Spectrum Design Concepts

History of Design Contests

What we are doing isn’t really new. There are lots of design contests.

Paper Airplane Contest
Cardboard Boat
MIT Class (see next slide)
Auto Racing - Formula 1 (first auto race was in 1895)
Drag Racing
Air races

Robot contests are relatively new

Robot Contests

Woodie Flowers — Father of Competitive Robotics

In his MIT Course 2.70, he developed a way to inspire students to work extremely hard, use engineering principles, compete like crazy, and work together with even their opponents.

Short

Long but really good

Robot Contests

FIRST Robotics Competition

The varsity level of high school robotics.

Building a quality robot and having a good season is hard. It's supposed to be hard. That’s the challenge. You have to put in the work to get the reward at the end.

It’s not just a robot

Our goal on the team isn’t just the robot. The robot is important but what’s more important is that we strive to be a good team.

That means

Our students are learning, being inspired, and having fun
We are helping other teams to become better
We are working in our community to make the world better
We are efficient & effective with our resources

money, supplies, space

Things you should learn

Most of what you learn on this team isn’t going to come from anyone standing at a whiteboard teaching you. It’s going to come from you putting in the time to learn it.

Using Google Drive
CAD/ Solidworks/ GrabCAD
Basic Shop Tools
3D Printing
CNC Router
Lathe
Video Editing
Live Streaming
Confidence

Basic Electronics

Voltage/Current/Soldering/etc

Basic Programming
Photo Editing
Communication
Public Speaking
How to take a good photo
Talking to Strangers
Kindness / Compassion

So what are we doing?

We are designing an entire program, not just a team. That means every year, every month, and every day. We should always be trying to make our program better.

What can you do today to make our team better?

Improving as a team requires everyone’s effort, which can be shown by designing a new feature for a robot, tagging photos, cleaning the lab, taking photos, creating a team handbook, etc.

Be passionate about making Spectrum better!

Design is a Passionate Process

Believe that what you are doing is important. Is this a problem worth solving? Do you feel a need or yearning to solve it?
“Passion is a necessary, but not sufficient, component of a good design engineer’s effort to solve a problem. “
“Most design processes typically involve repeating essentially the same steps as the design funnels down from broad concepts to details. “
“A good design process should be simple, flexible, and applicable to just about any problem one can think of.”

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

"Enthusiasm is one of the most powerful engines of success. When you do a thing, do it with all your might. Put your whole soul into it. Stamp it with your own personality. Be active, be energetic, be enthusiastic and faithful and you will accomplish your object. Nothing great was ever achieved without enthusiasm."

Ralph Waldo Emerson

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Karthik TED Talk

Speak UP!!!

If you believe you have a good idea, SPEAK UP!
If you see a flaw in the idea that the team is moving to, SPEAK UP!
Your team is depending on you to provide your input. Your idea or suggestion may be what's needed to push the team in a better direction.

Focus

“The ability to focus on a problem helps one create a good working solution in an appropriate amount of time using an appropriate amount of resources.”
“Just as the optical term implies, focusing on a problem means to define a field of view, clearly see what needs to be done, and then do it in depth!”

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Maximize aquatic avian linearity

Maximize avian termination with a minimum number of projectiles:

“Get your ducks in a row”
Dissect the problem into its components and requirements

“Kill two birds with one stone”
Systematically generate solution strategies and machine concepts
Look for similarities between elements of the problem
118 in 2015 - Can stacker mechanisms

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Lacerate bovine growth by-product:

Minimize deceased equine flagellation:

“Cut through the bulls#!t”
Identify the primary tasks that must be completed to succeed
Establish a set of goals and work efficiently to meet them
“Avoid complexities and make everything as simple as possible”

“Do not beat a dead horse”
Learn to recognize when an idea is destined to be intractable given your allowable resources, and then drop it
Keep your ego in check, and learn to put your failures on the front page next to your successes

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Impactus maximus ad gluteus maximus

Design of Prose - George Orwell

“Give the project a BIG kick in the butt and do not delay starting!”
Maintain momentum and strive to finish ahead of schedule!
Help others to get focus
Put in the hours
Be effective & Be diligent

Never use a metaphor, simile, or other figure of speech which you are used to seeing in print.
Never use a long word where a short one will do. If it is possible to cut a word out, always cut it out.
Never use the passive where you can use the active.
Never use a foreign phrase, a scientific word or a jargon word if you can think of an everyday English equivalent.
Break any of these rules sooner than say anything outright barbarous.

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Deterministic Design

Everything has a cost, and everything performs (to at least some degree)

If you spend all your time on a single tree, you will have no time for the forest
If you do not pay attention to the trees, soon you will have no forest!
You have to pay attention to the overall system and to the details

Successful projects keep a close watch on budgets (time, money, performance)

Do not spend a lot of effort (money) to get a small increase in performance

“Bleeding edge” designs can drain you!

Do not be shy about taking all the performance you can get for the same cost!

Stay nimble (modular!) and be ready to switch technology streams

It is at the intersection of the streams that things often get exciting!

Example: Going from limit switches to encoders, more complex but may be needed to solve the problem.

“If you board the wrong train, there’s no use running along the corridor in the opposite direction” - Dietrich Bonhoeffer

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Deterministic Design: Play!

Engineering is often a tactile, visual, verbal, cerebral, and physical activity:

Play with the field, game elements, and the kit parts.

You get a better understanding when you actually feel the items.
Listen to the sounds the objects and parts make.

Some things will just sound right, and you can often find problems by small noises, or a change in sound.

Sketch ideas (back of a napkin, MS Paint).
Play the game with people.
Talk about all your ideas. Your idea may spark someone else's next idea.

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Value of failure

Design instinct isn’t something you’re born with. It takes practice and it takes gaining knowledge to be able to see the right design and to quickly find the flaws in the wrong ones.

Look at lots of robots (Watch video, read books, read CD, etc)
Build a design library in your head

Work to be wrong, try to fail, and fail fast. Design your prototypes, your CAD sketches, etc., to find the flaws in your design. The more often you're wrong now the quicker you’ll be right the next time.
Listen to your crazy ideas and sketch them on paper. Then ruthlessly attack them to find what’s wrong with them.

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Reverse Engineering

Try to understand how the game designers designed the game.

This is crucial; ask lots of question about the game design.

Why is the field laid out a certain way?
Why are the vision targets located where they are?
Why are the tape lines the way they are?
Why are the height limits set as they are?
Envision the strategies the GDC thought of to play the game and look for ones they may have missed that give an advantage.

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Disruptive Technologies

Is there something new or from a different industry/field that can give you an advantage?

The Paintball hopper systems that inspired 971/125/1323/148 in 2017 are a good example of this.

Is there a design that guarantees a win? (Choke Hold Strategy)

71 in 2002
How do design to beat that strategy? Multiple robots working together?

How risky is this new design or strategy?
Do you have the technology to implement it?
Driver practice is always a disruptive advantage

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Best Engineering Practices

“Random Results are the Result of Random Procedures”

Prevent problems before they occur

Follow the process
Document everything
Performance (You only need to prototype the parts of your robot you want to work.)
Reliability
Repairability (keep it simple and have spares)
Field Tolerances (We couldn’t drive over the hopper plates in 2017)
Costs (keep within your budget)

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

Schedules

FRC has hard deadlines at every competition. It has to work during the match, or you aren’t going to get any points.
In FRC you can get creative with your schedule if you have the resources. Robot rebuilds or system rebuilds are common. Learn from others and never stop improving.

558 Full Rebuild

Risk Management

Constantly be looking for risks in every design choice, especially those made by other people on the team (more especially those made by Allen).
Which element, if defined or designed wrong, will neutralize the machine?
Which element will be hardest to replace/upgrade during the season?
Which element is most crucial to the robot success?
Spend time doing the design work to mitigate those risks.

More prototypes, more computations, more testing, etc.

Engineering Design Process

Evaluate your resources
Study the problem (solve the right problem)
Create possible Strategies
Create Concepts that can implement the best strategies.
Develop Modules - 2D Sketches and PROTOTYPE!
Develop Components - 2D Sketches
Detailed Design, Manufacturing, Drawings
Build, Test, Modify, Repeat
Document and create manuals

What do we have?

Team size, knowledge, experience?
Meeting hours and days?
Shop size and access to tools?
Materials, parts, etc. on hand?
Budget?
Events attending?
Sponsors/Friends/Parents/etc.?

1. Evaluate your resources

What are we trying to do?

READ THE RULES!!!!
Study the field

Watch the field tour videos, talk to people that see the real field in Manchester
Look through the CAD models, field drawings, and team drawings
Document the important field dimensions

E.g. goal heights, auton driving distances, game piece sizes, feeder station heights, shot distances and angles, obstacle heights

READ ALL THE RULES!!!

Game, Robot, & Tournament rules can all help you.

Document all penalties and restrictions

2. Study the problem

Analyze the scoring

How many ways can we score points?
What is the maximum number of points we can score?
How can we score the most points?
What is a realistic goal for the amount of points we should score?
What is a realistic goal for our alliance to score?

2. Study the problem

Create Possible Strategies

Imagine motions, interactions, match flow
Ask lots of questions WHAT, WHY, HOW, WHERE
Mock up the problem (game) with other people or on your desk, etc.
You want to find every strategy, even ones you don’t use, so you can defend them.
Take a shower, take a walk, run, stretch, do yoga, journal, or anything that allows you to think differently.

3. Create possible Strategies

Create Possible Strategies

Research

How is this similar to past robot games?
What are the key differences between this game and similar games?
How did teams succeed in similar games?

3. Create possible Strategies

Time Analysis

How long is a match?
How many points can we score in Autonomous?
How long does it take to score a disc in the low goal? Mid goal? High goal?
How long does it take to get a disc from the feeder station? Four discs?
How long does it take to get a disc from the floor? Four discs?
How long does it take to climb 1 level, 2 levels, or 3 levels on the pyramid?
How long does it take to score in the PYRAMID Goal?
How can we speed up these tasks?
For each method, how long does it take to score a certain amount of points?
Think about success rates (will you miss shots, will you fail?)

3. Create possible Strategies

Trade - offs

Speed vs. Torque (Move Fast or Push Hard)
Reach vs. Stability (Tall and easily tipped or short and stable)
Wide vs. Long Drive Base
Reliability vs. Complexity
Practice Time vs. Build Time

3. Create possible Strategies

Cost Benefit Analysis

Difficulty vs. Benefit

How much does it cost in $, lbs, volume, time, center of gravity, and many other constraints?
How much does it help you win a match?

The easy stuff that’s worth a lot is the best

3. Create possible Strategies

Scoring Analysis

The MOST critical thing you can do in a robot design contest is study the scoring algorithm and determine which are the most sensitive parameters!

In 2017 - Climbing and Gear Cycle times

In 2016 - Defense Crossings and then high goal cycle times

In 2014 - 3 Assist cycle times were critical

In Ultimate Ascent - ????

3. Create possible Strategies

Karthik’s Golden Rules

Golden Rule #1: Always build within your team’s limits

Evaluate your abilities and resources honestly and realistically
Limits are defined by manpower, budget, experience
Avoid building unnecessarily complex functions
On the other hand, as you get more experienced, start cautiously pushing a few boundaries

Golden Rule #2: If a team has 30 units of robot and functions have maximum of 10 units, it is better to have 3 functions at 10/10 instead of 5 functions at 6/10.

3. Create possible Strategies

Strategy Comparison Tables

3. Create possible Strategies

Strategy Comparison Tables - 2013 Example

3. Create possible Strategies

Design in Multiple Steps

Strategies -> Concepts -> Module -> Components

Strategies - How you plan to play the game
Concept- A specific idea for a machine that can perform the strategy
Module - A subsystem of the robot that performs a certain task
Component - An individual part of the robot

The design process is done of each of these steps. Sometimes you may have to go back up a step because a lower function reveals a flaw or is not obtainable with your resource or requirements.

Coarse-to-Fine

Planning a robot is like planning a party

Strategy - Cater, Restaurant, Potluck, Prepare a Meal
Concepts - Cook-out, Buffet, Family Style, Sit-down and Serve
Modules - Roast Beef, Mashed Potatoes, Lasagna, Mixed Veggies
Components - All the individual ingredients

Make broad decisions that enable you to plan the next level of detail. Sometimes you’ll have to make estimates before you know all the details and you will have to make adjustments as you go.

Coarse-to-Fine

1 2 3 4 5 6

1 2 3 4

1 2 3 4 5

Strategy

Concepts

1 2 3 4 5

1 2 3 4 5 6

Modules

1 2 3 4 5 6

Component

FRDPARRC Chart

Functional Requirements (events)
Design Parameters (design ideas)
Analysis
References
Risks
Countermeasures

Functional Requirements (FR)

Things the design must do

Should be expressed in words

Examples

Comply with Robot Rules

weight, size, wiring, materials, etc.

Drive around the field
Score points
Acquire/hold game pieces
Play defense

Design Parameters (DP)

Analysis

At least one Design Parameter for each Functional Requirement (FR).
These are the ideas for how to accomplish each FR.
These should be independent of the other DPs
These can be sketches or words

Here is where you show your work.
CAD sketches, lots and lots of CAD Sketches
Max. score math, motor usage, gear calculations
Motion sketches
Analysis can be used to create DPs!

Full Slide Deck on Design is a Passionate Process by Alexander Slocum

References

Risk

Countermeasures

Anything can help develop the idea
Look at past robots, books, youtube videos
Outside examples like construction equipment, design books, etc.

High, Medium, or Low and Why?

How do you plan to mitigate each risk?

Sample Chart

Image Source

You can always evolve your strategy

As you learn more about the game, your strategy should evolve.

More teams are doing one thing, and you think of a way to stop them.
The field acts differently than you thought

How is the PYRAMID going to be held together?
What if the goals start to overfill during all your matches?

Don’t be discouraged. Stay passionate! Keep working to be better!
You may end up rebuilding large parts of your robot.

3. Create possible Strategies

FUNdamental Principles

Occam’s Razor
Simple Machines
Newton and Conservation
Abbe’s Principle
Saint-Venant’s Principle
Golden Rectangle / Ratio
Symmetry
Reciprocity
Self Principles
Stability
Parallel Axis Theorem
Repeatability, Accuracy, Resolution

Sensitive Directions & Reference Features
Structural Loops
Preload
Centers of Action
Exact Constraint Design
Elastically Averaged Design
Stick Figures

Full Slide Deck on Fundamental Principles by K. Craig

Occam’s Razor

“Plurality should not be assumed without necessity.”

William of Occam (1284-1347) – English philosopher and theologian

A problem should be stated in its most basic and simplest terms.
Complexity is to be minimized in both design and manufacturing.
The less thought and less knowledge a device requires for production, testing, and use, the simpler it is.
Of course, it may take lots of thought and knowledge to get to a design requiring little of either – that is design!

Fundamental Principles of Mechanical Design by K. Craig

Occam’s Razor

Create designs that are explicitly simple. Keep complexity hidden.
Two common techniques for keeping things simple by keeping complexity hidden are:

Purchasing rather than making components
Specifying components by standards (use standard bolt sizes, parts, materials, etc)

Intrinsic complexity is is buried and invisible

Screw threads are complex but we don’t think about it.

Fundamental Principles of Mechanical Design by K. Craig

Simple Machines

Super Basic Definition: “They make work easier”
Broader Definition: “They provide mechanical advantage”
Less force over a greater distance instead more force over a short distance

Ramp and Wedges

In their simplest form they force things apart.
Pushing objects up a ramp is easier than lifting straight up
A nail or axe works in reserve because you are pushing the wedge instead of moving an object up the ramp.

Screw

A screw is a spiral ramp. It can take rotary force (torque) and turn it into linear force.

Screw

Either the bolt can rotate in a stationary material

Wood screw going into wood

Or the threaded nut can rotate on a stationary screw.

Nut turning onto a bolt

Or both could rotate opposite directions

When you turn a bolt head and nut at the same time

Mechanical Advantage = Circumference/Pitch (1/ threads per inch)

Lever

Load + Fulcrum(pivot) + Force = Lever

Power transmission elements such as gears, belts and pulleys, chain and sprockets, driven wheels, etc are all levers.
By exerting force at one end of the lever, force is applied to the other end of the lever.

Lever

Ratio of the Lever Arms (distance the forces are from the pivot) is how we determine our mechanical advantage.

Force Lever Arm x Force >= Load

Load Lever Arm

Critical in designing pneumatic actuations

Wheel and Axle

Reduces friction when used to push things (such as a dolly or cart)
A version of a lever
Mechanical advantage = ratio of the diameter of the wheel and axle

Gear Ratios are Levers / Wheels and Axles

Big Input gear, reduces force but increases distance

Small input gear, increases force but reduces distance

Pulley

A wheel and axle with a cable
Can help change direction of force
Multiple floating pulleys can divide the force and provide mechanical advantage.

With just a single pulley you are just redirecting force. 2 pulleys as shown to the right allow you to use ½ the force over 2x the distance to lift an object.

Newton’s Laws

Basics of Mechanics - lots of our problems can come down to Newton’s laws

Newton’s 1st Law

“Every body persists in its state of rest or of uniform motion in a straight line unless it is compelled to change that state by forces imposed on it.”

An object in motion tends to stay in motion.

Newton’s 2nd Law

“The acceleration of a body is directly proportional to the resultant force acting on it and parallel in direction to this force and that the acceleration, for a given force, is inversely proportional to the mass of the body.”

Force = Mass x Acceleration

Force = Moment of Inertia x Acceleration

Newton’s 3rd Law

“To every action there is always opposed an equal reaction or, the mutual actions of two bodies upon each other are always equal and directed to contrary parts.”

Conservation of linear and angular momentum

Conservation of linear momentum –

If no force is applied, then momentum is constant

Conservation of angular momentum

If no torque is applied to a body about an axis, angular momentum is constant about that axis • A force coincident with an axis does not apply torque about that axis

Golden Rectangle

Discovered by Pythagoras (He also has a theorem)
A rectangle whose sides are in proportion such that when a square is cut from the rectangle, the remaining rectangle has the same proportions. (Roughly 1.6:1)
Donald Duck: Mathmagic Land
Helps when designing the overall proportions of a module.

Full Slide Deck on Fundamental Principles by K. Craig

Motors vs. Pneumatics

Rotary motion
Use a plantary Gearbox
Can have more power than pneumatics for less weight and size
Doesn’t provide constant force well
Harder to control
Infinite positions
Limited to ~14 motors max.
Speed/Power is controlled using a speed controller (such as a Talon SRX, etc.)

Linear motion
Normally two positions
Repeatability is assured
Force can be changed with a regulator
Provides constant force
Speed can be changed with flow control valves
Simpler and cheaper than motors
In theory you can have unlimited pneumatic actuations

Motors vs. Pneumatics

Rotary Motion

If you need to spin something a lot, this is perfect
Especially if you need to spin it fast

Use a VersaPlantary Gearbox

Times you shouldn’t use a VP

Need a lot of torque and multiple big motors, CIMs and MiniCIMs
Needs to be a very small or light mechanism

Can have more power than pneumatics for less weight and size.
Doesn’t provide constant force well

Stalling the motors is normally not good

Harder to control
Infinite positions

This can be a feature and a problem

Limited to ~14 motors max.
Speed/Power is controlled using a speed controller (such as a Talon SRX, etc)

Motors vs. Pneumatics

Motors

CIM Motor

miniCIM Motor

775pro Motor

BAG Motor

Motors vs. Pneumatics

VersaPlanetary (VP) Gearbox

VP Encoder

Motors vs. Pneumatics

Linear Motion

Never use a rotary pneumatic actuator

Normally two positions

Can be more if you can add stops or dog two cylinder together.

Repeatability is assured
Provides constant force
Force can be changed with a regulator
Speed can be changed with flow control valves
Simpler and cheaper than motors

Than motor+motor+controller, etc.

In theory you can have unlimited pneumatic actuations.
Max working pressure: 60psi; Max storage pressure: 120psi

Motors vs. Pneumatics

Cylinders

Motors vs. Pneumatics

Spring Return Cylinders

Air is used for extension, but a spring is used for retraction.
Doesn’t have equal forces both ways
Uses less air
Spring extend cylinders do exist but they are rarer.

Double Acting Cylinders

Air is used for both extension and retraction
Equal forces both ways
Uses more air

Motors vs. Pneumatics

Force can be changed with a regulator

Changes the pressure
Ideally use the lowest functioning pressure
Less pressure uses less air if the volume

remains the same

Speed can be changed with flow control valves

They normally control the air being released from a cylinder. So if you want to slow down the extension you flow control on the retraction side (nose) of the cylinder

Abbe’s Principle

“If errors in parallax are to be avoided, then the measuring system must be placed coaxially with the axis along which the displacement is to be measured on the workpiece.”

Small errors in angle are amplified as you get far away from the origin.

It was discovered when working on manufacturing better microscopes.

Full Slide Deck on Fundamental Principles by K. Craig

Abbe’s Principle

The implications of this observation on the design of instruments and machines are profound:

Always try to place the measurement system as close to the line of action (the process) as possible.
Always try to place bearings and actuators as close to the line of action (the process) as possible.
A small angular deflection in one part of a machine quickly grows as subsequent layers of machine are stacked upon it…

A component that tips on top of a component that tips…
If You Give a Mouse a Cookie…

Full Slide Deck on Fundamental Principles by K. Craig

Abbe’s Principle

Full Slide Deck on Fundamental Principles by K. Craig

Abbe’s Principle

Abstractions can be taken to other systems as well.

When measuring temperature, it is important to place the temperature sensor as close as possible to the process to be measured.
The idea is the same for pressure, flow, voltage, current, etc.
In each case, the farther away you are from the process to be measured, the greater the chance for errors to reduce the accuracy of the measurement

Full Slide Deck on Fundamental Principles by K. Craig

Saint-Venant’s Principle

The principle says that several characteristic dimensions away from an effect, the effect is essentially dissipated.
Or if an effect is to dominate a system, it must be applied over 3-5 characteristic dimensions of the system.

To NOT feel something’s effects, be several characteristic dimensions away!
To DOMINATE and CONTROL something, control several characteristic dimensions

Full Slide Deck on Fundamental Principles by K. Craig

What’s a characteristic dimension?

It depends

Often it’s diameter

Examples, shaft diameter or bolt diameter.

Sometimes it’s width or height, if the object isn’t round.

Basically it’s the cross sectional dimension that you are looking at.

Saint-Venant’s Principle

Full Slide Deck on Fundamental Principles by K. Craig

Saint-Venant’s Principle - Applications

When mounting bearings to support a shaft, the bearings should be spaced 3-5 shaft diameters apart if the bearings are to effectively resist moments applied to the shaft.

Full Slide Deck on Fundamental Principles by K. Craig

Saint-Venant’s Principle - Applications

Linear slides with large contact areas compared to their width will not jam.

Linear Slides that have too small a contact area will jam when they are twisted even the slightest amount.

Full Slide Deck on Fundamental Principles by K. Craig

Self-Principles

Self principles utilize the phenomena the machine is trying to control to help control the phenomena.

A design that uses the inputs to assist in achieving the desired output

4 basic types of self principles:

Self-help
Self-balancing
Self-protecting
Self-checking.

Full Slide Deck on Fundamental Principles by K. Craig

Examples of Self-Help

Pressure systems such as boilers and airplanes

Putting a door in them is scary (it might cause a leak) but you can use the pressure to ensure a seal.

Ice tongs
Scissors force the blades together

Left handed scissors are mirror images of right handed ones

Balanced doors can be opened easily in the wind

Full Slide Deck on Fundamental Principles by K. Craig

Accuracy, Repeatability, and Resolution

Accuracy: the ability to tell the truth

Can you hit the target

Repeatability: the ability to tell the same story each time

Can you hit the same spot every shot

Resolution: the detail to which you tell a story

How small of an adjustment can you make

Full Slide Deck on Fundamental Principles by K. Craig

Accuracy, Repeatability, and Resolution

Design for the needed resolution of your goal.

How your sensors are mounted.
How you adjust shooter angle, wheel speed, etc.

Design that your machine can be repeatable.

lots of compression is normally worse for repeatability
Test lots of shots
Have the ability to mark, reset, and remember your positions/settings.

Create a setting log google form, or spreadsheet, etc, to document critical settings

Adjust your system until you are accurate.

Use your resolution to fine tune your device till it’s accurate.

Full Slide Deck on Fundamental Principles by K. Craig

Sensitive Directions

Identify the variables in which accuracy and repeatability are most important.

For 2013 the altitude (vertical angle) was the most sensitive directions.
Velocity and azimuth (horizontal angle) were less sensitive when shooting in a straight line and having a wide target. (not assuming full court, Abbe tells us that full court is harder)

When making parts, know which dimensions are critical and in what direction.

Shafts that are held in place by shaft collars can be longer than needed but not shorter.
Parts can often be smaller at the edges if nothing interacts with the edges but may run into something if they are made too big

Full Slide Deck on Fundamental Principles by K. Craig

Triangulate for Stiffness

Triangulate parts and structures to make them stiffer.
Consider a swinging fence gate. Triangulating members prevent, or correct, sagging.

A tensile cable connects the lower outer corner to the upper inner corner, and transmits load to the gatepost.
Alternately, a compression brace can be added to the diagonal to transmit the load to the gatepost.

Full Slide Deck on Fundamental Principles by K. Craig

Centers of Action

Minimizing twisting forces (moments) on a system reduces angular motion, which reduces angle errors (Sine errors) and makes designs more robust.
Centers of Action = virtual points within an object (a body) such that forces applied through them generate no moments on the object.

Center of Gravity (Center of Mass)
Center of Stiffness
Center of Friction

Full Slide Deck on Fundamental Principles by K. Craig

Center of Gravity

Mount your heavy stuff low towards the ground when possible

The Battery is the most dense (heaviest for its size) part of your robot.
Compressor, and motors are your next heaviest items

Ideally your mass should centered left-right and front-back.

This will make your robot the most predictable.
There may be reasons to move your CoG forward or backward based on game mechanics such as if you are going to have to lift something heavy during the game. You’d want your normal CoG on the opposite end of where you lift the heavy object to keep you stable while lifting.

To high a CoG and your robot will do wheelies and might tip over

It will also be hard to control as it will start to rock when you try to accelerate or turn

Bumpers are your friend

Be cautious of anything that is designed to deploy outside your bumpers/frame perimeter

Use lexan where possible because it is more forgiving to bending loads and impact than sheet metal

Things that stay inside of your frame don’t have to be as robust

Still analyze if they may take impact based on the game, field, other robots, etc. and build accordingly.

Acquisition Zone

The effective intake area of the robot
The bigger the better!
How will the object react to the robot, field, intake device?
Can the driver pick up an object 50ft away without a direct line of sight?

“Touch it, Own it!” should be your goal

1678 - Strategic Design Full Workshop

Continuous intake > Single Intake

Rollers and wheels are better than claws, grippers, etc
Allow you to pick up multiple game pieces quickly
Are much easier on your driver and they are faster.

Speed is always important in FRC

Easier to automate rollers and wheels than claws and grippers.
Also we have lots of motors and spinning things is easy.

Sensors

Plan for sensors from the beginning

“Failing to plan is planning to fail”

VersaPlanetaries are easy now with VP encoders

Encoders allow you measure position and/or speed of rotary mechanisms.
We use one to measure position of gear intake

Pneumatics don’t have to have sensors but their mechanisms could

The trigger on our 2017 gear back pack is a good example of a pneumatic mechanism that uses a switch to activate it.

Current is super useful feedback

TalonSRX and PDP both give current feedback
You can tell when a motor has resistance like from grabbing a game piece, etc.
We detected when we had a gear in our intake by monitoring for the current spike.

Simple Sensors

Limit Switch / Bump Switch / Switch

Detect when something runs into them
Digital Sensors either true/false (1/0)

Simple Sensors

Limit Switch / Bump Switch / Switch

Simple Sensors

Proximity Switch / hall effect switch/ inductive proximity sensor

Detect a magnet or ferrous metal depending on the sensor
Similar uses to limit switch but no contact is needed.
The magnet or metal need to be very close to the sensor

Proximity Sensors

Proximity Switch Mounting #971 2016 Robot

Reflective / IR / Light Sensors

Detect objects crossing a path
Digital sensors like switches or analog sensors give distance

Encoders

Give you rotational speed or displacement (how many times has it turned)

How encoders work Sparkfun Video

Chinese LPA3806 Encoders

VersaPlanetary Encoders

Modified VersaPlanetary Encoders with 3D printed gear

for hex shaft

Encoders

Encoder mounting #971 2016 Robot

Gyros / IMUs

IMU (Inertial Measurement Unit) combination of gyros and accelerometers
Like in a phone or Wii-mote, etc
Gives rotational displacement (how far you turned)

Pigeon IMU connects to Talon SRX

Nav-X connects to RoboRIO MXP port

FIRST Choice Analog Devices Gryo

Fuses vs. Breakers

What is a fuse: https://www.youtube.com/watch?v=2MWwwrOQOUc

How the main breaker works - https://www.youtube.com/watch?v=KNWFCxhootY

Fuses don’t reset, you have to throw them away.
Breakers can be reset, on the robot they self reset(except main 120A breaker).

Taps and Dies

Taps allow you to form threads inside a hole
Dies cut threads on the outside of a shaft (we rarely need these)
Speed taps or machine taps can be used with drills or lathes
Always use lubrication when cutting threads (using a tap)
Look at a Tap size chart to know what hole to drill.

Manage Friction

You will have friction in any mechanism design. What is Friction?

Full Slide Deck on Fundamental Principles by K. Craig

Gravity

Pushing Force

Friction Force resists motion

Friction = μ * Perpendicular Force (sometimes gravity, but not always)
μ = Coefficient of Friction (how well the two objects grab each other)
For real object interactions there are more forces but we can use this as an approximation

Manage Friction

Avoid sliding friction where possible

Wide variation in friction coefficients due to surface finishes, damage, etc
Uncontrolled lubrication statuses and effects
Stick-slip behavior because of static vs dynamic friction

Rotary motion is easier to manager than linear motion.
Bearing use rolling friction instead of sliding friction. Use rolling elements whenever possible

Full Slide Deck on Fundamental Principles by K. Craig

Manage Friction

Rolling Friction in Linear Motion

High Quality tool boxes use ball bearing drawer slides
Cheap tool boxes have plastic linear slides

Use our two different red toolboxes to feel the difference

Full Slide Deck on Fundamental Principles by K. Craig

Ball Bearings

Simple way to reduce friction
Whenever possible use ball bearings for rotational motion
When not to use ball bearings

Low speed, low load applications (small pivots)
When space is very tight; plain bearings are smaller
Quick bench tests

Some Bearing features

Hex bore
Flange to prevent them from coming

out

Plain Bearings (aka bushings)

Use sliding friction but with oil impregnated materials that reduce friction normally bronze
Can have small diameters than bearings for the same shaft diameter.
We used them on our climber in 2017 and our elevator in 2019.

Over Constraining

Three bearings on one shaft won’t work, the system is overconstrained.

Full Slide Deck on Fundamental Principles by K. Craig

Exactly Constraining

Ideally all systems should be exactly constrained, only the degrees of freedom (movable parts / directions a thing can move) that you want to move should be able to.
Exactly constrained machines

No binding
No play (wiggle)
Repeatable positions
No internal stress
Loose-tolerances on parts
Easy Assembly
Robustness to wear and tear

Full Slide Deck on Fundamental Principles by K. Craig

Exactly Constraining

3D (three-dimensional) objects have 6 degrees of freedom

3 translations and 3 rotations

Constrain the motions you don’t want to allow for the motions you do want (rotations, slides, etc)

Full Slide Deck on Fundamental Principles by K. Craig

Exactly Constraining

2D Example

Full Slide Deck on Fundamental Principles by K. Craig

Exactly Constraining

2D Example

Full Slide Deck on Fundamental Principles by K. Craig

Exactly Constraining

2D Example

Full Slide Deck on Fundamental Principles by K. Craig

Examples

Full Slide Deck on Fundamental Principles by K. Craig

Constraint Design Notes

Nesting Forces

Can’t just be another post.

They are either too big or too small never exactly the right dimension

In practice nesting forces are created using weight, cams, wedges, springs, or screws.

Constraints in Practice

Never Over-constrain, unless it’s done with parts that can deform to mitigate the constraints
Over-constraining a motor and shaft with multiple bearings is common in FRC. Designing for flexing in the motor mount, bearing mounts, or shaft coupling is needed to avoid binding.

Full Slide Deck on Fundamental Principles by K. Craig

Elastic Averaging

“When there are many compliant elements, each of which locally deforms to accommodate an error, in total they can form a very rigid and accurate system.”
5 wheeled office chairs are over-constrained since all 5 won’t be on the floor at the same time if the structure were rigid. The feet flex to allow all 5 wheels to contact the ground.
Gears, bearings, screws, all use elastic averaging

Full Slide Deck on Fundamental Principles by K. Craig

Torque Transfer

Hex Shafts

ThunderHex

Keyways

D-shafts -Double D Shaft

Splines

Hex Broach

Little sharp edges slowly cut the correct profile into the hole.
Keep the broach straight and use lots of lubrication to avoid breaking the broach.
This is a broach machine, we will just push the broach through but it’s the same concept.

Hex vs Thunderhex

Regular Hex stock with sharp corners
Allow you to transfer torque without using keys, etc
Most FRC parts now have ½” hex bores
Regular hex shafts don’t fit into Thunderhex bearings without modifications

Upgraded with rounded corners so they fit in 13.75mm Bearings
Round bearings are more concentric and stronger than hex bearings.
Thunderhex fits into hex bearings and hex bores
Thunderhex bearings are round but they have a bigger Internal Diameter than ½” round bearings. Don’t get these confused.
Any shaft in a bearing shouldn’t wiggle around at all.

Spacing and securing shafts

Shaft Collars

Snap Rings

Grooves cut into a shaft

Spacers

Hex Spacers from VEXpro

Cut Tube
3D printed Spacers

Spacing and securing shafts

Retaining Rings (CIM pinions only)

They don’t take lateral forces well

Tapped threads + bolts and Washers

Shoulder Bolts

Triple-Helix Gear linkage - Example

Triple-Helix Gear linkage - CAD Sketches

Video

Triple-Helix Gear linkage

CAD Link

How would we modify this?

Material selection?
Reduce Cost?
Exact Constraints?
Line of Action?
Lever Arms?
Gearbox Selection?

Avoid Bending Stresses

Tension and Compression are better stresses on materials.

This is why the hole in Thunderhex shaft doesn’t weaken it much.

Full Slide Deck on Fundamental Principles by K. Craig

Load Paths or Structural Loops

Plan the load paths in parts, structures, and assemblies
Load Paths should be

Short
Direct
In a line or in a plane
Symmetric
Non-redundant or elastic
Locally Closed
Easily Analyzed

Full Slide Deck on Fundamental Principles by K. Craig

Load Paths or Structural Loops

Imagine if bike brakes were a push or pull operation instead of a squeeze.
You’d have to resist the force on the handlebars with your other hand or your body to the seat, etc.
The closed load path allows you to break

without inadvertently steering the bike.

Full Slide Deck on Fundamental Principles by K. Craig

Preload (why structural bolts should be tight)

Best Explanation on Preloaded Bolts
What do we expect to happen in C?

Preload (why structural bolts should be tight)

Best Explanation on Preloaded Bolts
What do we expect to happen in C?

The clamping force between the plate and bracket is reduced by 1

With no load applied the clamp force is 2 units, with the load applied this decreases to 1 unit of force. The bolt would not actually 'feel' any of the applied force until it exceeded the bolts clamp force.

Spacers vs standoffs

Standoffs have internal threads
Spacers are just tubes.
By bolting through a spacer you get the advantages of preload forces.

When tight the outside of the spacer undergoes compression.
Bending forces will cause less deformation when it preloaded.
Rigid steel bolt is now the core of the tube also harder to bend and takes some of the bending forces.

TIGHTEN THESE BOLTS!

¼-20 Grade 8 bolts can take 108 in. lbs. of torque
Remember levers, so the longer your tool the less you force you need.

How to build your “everything” really really fast

Spacers vs standoffs (Intro to FEA)

How to build your “everything” really really fast

Live Axle vs Dead Axle

Axle spins and transfers torque to objects, wheels, etc.
Shaft is in bearings that are mounted to the robot.
Has a weaker shaft
Shaft must be removed from the side and everything must come off the shaft
Shafts can often be a little too large and it’s not a problem.
Hex bearings and shafts
More expensive

Axle remains motionless and wheels, etc spin on the axle.
Bearings go in the wheel
Shaft is mounted with a bolt going through it.
Provides a stronger shaft support and helps stiffen the frame.
Shaft, spacers, wheels, etc are removed as one unit from the top or bottom.
Shafts must be the exact right length
Sprockets/Gears must attach to wheels
Round bearings and shafts
Normally Less expensive

Live Axle vs Dead Axle

Shoulder Bolts and Bearings

This is a combination of the two methods.
The shaft spins but it’s still bolted into the place.
The shoulder bolts spin in the bearings instead of the shaft.
Uses a hex shaft but with smaller round bearings (⅜” ID).
About the same price as live axle once you account for shoulder bolts.
Make sure to put threadlocker (for us it’s LocTite) on the shoulder bolts or they will spin loose.

WCP Shoulder Screw Roller System

⅜” Shoulder Bolt + ⅜” Bearing + Hubs/Shaft with 5/16-18 tapped holes

WCP Shoulder Screw Roller System

⅜” Shoulder Bolt + ⅜” Bearing + Hubs/Shaft with 5/16-18 tapped holes

Power Transmission: It’s all just ratios

Sprockets/Pulleys/Gears are all just levers. We will use the word gear for a bit but know it applies to sprockets and pulleys too.

If they are same size they just transfer power at the same speed and torque. This is called 1:1 (1 to 1) gearing.

If the powered gear is smaller you increase torque but decrease speed. This is called “gearing down” or the motor is “geared down to” some RPM.

If the powered gear is larger you decrease torque but increase speed.

This is called “gearing up” or the motor is “geared up to” some RPM.

Gearing Problems