New to 3pi

Hi - I just saw 3pi at the Maker Faire in Austin, Texas and have a few comments.

  1. It would be fantastic if there were a way to hack the motors to support some form of position encoder. A full-blown quadrature encoder would be nice but not necessary. What I was thinking of is painting one half of a gear in the gearbox white, the other half black (on the face, not the teeth) then using a tiny SMD-sized IR emitter/detector glued into position in a hole cut into the mounting bracket. Has anyone done this - or any other form of encoder for 3pi?

  2. If hack #1 above were possible, then IR wall detectors would make 3pi into a nice micromouse platform. I would buy one immediately.

  3. Late Sunday afternoon at the Maker Faire, there was a 3pi running around on a line on top of the table where they were being sold. I watched it a while then walked away. Roughly 5 minutes later I came back and the poor thing was spinning in circles. It appeared one wheel stopped working. I tried to put it back on the line but one wheel refused to turn. To prevent it from hurting itself, I removed one of the batteries. A short while later I went back and saw that there was a 3pi happily line following again. Does anyone here know what happened? Did the motor really stop working and someone replaced the 3pi with a new one? Was this just a software issue and a “reboot” fixed it? How reliable are these little motors?

  4. I think the 3pi is an excellent value for such a powerful platform. If I knew the motors had some form of encoder, I would have bought one on the spot at the Maker Faire.

  5. Thank you for choosing the AVR for 3pi instead of the horrid PIC! (Although the TI MSP430 would have been even better! :wink: )

- Dan

Hi, Dan,

Thanks for the feedback. We’ve thought a bit about a version with encoders, and we designed our larger wheels with that option in mind. However, we would probably have to go to another processor or to a multi-processor design like the Orangutan X2 to handle the encoders (which needs both extra I/O lines and more interrupt and timer/counter resources). I don’t know of anyone adding encoders to a 3pi, but they are relatively new.

What do you like about the MSP430, and why do you hate the PICs? Have you tried their new 16-bit architecture?

- Jan


You could potentially consider trying to craft some sort of encoders that hang down from the edges of an expansion deck and look in at the wheels from the outside. I have no idea how well this would work, if at all, but it seems like it could potentially make an interesting project.

We didn’t hear anything about a 3pi breaking at Maker Faire, though they might still be too busy wrapping things up to contact us about something like that. In general, the motors seem very reliable. We’ve been testing 3pis since May and selling them since August, and we haven’t yet heard of any mechanical failures in any of the hundreds of units we’ve shipped so far.

- Ben