IR Beacon

This is the first finished beacon. It has 24 IR (infrared) LED's. The idea was that, since the tracking camera must have a wide angle in order to see the entire stage (which is about 6x6 meters, much smaller than I expected) from above, we needed an array big enough that would be easily tracked.

What I did not realize was that the angle of the LED's that I got was extremely narrow, so that when the performer lowers or tilts her head (the beacon is on top of her head) the LED's practically disappear. So we came up with the idea of using a diffusion dome to spread the light. That of course is half a ping-pong ball which happened to have the exact required diameter.

The ball was too thick and did not let enough light through, so I sanded it until it felt like a turtle egg, if you ever touched one. The solution worked, however there was still a considerable loss of light.

So I started to look for new LED's. This time I made sure that the lens of the LED would be wide enough to allow the free movement of the performer's head. This is what I found:

Ultra Wide Angle IR 850nm

These LED's are awesome. We could not believe how wide they emit light and how bright they are. You can almost turn the away from the camera and you can still see them!. So they will definitely do the trick without the need for a diffuser. We will use a set of ten which has the added benefit of resulting in a much smaller device and, because it is IR, it will be invisible to the audience.

I bought them form the guys at NaturalPoint which have a wide (yes, intended) variety of optical devices, mostly for motion-tracking. A set of ten cost me US$ 15 which is about half of the price of "cheap" LED's at RadioCrap.

So now we will design and burn another circuit and probably use a coin battery instead, to make everything really compact and unobtrusive to wear.

As soon as the UI (user interface) is ready for the tracking and motion-assigning program I will post pics of the UI and the tracking screen which is a lot of fun to see in operation.

Command and Control

The recent integration of the Make controller with Flash, its scripting language and image processing capabilities, solves many of the problems I was dealing with, from the choice of microcontroller to the controlling software.

The program currently reads the position of the performer on stage and even the distance from head to ground, all with only one cheap webcam as an input device. There is so much information that can be acquired through image analysis that effectively eliminates the need for a variety of sensors that I had planned to use.

The only limitation is the amount of servo ports in the controller. I will have to daisy-chain at least two, to handle all the servos I think I need.

The servo that supports the weight of the marionette most of the time needs much higher torque than the ones I have. I have not calculated the minimum torque yet, but need to do that ASAP to order it and start testing the software that Philip and I are designing. I am very excited and happy with the progress so far. At first I had my doubts that the solution he proposed would work, but now I see it can, and in a very simple and elegant way.

The two sizes of spools we currently use (5 and 8 cm diameter) happen to be just perfect to provide most of the travel that I need without using continuous rotation motors instead of standard servos. This simplifies programing. We found out by testing a variety of "identical" modified servo motors that the speed of rotation, given equal parameters, is quite different, which implies writing routines to address each one of them to synchronize, a royal pain!

The fish-line spools with their bushings in place

The only continuous rotation motors I need are for the arms since they travel a much greater distance.