I bet that if you use the S2 robot for scribbling activities you have also dreamed a pen lifter for your robot.
Personally I was inspired from two amazing projects in order to create my own Kit:
1) The Savage Circuits TV Episode 9 from Chris Savage
2) And the Parallax S2 internal Pen lifter mod from Rich Harman (W9GFO)
My suggestion combines characteristics from both above proposals.
The Kit I suggest is very easy to install and it is also internal and a 100% invisible from the outside of the robot. So it doesnt change at all the external characteristic of your S2. However the best advantage of this kit is the fact that you can build it without open the robot. So you avoid the complicate measurements and tests. When you finished the kit construction you can open your S2 and install it into the robot following 2 simple modifications.
Here is my kit:
The kit consisted of : a Hitec Hs-55 servo(1), an aluminum servo bracket (2), a plastic lift cup (3), a servo horn that it is inclouded on the Hitec servo(4), a small srew that is inclouded in the Hitec servo pack (5) and three 4-40 x3/8 screws and nuts (6).
In order to build and install the kit into your S2 robot you also need two spin codes:
1) S2_Servo_pen_center.spin which centers the servo Pen and 2) the S2_pen_lifter_test.spin which tests if the kit lifts Up and Down the pen properly.
Two mondifications are nessesary in order to install the Kit into your S2 robot chassis:
1)You have to drill a hole of the botton of the S2 chassis (you can avoid this modification if you use some glue in order to stick the Kit into the robot) Personally I dont like very much the use of glue .So I recommend to open the hole and use a screw and a nut.
2)You must remove 10mm from the pen tube on the upper part of the robot chassis using a Dremel tool in order to give the necessary space for your pen lifters movements.
I hope that the following video will give you answers for any questions you may have about the kit.
I also send you the SketchUp model with the pen lifter Kit. Users who have a 3d printer will be able to create easily the lift cap and the servo bracket using this model.
I would like to thanks Phil Pilgrim (PhiPi) and Rich Harman (W9GFO) for their precious help in order to overcome my difficulties with the Pen lifters software and Ken Gracey (Parallax) for his generous offer (the S2 Robots) which gave me the opportunity to experiment with the robot.