port at desired ratios
3. Find gears and gear prices to satisfy ratios

Torque on Tiller:

The formula to calculate the torque on the tiller is:

T  = w * h * [(0.4 * w)-c] *v2 * k * B

w - width of rudder = 0.43 m

h - height of rudder = 1 m

c - distance from turn center to end = 0 m

v - speed in knots = 20 knots

k - coefficient of turning angle = 10.84

B - Boat correction factor = 0.5

With the following numbers, the maximum Torque on the tiller is 375 Nm. Since a Boat sailing at a Broad reach can sail faster than the true wind speed, that boat speed was slightly increased to 20 knots to compensate. The turning angle was set to the maximum turning angle to accommodate extreme cases. our device will be limited to +-40 degrees instead of the full +-80 degrees. SailBot will be designed to work under 400 Nm for an extra factor of safety.

Speed To Turn:

An Excel document was created to calculate how fast each method would be able to turn the tiller at max force.

Summary of Tiller control calculations

Based on the calculations, The gear method would allow for a faster turning speed. In addition, the lead screw length would have to be 1.5m long which would exceed the distance of the boat. The lead screw would also require gearing to increase the speed of the motor. The Gear option appeared as the more ideal choice. However, achieving a 220:1 gear ration was significantly more expensive than a lead screw.

The lead screw method was redesigned to address some of the issues that came with this method.

A linkage was used to allow SailBot to mount in the stern of the boat (where no one sits) and use a smaller travel. With this reduced travel, the lead screw ration decreased to have the ability to direct drive off a motor.

Calculations for new lead screw method

The new method reduced the size of the lead screw became 26 cm which fits well inside the back of the boat. The force on the Lead Screw increased to 2.2 kN, but the lead screw is rated for 5.3 kN and therefore still satisfactory. Since the rpm of the lead screw was decreased, SailBot was able to reduce the torque on the motor to 0.5 N for a better Power efficiency. The new gear ratio would be 3:1 which can easily be done with \$10 spur gears.

Calculations with better Motor efficiency

With the Tiller control selection, SailBot can start developing a CAD model in addition to a tiller attachment method. The mechanical team will work on these two projects as well as building a test rig for the new design phase.

#### Electrical Prototyping:

From the engineering requirements defined previously tasks were developed which are listed as follows:

1. Read Analog & Digital Inputs
2. Produce PWM & Digital Outputs
3. Wireless Communications
4. Wireless Control
5. Wireless Feedback
6. Discrete Override Control

Prototypes were developed to accomplish the required task functionality for SailBot. Each of the diagrams displayed herein show the flow of the code for each of the prototypes.

Prototype Stage 1 - Servo Control

Single Arduino reads potentiometer value, converts to servo angle, and outputs to servo

Prototype Stage 2 - Wireless Control

Master Arduino reads potentiometer value and converts to servo angle, then transmits wirelessly

Slave Arduino receives servo angle and outputs to servo

Video of Prototype 2

Prototype Stage 3 - Wireless Feedback

Master Arduino reads button press and transmits wirelessly

Slave Arduino receives button press and controls LED

Video of Prototype 3

Prototype Stage 4 - Discrete Override

Single Arduino reads joystick value if override button is pressed or potentiometer value if not, then converts the selected input value to servo angle and outputs to servo

Video of Prototype 4

User Interface

Concept 1: Utilize suction cups to attach the controls to the side of the boat (shown below)

Concept 2: Attach a swing arm to the side behind the benches that will swing around in front of the sailor. Able to be adjusted to desired height and exact position.

Concept 3: Attach a table stand to the bottom of the boat so the controls will be set in front of the sailor.

Concept 4: This box will be placed on the sailor's lap. There will be an option to tip the interface up like a laptop for users who cannot move their head. This concept is currently the favorite and will pursued in the Detailed Design Phase.

## Bill of Material (BOM)

The BOM document is linked here.

## Test Plans

Initial test plans for SailBot subsystems were created for demonstrating functionality while considering all associated risks. The ISO Wheel Chair Control and IEEE Standards have been found to correlate with our design. These will be researched in the Detailed Design Phase and additional test plans will be made to satisfy their requirements.

Force Test

• Purpose: to simulate forces of water acting on tiller

• Related Risks: 5, 6, 10, 12, 15

• Materials needed (besides SailBot)

• Force Gauge

• Spring

• Wooden model of sonar back half

• Tiller

• Timer

• Systems that must be completed to perform test

• SailBot Tiller movement

• SailBot Electrics (motor)

• No need for wireless communication or controller

• Basic Procedure

• Hook up spring to tiller.

• Turn SailBot all the way to port (record turning time)

• Ensure correct force (400 Nm) to simulate water

• Hold for 10 second

• Turn SailBot all the way to Stbd (record turning time)

• Ensure correct force (400 Nm) to simulate water

• Hold for 10 second

• Estimated time: 30 seconds

• Number of times to repeat: 20

• Total time required: 10 minutes

• Alternative versions to test

• Have SailBot say on one side based off gearing- requires no motor control

Battery Life Test

• Purpose: Ensure that SailBot can last a two hour session. This includes battery, motor, and mechanical life

• Estimated time: 2 hours

• Number of times to repeat: 3

• Total time required: 6 hours

• Related Risks: 8, 13, 15

• Material needed (besides SailBot):

• Battery

• Oscilloscope or Voltmeter

• Equivalent load to motor at max torque

• Systems on SailBot that must get done:

• Arduino Motor Control

• Motor selected

• Basic Procedure:

• Connect battery to equivalent load.

• Run test for 2 hours.

• Measure the voltage/current level of the battery every 15 minutes or continuously if possible

• Stop test when motor stops moving or at 2 hours

• Calculated battery life based the voltage/current drop

• Alternate versions of procedure:

• Use a battery life calculation based on the load amperage

• Test just battery or just mechanical components

Water Test

• Purpose: Ensure water resistance

• Estimated time: 2 minutes

• Number of times to repeat: 3

• Total time required: 6 minutes

• Related Risks: 3, 6

• Material needed (besides SailBot):

• Spray bottle filled with water

• Systems on SailBot that must get done:

• SailBot electronics enclosure

• SailBot carrying case

• SailBot user controls

• Basic Procedure:

• Spray the SailBot carrying case and electronics enclosure with water, enough to saturate all exposed surfaces.

• Open the case and ensure all components are dry inside

• Spray the user controls with water

• Connect the user controls and ensure they function correctly by steering to port and starboard

• Alternate versions of procedure:

• Repeat with all user control methods

Emergency Override tests

• Purpose: Ensure that emergency release works correctly always

• Estimated time: 2 minutes

• Number of times to repeat: 3

• Total time required: 6 minutes

• Related Risks: 22

• Material needed (besides SailBot):

• Systems on SailBot that must get done:

• Emergency override

• SailBot tiller attachment

• Basic Procedure:

• Connect SailBot to the tiller

• Move the tiller all the way to port

• Employ the emergency quick release and ensure the tiller can be fully used manually without SailBot

• Reconnect SailBot and move the tiller all the way to starboard

• Again, employ the emergency quick release and ensure the tiller can be fully used manually without SailBot

• Repeat a third time, this time starting with the tiller at canter

General Use Test

• Purpose: Ensure SailBot functions correctly as a unit (without need for overrides)

• Estimated time: 30 seconds

• Number of times to repeat: 3 (with each user control method)

• Total time required: 1.5 minutes (per method)

• Related Risks: 10, 11, 12, 15

• Material needed (besides SailBot):

• Stopwatch

• Systems on SailBot that must get done:

• SailBot tiller attachment

• SailBot electronics

• Wireless communication with user controls

• Basic Procedure:

• Hook up SailBot to the tiller

• Connect the first user input method

• Turn SailBot all the way to port (record turning time for reference)

• Let go of SailBot and ensure it returns to center with no applied user input

• Turn SailBot all the way to starboard (record turning time for reference)

• Let go of SailBot and ensure it returns to center with no applied user input

• Alternate versions of procedure:

• Repeat the same procedure using each of the different control methods

• Test SailBot in varying weather conditions

User Test

• Purpose: Ensure controls are comfortable and easy to use, SailBot clearly displays its information

• Estimated time: 30 seconds

• Number of times to repeat: 3 (with each user control method)

• Total time required: 1.5 minutes (per method)

• Related Risks: 9, 14, 17, 21

• Material needed (besides SailBot):

• Systems on SailBot that must get done:

• All user input controls

• Wireless communication with user controls

• Basic Procedure:

• Connect the first user control method to SailBot

• Confirm that the battery life is clearly displayed

• Confirm that the race clock/timer is clearly displayed

• Have the user steer to port, back to center and to starboard

• Confirm that the tiller direction feedback displays the correct direction for each position

• Ask the user to rate their comfort level and the ease of use

• Alternate versions of procedure:

• Repeat the same procedure using each of the different control methods

## Risk Assessment

Given our customer and engineering requirements, a list of potential risks was developed and ranked by importance with respect to the project goals. Updates to the list have been made based on discussions with the customer and the system design that was decided on. At the end of this Preliminary Design Phase, our main risk concern continues to be with receiving sufficient funding. The next highest risks have shifted to the safety and technical concerns for parts and electronics with durability and specifications that match our requirements.

Risk 2 was deleted because we have solidified our communication with Rochester Yacht club and have guaranteed use of their facilities. The water resource is secure, but the time to test remains and is included into risk 1. Risk 16 was also deleted because whether or not an individual has experience sailing should not impact their ability to use SailBot since it is a unique control method.

Risks 21 and 22 were added during this phase. Having enough control methods to accommodate the maximum number of sailors possible is one of the main customer requirements. Having an emergency override which can be used to completely disengage SailBot in an emergency situation is critical to maintaining the safety of all sailors in situations where SailBot is not needed or is inhibiting complete control over the sailboat.

## Plans for next phase

During the next phase, Detailed Design, we hope to finalize our system design and all of the preliminary documentation defining our project requirements, goals, risks, finances, and material needs.

• Finalize drawings, schematics and proof of concept for all subsystems
• Obtain responses from most, if not all, companies we have contacted about financial assistance and rework our budget based on the amounts received.
• Research and understand the ISO Wheel Chair Control and IEEE Standards. Implement them into our design and test plans.
• Finalize BOM and confirm that it coincides with the budget
• Finalize test plans for MSDll and discuss what needs to be accomplished, if anything, over break before the start of the spring semester

Below are the three-week plans for each individual team member of the next phase:

Amit Rogel

Matthew Miller

Max Messie

Mike Robinson

Thomas Davis

Erica Kabat

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