Kyle Vogt

Wheelchair robot with cover and seat removed

I responded to a summer job offer to work at Panasonic Boston Laboratory doing robotics research.  It turns out that an engineer there just wanted to see if he could find an intern to whip up a cool robotic wheelchair to help disabled people navigate their homes.  He wanted it done over the course of a few months, which is the length of a typical summer internship at Panasonic.  I had my doubts about the timeline, but I was still happy to take him up on the offer.  We set a few long term goals, put together a budget, and starting buying parts.

The wheelchair started as a Jazzy Powerchair.  I stripped the heavy lead-acid car batteries in favor of some smaller gel cell batteries.  It had really powerful gearmotors, but I dropped the voltage down to 12v to extend the battery life and make things a bit safer.  The joystick interface looked fairly cryptic, so I ordered a Roboteq motor controller to wire up to the single board computer running Linux.  One of the project goals was to make every wheelchair modification easy to replicate.  I had a rudimentary picture of design for manufacture in mind. We had a steel frame welded at a local shop.  It contained the batteries, computer, motor controller, and power supplies.  I ended up with a nice, self-contained “power box” suitable for running anything from a wheelchair to a Battlebot.  The entire frame lowered directly into the space where the two large car batteries once lived.

Screenshot of object tracking code

One of my favorite sensors for use in robotics is the SICK Lidar, but that just didn’t make sense for a project like this.  Few people can afford an extra $6K for that kind of sensor, and it certainly wasn’t in the Panasonic budget.  I chose analog infrared sensors with a range of about one meter and sonar sensors with a range of several meters.  I ordered eight of each sensor and wired them to give close to 360 degree coverage of the perimeter of the wheelchair.

I also used this project as an excuse to dive into basic machine vision.  I played with stereoscopic cameras for a while when working on the DARPA Grand Challenge project, but in this case a simple webcam like the QuickCam Pro 5000 worked fine.  In fact, I enjoyed writing software for the webcam under linux so much that it spawned an a little robotics library.  Anyways, I didn’t get very far with the camera other than writing an library for it and doing a couple basic demos.  I did get the wheelchair to follow around a person wearing red, which basically killed productivity at Panasonic Boston Laboratory for the afternoon.

Layout of custom sensor board

As usual, I chose to build my own sensor processing electronics for this project instead of just buying something off the shelf.  In hindsight, it would have made more sense to just buy a USB data acquisition board, but I enjoy making these kinds of boards, and it’s at least a good learning experience.  This one used an ATMEGA128 to read the sensors and communicate with the Linux SBC. My supervisor also had some data-logging projects in mind, so he had me add a few connectors and write software for several other sensors.  It ended up supporting temperature sensors, thermocouples, flow meters, and some weird light sensor.  The resulting product was a pretty useful board, but it probably wasn’t worth the week it took to design the pcb and write software and firmware for everything.

At the end of the summer, Panasonic generously agreed to donate my robot wheelchair to the student-run robotics lab sponsored by MIT’s Edgerton Center.  I’ve been heavily involved in the group’s projects so far.  We’ve entered the DARPA Grand Challenge with an $80,000 robotic pickup truck and built a $30,000 robot to give tours to prospective MIT students.  Needless to say, I’m glad the wheelchair ended up in the hands of other robot enthusiasts.