It is impossible... ...until there is no other way...

[FRC4ME]

Originally Posted by Formerly Famous

Another thing I would say is in the design. Does anyone else have times when they sit there for hours thinking about something and how to fix this one little problem, and then someone walks in and tells you the solution? I know that has happened to me many times. I am always shocked at how simple an impossible solution is.

I had a similar experience when working on autonomous code in 2008. We had the robot running laps around the practice field just fine, using encoders for distance and a gyro for turns. We had SuperShifters on the robot. Our turn loop wasn't very well-tuned, so we had to turn corners in first gear while going forward in second gear.

So the robot would go across the field in second gear, shift to first, turn left 90 degrees, traverse the field (still in first) turn left 90 degrees, shift to second, go across the field...etc until time ran out.

The problem is, the second turn would always overshoot by 10-20 degrees. We had no idea why this was occurring. We looked through the code and verified that the code being called for the first turn was exactly the same as the code being called for the second turn. Both turns took place in first gear, both were 90 degrees using the same feedback loop, and both were followed immediately by a straight section. We spent hours working on this, but couldn't figure out why the turns should be any different.

Then, we asked a mechanical mentor to watch autonomous run. He immediately understood the problem: "you're shifting into second gear immediately after that second turn. It takes about a half-revolution for the gears to engage after a shift."

Swapping the position of two lines of code, to stop the motors before shifting gears, solved the problem.

[thefro526]

I have two, both of which are fresh in my mind from last weekend.

Sometime Friday afternoon my Driver Begins to complain about the left side of the drive, he says it feels "Funny". We get the robot off the field and look at the drive, and nothing appeared to be wrong, I turned it by hand and there was no binding, no noise, and it just felt okay. So, I told him we'll worry about it if it becomes serious. Three or Four Matches go by and we notice our Autonomous Mode is drifting hard towards the side in question, and it almost looks like there's some sort of mechanical problem with the drive, and each time I spin it and it feels okay, so I'm stumped and just tell him to Drive through it, which he did very well. Fast forward to Lunch Break before Eliminations, when one of the other mentors tells us that one of the PWMs to the left side of the drive was unplugged... We plugged it in and it worked perfect.

Match 64 was to be our final Qualifying match, and it was with 103, and I've been dying to play alongside 103 for years. So the match starts, our Autonomous goes and the robot stops like usual, and then a little bit of smoke starts coming from the robot. A little bit of smoke turns into a lot of smoke, at which point the match is called. I ran onto the field without hesitation and turned the robot off and open the cover as more smoke came out. We began frantically looking for the problem (still on the field) and I see that two of our PWM Cables have shorted together which caused them to burn the insulation off of the wires. Luckily, due to the setup of Philly, our head pit guy (aka Pitmaster) was standing within yelling distance of the field, and I got him to run back to the pits and grab a handful of PWMs. I rewired the bot, in the most quick and nasty fashion I could, and we went on to play the match. We won the match 5 to 3. Most people saw the smoke and figured that our robot was toast, but some quick thinking saved it, and a win.

[FRC4ME]

Originally Posted by thefro526

Fast forward to Lunch Break before Eliminations, when one of the other mentors tells us that one of the PWMs to the left side of the drive was unplugged... We plugged it in and it worked perfect.

Heh, this reminds me once again of 2008. We wanted to make the robot maintain a straight heading in autonomous mode. So I added a gyro and a PI loop, which worked very well. So well, in fact, that we decided to use it in teleop as well. It did an excellent job of keeping our four-CIM, six-wheel drive train going in the right direction.

So we went through VCU with this drive system, and for the most part, it worked wonderfully. There was just one problem: our driver kept complaining that the drive was slower than usual. He said it didn't seem as powerful as it used to be. When asked if he had any difficulty turning, he said no: it just didn't feel as powerful as before. We figured the motors and bearings were just wearing down and kept playing without any changes. We made it to the quarter-finals, I believe.

Fast-forward to Chesapeake, and we had completely forgotten about the drive train. That is, until we were testing some sort of autonomous routine that required me to print out the actual voltages the PI drive loop was sending to the motors. I instantly knew something was wrong: the software was sending half the power to the right motors that it was sending to the left motors, and yet the robot was driving perfectly straight! We investigated the problem, and found that one of the left motors was completely dead. No one knows how long it hadn't been working; it was probably dead before ship. It could even have been dead since before we installed it in the robot! The PI loop was so good at keeping the robot straight, it was able to compensate for a dead motor well enough to make the problem virtually invisible. Unless, of course, we tried to push another robot with all four of its motors working.

[Mr. Pockets]

So we were weighing our robot before re-bagging it. We had built our hanger and upper superstructure separate and easily detachable so that we could keep working on the hanger as part of the withholding allowance.

Anywho, so we had apparently already weighed the upper segment and it had come in at like 44 lbs. We put the bottom half on the scale and it comes back at 80 lbs. So naturally, what with it being only a day or two before competition, everyone is less than happy. There were a bunch of bouncing suggestions, but quite frankly 4 lbs is quite holes to drill.

While everyone is proposing different ideas I went over to the upper section with a few of the other mentors. We figured that it was worth a shot weighing it again, it'd have been a big shame if the robot were torn apart over a mistaken weight. To everyone's surprise and relief the upper half had managed an impressive dieting program over the past few days. The scale read it in at 36 lbs. We're still not quite sure how the whole thing happened, but we certainly aren't complaining.

When it was inspected and weighed at competitions it came in at 120 lbs exact. Gotta love those sort of numbers ^_^

[Grim Tuesday]

Originally Posted by thefro526

Match 64 was to be our final Qualifying match, and it was with 103, and I've been dying to play alongside 103 for years. So the match starts, our Autonomous goes and the robot stops like usual, and then a little bit of smoke starts coming from the robot. A little bit of smoke turns into a lot of smoke, at which point the match is called. I ran onto the field without hesitation and turned the robot off and open the cover as more smoke came out. We began frantically looking for the problem (still on the field) and I see that two of our PWM Cables have shorted together which caused them to burn the insulation off of the wires. Luckily, due to the setup of Philly, our head pit guy (aka Pitmaster) was standing within yelling distance of the field, and I got him to run back to the pits and grab a handful of PWMs. I rewired the bot, in the most quick and nasty fashion I could, and we went on to play the match. We won the match 5 to 3. Most people saw the smoke and figured that our robot was toast, but some quick thinking saved it, and a win.

Oh man, your win in that match was amazing. I have been wondering for quite a while now why your robot went up in smoke. I was also surprised to see that the E-Stop button didn't work (I have this memory of your driver jamming it and yelling at the refs...)

[thefro526]

Originally Posted by Grim Tuesday

Oh man, your win in that match was amazing. I have been wondering for quite a while now why your robot went up in smoke. I was also surprised to see that the E-Stop button didn't work (I have this memory of your driver jamming it and yelling at the refs...)

Thanks! I was actually the one who hit the E-Stop (Nick, the driver may have hit it after me - I'm sure it was hit more than once), it's the first time I've ever had the pleasure of doing so since I first got involved back in 2005. In retrospect, hitting the E-Stop was a bit pointless, because the only way to get the smoke to stop was to turn the robot's power off - but at the time it seemed like the correct action.

I'm still waiting for Pictures of the smoke cloud to surface...

[kirtar]

*looks at title*
I cite Clarke's Three Laws of Prediction (couldn't resist)

1. # When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2. The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
3. # Any sufficiently advanced technology is indistinguishable from magic.