Quote:
Originally Posted by AdamHeard
I agree wholeheartedly. I fear people will assume that because the safety and disable features of the IFI system were so robust and worked so well, that this new system must work the same way (I mean, all control systems must be the same, right?  ).
I for one won't be trusting the robot nearly as much as before. |
Ahem. I wouldn't be so quick to condemn the safety features of the current control system, really. In particular, the new control system uses a much better philosophy for the disable switch. On the IFI hardware, the disable system was normally open, so you could run the robot without a dongle. This means that you couldn't be
certain your disable switch would work when you hit it. You could be fairly sure, since it'd worked the last several times, but if a wire had silently broken, the contacts corroded, a bad solder joint worked loose, or the thing just plain wasn't plugged in... Well you were in for a surprise. The only actual secure option for disabling last year's robot was to pull the tether or radio cables.
The new DS's disable system works on a normally closed principle. Which means that your robot won't run at all unless you have a valid disable switch in place. Or unless you're foolhardy enough to just short the contacts together with a paper clip or something. Broken wires and bad soldering will annoy you with a non-running robot instead of betray you with a robot running amok. And while it's possible for contacts to freeze shorted or be bridged somehow, it's must less likely. If you're really safety minded, you'll get an E-Stop style switch with two physically separated NC contact blocks and wire them in series. So, I think the new system's safety and disable function are as or more robust than IFI's. That's definitely something I'm not going to be worried about.
For the joystick related issues in Joe's post... I think that has to do with the decision to based the DS on a micro Linux platform. What we try to do with joysticks and such presents a unique challenge to the control system, compared to what OS's usually do with USB devices. On a Windows machine, the OS uniquely identifies each USB device and tags settings and functionality to follow it around based on its ID, as opposed to what port it's plugged into. You wouldn't want to have to reconfigure your mouse if you plugged into the top port instead of the bottom port, after all. For the DS we expect it to identify the joystick based on what port it's plugged into. If arm control functionality always followed our steering wheel around after we accidentally plugged it into port #2 the first day, I think we'd all be a bit miffed. Even my limited knowledge of USB driver programming informs me that pinning things to an exact physical port is pretty darn difficult. And it doesn't strike me as at all likely to be amenable to hot-swapping. If it takes the controller 15 seconds for each port to identify the joysticks on boot-up, I don't think you want the process constantly occurring while you're trying to drive.
The problems with old and uninitialized values being sent are slightly more worrisome, but aren't likely to be life-threatening if you're following commonsense operating rules. Also, if the 127 default startup and unplugged joystick values from the IFI OI made you feel safe enough to put yourself in harm's way, then you weren't operating under particularly safe rules in the first place. I mean, 127 isn't a guaranteed safe value for every system on a robot. Pots controlling shooter wheels or telescoping slides are likely safest at 0, not 127. Pots controlling arm positions are likely to be safest at heaven knows what value. To be blunt, if you were trusting your previous robots not to try to kill you just because you were only starting them up or didn't have anything plugged into the joystick ports... You were putting entirely too much faith in Murphy looking the other way. If the new DS makes you more cautious around operating robots, it's probably a good thing.
Finally, I'm confident that a large amount of thought went into making the new system safer than the IFI system. In fact, much of what I heard at the recent training at NI was pointing out the focus on safety as well as features in the new control system. Insinuating it was an afterthought is uncalled for. In addition to the NC disable system, the designers are looking at running practice fields on the 2.4GHz band (the field will run at 5GHz) to eliminate students racing about with tether cables, attempting to both not tangle the cords AND not be run over. The new Jaguar speed controllers have NC limit switches to make devices safer for teams that use them, as well as actual barriers between the positive and negative terminals to reducing shorting. E-Stops will now latch inside the robot instead of the field, so an E-Stopped robot will need to be power cycled before it can become dangerous again. Instead of waiting for someone to plug in a tether cable to do so. I'm certain there's some other features that I haven't recalled at the moment, but this post is probably long enough at is it.