I got my EggBot as a present on the 25th. I assembled and ran into problems with the pen stepper motor. When I tried the first demo pattern, the pen arm moved up the to top of the egg and just shuttered during the entire plot. I retired with the arm centered at the far end and I encountered a similar problem.
In the manual mode tab, I can send commands to the pen motor of 100, -100, 100, -100 and everything works fine and the arm returns exactly the starting position. If I do the following sequence, 100, -100, -100, 100, on the second 100 command the arm shutters and moved in the (-) direction. (if looking at the eggbot the (-) direction is to the right. I tried some other test patterns from the example folder and some very strange results. With no egg installed, and the two ends moved to the farthest position so as to not interfere with the pen arm. I ran one of the tests. The Pen arm started in the center of there the egg would have been (12-o-clock position), but as the plot continued it moved more than 180 degrees clockwise, and the pen arm was inverted when the plot finished. I re-ran the plot with the arm starting at the 6-o-clock position, the plot progressed but the arm stayed between 5 and 7 o-clock positions, and the motor movement was not smooth.
I swapped the egg and pen steppers and swapped the connections on the EBB. Same problem.
I have re-flashed the FW with the latest build from the support site. I have pressed the RST button after connection to the USB. The problem remains.

Any thoughts on what to try next?

Hi Steve,

Have you tried adjusting the current to the steppers, using the current adjust potentiometer (tiny pot marked "CUR ADJ" on the EggBotBoard)? The current increases as you rotate CCW. Starting all the way CW, both motors should be very weak. As you increase the current (turning the pot with a small screw driver CCW) you should be able to feel the motors increasingly resist moving by your hand. The ideal setting is one that provides smooth, relatively low-noise moves from the steppers, but has enough torque that the pen arm is not "floppy." For me, this is about half way CCW, maybe a little less. More current, while increasing the motors' torque, leads to jerky moves, with position errors.

In the manual mode tab, I can send commands to the pen motor of 100, -100, 100, -100 and everything works fine and the arm returns exactly the starting position. If I do the following sequence, 100, -100, -100, 100, on the second 100 command the arm shutters and moved in the (-) direction.

As Bruce says, this could be due to a problem with the motor current setting. The tests with the sample plots are not generally helpful for understanding what's going wrong. Please try setting the motor current. Then, try (with only the pen arm backer in place) full +/- 3200 step rotations. You should be able to move in a full circle each way, and exactly one circle in each direction.

Bruce was correct. I adjusted the pot and the EggBot works perfectly.
Thanks for the support and quick response.
I love your product and I really love the documentation; it is the best ever!
The EggBot is the single coolest thing in the world. I hope you guys make a ton of money.

steve