To gauge how far the robot has traveled and to count the number of rotations on each wheel some sort of sensor is needed. This design has two 5mm holes to accept Infared (IR) LEDs which will shine light through the matching holes in the wheels. This will then reach two Infared Phototransistors inside the chassis where the pulses can then be sent to the electronics to be counted. The tabs are the ONLY parts that get any glue on them.

Sand the surfaces with some 150 grit or 220 grit sandpaper to remove the laser cutting marks and make the model look better. The wood can be stained if desired while it is in individual peices. Once the surface is the way you like it, apply a small amount of white glue to the tabs and insert them as shown. Be sure they sit flush and square, then allow them to dry.

Use the supplied screws from the track kit to attach the parts as shown. They should rotate freely when you are finished... if not, then back off the screws about 1/4 turn until they rotate without binding. If they bind it will effect how the track robot moves. The large diameter wheel has three holes where the light from the sensor can shine through. If you look through the hole in the wall plate, you should be able to see through when the wheel is rotated. It may be required to paint the inside of the wheel black to assist the sensor in working better and avoiding stray light energy from getting through. You can obtain plastic spray paint at any home improvement store or hobby store. You can also use hobby paint... but DO NOT use airplane dope as it will melt the plastic!