Below are some things we learned about designing and programming a competition Lego robot using the NXT. Keep in mind a robot that is consistent and accurate has a better chance of completing all of the missions. You can scroll down or quick link below.

MMRA rookie Workshop Fll robot design tips

MMRA rookie Workshop Fll sensor tips

FLL HELPFUL DESIGN TIPPS

Working with the students

  It is a balancing act working with the students, you want them to do 100 percent of the build but you also want to teach them about engineering, science and math.

  The students do not have a clue of what they are doing so you will have to help guide them through the design and build. You can give them work exercises that allow them to test design ideas like.

a.       Wheel sizes

b.      Gear ratios

c.       Motor speeds

d.      Drive systems.

   It is good to come up with a few designs and test them. Use test results to choose the best design not popularity. Students tend to be bias toward there friends as apposed to the best design.

  Have the students write down the tests and the results as they can share this information with the judges. The judges like to hear about problem solving by the students.

 Game Specific Designs

  It is great to design a robot to do all of the missions but may be overwhelming for rookie teams to do and unnecessary.  To impress judges you only need to accomplish a few missions very well. You will be showing the judges one or two missions and if you can do them well many times in a row they will give you good reviews.

 The judges will be looking for:

a.       Durability – Evidence of structural integrity; ability to withstand rigors of competition

Build a robot that is of sound construction that does not break or rarely breaks.      

b.      Mechanical Efficiency – Economic use of parts and time; easy to repair and modify

The robot should be streamlined and efficient with out excessive parts. (Like algebra reduce it to its simplest form after it is built)

c.       Mechanization – Ability of robot mechanisms to move or act with appropriate speed, strength and accuracy for intended task (propulsion and execution)

The robot devices should be sound and work well with the speed being used

Build the robot than modify it as needed. It is easier to redesign a robot than build a new robot. Add strength, efficiency as you go.

  It is common practice to use two motors for the drives and one motor for the arm. The arm should be built in a way that the attachments can be changed with ease. If you plan on doing most of the missions you have to pay close attention on the speed of attachment change out but if you stick with three or four missions and do them well you will not need to worry about change out time.

  Gears can be used to lift items or you can go with a simple direct drive lift. The students can work with both and determine what is best for their game.

Judges

  When in the Technical judging room the students should be ready to answer any questions by the judges about the robot design process. One student should not answer all of the questions, it is always better if all the students can make some input to the judges. They will be asked questions about gear ratios, why did they choose the size of wheels, how did they come up with the design, what makes your robot unique, show us a mission, who built the robot (hopefully all the students had some input) and many more questions. If they do well they may get a call back and must answer more questions from more judges. The questions will be harder but the students should have no trouble if they have made it that far. Mentors are not to assist in the judging process, the students must do it all on there own.

Innovation & Strategy

  The judges will be also looking for the following in your robot design explanations.  

a.       Organized and well explained – Ability to develop and explain improvement cycles where alternatives are considered and narrowed, selections, designs improved

Must be able to explain and document the development process of the robot build.

b.      Mission Strategy – Ability to clearly define and describes the teams game strategy

Must be able to explain a clear strategy for the game missions

c.       Innovation – Creation of new, unique or unexpected feature(s) (e.g. designs, programming, strategies or applications) that are beneficial in performing the specified tasks

Come up with a creative new design (do not use previous years designs)

   A mission contains items that are moved, pushed or picked up. Your robot will travel to the game piece and interact with it and return to home base. Your students should not touch the robot once it leaves the home base or points will be deducted from the score. It is common for the robot to be returned to base by the students but that mission will have to be started over to gain the points. There are specific rules regarding this and they should be studied.

  The game is time limited and consideration for the amount of time needed to complete the missions should be taken. It is very difficult to complete all of the missions but some teams do. Because the robot mission portion of the competition is a small percentage you should not make it a top priority to complete all of the missions. Do three or four missions very well and your students will feel much better about themselves than if they fail at 10 to 12 missions.

 You will want to get the design and build process done as soon as possible that way you can get the bugs out and practice. Practice and time the missions as many times as you can.

 It is helpful to have a box to carry your robot and attachments to the field but it is even better to have a small cart 2 to 3 ft tall. You are allowed to set your robot up, turn in on and select your program before the match starts.

You are allowed a maximum of two drivers (students) at a time at the field. Once the match starts you are allowed to tag the two drivers out and two new ones in. it is good to do two to three missions and change and allow the other drive team to take over as it makes it easier for the students to remember there missions. You can do this up to five times. (10 students / 2 drivers = 5 drive teams max)

 Tournaments

  Our first tournament is a practice tournament (Lego Fever I) and does not count but will help you refine your team and any problem can be solved before the next tournament. Our second tournament (Lego Fever II) counts toward going to the state championship and is not as relaxed as the first. The State Championship is a very serious competition and you would be going against other winning teams from around the state. The winner of the State Championship has a chance to go to the world robotics competition and compete against teams from around the world.

Robot Balance

Placement of the axel "A" will determine how straight the robot will go, if it is too long it will not turn well and if it is too short it will not run straight. Experiment.

Placement of the center of the weight "C" will determine how well the robot will turn, if it is too far forward it will tip and not turn accurate. If it is too far back it will turn hard. We place the arm and attachments on the front of the robot to allow for the balance to be close to the drive wheels. with the balance close to the drive wheels it puts most of the weight on the drive wheels which gives good traction and makes for accurate rotation count.

Drive Wheels

The size of the drive wheel is very important, a large wheel will not give you accurate rotations, and a small wheel will not give you enough speed. If you must climb items in a game  than the large wheel is important but you must than gear it down for accuracy.

We have found that using tank tracks restricts how well the robot will turn accurate. Using a set of front drive wheels with a skid roller wheel in the rear is the most effective. It rolls forward very easy so it will allow for good count of the rotations and if the skid rollers are thin than it allows for the turn to be with little effort making the turns accurate.

 Other things will affect the accuracy of the robot are the temperature of the tires, warm soft tires grip better than cold hard tires, and dust on the surface, which allows the tires to slip. If the drives are cold they will not move as easily as warm drives. Weight shift from use of the arm by lifting items will also change the accuracy. A fully charged battery verses a week battery will affect the accuracy count also. 

If you have small wheels with the power level at 100 percent you will get more rotations thus give you a more accurate count but you must be careful that the wheels do not slip or jerk the robot and held parts with the high power.

Programming using meters is more accurate than using inches, but using degrees is even more accurate because their are 360 degrees in a rotation. So if you program for one rotation than the wheel rotates 360 degrees and if you program 1 degree your wheel turn a fraction of the 360 degrees. You will also have to insert a motor reset block to reset the rotation count. If you use coast the rotations can accumulate and give false rotation counts. Brake is more accurate but can slow down the movement of your robot.

To help with turn accuracy you can drive one wheel at a time for turns. Using the turn program built into the blocks, both wheels are driven (oppositdirections) which can give you a double count . One degree of turn drives both wheels one degree which in reality is two degrees which doubles the desired distance but if you run one wheel one degree and the other does not move you are actually moving one degree. The diagram below shows this and you can see that the turn circle is larger for a one drive turn thus more accuracy.  If the wheels are farther apart your turn will be more accurate.

Arms & Attachments

Arms and attachments: if you make your arms and attachments simple it makes changing them easier. You have less that will go wrong. Design your missions using one attachment as many times as possible and as the missions progress detach items not needed as you go. It is easier to take parts off the robot than it is to install them. An example is lets say you have an arm with many parts to do multiple missions and as the missions progress you take off the items you don't need and by the end of the missions you may not have any thing left, than the last mission is the one where you must push something to place it. If you design the attachments to be added during the matches it may take additional time to assemble and make it all fit. One way of making this attachment easier is using pins and loops for the attachment. Another words provide a part on the robot that has a loop sticking out that you can slide a pin through it and your attachment. When attaching the item you mate it to the robot and slid a rod with a handle through it. Removal is just as easy. Some times your items do not even need to be attached, just drop it into a hole area in your robot and gravity will hold it in place.

 Build two robots

Build two robots if you can. After you build the robot you are going to compete with, build a second identical robot. This will allow two teams to program at the same time by taking turns with the computer and the field. This will cut your programming time in half. Also while working together like this they can see how each others missions will come together at the end. When all the programs are completed and because their are slight differences in the movement of the two robot you must reduce to one robot. Choose the best robot of the two and use that robot for the final fine tuning of the missions. The drivers should be selected from the two Program teams, they are familiar with their programs and should drive that portion of the programs. This would be two drivers for the first half and two drivers for the second half. This will also make it easier for the drivers to remember what they must do for their missions.

 Remember to place the access door for the battery in a way that you can remove it with out taking apart your robot. This will make battery changing quick.

Sensors & Zero Point

Don't be afraid to try the sensors. Once you use them they become easy. Using the mat lines to locate your robot is always a plus. If you build a light guard around the light sensor it will protect it from unwanted light or different light levels. Using the ultrasonic sensor is useful to have your robot stop or turn at the right spot. It can check the distance to the wall or the item.

 As you program turns the more turns the farther off the robot can get from the intended finish point. If you can find a way to have a zero point one or two turns in, its like having a new start point. Just make sure your robot is at the same angle every time you reach that point.

 If you can have two lines to check ("A" above) or a wall to run into or a game piece that don't move, you can use it to bump the robot into, its like telling the robot it has a new start point. When running into items the program may freeze the program because it can not finish the count when using degrees or rotations so you use them to get close than switch to timed distance to  continue with the program and bump into the item.  Also build the bumper solid and flat so it will help square the robot against the wall ( add a burst of timed full power to square the robot) and from that point you can go an additional two turns and be accurate at the final destination.

Above: You can put a complete mission in a My Block than in between add a Program that waits until the button is pushed before it will proceed to the next mission. Doing this you only have to push one button for the next mission and do not have to look through the missions to continue. Notice that we added mission 3 as a do over just in case of failure (the my blocks save on memory space also).