Category Archives: Robot Design

EV3 FLL Robot Design – 4 Motor Challenge

My girls team has a great robot.  I gave them a challenge: build a new robot with 4 motors.

This season I will post a bunch of robot pics.

They started with the EV3 starter robot as the base and customize it.

Notice the wheel design.  Two seasons ago after doing a straight test, they realized the marble ball design had issues going straight.  For the back, they use rims, no treads.  This allows the FLL EV3 robot to pivot.

Here is the Capital Teens World Class First Lego League robot design.  It uses a turtle model, allowing different shells. The cool innovation was the motor gear interface.  She’ll attachments just snap on.  It has three color sensors and a gyro sensor.


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Center of Gravity

One challenge my team faced was a front heavy robot.  When it stopped fast, it was like a wild bronco and the back would kick-up.  After they realized the issue and its impact on consistency, they started looking for solutions.   Thanks to Wally’s site, I had some 2 x 6 x 2 “heavy crane” bricks, LEGO part number 73843, that weigh 2 ounces each.   The girls added two bricks, 4 ounces, and now it is not front heavy.

Checkout Wally’s site,


Hard Reset

What a great opportunity, the Code Crackers robot locked up when starting up before they walked into technical judging.  The Robot, Argo, was stuck in start up mode and they could not demonstrate any programs.

I was not in the room but just watched the video being taken by Brian, the 6th grader they adopted as their historian so he could have the FLL experience.  What excited me was they did not panic.  They just started talking about their robot and programs.  I applaud the judges, they were very supportive.

DSC_0629What started as a bad situation turned into a blessing. The team talked about the robot, walk through their runs and showed the print out of their programs.  I was very proud of how they handled this situation.   This is an advanced team, they have 7 sensors on their robot and even use the gyro.  Their robot is solid and they have some innovative attachments.  One of my favorite features is the wheel guard.  When they picked up loops, it was getting caught in the wheels.  They built a wheel guard.  I thought that was innovative.  I will share more about the teams robots and programs later.

In looking at the judging comments, they were considered for Robot Design.  It probably helped they had a high score in their runs, 358 was their high score and they won robot performance.

When I saw them after technical judging, they came running up saying something is wrong with the robot.  What do we do?  Being a geek, I knew there had to be a hard reset.  I can press the power button on my computer or two buttons on my iphone to hard reset.  I guessed, I pressed the center and left corner button.  It worked.  I know, I touched the robot. If this happens again, they will know what to do.  As a result, I did work with them to refresh the firmware.

Resetting the EV3 Brick (from EV3 Help)

“If your EV3 Brick suddenly stops working and cannot be shut down through the normal process, you will need to reset your EV3 Brick . Resetting the EV3 Brick does not delete existing files and projects from previous sessions in the EV3 Brick memory . Files and projects from the existing session will be lost”

  1. Make sure that the EV3 Brick is turned on .
  2. Hold down the Back, center, and left buttons on the EV3 Brick .
  3. When the screen goes blank, release the Back button .
  4. When the screen says “Starting,” release the center and left buttons

Everyone’s robot is consistent

On Sunday, I was a technical judge for Division II.  If you are a coach, you should judge.  It is a fun learning experience and a great way to help FIRST.   It is one of my favorite components of FLL.  You will be amazed by these kids and the contrast between teams.

What I found funny was when a team had a mission that did not work, you would hear “That never happens.”  My co-judge and I both noticed this trend.  It happened almost every time a mission did not work.  We kept a straight face and reminded the team that the board is not set to competition standards.  We wanted to lift them up.

What I found disappointing was that my 14 year old son who was volunteering and working the pit had to breakup an argument between two coaches about who had the practice table. As a judge, I cannot discuss what happens in the judging room but I will tell you that acts that do not represent gracious professionalism can impact your team.  Parents and coaches are expected to demonstrate core values and gracious professionalism.

Even with the negative situation, my son did find inspiration from a rookie team.   He would not stop talking about them and had a great time interacting with them and their coach.  It started with a simple act, putting up tables.   The tournament was finishing up and he was helping reset the school.  This team started helping without being asked.  You would be surprised how many teams sit and watch volunteers do the work.  This simple act inspired my son.

This Sunday, I will be helping referee. I cannot judge because of conflicts and it gives me an excuse to get a silly hat.  Turns out three Division I teams are from our elementary school and I have helped mentor one of the Division II teams. I was planning on taking the weekend off from FLL but my son really wanted to volunteer and talked me into it.  My daughter wanted to volunteer but I played the 13 and older card.  What is cool is I have three Code Crackers volunteering,  They are not looking for an advantage, they really want to do it.  One of the team member’s email response was,  “I would really like to do that!  Count me in.”  My teams takes core values serious and working a tournament without the stress of competing is fun.   We could have left after judging but we stayed for closing.  It is great to see the reactions of teams, especially a rookie team that has the highest score.

There are many opportunities in FIRST.  Volunteering at a tournament is very rewarding and every coach should do it!




Don’t Touch the Table!

We have a rule, Don’t Touch the Table!  It applies when the robot is running so no one bumps the table and throws off a run.  I should follow this rule.  Last week, I noticed a flaw in our table design, some nails were starting to pop up.  Simple to fix, pull out all the nails and use some liquid nails.  Out table is a light weight table, thin backing board supported by some stiffeners.  Saturday morning, fixed the table.

Saturday afternoon at the Code Crackers practice I noticed the robot looked like it was a roller coaster, bobbing up and down hills as it moved.  That’s strange, why would it do that?

Then it gets more interesting, the robot would pivot in some areas and not others.  Must be something wrong with the robot.  Must be friction from the mat!  

Sunday at the Capital Girl’s practice, I noticed other strange things.  Sometimes the robot would make this strange sound, like the motors were dragging.  After this sound discovery it became apparent, the board had very small chasms between the stiffening boards.  Not enough to notice when looking at it but enough that the light sensors would drag and create all kinds of friction and inconsistencies.

Needless to say, I spent Columbus Day building a new table.  Good news is all the programs work and consistency is back.  So remember the rule, “Don’t Touch the Table”.


Lego Pneumatics for FLL

James Jeffrey Trobaugh. Winning Design!: LEGO MINDSTORMS NXT Design Patterns for Fun and Competition (Kindle Location 1698). Kindle Edition.

James Jeffrey Trobaugh. Winning Design!: LEGO MINDSTORMS NXT Design Patterns for Fun and Competition (Kindle Location 1698). Kindle Edition.

Lego Pneumatics are a little hidden secrete for FLL teams.  Lego Pneumatics uses air to power an actuator.   They can be great for powering an attachment or distributing power.

For Food Factor, the Code Crackers used pneumatics to turn the thermometer. Bumping into the wall to triggered the switch, raising an arm up to move the thermometer.

For Senior Solutions, the Capital Girls Too team used pneumatics to distribute power and had the motor trigger the switch.  It was used to release the ball and pick up the green medicine.

What is great about pneumatics, kids love them and will try to use them.  All you have to do is make them available and use the Edge method to educate them.  Everyone loves pumping the pump and seeing how much pressure they can get in the tank.  For Nature’s Fury, the Capital Girls actually set a requirement they would use pneumatics.  The girls team came up with really cool self-contained pneumatics powered attachment for getting the buildings that is triggered by an arm.  The Code Crackers team are using pneumatics as part of their Nature’s Fury research presentation.

Lego Pneumatics are available from Lego Education and can be found on eBay.



Sometimes you have to fail to succeed

Last night, I had a sub-team meeting with the Capital Girls working on the truck and ambulance mission.  This team made great strides, they had a great attachment and a working mission after their first meeting.  At the start of their second meeting, it would veer off into the buildings.  Turns out the friction from the truck and ambulance wheels play a big role in the success or failure of this mission.  Something that looks simple can be very hard.

This will happen during every teams season and is very frustrating.  Something will work, then it want.  Sometimes it is battery level but for the most part, there is no rhyme or reason. I tell my team we just increased the sample size and it is better to know now than later.  The more your teams test, the better they will understand the characteristics of a mission and can adjust.   The girls did not realize it was the truck and ambulance wheel friction that was causing the inconsistency until after 20 runs.  By then the meeting was over.  They have some stuff to figure out. 

You can count on luck, it has helped us, but having a large run sample size really matters for having a consistent robot and knowing what to expected at tournament.  Log each run, note if it was a happy or sad face.  I don’t like using the terms successes and failures, the terms are to black and white and just because a mission did not work perfect does not make it a failure.  If you learn something from an unsuccessful run, then you succeeded at learning something.  Download a copy of our Mission Log to use with your team.  It uses :) and :( faces to indicate how the team felt about the run.





Robot Design: The Straight Test

For a robot to be consistent, it must go straight.  As my teams build, they can earn badges for performing robot tests.  The straight test is simple:

  1. Program the robot to go straight 4 rotations using a motor power starting at 30.
  2. Run the robot and observe if it goes straight.
  3. Record the results.
  4. Repeat with motor speeds of 50, 70, 100.

The Capital Girls, had a build meeting today with four out of the ten girls.  Their goal was to finish the robot by adding a third wheel, bumpers and sensors.  After 2 hours, they managed to just add the wheel and bumpers.

The third wheel was a challenge, and a discussion erupted about using fours wheels.  In the design meeting, not everyone agreed on three wheels but majority ruled.  The build team elected to following the design plan and extended the bearing wheel from the EV3 base robot so the robot was level.

IMG_1766 IMG_1760

As the meeting was ending, the girls ran a straight test.  The robot went sort of straight but waddled badly.  The waddle was very obvious.

After everyone left, my daughter asked if she could try a four wheel design.  I said yes, with the understanding she had to keep the bearing third wheel component so she could share both designs with the entire team and let them decide.

After her build, we did the straight test and, as you might have guessed, fours wheels ran straight as an arrow.

After her brother saw her design, he accused her of copy his team’s design.  Being who she is, she said, “Yes, we copied your design.”  She had not even seen his design – siblings!

For the design process, each team used the Robot Design Guide and had similar answers but different rationales.  The boys wanted a three-wheel robot for fast pivot turns.  The girls wanted a smaller robot.  As of now, they each have 4 wheels designs but got there for different reasons and have different chassis designs.  The Code Crackers wanted to tackle the debris challenge and thought four wheels would make the robot more stable going over the obstacles.  The Capital Girls were going to ignore the debris challenge but could not get a three-wheel robot to go straight.  Below are both teams’ designs.  You might notice the back wheels for both teams do not have a tire, just a rim.  When doing design planning, there are two wheel tests the teams perform to understand the speed and traction characteristics of the wheel options.  The tests teach two wheel concepts: 1) the bigger the wheel, the faster it will go, and 2) the more contact surface and wheel material, the more traction/friction.  This learning exercise, along with the straight and balance tests, guides the robot design.  What I like about the exercises is that they guide the design process through testing and exploration, helping the teams determine why, not just what.   To learn more about the robot testing, download our Robot Design Guide.


Capital Girls (Left) | Code Crackers (Right)


Code Crackers Research Kickoff turned into a Sumo Challenge

The Code Crackers team hurt my feelings. I spent all this time creating this Nature’s Fury guide, and they just went in their own direction. In the end, their approach worked for them, and I got over it. They listed all the Nature’s Fury disasters they could think of, including going out-side the box with Solar Flares, Zombie Apocalypse and my favorite, Limnic Eruption. Using the process of elimination, they ended up on floods.

Once they were ready for a break, we decided to put their base robot to work.  I pulled out the Sumo Challenge Board and challenged them to find an object, push it out of the white ring without the robot going out of the ring.  Below is the video of a somewhat successful run.  The object was moved around and we had to keep legs out of the way.

Here is the program the team wrote. It did not work perfectly, but it gets the job done

Ultrasonic Following Program

Ultrasonic Following Program

G adding a third motor to the base robot

Code Crackers Base EV3 Robot

Like the Capital Girls, the Code Crackers built the base EV3 robot. They also elected to go with the big wheels for speed.  Being 8th graders, when they are focused they can get a lot done. For our robot build meeting, they split between builders and programmers.  The programmers built a music master program and base escape.

Below is the program the Code Crackers wrote for the music challenge.  They used notes, not sounds like the Capital Girls.  I am always amazed at the different solutions the two teams come up with when given the same challenge.  Sometimes they are very similar, other times they are polar opposites.

Master Music Program

Master Music Program

The Code Cracker’s Base Escape program has recovery logic incorporated. To start, I challenged them to stop at the line.  Once they had that master, the challenge was to stop at the line if the light sensor stop working (unplugged in this case).  At states in 2011, they had some big issues with light sensor and learned this recovery concept.  In 2012, the mentored the Capital Girls Too, who then used it for the Senior Solutions medicine mission.  Ironically, the mentoring team, 7th graders, learned from the 5th team.  Who was mentoring who?  The workshop challenges and programming posters have really advanced the teams’ programming capability.  They have learned that you can do some cool stuff with a loop, switch and logic block.  This is case where the solutions are the same, the only difference may be some block orders.


Capital Girls Building a Base EV3 Robot

Both my teams are very familiar with the NXT, and we had to to figure out how to get them familiar with the new EV3 platform in way that did not take up too many meetings.  Lego made this easy by including an instruction book for building a great base robot.  Our goal was to build a base robot to get familiar with the new set and begin learning the programming interface.


 The Capital Girls Team built the base robot in about 30 minutes, including using the wheels they elected to use when doing robot planning.  With 6 of the 10 team members at this meeting, we split into build and program teams.

The base robot the girls built was basic, with two motors for differential turning and a color sensor.  C, my daughter, later spent some adding a third motor.


Color Widget

While the build group was building, the program team wrote a program they called Master DJ.  It plays a different animal sound based on the color detected by the color sensor.  The goal here was to teach advanced program flow by doing something fun.  We discussed how this program might be used for the challenge.  The girls came up with using it to detect objects and to determine which program to run.  By doing the challenge, they reinforced their understanding of the loop and switch blocks.  To figure out the logic, the girls referred to our Program Logic Poster.

Here is the first version the Master DJ program; it has evolved to exit on the color sensor detecting white – and makes me want to invest in earplugs.






EV3 vs. NXT: Hardware

I love what Lego did with the EV3.   The new brick power and functionality is fantastic, but I think the addition of the new elements and attachment interfaces will make for stronger, more consistent robots.  Yes, I used the words ‘consistent’ and ‘robot’ in the same sentence.

New Chassis Pieces


Lego added two chassis pieces to the the set.  This may not seem like a big deal until you join them with the new motor.  The connection is very strong, which should create a robot that goes straighter and is more consistent.  I know, I used a bad robot word.


znapNew Treads

Lego did add a new tread system to the EV3. Treads look cool and every boy wants to use them, but in my experience, only use treads for FLL if you don’t want a robot to go straight.   They are great for climbing but the consistency trade off is not worth the gain.  Neither of my teams nor I have tried out the new treads yet.  The new system may work better, but I still have nightmares about treads.



Not in EV3 Kit

Motorcycle Wheel

wheelI want the old wheels back.  I am not a fan of the new fat tires.  I have not tested or seen my teams test them but the bounce screams inconsistency.  I am sure there is a reason for this fat tire design, I just don’t see it.  Also, the bigger the wheels the faster the robot.  There are no big wheels.  To satisfy my team’s big wheel addiction, we added the Lego Motorcycle wheels to our kits.


Robot Design Kick-off

Our team looks at robot building as a collaborative team building activity.  Before any pieces are connected, the team goes through a robot planning meeting using the Robot Design of Team Notebook. This allows the entire team to collaborate on a design and for a few to build it prior to the challenge release.  Everyone feels they own the robot, even if they did not build it.  This process takes about an hour but saves so much time later on. It is also a great team building activity and forces the team to document robot design.  We do this mid August, before the challenge is released but when the challenge is assembled.  The key here is to get a good base robot base and understand that it will be modified once the challenge is released.

Below are the questions the team uses for planning.  Part of the process is explaining and documenting why they selected a design.  In November, they will not remember why they made a decision but they can refer to their notebook.   If someone misses a meeting, they can refer to teammates notebook to catch up.

  1. What type of robot do you want to build?
  2. What type of wheels?
  3. How do you want to support the wheels?
  4. Will you use sensors for navigation?
  5. What sensors do you want to use?
  6. Will you use a starter jig or line following?
  7. How will you attach attachments?
  8. How will you power attachments?
  9. Can you use gears?
  10. What are the goals for the robot?  (e.g. consistent, fast, strong)

icon_pdfDownload the Robot Design Section of the Notebook.