Attaching a pen to the 3pi

Does anyone have any ideas how to attach a pen to the 3pi so I can use it to draw on large sheets of paper? It would be easy enough to attach it to the back but I want to have my turns as sharp as possible. Under the center of rotation would be perfect but there’s basically no clearance there. It’s been suggested to use large wheels to get more space but even an inch wouldn’t help much, and I lose the use of the line tracking sensors.

Also there’s a lot of material on people building line-following and maze-solving robots with the 3pi, but these projects were intended by design. What sort of things are people doing that the designers didn’t have in mind


Can you make use of the prototyping holes between the motors, or have you already soldered a header strip there? I know they’re small, but maybe you can fit some sort of really thin pen through the lower AD6 hole, which is the dead center of the PCB? I’d love to hear about it if you get your 3pi drawing something!

There are a few non-standard 3pi applications that have been mentioned on this forum so far:

I know of several people who are trying to use groups of 3pis for swarm behavior, but I haven’t heard any results yet.

- Ben

Oh, and I should add that one fun but rather pointless application is using the 3pi as a simple musical instrument. You can program the buzzer to play notes based on what the reflectance sensors are seeing, and then you can use your fingers to selectively “strum” (i.e. cover and uncover) the sensors to produce music. If you want to make better use of the 3pi as a robot, you could it drive around an irregularly shaded course and play notes based on what the sensors see as it drives.

I’ve wanted to write a program like this for a while, but I just haven’t gotten around to it yet.

- Ben

Hi Ben,

Thanks for replying. My 3pi is in the mail now so I don’t have it in hand yet, but looking at the pictures, it looks like you mean the 2x7 row of 0.1" spaced headers? I’m not sure what would fit through there besides a mechanical pencil lead. I guess that could be used as a mounting point if I can find some sort of marking instrument short enough to fit between the robot and the paper underneath.

My short-term goal would be to make a rudimentry LOGO implementation and have the bot as a physical turtle. If there were space I’d even want a solenoid to raise and lower the pen since that’s supported in LOGO.

Hello Oracle,

Experimenting with the marking devices on my desk I found what you suspected. None of my pens would fit through any of the holes on the 3pi, including the expansion kit mounting points. I was able to put mechanical pencil lead through the holes and mark a piece of paper without breaking the lead. This may work for a short time but the lead will eventually get used on the paper and stop touching the writing surface.

- Ryan

hi there. let’s say the pen’s problem is solved … is there any sample program out there that enables the 3pi to become a tutle/drawbot? thanks!

Hi, pmgomez.

I haven’t heard of someone making a program like that. If you decide to make it, I’d be interested in how it goes.

- Ryan