[DFTF] We eat what we CAN, and what we can't, we CAN...

[Hugh Meyer]

Joe,

2CAN:
Last year the 2CAN and serial port were the two options. NI must support them. This year may be different.

Loop Time:
100 msec is fine. We would like faster, but it is a trade off between CAN communication time and periodic rate. Our drivers couldn't perceive much difference between 100 msec and 50 msec. Fastest Windoze can do is 35 msec anyway. Anything faster is just an illusion.

Data Logging:
We log just about everything we can think of. Attached is a typical log file from a match during autonomous mode. We send data back in the user packet. It is 934 bytes (or something like this), which allows for lots of data. We have yet for that to be a limit. This data shows up in the dashboard. That lets us view on the dashboard in real time and write it to disk for later review.

2CAN Web Page:
The 2CAN will show much data if you hit it with a web browser. We could not do that and control the Jaguars from the CRIO at the same time. It is one or the other. Also, the configuration to get to connect the web interface to the 2CAN is not a legal mode, since you must have a path directly from the browser to the 2CAN. Normally the 2CAN must be connected to the CRIO for normal robot operation. This year may be different, since the 2CAN will be connected to the switch.

PID with two CIMS:
Last year I made a significant effort to make this work by connecting one encoder back to two Jaguars. We solved the ground loop issues with optical isolators. Every once and a while for some reason we would see the jags driving opposite directions. As best I could tell it was from the backlash in the gears. I used lower line count encoder wheels to reduce the ability of the system to see the backlash, which helped, but it didn't solve the problem. This caused us problems at Purdue, so we abandoned the effort and changed to voltage mode. The drivers said it was much more responsive when it worked. There are several threads where I talk about what we did last year with much input from others. Seems the only way to do this is to make the loop in the CRIO and just drive the two jags with PWM.

Fast Reversals on Jags:
This has been mentioned several times. During testing last year I discovered that the jags would reset when a fast reversal was attempted. Connecting a larger capacitor on the power supply seems to help this problem. We did this by installing it on the encoder pins in the jag. If you review the schematic you will see there is not much filtering on the 3.3 volts. Again, there are threads from last year where this is discussed.

-Hugh