Great end to 2015

This fall we attended 3 off season events; the Battle O’Baltimore, Girl Power and Rumble in the Roads. Our alliances placed 6th, 1st and 2nd at the three events which resulted in two additional trophies for the team.  As per tradition (a tradition we started this season) we are presenting the school with our trophies.

award 1 award 2

Thanks for all of your support Dr. Goodwin and all the Walt Whitman Staff for helping our team have its most successful season ever.

Strategy Selection

Every game has rules, and in early January thousands of FRC teams around the world get see the rules for the new game and kick off their season. But before you dig in to the rules and get going your needs to do two very important things. Set goals and identify the team’s realistic capabilities.

 

Create Team Goals for the Season

Your team needs to know what is trying to accomplish as a team. Are you trying to inspire the most kids, teach kids how to try or win an event. All of these goals should be documented so that the team can use them to drive priorities during the strategy discussion. Here are some examples of competition goals that will have a big impact on your strategy.

  • Make it to elimination as a 2nd pick at districts
  • Make it to elimination as a 1st pick at districts
  • Make it to elimination as an alliance captain at districts
  • Make it to elimination as a 2nd pick at super regional
  • Make it to elimination as a 1st pick at super regional
  • Make it to elimination as an alliance captain at super regional
  • Make it to elimination as a 2nd pick in a CMP division
  • Make it to elimination as a 1st pick in a CMP division
  • Make it to elimination as an alliance captain in a CMP division
  • Win a district event
  • Win two district events
  • Win a super regional
  • Win a CMP division
  • Win CMP

Here are some examples of team goals that will have a big impact on your strategy:

  • Build 1 robot
  • Build 1.5 robots
  • Build 2 robots
  • Build 3+ robots
  • Robot needs to fit easily into a mini van

 

Identify your Strengths & Weaknesses

Every team has limitation has strengths and weaknesses that need to be well understood to make good decisions about strategy. We really recommend teams use the SWOT tool break down the team and its resources prior to kickoff every year so that the team can select a strategy that has a high chance of being realized. SWOT stands for Strength, Weakness, Opportunities and Threats. You can learn how to use the SWOT tool here. Let’s walk through an example SWOT analysis so we can demonstrate how it impacts strategy selection.

  • Strengths
    • Have and know how to use drill press
    • Have and know how to use band saw
    • Have and know how to use a variety of hand tools
    • Know how to CAD and have 1 robot’s worth of experience
    • Have $6,000 to spend on a robot
    • Have 2 very good technical mentors
  • Weaknesses
    • Do not have access to CNC mill
    • Do not have access to lathe
    • Do not have access to supplier who can do sheet metal
    • Do not have access to supplier who can weld
    • Can locate drill and cut features within .2 by hand
    • Have not done CAD during a build season
    • Will only be able to get into workshop 2 times a week for 3 hours a piece
    • Have a student to mentor ratio of 20:1
    • Team has not used pneumatics on several years
  • Opportunities
    • Maximize use of versa frame
    • Pre-select and pre-order parts for drive train
    • Standerdize fasteners
    • Standerdize motor controllers
    • Use pneumatics to keep weight low
    • Be very organized and maximize limited lab time
    • We may get additional mentors
  • Threats
    • Versa frame is heavy
    • Versa frame is expensive
    • Snow days – last year the team had 6
    • School usage costs could go up
    • Several sub team’s have members with low attendance

 

Read the Rules

  • READ THE RULES!!!!!
  • Understand how teams will be measured at competition
  • Understand how teams will advance
  • Understand limitations defined in the rules

 

Break the game down

  • Identify every way to get points
    • In 2015 we had the periodic of the stack
      • 64NrPJU
      • This was a great example of all of the possible ways to score. The same needs to be created for each year’s game
  • Identify every way to win
    • Start running game simulations in your head or on the board to create scoring scoring solutions
    • Watch the 3 day builds
    • Read chief delphi to see if you missed any and then add them to the list
  • Identify the every type of robot task needed to get every point and execute every way to win
    • List all of the the ways a robot could play the game during auton.
    • List all of the the ways a robot could play the game during teleop.
    • List all of the the ways a robot could play the game during coopertition.
  • Identify what percentage of teams at a district, regional, CMP division, CMP championships will be able to perform each capability
    • We use the common, uncommon, rare or impossible method. Refer to your team’s goals for which level you do this for. The numbers below are for a regional. The should change based on the event type and level.
      • Common 25-50 teams could do it
      • Uncommon 10-25 could do it.
      • Rare 2-10 team could do it
      • Impossible 1-2 teams could do it.
  • List everything your team could do based on its SWOT
  • Go through and pick which strategies your team should design for
    • For most teams limit yourselves to 1 rare or 2 uncommon or 3 commons
  • Start brain storming ways to make your strategy a reality
  • List all of the mechanisms you need
    • Looked at past robots
  • Put together a baseline solution based on your team’s risk level

 

Sub Pages

 

Additional Resources

 

Loads and Free Body Diagrams

Understanding what loads are and how they are transferred from each component of the robot down to the ground will go a long way to increasing your understanding of how to design structural and mechanical systems. Here is a quick primer on loads and visualizing them via free body diagrams.

 

Newton’s 1st Law

An object in motion stays in motion in a straight line, unless acted upon by unbalanced force. A push or pull will cause object to speed up, slow down, or change direction.

force 1

Basically, objects just keep on doing whatever they are doing unless they are acted upon by an unbalanced force.

  • Ketchup stays in the bottom (at rest) until you bang (outside force) on the end of the bottom.
  • A headrest in a car prevents whiplash injuries during a rear-end collision ( your head goes forward and then jerks backward).
  • Animation 1 – ladder truck
  • Animation 2 – no seatbelt

 

Load Types

 

Free-body Diagram: Single Body

Free-body diagrams are used to show the relative magnitude and direction of all forces acting on an object.

force 2

This diagram above shows four forces acting upon an object. There aren’t always four forces, For example, there could be one, two, or three forces. If a block is at rest on a table top. Here is the diagram of the forces acting on the block.

force 3

In this diagram above, there are normal and gravitational forces on the block. Below a block is free-falling in a vacuum. Neglecting air resistance, below is the free-body diagram showing the forces involved.

force 4

In this diagram above, gravity is the only force acting on the block. Below a block is free-falling from a tree to the ground at constant velocity. Considering air resistance, below is the free body diagram for this situation.

force 5

In this diagram above, gravity pulls down on the block while air resistance pushes up on the block as it falls through air. Below a rightward force is applied to a block in order to move it across a desk. Considering frictional forces and neglecting air resistance, below is the free-body diagram.

force 6

In this diagram above, the applied force arrow points to the right. Notice how friction force points in the opposite direction. Finally, there is still gravity and normal forces involved. Below a block is descending with a constant velocity. Considering air resistance, below is the free-body diagram.

force 7

In this diagram above, gravity pulls down on the block, while air resistance pushes up as the block falls. Below a block is dragged across loosely packed snow with a rightward acceleration. below is the free-body diagram.

force 8

The rightward force arrow points to the right. Friction slows the blocks progress and pulls in the opposite direction. Normal forces still apply as does gravitational force since we are on planet Earth. Below is a block moving upwards toward its peak after having been launched into the air. Neglecting air resistance, below is the free-body diagram.

force 9

In this diagram above, the force of gravity is the only force described. Below a block rolls down hill.

force 10

In this diagram above, the lock is coasting down the hill, there is still the dragging friction of the road (left pointing arrow) as well as gravity and normal forces. Now let’s take a look at what happens when unbalanced forces do not become completely balanced (or cancelled) by other individual forces. An unbalanced forces exists when the vertical and horizontal forces do not cancel each other out. Below, notice the upward force of 1200 Neutons (N) is more than gravity (800 N). The net force is 400 N up.

force 11

Below, notice that while the normal force and gravitation forces are balanced (each are 50 N) the force of friction results in unbalanced force on the horizontal axis. The net force is 20 N left.

force 12

Another way to look at balances and unbalanced forces.

force 13

Balanced

force 14

Unbalanced

force 15force 16

Free-body Diagram:2 dimension examples

FB 1 FB 2 FB 3 FB 4

 

Free-body Diagram:3 dimension examples

FB 5

 

 

 

Load Cases

A load case is a combination of different types of loads with safety factors applied to them. A structure is checked for strength and serviceability against all the load cases it is likely to experience during its lifetime.

Typical load cases for design for strength (ultimate load cases; ULS) are:

1.2 x Dead Load + 1.6 x Live Load
1.2 x Dead Load + 1.2 x Live Load + 1.2 x Wind Load

A typical load case for design for serviceability (characteristic load cases; SLS) is:

1.0 x Dead Load + 1.0 x Live Load

Different load cases would be used for different loading conditions. For example, in the case of design for fire a load case of 1.0 x Dead Load + 0.8 x Live Load may be used, as it is reasonable to assume everyone has left the building if there is a fire.

In multi-story buildings it is normal to reduce the total live load depending on the number of stories being supported, as the probability of maximum load being applied to all floors simultaneously is negligibly small.

It is not uncommon for large buildings to require hundreds of different load cases to be considered in the design.

 

Additional references

Equations of Motion

We are starting a collection of equations, white papers and calculators that team’s can use to build better systems and robots. Please feel free to recommend something we should add.

Forces

  • force force
  • mass mass
  • accelerationacceleration

 

Equations & Calculators

 

Additional Resources

Welding Fasteners and Adhesives

A joint is a junction where structural elements meet without applying a static load from one element to another. When one or more of these vertical or horizontal elements that meet are required by the design to have be fixed

Permanent fixed joint – joints that can not easily come apart. Permanent fixed joints should be used when the detail parts or assemblies being joined have low or no repairability requirements.

  • Welding
    • Useful method of joining materials
    • Strong joint if welded properly
    • Joint is susceptible to fatigue failure, so make sure the material is think enough to withstand the number of cycles you are expecting
      • A cycle could be something like there will be 40 joint flexures per match, the team expect 100 matches so make sure the joint could withstand 40 x 100 x 2.5 = 1,000 or 10^3 joint flexures for the season
      • Weld fatigue life calculator
    • Only weld in properly set up designated areas with a trained professional while wearing the correct safety gear
  • Adhesive
  • Rivets
  • Mortis & Tenon
    • Use only if fabricating robot parts with wood

 

Temporary fixed joint – joints that can easily come apart. Temporary fixed joints should be used when the detail parts or assemblies being joined have high or mandatory repairability requirements.

  • Bolts & Nuts

    • FRC team should standardizing parts to reduce the number of tools needed, to reduce confusion, speed up repair times and reduce weight. Here are the bolts we recommend;
      • 8-32
        • Use socket head for FRC application
        • Come with protruding and flush head configuration
      • 10-32
        • Use socket head for FRC application
        • Come with protruding and flush head configuration
      • 1/4-20
        • Heavy weight steel fastener that is very strong
        • Use only when absolutely necessary
        • Use socket head for FRC application
        • Come with protruding and flush head configuration
    • Bolt size selection guide
    • Nuts
  • Screws
  • Pins

 

Additional Resources

 

Structural Systems

Two major systems of every robot on the planet are the structures and mechanical systems. Structural systems allow the machines and buildings to hold themselves together and up off of the ground. Listed below are some of the more common structural systems that teams use in FRC.

Structures

In FRC there are two major off the shelf structural systems; versa frame and aluminum slotted framing. Many teams will use one or both of these structural systems because they require a minimum amount of fabrication knowledge and access to tools. Here are some details about each of these basic structural systems;

  • Versa frame
    • Versa frame comes pre-drilled 5/32 holes
    • Versa frame comes in a variety of shapes and lengths
    • Versa frame has a wide variety of brackets to allow for joining pieces
    • Versa frame has scribe lines to help with drilling additional holes on center
    • Versa frame can easily be pared with West Coast Drive mechanical system components
    • Versa frame can easily be paired with Vex Pro mechanical system components
    • Versa frame is moderately expensive
    • Versa frame is heavy
      • Team’s can drill lightening holes in 1″ x 2″ frame components
  • Aluminum slotted framing (referred to as 80/20)
    • Slotted frame comes formed with a variety of profiles
      • Profiles are the cross section of the extrusion
    • Slotted frame profiles work with a variety of fasteners
    • Slotted frame has a wide variety of brackets to allow for joining pieces
    • Slotted frame has scribe lines to help with drilling additional holes on center
    • Slotted frame can easily be pared with 80/20 mechanical system components
    • Slotted frame is heavy

 

All of the other structural systems should be considered custom solutions. Custom solutions may require more in house fabrication skill and knowledge than most teams have. They may also require some specialized tooling. Here are some of the more popular custom solutions in FRC;

  • Fastened or welded tube
    • Square tube (tube with no pre drilled holes)
      square

      • Weight based on material
        • Carbon tubes – light
        • Fiber glass tubes – light
        • Aluminum tubes – moderately heavy
      • Easy to work with
      • Lots of standardized brackets available
      • Need to be able to precisely drill holes
      • Can be welded or joined mechanically
    • Rectangular tube (tube with no pre drilled holes)
      rectanle

      • Weight based on material
        • Carbon tubes – light
        • Fiber glass tubes – light
        • Aluminum tubes – moderately heavy
      • Easy to work with
      • Lots of standardized brackets available
      • Need to be able to precisely drill holes
      • Lightening patterns can be custom machined
      • Can be welded or joined mechanically
    • Circular tube
      round tube

      • Weight based on material
        • Carbon tubes – light
        • Fiber glass tubes – light
        • PVC tube – heavy
        • Copper tube – heavy
        • Aluminum tubes – moderately heavy
      • Need special tools for bending
      • Need special tools for crimping
      • Moderately hard to source brackets
      • Can be welded or joined mechanically
      • Need radius blocks for fastening
      • Need to be able to precisely drill holes
        • Some suppliers do have tube with pre drilled holes available
  • Bent sheet metal
    sheetmetal

    • Usually joined with rivets and bolts
    • Light weight
    • Need to create CAD
    • Need to be able to create flat patterns
    • Need to be able to manage CAM package
    • Need to be able to precisely drill holes
    • Need to be able to cut sheet metal precisely
    • Need to be able to bend sheet metal precisely
    • Need to be able to accommodate spring back
  • Machined sheet or block
    • If metal usually joined with rivets and bolts
      machined

      • Light weight
      • Need to create CAD
      • Need to be able to manage CAM package
      • Need to be able to precisely drill holes
      • Need to be able to cut metal precisely
      • Need access to vertical mill or CNC router
    • If wood usually joined with mortise joint and glue
      wood

      • Light weight
      • Easy to work with
      • Need to create CAD
      • Need to be able to manage CAM package
      • Need to be able to precisely drill holes
      • Need to be able to cut wood precisely
      • Need access to vertical mill, CNC router or laser
      • Need to be able to clamp and glue wood precisely
  • 3D printing
    3dprint

    • Light weight
    • Need to create CAD
    • Need to be able to manage CAM package
    • Need to be able to model supports

 

Fixed Joints

To avoid high material costs and the need for large scale 5-axis CNC mills most teams will need to design their structure so that it can be easily manufactured with the tools or sponsors they have. This usually results in a structural system that will require many fixed joints. Fixed joins are joints that resist motion along and around all three axis. Check out our page on free body diagrams to learn more about how motion along and around all three axis can be understood. And then check out the page on welding, fasteners and adhesives to lean more about how to create a light weight fixed joint.

 

Structural System Design

Structural Systems need to be able to withstand the expected structural loads over an expected number of cycles. Teams will need to follow these steps necessary to design their structural system.

  1. Sketch out a idea
  2. Build prototypes
  3. Refine the sketch
  4. Refine the prototype
  5. Create a free body diagram
  6. Understand the loads
    1. Understand ultimate load case for each type of loading
    2. Understand the number of cycles for each load case
    3. Do the math
  7. Select materials that can resist the loads
  8. Define the shape that will resist fatigue and is manufacturable

Note – steps 3 and 4 may need to be repeated many times to find the right combination to reduce weight and fabrication complexity

 

Additional Resources

 

Mechanical Systems

Two major systems of every robot on the planet are the structural systems and mechanical systems. Mechanical systems allow some or all of the robot to move. Before we get into how to design a mechanical system we are going to go through all of the things FRC, FTC and Vex robots have been asked to do over the years.

Tasks in FRC

 

Tasks Unique to FTC or Vex

When you are doing research look up the past games to get an idea of what the various types of tasks were and what the game pieces looked like. Next we will go through some of the popular mechanical systems that teams have used to do all of the above tasks.

 

Mechanisms Examples

 

Passive vs Active Mechanical Systems

You can design a mechanism to be completely active, meaning that all functionality is a result of powered motion as demonstrated above. Or you can design a mechanism to be partially or completely passive meaning all functionality is a result of the shape. The benefits of passive mechanism are that the reduce the likelihood of mechanical or human failure occurring. Here are some examples of passive mechanisms;

  • Intake mechanisms
    • Passive claw: tote
  • Robot lifter mechanism: example 1

 

Understanding Motion

Once you have selected the desired capability you will need to select the type of motion you need. Here are the different types of motion you are most likely to see in FRC;

  • Linear motion – motion in a straight line (example: train on a track)
    linear_motion
  • Rotary motion – circular motion (example: the hands of a clock moving, or a wheel on an axle)
    engineanimation

 

Mechanical Joints

A mechanical joint is a section of a machine which is used to connect one mechanical part to another. Mechanical joints may be temporary or permanent, most types are designed to be disassembled.

 

Mechanical System Design

Mechanical Systems need to be able to withstand the expected structural loads over an expected number of cycles. Teams will need to follow these steps necessary to design their mechanical system.

  1. Sketch out a idea
  2. Build prototypes
  3. Refine the sketch
  4. Refine the prototype
  5. Create a free body diagram
  6. Understand the loads
    1. Understand ultimate load case for each type of loading
    2. Understand the number of cycles for each load case
    3. Do the math
  7. Select materials that can resist the loads
  8. Define the shape that will resist fatigue and is manufacturable

Note – steps 3 and 4 may need to be repeated many times to find the right combination to reduce weight and fabrication complexity

 

Additional Information

FRC Team 1389’s 2016 Budget

FRC teams are expensive, costing between $10,000 $120,000 per year. Here is our team’s budget for 2016 based on the fund raising we have done so far.

  • Revenue – $25,000
    • Student fees – $16,000
      • 40 x $400
    • Grants – $2,000
      • Walt Whitman Foundation $2,000
    • Monetary Donations – $5,000
      • Lockheed $2,500
      • Booz Allen Hamilton $2,500
    • In Kind Donations – $2,000
    • Fund Raisers – $2,000
  • Expenses – $24,500
    • Registrations – $11,000
      • 2 season events x $5,000
      • 3 off season events x $300
    • Robot – $8,000
    • Team food – $2,000
    • Tools – $2,000
    • Miscellaneous – $1,500

Each year the team tries to put more in than they take out so that the team can cover the expenses of future years or deal with emergency costs.

  • It does include registration for the super regional, if the team does not earn a slot those funds can be saved for next year
  • It does not include going to nationals.