Size Matters and the really nifty trophy he won at the Chibots advanced line following contest April '03 An advance line follower with two modes of operation The idea behind Size Matters was to create a line following robot that could handle the wide variety of elements in the Chibots advanced line course. Here is the 2002 course. There were two main challenges in the course beyond the normal line following, the acute angle turns and the hill. The other obstacles seemed to be handled well by most line followers. The problem with acute turns was solved with two modes of operation controled by the line sensors. The hill was overcome by carefully watching ground clearance and center of gravity. Below are some details of the design.

General Design Thoughts The base of this design was built around the processor board, servo chassis and servos of a PARTS Mark III mini sumo robot. I had gotten these basic parts from their store at www.junun.org. It's a great place for quality low cost servos, sensors and OOPic controllers. Line following contest are judged by the time it takes to complete a set number of laps. So speed was one of the major design considerations. Using only hobby servos limits the speed a robot can travel. I standard servo turns at only around 50RPMs. To over come this I ran the servos at 8 volts and used oversized 5-1/2" tires. Thus the name Size Matters. The faster a robot goes the more problem the acute angle turns are. By the time the front sensors on a fast robot sense the turn they are beyond it and over blank space. It seemed to me I needed two modes running at the same time. One for the normal line following over smooth turns and another to pivot in place to make the acute turns. To do this I added two additional sensors back close to the wheels. These sensors pickup the acute line after the main sensors have lost it. Here is a movie of Size Matters showing both kinds of line following. 320 x 240 mov - 400K Test course This is one of the test course that I ran Size Matters on during building and testing. I contains many of the elements of the Chibots advanced line following course. The full Chibots course has: Smooth turns 90 degree turns Acute angle turns Line breaks and offset lines Wide lines Crossed lines Hill I mocked up each of these during testing.   Size and Power Size Matters is 6" wide by 8" long and weighs 650g. Power is from 6 NiCad AA cells, to reduce speed for the advanced course one battery is removed and replaces by a jumper. This brings the voltage to 6.4V and brings the motor speed in line with what I needed. Processor and Motors The controller board is from a PARTs MarkIII with an OOPic processor. I've added an extra board on top to give room to connect the extra sensors and add DIP configuration switches and a start button. See the programing section for more information. The motors are ball bearing R/C servos that have been hacked. They currently use the servo electronics but I will be changing to an external H-bridge and PWM in the future to get better motor control. Wheels The over sized wheels, about 5-1/2" in diameter are turned from expanded PVC. I turn these on a drill press and epoxy round servo control horns into recenses cut into the sides. The edge of the wheel has a groove cut that holds the tire. The tires are made from o-ring cord cut from bulk and glued into circles just smaller than the wheels. Sensors There are a total of six sensors on Size Matters. All of them are digital IR sensors similar to Fairchild QRB1134s. The front four are used for normal line following and gentle curves. The two outboard sensors are used to detect 90 degree and acute turns. The outboard sensors are pivoted to ensure ground clearance over the hill. See the programing section for information on how the sensors are used.   Programming and Logic Here is information about the processor and programing. The exact code for Size Matter would be of little use to most builders but the logic and how the OOPic works is covered.

If you have any questions or comments please email me at: mdavey@new.rr.com