Servo - November 2008

all but red and green colors.

Like many others, I have a man-child obsession with building a robot that is capable of fetching me a cold adult beverage. I soon learned this was much easier said than done, but I had to start somewhere. The basis of locating specific physical items within an environment is known as “object tracking,” and can be done a few different ways. The easiest way for me was to implement colored object tracking. The concept behind this is fairly simple: RGB color filters are applied in Roborealm to remove all but a specific FIGURE 5 color. I had a red ball handy that proved itself to be an excellent prop for this. To remove some background noise, I applied a mean color filter which essentially blurs the image. Roborealm also has a very handy center of gravity (COG) filter which places a box around the largest concentration of same color pixels on the screen, and outputs an X,Y coordinate of its location. The SSC- 32 servo controller has an interface module that can be added to the pipeline, allowing variables to be assigned to different channels. Lastly, there is a VBscript module that provides a simple programming interface to tie all of the variables together.

I created a program that tracks various colored objects using the pan and tilt head of my robot. Figure 4 shows the VB code I used; the entire .robo file containing all pipeline settings is available for download from the SERVO website ( www.servomagazine.com). This program works by filtering out everything but a specified color, placing a COG box around the mass of same colored pixels (the object), and the VB code reads the X,Y coordinates of the COG module and translates those into servo positions on the pan and tilt to keep the object in the center field of vision. I have a video hosted on You Tube showcasing this object tracking ability at Robogames 2008, found here: www.youtube.com/watch?v=GfMCaaePFBw. Figure 5 shows what my RDP session looks like when piloting my robot around the house via telepresence.

The next step for me will be experimenting with object chasing. I can easily track the size of an object using Roborealm, and have been somewhat successful in being able to drive towards the objects, but I still hit a lot of walls. I’ve seen some work done where Roborealm can draw lines at the floor to ceiling junctions and use those to avoid running into walls, so implementing that will be the logical next step.

the possibilities of PC-based robotics. As my own programming knowledge grows, I think my robot’s potential will grow exponentially, as the ceiling of possibility is nearly limitless with this much computing horsepower at my disposal. While it’s hard to sum up a year long project in only three short articles, I hope that some of what I learned in the process can be passed along to others. I think the biggest thing I’ll take away from this project is that we can’t always hold on to what is comfortable. Microcontrollers are still great tools but they are severely limited in what they can do when compared to a PC-class processor. Start thinking of them as complementary electronics to a larger, more powerful system and you’ll be surprised what solutions become available to you as an experimenter.

Welcome to the realm of PC-based robotics! It’s here now and is the future of our hobby. For updates on the progress I make with this project, visit my project page at the Trossen Robotics Community. SV