Once the egg is loaded into Sphere-Bot™ it should be rotated and adjusted so that it rotates parallel to the base. The egg will probably never be completely parallel to the base and thats fine. There will always be some variance, considering that one end of the egg holder is a flexible spring that may move up or down by varying degrees. I guess a better term would be to try to get the egg to rotate mostly parallel.
Before attempting to program Sphere-Bot™, you need to find the range of movement for you pen holder. To do so you need to use your servomotor controller. For the example in this article we will use the SMC-04 USB controller.
The Servobotics SMC-04 controller can control four servomotors, see figure 17. They are attached to three pin headers on the board labeled P1 to P4. Attach the pen holding servomotor to P1 and the rotating egg servomotor to P2. On the SMC-04 board set the Manual/PC switch to PC interface. Attach the USB cable to the board and start the SMC-04 program. The program starts by rotating the servomotors to their center position.
Place an egg in Sphere-Bot™. Attach a fine point marker to the pen holder. The pen is placed inside the pen holder hole, and the 6-32 screw is tighten up against the pen to lock it snuggly in place. I usually set the marker height so that at center egg position, the pen holder plastic is tilted upwards. This insures writing on the end as the pen holder is moved to the lower portions of the egg.
Set the speed control on the programs interface to 10. This will slow the servomotors speed forcing the pen to move slowly. Then using the slider controls or text box by the slider controls slowly increment the numbers until you have written a line close to the end of egg. When entering numbers in the text box, you must hit the tab key after the number is entered to move the servomotor to that position. As you enter numbers, or move the slider the servomotor will move the pen holder writing a vertical line on the egg. Next decrement the numbers until you reach the other end of the egg. Keep at least a 1/4 boarder on top and bottom of the egg. The two numbers you have for the top and bottom of you egg will be used to write programs.
In my test, the range of numbers I obtained were 175 to 115. Your mileage will vary depending upon the size and shape of your egg, diameter of pen, height of pen when placed in the pen holder and of course the tolerances in the components.