FLL – The Chassis

The chassis is the base of the Robot on which all missions are completed. The motor, the wheels, the brick are typically all built onto the chassis to become the chassis of the FLL robot. Everything here is my opinion and should not limit any design. Kids can come up with designs that over come any limitations.

There are lots of different chassis, some good and some not good for FLL. There are a lot of things to consider. Some things to consider are:

  • Number of drive motors
  • Tracks or wheels
  • How, where, number, and size of wheels for the robot
  • Caster vs. 3rd wheel, vs. slider
  • Chassis size
  • How to attach attachments
  • Make the robot go straight

Number of Drive Motors

Typically there are 2 drive motors so 2 wheels driving the robot. Another design could be one drive motor and one motor to steer the robot sort of like a car. A motor driving two wheels and a motor to turn the robot left or right. With 2 drive motors, the 3rd motor is available for attachments.

Wheels or Tracks

When thinking tracks or wheels, the missions need to be considered. Tracks typically make for a slower robot and the turn can be inconsistent because the point on the tracks that make the turn may be inconsistent. However, for traction and going over small obstacles, tracks are great.

For wheels, they are move consistent on turning, wheels are typically faster, smoother, and more accurate. Wheels can have trouble getting over obstacles.

How, Where, and Size of wheels for the Robot.

The placement of the wheels are restricted by the placement and size of the motors. With ingenuity, there isn’t a lot of restriction because of the placement of motors.

The number of wheres is a big choice. With 2 wheels your robot is a teeter-toter. If you go to 3 wheel you now have a more stable robot but could have problems with turning. 4 wheels are stable but with only 2 wheels attached to motors the wheels not driven may be drug as the robot turns, and wheels to drag to well. With 4 wheels being driven by the motors (2 wheels for each motor), there still may be issues driving.

5 wheels…hmmm. I’ve never seen 5 wheel robot, but if someone has one, send me a picture. Six wheels may be OK, however there are problems turning and dragging wheels.

The size of wheels are important, too. Large wheels make the robot go faster. However, they also make the robot larch to start and stop. Going small distances may not be very easy. It may also raise the center of gravity where it may turn over easier. The smaller wheels are slower, but more powerful for going up ramps.

Caster vs. 3rd wheel, vs. slider

If you’re going with 3 or 4 wheels, the back wheel can be a wheel, a caster or a slider. A slider is simply a Lego piece that slides around the mat. It doesn’t roll so it can slow down the robot slightly and may not be able to be drug over obstacles. Below is a picture of a robot with 2 rear sliders.

Robot slidersA rear caster using a Lego ball as a 3rd wheel. It can roll any direction for turns but it is harder to build. Below is a picture of a Lego caster.

Caster RobotA 3rd caster wheel works well for going forward. However, if the robot backs up the caster wheel may push the robot to move at odd angles. And then when it moves forward again the wheel may start the robot out at an odd angle.

Caster wheel

Chassis Size

First, the chassis needs fit in the base. Also, it needs to be the right size to move around the mat, between the missions and other obstacles. It also need to be low enough that it doesn’t fall over while moving around the mat.

Chassis Attachment Attaching

The front of the robot needs a place to attach attachments. it needs to beams with holes in in places that allow other beams to be attached. It needs to allow for quick connect and quick disconnect. Below is my chassis attachment area. It’s probably not the best but it works for me. And that’s the key, it works for you.

How to make the robot go straight.

The best way to do this is by building the chassis correctly. Here is a video that helps with how to get your robot to go straight. The wheels need to be straight up and down. If they bent out at all, it could cause the robot to go crooked. Also, one thing to give the wheels more support is to put a frame around the outside of the wheels that supports them. This is shown below on my robot. The motor is on the inside of the wheels and a frame goes around the outside. The axle that goes between the frame and motor for support.

Also, just finding wheels that are the same size is really important. Sometimes, the wheels are slightly different and that can make them turn to the side.  If you choose 2 wheels, put an axle through the center of the wheels and roll them it shows if they’re the same. If the wheels roll to one side, then they are slightly different.


FLL Organizing a team

There are many different ideas about how coaches should organize an FLL team. Some of the organizational methods are good, some not as good. The key thing is to come up with a way that fits you’re (or the coaches) organizational style…unless that style is chaotic, I haven’t seen that style work yet.

These are my thoughts based on watching teams from either a mentor’s perspective or as someone who was brought in to teach/trouble shoot/guide for a short time, which seems to be something I do a lot of. I’ve also read others FLL’ers thoughts on team organization. Here are some of my thoughts.

  • The coach doesn’t need to be technical – just good with kids and organized. Understanding NXT-G programming and building helps. The FIRST organization has some good information on coaching on their international FLL site.
  • Recruit parents/mentor’s – The coach can’t do it all, you need help. They can help keep the kids on task with the project and robot missions moving. Mentors can really help with the programming and building ideas.
  • Manage and Administer the team – keep the team organized and moving toward the FLL competitions. Set practice schedule, meet deadlines from FIRST (i.e. registration, event sign up, etc.), and getting things done on time. A bigger task is sometimes managing the parents (probably the hardest part). Don’t let the parents use the FLL meetings as “babysitting”. If kids don’t want to be there, then they don’t need to be there.
  • Kid interaction – Depending on the mix of maturity of the kids, this can be tough. And, yes, there may be some crying and hurt feelings. Also recruiting the right mix of kids. Some want to be technical only (i.e. work on the robot) and some want to be project oriented. Some want to tell everyone else what to do. All of this needs to be managed.
  • Time management – have a schedule and stick to it. As an Engineer, I know the schedule will most likely be missed, but it’s a goal to shoot for. Keep the meetings on time (for the sake of the parents).
  • Area organization – There needs to be enough room for kids to work on the robot missions (4×8 ft table plus area to move around the edge, about 2 ft on each side. There also needs to be enough area for work on the project. This depends on the project, building/creating the parts of the project and area to practice. Also, a storage area for mission models, project parts, and table storage.
  • Stay connected – Communicate with other coaches and regional groups. The North Texas FLL forum is at (). Don’t go through this on your own. If you need to contact me (frc704mentor@qweztech.com) and I’ll check my contacts to find out who can help in your area. If you’re in North Texas, I can help.

Volumes have been written on coaching so do some reading.

Kid management and robot resource management is another topic. If there is only one brick (Robot Brain) this can be tough.The main thing I have is patience. Since all kids are different this is more of a coaches issues to determine how to organize the kids based on their personalities. Here are some suggestions on organizing the kids.

First, have the team come up with a basic chassis design that will accommodate attachments and can move around the field. This would include, at minimum, a light sensor for line following. Have the best builders build the chassis.


1.       My belief is to let every kids who wants to work on the robot, work on it. The robot portion FLL is organized into missions. They can be logically grouped for the robot to do multiple missions after leaving the base. A good idea is to pair up the kids and have them make the robot do a set of missions. They both work on the programming and the attachments for the mission. Not all kids have a technical aptitude but, I believe, that if they do, it should be nurtured. Also, have the kids help each other if some of them get stuck.


2.       At significant milestones in the missions, have the robot pair present what they did to the group (not every meeting). That way, every one kind of knows what’s going on and it helps toward team work.


3.       All the kids need to work on their project. Most of the time, when one pair is working on the robot, have the others working on the project. Occasionally everyone will need to work on the project for presentation organization.


4.       The kids need to work as a team. Work together, value each other’s ideas, and value each other. There will be the overpowering kids, the ones to talk a lot and telling others what to do. However, there will also be the quiet kids who think things out. These kids need to be given the time to be heard and their ideas are  listened to as much as the overpowering kids ideas. These are the introverts (which is a great thing) whose ideas will become the next Google or get a colony on another planet.


·         Los Altos Robotics (http://www.losaltosrobotics.org:8080/Main/FLL/coaching.html)

·         FIRST Lego League Coaching (http://www.legoleaguecoaching.org/)

·         FLL Resources (http://firstlegoleague.org/challenge/teamresources)

Dr. Ken Berry (Head Referee for the North Texas Region)

Get Prepared for FLL

As most of us FLL’ers know, the kickoff date for Senior Solutions is August 28, 2012. WooHoo! (link to where the material will be) Here in North Texas the Dallas Museum of Nature and Science will host a kickoff, tentatively planned for Sept. 8, 10 am to 12 noon in the auditorium at the Museum. There will be more information at the Museum FLL Link.

There are many new teams out there who are saying “what does that mean?” What it means is the field and missions will be released as well as the Rubrics for each area being judged.

For all the new coaches and mentors out, there are a lot of questions. While I’m happy to answer any and all questions, here are some links to information to get coaches and mentors started.

Official Resources:

Some other FLL resources:

Programming Resources

Mentoring and Robotics

“Tell me and I forget, teach me and I may remember, involve me and I learn.”
— Benjamin Franklin

Technical mentoring is very important in any STEM (Science, Technical, Engineering, and Mathematics) and especially in Robotics. The kids typically have the desire but not the know how. They need the proper guidance and knowledge to go forward. I’ve worked with several FIRST teams and seen various styles of mentoring. Some good some not as good. I would like there to be more of the good mentoring.

First, some general ideas on mentoring. I was looking around the web at mentoring and there was a pretty good blog on mentoring at the Center for Mentoring Excellence where there is a wealth on Mentoring. I would like to encourage everyone to read about mentoring in general.

Second are some of the things I’d like to share on being a mentor in FIRST. Here are FIRST’s mentoring resources . Here are some of my thoughts specifically on Robotic mentoring.

  1. Before the Robot season starts, get to know the kids. Talk with them what they like to do, what are there area’s of interest, and who they are. A lot of the kids won’t know much about robotics or engineering, but if they have a desire, then it will be up to you to help them explore different area’s.
  2. Share your experience with the kids – let them know how you work in the real world. What is your job like, what you work on, how you work, and how your company works. Let them know sometime you make mistakes.
  3. Talk “With” the kids, no just to them – That means listen as well as talk. Listen to what the kids are saying and ask questions to draw out there thoughts and ideas.
  4. Guide the kids in their learning – Show the kids how to do something. Get the kids to do it while you watch them Then get them to do it. Get the kids to check each others work, because here always needs to be quality control.
  5. Help keep the kids focused – Sometimes this means keep the parents and other  mentors focused, too. When it’s time to work, try to guide the conversions toward the issues, at hand. That means if your brainstorming keep the conversations on the robot and not on the days events. Leave the other conversations for later.
  6. Have fun – Try to make it fun for the kids and have fun yourself. It all goes easier when there is some fun mixed in with the work.
  7. Learn from the kids – The kids have lots of ideas and creativity and you should always listen and learn. They have a lot to give.

One more thing, always watch for the quite kids. These kids have a lot to give and don’t always know how to express themselves. Work with these kids, get them involved, and guide. Theses are the introverted kids with more to give than you can imagine. I know because that was me when I was young and I needed a good mentor to draw me out.

For First mentoring, here are some preseason reading on FIRST resources.

Mentoring is a big part of FIRST Robotics program, or any of the robotics or STEM program for that matter.

We make a living by what we get, we make a life by what we give. – Winston Churchill