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DougHogg
04-26-2005, 03:25 PM
Our team learned some lessons this year the hard way by experiencing a problem or loss that we could have prevented.

1) In the third match of the finals in the S. California Regional, we couldn't lift our arm for the last 20 seconds because we our battery voltage dropped too low. :(

We learned that if a battery isn't allowed to complete it's charging cycle, it can show a high voltage because of a "surface charge" but still not be fully charged. In fact, if you disconnect a battery from a charger (or unplug the charger) part way through the charging cycle and then put the battery back on charge, often the charger will get fooled by the surface charge and refuse to continue charging the battery. That battery will then be only partially charged, although showing a voltage over 13 until the surface charge dissipates overnight or until a load is put on the battery for a few minutes.

2) As posted in another thread, having a wedge on the front of your robot is great when other robots are trying to push you, but it isn't so great when you get your alliance dq'ed (disqualified) twice in the same quarter finals for tipping opponents. We were trying to defend a goal and were not trying to tip anyone, but it still happened. (Amazingly, we still won the quarter finals in Archimedes because in one of the matches, our opponents were dq'ed for tipping also, so that match was a tie: 0 to 0.) :confused:

3) In previous years, we had used velcro or zip ties to secure the two halves of the Anderson connectors during a match (something that we learned from other teams), but it didn't seem to be a problem this year, so we didn't bother. In the second match of the semi-finals on Archimedes, our battery disconnected after two collisions right at the beginning of the match. :ahh: (My apologies to our partners, teams 997, 65 and 138.)

Did your team have similar experiences? If so, post them and maybe we will save other teams (or even our own teams) from a similar fate in years to come, because it seems to be easy to forget some of the successful things that we have done in the past.

Doug Hogg

Hunter
04-26-2005, 03:54 PM
1) In the third match of the finals in the S. California Regional, we couldn't lift our arm for the last 20 seconds because we our battery voltage dropped too low. :(

We learned that if a battery isn't allowed to complete it's charging cycle, it can show a high voltage because of a "surface charge" but still not be fully charged. In fact, if you disconnect a battery from a charger (or unplug the charger) part way through the charging cycle and then put the battery back on charge, often the charger will get fooled by the surface charge and refuse to continue charging the battery. That battery will then be only partially charged, although showing a voltage over 13 until the surface charge dissipates over night or until a load is put on the battery for a few minutes.



We overcome this by finishing charging our batteries on a really old charger that doesn't have a safety shutoff, It is still a 6 amp charger so it is legal for FIRST use, but gives the batteries a much fuller charge, we get a lot more power out of them after giving all our "fully charged" batteries an hour on this charger.

At least in Canada, stores won't sell these chargers anymore, but you should be able to find one stashed away in someones garage somewhere. You can't fool these old chargers so you'll always have full batteries.

Ken Patton
04-26-2005, 04:16 PM
having a wedge on the front of your robot is great when other robots are trying to push you, but it isn't so great when you get your alliance dq'ed

We learned this in Atlanta, also the hard way.

In our first Saturday qualifying match, we had a team get between us and the loading zone. They drove up on our wedge-shaped wheelie bar while attempting to push us. I told our driver David to drive forward - my intent was to push them until we touched the loading zone. Well, I was too enthusiastic in my words to David, and we ended up tipping them. So even though we were now in the loading zone, we were also in violation of the rules. Head Ref Aidan quickly shut us off.

We deserved it. I was wrong. It cost us and our allies 20 and 494 an important win. It was only our second penalty all year (the other was touching a tetra before entering the auto LZ).

Lesson learned: if you have a wedge, learn to use it legally - or pay the consequences.

Ken

eugenebrooks
04-26-2005, 09:15 PM
We learned that if a battery isn't allowed to complete it's charging cycle, it can show a high voltage because of a "surface charge" but still not be fully charged.

3) In previous years, we had used velcro or zip ties to secure the two halves of the Anderson connectors during a match (something that we learned from other teams), but it didn't seem to be a problem this year, so we didn't bother.

Doug Hogg

Battery charging is a perennial problem. Managing a number of batteries on a hodgepodge of chargers by picking the one with the highest voltage can leave you very surprised. Having dealt with this problem for a number of years, we bought a 5 independent channel, 6 amps per channel, three stage charger this year and it does a great job of keeping up with 6 batteries (one being in the robot). The charger is
http://www.batteryweb.com/interacter_x5.cfm
using the LS1206 charger (5 of them) in the unit. It is expensive, but it keeps up with the battery charging even when going through the finals and has reliable indicators for the state of the charge cycle. We also test our batteries for capacity with a constant current load tester before the season and remove any that do not measure up from competition service. Our used 2004 ES batteries had about 50% more capacity than new 2005 EX batteries, this year.

You gotta keep the religion on that velcro strap for the power connector. Keep spares in case the one on the robot is lost.

Now for at least some of Team 1280's lessons learned, no shortage here:

* We must have the record for the most broken axles at the Sacramento and San Jose regionals. We were using heat treated O-1 steel that was far too brittle. By changing this to heat treated chrome-moly (4130, or 4340) we got axles that are tough enough for outboard wheel use. After any welding is done using rod of the same alloy, heat treat, quench in oil and then temper at 800 degrees. Such axles are very strong but still bend instead of snapping when hit with a sledge hammer.

* The PWM style connectors used on the RC controller have a bad habit of working their way off when robots interact strongly. An open loop
PID control system is not a pleasant thing. You need to add a means
means of keeping these connectors in place.

* Setting your drive victors for coast when the power goes out is good for that last foot or two going home when the clock runs out, but is a real disaster when a robot is giving you a shove. You can set up an RC controlled relay to get "brake" during normal operation and "coast" when the robot is disabled at the end of the match.

* A cast iron worm gear is very incompatible with a hardened steel worm, always use a brass worm gear in such a gear box. We learned this just prior to ship when we found the cast iron worm gear in the bottom of the gear box as black dust.

* It is important that the couplings to pots in a PID control system are absolutely bullet proof. Glued on rubber hose can break loose and slip,
leading to potentially destructive a loss of control. If the hose is flexible,
like latex tubing, it flexes a bit and you lose precision in the control.

* Your robot had better be built to take a high speed collision from all sides, or the weak side will likely get bashed in.

* Your robot had better not be too close to the size limits, or any
change in the dimensions of the frame due to collisions might result
in a robot that is "out of the box." It is not fun to be shortening a robot
with a sawsall in order to pass size inspection at the Nationals.

* After spending countless hours, and much money, building a good robot to go to a competition; take your scouting very serously or you will make serious mistakes in alliance selection. If you get the opportunity to go to the nationals, take your scouting even more seriously because you have no "corporate memory" for teams arriving from other parts of the country, and you don't see a given robot as much in the seeding matches due to the larger number of robots in the division.


Doug, We hope to see you at the Cal Games next year!


Eugene

Jeff Pahl
04-26-2005, 09:46 PM
It made my entire season when, at dinner Thursday night of regionals after the team finished the robot at 7:55 PM, one of next year's team leaders stated "you were right, we needed to finish the robot 2 weeks before the ship date. Next year, we are going to stick to the schedule."

Now I just have to hope that they remember that until next year, and I truly hope that they carry that lesson with them into their engineering careers. If they do that, then all the blood, sweat, and tears of the entire season is worth it.

In the team's defense, we were only a second year team this year. Even worse, not only did all but two team members graduate last year, but we also lost the teacher at the school that was the team leader, so there were just 2 students and 2 engineers who had even ever seen a FIRST competition. We tried to encourage them to keep on the schedule, but we also considered it important to let them manage the project, make their own mistakes, and learn their own lessons. However, almost the entire team is back next year, so watch out!!

The other thing we learned is that your first match on Friday is a bad time to start learning how to drive the robot.

sanddrag
04-26-2005, 09:54 PM
Here's our master list attached. And too add to that:
-Looking back I would have put two of the Chias in the arm instead of in the drive because the arm was too slow. I thought there would be a lot of pushing and shoving with 6 robots but I was wrong.
-I think the arm is much longer than it needs to be
-We need wheels that will not bend when hit (I was surprised they did since they were one piece 6061-T6)
-The integration of the arm structure into the frame structure (mounting) was not thought out well enough at all.
-Much more prototyping and testing needed for the end effector
-Shoot for making two robots next year.

But on the plus side of things, it is cool to have the most powerful drive system in the country. Also, I believe we were the only team with a riveted sheet metal box arm with two worm gear joints. That was cool.

David Brinza
04-27-2005, 12:53 AM
Our team learned some lessons this year the hard way by experiencing a problem or loss that we could have prevented.

1) ...

2) As posted in another thread, having a wedge on the front of your robot is great when other robots are trying to push you, but it isn't so great when you get your alliance dq'ed (disqualified) twice in the same quarter finals for tipping opponents. We were trying to defend a goal and were not trying to tip anyone, but it still happened. (Amazingly, we still won the quarter finals in Archimedes because in one of the matches, our opponents were dq'ed for tipping also, so that match was a tie: 0 to 0.) :confused:

3) ...

Doug Hogg

Actually our robot contacted the opposing robots high in these DQ incidents.

In QF3-2, we hit 435 with our arm and managed to rip a tetra out of 1071's grip as they were attempting to cap the center goal as time ran out. Dramatic, but illegal...

In QF3-3, we hit 435 with a tetra and our arm just after we snagged the tetra from an automatic loader. We were just driving out of the loading zone (maybe still just in) when we made contact with 435 on their extended arms.

I wouldn't attribute the tipping to our ramped body, we just hit them high. A no-no in FIRST's rulebook.

mathking
04-27-2005, 07:08 AM
One hard lesson we have finally learned: Have a tray/bin in which you put everything that comes off the robot during maintenance. After 3 seasons, we finally realized this one at the chamionships. It is a pain to go looking for missing nuts, bolts, machine screws, connectors, breakers, etc. If there is one place to put everything you take off the robot you won't have to go looking very far.

DougHogg
04-27-2005, 12:24 PM
Actually our robot contacted the opposing robots high in these DQ incidents.

In QF3-2, we hit 435 with our arm and managed to rip a tetra out of 1071's grip as they were attempting to cap the center goal as time ran out. Dramatic, but illegal...

In QF3-3, we hit 435 with a tetra and our arm just after we snagged the tetra from an automatic loader. We were just driving out of the loading zone (maybe still just in) when we made contact with 435 on their extended arms.

I wouldn't attribute the tipping to our ramped body, we just hit them high. A no-no in FIRST's rulebook.

Dave,

Thanks for clearing that up.

Very interesting. That gives us another thing to watch for next year: hitting robots high with arms.

Doug Hogg

Scott Morgan
05-01-2005, 02:47 PM
we learned not to mess around with the gripper design when we have one that works we lost a few matches due to that

we also learned not to try to due more than our bot is designed to our robot like most is designed for just one tetra at a time and there were many occasions where we tried to load two tetras at once this is fine with the arm design as it has proved to be able to lift,three regular tetras at once, two vision tetras, and a center goal!, however the gripper is not designed for this and we frequently lost tetras, or got tetras too far back to easily get off, or in one instance in the LA regional getting one tetra nested inside the other, like stacking but from the side, and then having to put that mess ontop of a stack

also know what effect retreading your tires will have on you manuverablility before you do it in competition, as it turned out we could barely turn due to too much side traction

StephLee
05-01-2005, 04:11 PM
Lesson learned the hard way: When testing autonomous mode for the first time(especially if your programmer has never programmed a FIRST robot before), put the robot up on some type of blocks so it can't move. If you insist on testing on the ground, make sure your speed is not set all the way up. If, for some reason, you ignore this advice, don't test it somewhere with a glass wall, no matter how far away from said wall you are. (We didn't hit the glass wall, but we nearly hit several people and then pinned a mentor to the wall.)

Another lesson we learned the hard way: If you're in a room about 35' by 30', don't go in the 5'-wide hallway to drive the robot for the first time, especially if the walls in the hallway are drywall and the building is brand-new. (I'd post the picture that goes with this, but I don't have a copy...)

Speed, reliability, and simplicity will win almost every time.

BandChick
05-01-2005, 04:37 PM
Here's a big lesson 1089 learned at their first Championship. We ended up seeded #1 and though our scouting team worked INCREDIBLY hard to find out which teams to pick, we still came up a little short. We took a lot of advice from a lot of other teams, but ultimately, we needed someone who had more experience. We needed to look at the top 8 and correct our list a little bit.

In Galileo we ended up running down the Top 8 list so we could break up "super alliances." What ended up happening, because we didn't discuss anything with other top 8 teams was we asked for seed 2 and they said yes (something we hadn't expected). Don't get me wrong, 1280 were great partners, and we were more than happy to be paired with them, but our team captain needed to be able to think on his feet a little bit more. He needed to realize which teams had these possible "super alliances" rather than just running straight down the list.

Billfred
05-01-2005, 04:41 PM
1293 learned a bit this year...

-Don't jam the joysticks on the robot if it's anywhere near Billfred. (Hit again--and this time, with no window motor drivetrain. Two CIMS. Kitbot. Ouch.)
-Robots can be built in six weeks.
-Dump your tetra before heading toward the end zone. (Man, that hurt.)
-Sexy use of aluminum can be functional. (If you look at this picture (http://www.chiefdelphi.com/forums/pictures.php?action=single&picid=10223), you'll note that oval-looking 1293 behind our arm. Turns out that with a bit of bending, and a well-placed rubber band, it does wonders for knocking down the arm at the start of the match.)