OK, you've assembled the pan-tilt mechanism and it looks cool, but it would look even cooler if it moved. One nice thing is that you don't need a battery to move the pan-tilt – the pan-tilt can use the USB cable for power. The USB cable that came with your Pixy2 is recommended for powering your Pixy and pan-tilt. But as long as the cable is 4 ft or shorter (3 ft is common.) If you use a longer cable, there can be up to 1 volt of voltage drop along the cable, which is fine for Pixy, but the servos will malfunction. Also, before you run the pan-tilt demo, go ahead and teach Pixy an object if you haven't already.

We should also mention that the pan-tilt base needs to be anchored to the table somehow before running the demo. Attaching your pan-tilt to an Arduino is sufficient. Otherwise, you might try placing the pan-tilt base between two books. If you don't anchor the base, the base will tend to rotate under Pixy, leaving Pixy more or less stationary (and we want Pixy to move/rotate!)

Note: if you're having trouble making the pan-tilt run properly, here's a handy troubleshooting page.

There are a couple ways to run the pan/tilt demo.

If you're running PixyMon, you can run the demo (or any other program) at any time by selecting it in the Action menu. In particular, select Program➜pantiltdemo.

Pixy should then track your object and plot the detected objects in the video window. Yay! Note, Pixymon will switch to a block-only view of what Pixy sees, so the video window will turn black except for what Pixy is detecting. The pan-tilt demo switches to this view because it doesn't slow Pixy down.

From PixyMon, you can also play with the pan-tilt demo parameters:

For example, try reducing the Pan P gain (pan axis proportional gain) to 100 and see how the pan axis slows down. Or increase the P gain and see what happens. Many times, increasing the gains results in some erratic behavior, but don't worry – you won't damage anything. If you want to go back to the default values select File➜Restore default parameters. There is more information here.

You can have your Arduino perform pan/tilt tracking too. The Arduino reads in the object blocks and calculates the positions of the pan and tilt servos and sends the calculated positions back to Pixy, and Pixy then updates the servo positions. This is great for getting your Pixy and Arduino better acquainted and getting them both collaborating in some kind of application that you write.

This requires that you run the “default” Pixy program – not the pan/tilt demo program. The default program is the program Pixy runs upon power-up by default without pressing any buttons. You can also run the default program by selecting it in the Actions menu in PixyMon.

OK, start by getting the latest Arduino-Pixy code, described here. Load the pantilt demo by selecting it in File➜Examples➜Pixy➜pantilt in the Arduino IDE. Upload it, and as long as Pixy is running the default program, you should start seeing the pan/tilt move to track any object that matches signature 1. (Note, you'll need to teach Pixy an object if you haven't done so already.)

You can also play with the Arduino code, such as changing the proportional and derivative gains.

ServoLoop panLoop(300, 500);
ServoLoop tiltLoop(500, 700);

Here, 300 is the proportional gain and 500 is the derivative gain for the pan servo. Likewise, 500 and 700 are the proportional and derivative gains for the tilt axis. Try reducing the proportional gain in half and see what happens. Many times, increasing the gains results in some erratic behavior, but don't worry – you won't damage anything.

With a little tweaking and modifying, this code can become a “chasing” instead of a “tracking” algorithm. That is, instead of calculating servo positions your Arduino can calculate motor speeds. So now your Pixy-Arduino robot creation can chase a ball, toy, etc. Adafruit created just such a robot, and they describe how to build and program one here.