Demystifying autonomous...

[Greg McKaskle]

I'm a firm believer that programmers need to learn how to anthropomorphize with the computer/robot. Don't go through life that way, but think of it like a pair of glasses or a hat you can put on when you want to see and think, knowing only what the function or algorithm knows, or being able to identify exactly what they will need in order to function.

As for the camera and dashboard discussion. The upper rate on the dashboard data is 50Hz and about 1KB per packet. The default framework doesn't read sensors and transmit them at that rate because it would load up the CPU reading a bunch of unallocated channels. I suspect that the framework will start to take advantage of the Open list of I/O to do a better job of this in the future.

Video back to the PC involves lots of elements, meaning that each must perform well, or the frame rate will drop and/or lag will be introduced. Thinking it through, the camera doesn't introduce much lag, but be sure that it is told to acquire and send at a fast rate. The images are delivered on port two over TCP, then sent out over port one over TCP with a small header added for versioning. The issue I've seen with the cRIO is with the memory manager. Big image buffers can be pretty slow to allocate. Keeping the image buffer below 16KB gets rid of this bottleneck. Next in the chain is the bridge, then the router. I haven't seen issues with these elements as they are special purpose and that is all they do. Next is the dashboard computer. If the CPU gets loaded, the images will sit in the IP stack and be lagged by up to five seconds. The default dashboard unfortunately had two elements which are both invalidating the screen and causing drawing cost. The easiest fix is to hide the image info. I believe I've also seen lag introduced when lots of errors are being sent to the DS. With a faster computer, this wouldn't matter as much either.

As I mentioned, an issue at any link in the chain, and the fps can drop and lag can be introduced. If each of these are handled well, I believe you can get less lag down to about 100ms, and frame rate above 25.

Greg McKaskle