November 18, 2007

Computer Vision Platform

Filed under: PicAXE,Robotics — profmason @ 1:27 am

oldremote.jpgI experimented previously with making a color tracking missile launcher. I am slowly working toward building a laptop carrying robot platform. However, I had thought that instead of putting the laptop on the robot, put a wireless link between the robot and the laptop. One of my primary interests is doing computer vision, so I also needed a wireless camera mounted on the platform.

I finally found a useful wireless serial link in the form of the XBee modules which are discussed here. I purchased a wireless camera and put things together. Here is the first iteration of the platform. I used the based of an old toy that was put out as a donation at a RSSC meeting. I wired it up to a pair of Toshiba TA8050 motor controllers and drove it with Picaxe 08M microprocessor. The microprocessor reads the serial value from the transmitter and drives the motors appropriately.

Unfortunately this base was far to jerky to do reasonable computer vision based navigation. I had several problems to work out including keeping the fact that the XBee modules really need exactly 3.3V volts. If the supply voltage to them fell to 3.1 volts they stopped transmitting. I started feeding a 9V battery into the regulator that supplies the XBee and many of the pronewremote.jpgblems went away.

To solve the problem of the jerky toy platform, I built a new platform based on a a tamiya dual motor and a tank track kit. After putting the tank tracks together, I used some standoffs and put a larger platform on top to mount the camera, breadboard and batteries.

The new platform seems to be much smoother then the old. I wrote code in Roborealm to track red squares on a the table, moving left or right until the square was centered and then moving forward until the square reached a certain size in the image.

Here is the cost breakdown on building a fairly robust computer vision platform. (As usual labor is NOT included!)

  • Tamiya Dual Motor $9
  • Tamiya Tracked Vehicle Chassis Kit $13
  • XBee Module Pair $38
  • USB Wireless Camera $69
  • Recharagable batteries from old laptopnewremote2.jpg
  • Motor Driver Chips $2
  • 2 Pic-Axe 08M $7
  • 2 3.3 Volt Regulators $1
  • misc Resistors and Wire $1
  • Breadboard $6
  • Things I am forgetting $4

Total Cost: $150

This seems pretty reasonable for a nice vision platform. After software development, it probably takes four hours to build one from scratch. I will post more details later.


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