Generalized Constraints and Metrics with Codes and Standards

In any engineering endeavor, more than context to the problem is needed before a solution can start being drafted. Constraints are limits, often defined by the clients and future users, that restrict aspects of the design. These restrictions can set both maximum tolerances, minimum performance levels, and more; constraints must all be satisfied for the solution to work. On the other hand, metrics are additional parameters that help designers gauge how effective their solutions are. While it is not essential to meet every metric, an ideal solution would surpass many metrics set by the engineers. Similar to constraints, codes are widely accepted sets of rules and guidelines that describe what engineers must do for a given endeavor. While not intrinsically legally binding, they are set to improve safety, quality, and other industry practices. Standards supplement codes by defining specifically how to execute codes. These include documents for any required products, practices, methods, or operations and also help reduce production costs by building a standardized foundation for solution architects to build off of.

For a more detailed analysis of these metrics and constraints from an engineering perspective, see our Technical Specifications Report.

Constraints

  • Able to transition from a fluid environment to a surface environment in under 30 seconds (assuming dirt or hard transition surfaces)
  • No longer than 6 ft and no wider than 3 ft
  • Weighs less than 400 lbs
  • Able to withstand a depth of up to 10 ft for 1 hr
  • Able to cross a 12-inch gap
  • Able to move up a 60º incline
  • Can operate remotely without charging for 2 hours

Metrics

  • Able to withstand a depth of 25 ft for 30 minutes
  • Able to cross a 2 ft gap
  • Can move up and down steps
  • Can operate without charging for 5 hours
  • Can store up 0.75 cubic feet of material and supplies
  • Can move up to 6 mph on land
  • Can move up to 4 knots when submerged in water
  • Able to flip itself over in under 60 seconds

Specifically with respect to our desired minimum viable product design, we have identified the following categories of metrics and constraints, as well as our intent to either maximize or minimize them where applicable:

Global:

  • Weight of Robot (goal: minimize)
  • Main Body Size (Envelope l,w,h)
  • Overall size (Envelope l,w,h)

Land Movement:

  • Wheel
    • Diameter
    • Width
    • Tread specifications
  • Extended leg length 
  • Minimum ground clearance (maximize)
  • Leg degrees of freedom (minimize)
    • minimum 2 (3 including rotation of wheels)
  • Minimum wheeled speed (maximize)
    • Over smooth terrain
    • Over rough terrain
  • Minimum track speed (maximize)
    • Over smooth terrain
    • Over rough terrain

Water Movement:

  • Velocity (maximize)
    • Acceleration Rate
    • Translational (Up/down, Left/Right, Forward Backward)
    • Angular (Pitch, Yaw, Roll)
  • Propeller Angular Speed
  • Internal Drag (minimize)
    • Friction across propeller/pump
  • Displacement/Length Ratio
  • Ballast/Displacement Ratio
  • Buoyancy 
    • Vertical surface speed
  • Dive Depth (maximize)
  • Pump Efficiency (maximize)
  • Jet Outlet Range of Motion (maximize)
  • Outlet to Outlet Distance
  • Overall Coefficient of Drag (minimize)

Transitioning:

  • Transitioning Time (minimize)
    • Land to Water Transition:
    • Water to Land Transition:
  • Distance from land in water to begin transitioning
  • Distance from water in land to begin transitioning
  • Max Leg Extension:
  • Min Leg Extension:

Many have been left without specific associated values in an effort to avoid unnecessary and premature conjecture in these areas. We fully expect to gain an improved understanding of these areas and what values would be reasonable as we progress in our design efforts.

Codes & Standards

The design process can be difficult without somewhere to start.  Codes and standards will give us some relevant design metrics as well as keep us safe while working. As discussed earlier, standards supplement codes, which set safety, quality, and other industry practices, by defining specifically how to execute codes. One standard we have thoroughly investigated includes the IEC 60529 Ed. 2.2 2013 standard, which outlines the guidelines for determining the Ingress Protection (IP) rating and the differences between different ratings. Learn here about how we will apply this standard to our robot and the resulting constraints and metrics we have derived as a result of our investigation into this document.

Other codes and standards we intend to use to inform general decisions for our robot can be found below. Function and system-specific codes and standards can be found on their relevant sub-pages

  • Lafayette ME Safety Rules & Procedures
    • During working hours of the machine shop and project rooms, students are expected to follow certain rules to avoid any accidents.  These include not being impaired (alcohol, drugs, exhaustion, etc.), consulting with technicians before machining, proper dress code (safety glasses, long pants, etc.), and many standard operating procedures for the individual machines.  These rules also cover emergency incident procedures, prototype testing, and disposal of hazardous materials.  See safety for what HARRT is specifically doing to keep ourselves and others safe while innovating.
  • OSHA Robotics Standards
    • While OSHA has no specific standards for robotics, there are many that pertain to the field.  These include outlining methods of safeguarding robotic systems, methods to test robots, risk assessment, safety especially pertaining to robots that will be brought to market, and more.
  • Osha Instruction: Guidelines for Robotics Safety
    • An OSHA code of particular interest to us, this standard describes how robots and robotic systems should be safely operated.  This includes construction, reconstruction, modification, safeguarding, care, testing, start-up, and more.
  • List of Machine Safety Standards
    • Machine Safety Specialists have compiled a long list of standards, many of which will be relevant to our project.  ANSI covers safety standards and technical reports, OSHA appears again with more safety, and IEC and ISO is involved in international safety standards.
  • IP Rating Chart
    • The IP Standard rates how protective mechanical cases and electrical closures are against a few different hazards like dust and water.  Since our robot will be operated on land and submerged in water, it may be necessary to find products like wiring and batteries that are rated for safety in these environments.  This chart will be an easy way of knowing what products are better suited for our project. While we go into more detail here about how we will use this standard, this link is a useful tool to quickly learn a bit more about this standard.