Design your own robot

Every robot is unique. There are things one may want to consider when designing a robot. Some are related to the challenge of the year and some are general.

General Design Constraints:

• at most 4 motors, ideally
  • two motors for the wheels +  for stability
  • 1-2 motors for the attachments

• balanced left-right to be able to move in a predictable way
• accesible EV3 brick
• no wires in the wind
• check the height of the obstacles over which the robot has to go (the dog barrier of FLL Allies 2016 was quite a problem)
• check the width requirements set by the challenge: small enough to pass between the pieces set on the table (we had a true tunnel for Animal Allies 2016)
• light enough if you want to hang the robot on a wall as in Animal Allies 2016 ( we did not want to)

Those are not bugs, but features one has to deal with:

• sensors are fragile, and need to be reset periodically in your program. Once you reset them, wait a second to allow the reset to take place.
• color sensors need to be in front of the wheels, and at a certain distance from the wheels (our rule of thumb is at least the radius of the wheel away from the wheel) to be useful for line following
• color sensors readings depend on the intensity of the ambient light, thus they have to be placed close to the mat (according to documentation 4-12mm (1/2 – 1 1/2 studs) off the surface you are detecting )
• the battery has an effect on the motors. A recently charged robot will turn faster, more, or go further.   At low levels the programs are just not working in the same way. Is there a way to go around? Yes, programming with safety checks, and tweaking your programs to work well at medium battery levels.

Looking at Animal Allies challenge, we made a list of the missions we could do, and a list of missions we dreamed of doing. As only two members of our team are not new to FLL we had to be realistic.

List of  practical tasks for the robot :

• turn, turn in narrow places,
• follow black lines, stop at black lines,
• pick up things, push things in specific areas, gather things,
• put things on heights
• align itself at beehive,
• align itself at the milking station and kick the cow first

Our Design Choices :

• symmetrical construction left-right
• guarded wheels to prevent wheel slippage, objects getting entangled under the robot, easier aligning with the walls, black lines
• use medium wheels
  • larger wheels travel faster, need very precise algorithms which catch up errors very fast (not our case)
• use wheels with a flat profile
  • we used initially the standard NXT wheels and the rubbing over the barrier made them slightly detach from the rim, and our robot veered constantly
• use wheels as sensors, measuring precisely (using your robot’ control panel) the number of rotations needed to arrive at a certain point, the number of degrees a robot needs to turn
• a robot without additional sensors is not very reliable so we used:
  • color sensors can detect the black lines of the mat or follow them
  • an ultrasonic sensor  can detect the distance from the walls
  • a gyro sensor to tell us if we were indeed moving straight, or turning enough, and we placed it parallel with the axis of the robot to accurately measure turns

Save your designs using the free Lego Design application:

http://ldd.lego.com/en-us/