Creating a home made 3D printer pen (3Doodler)

I am looking to design and build a homemade version of the 3doodler for use at a table at a local science expo. Knowing there is bunch of engineers on these forums, I chose to bring this little project to the RepRap forums. So please, if you have any input at all, post it!
I will break down what I am looking for / currently thinking regarding the design of the printer pen.
Extruder:
Considering the fact that I won't have to compensate for variable speed, temp, and layer height, I don't think the use of a stepper motor is required. What hi-torque / low rpm motors do you recommend? As for the actual extruder body, I was planning on using a reprap design.
Nozzle:
Should I just drill a .5mm hole out a bolt and go from there or should I go the machined nozzle and heater block route?
Hot End:
I do think a variable and monitored hot end with a thermistor is required. This will allow me to switch between PLA and ABS. As for monitoring and adjusting the temp, how should I interface that with a computer? Or should I go the soldering iron approach (no thermistor, just a heating device that will stop at a certain point)? I am open to any and all suggestions regarding the hot end. This will be the most difficult part.
Hot End to Cold End Insulation:
Fiberglass wool? Bamboo? Peek? Not sure what the best material to use is. Any ideas for the transition between the extruder and the hot end w/ insulation?
Plastic Filament:
I am currently leaning toward ABS as it has a smaller cooling window and is a bit less brittle than PLA. However, I cannot chose between 1.75 and 3mm filament. 1.75mm is easier to procure for me but 3mm may be more feasible.
I apologize for all of the open-ended questions. I am still in the feasibility check phase and have not yet begun the design process. I thought I'd bring it to the creative RepRap forum for ideas before I began. If you think of anything else I did not mention above, please post!

Hi ascherr, welcome.

Sublime built a "homemade version of the 3doodler" years before 3doodler existed. You can find his files for it here: [github.com]

It sounds like you are interested in designing a new system from scratch. You might want to consider purchasing an off-the-shelf extruder, and then simply sticking a custom-made ergonomic handle on it. The drive electronics could be some simple standard RepRap electronics (for example RAMPS 1.4 with an Arduino). You can make minor modifications to the firmware so the extruder is basically controlled on/off with a push-button (or speed controlled with a potentiometer if you like...). It would be like building a 3D printer but without the XYZ part.

You might save time and money in the long run by just getting one of the established products that already exist and modifying it to suit your needs.

You will certainly need to make a small hot-end. That might be useful for many other printers in the future. I think you need to have the feeder and hotend separated, you don't mention it but that will make the 'pen' much smaller. For cooling why not try some version of water cooling? Someone in this forum had made a dual feed watercooled printhead. That will make a twopart solution: one is the hotend with nozzle, heater and handle, the other will hold the feeder mechanism, waterpump with cooler and the electronics. Unfortunately the 'cable' between the two units will be thick and have a tube for filament, two water hoses, wires for heater, termistor and on-off button.
I think it is possible to do this.
/Nils-Olov