Murphy's law

This thread is dedicated to the Murphy’s law moments at vex competitions, catapults snapping, Axel’s bending, code going wrong for the first time. Stuff that never went wrong in practice but always goes wrong at a comp. Mine is when my V5 battery wire snapped

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One time at a comp the judges had us wait for about 30 minutes with our robots on, it was a very slow match

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Lets keep it on topic.

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@224x, that’s a great topic! Murphy’s law is very relevant to the field of engineering. At the first glace it may seem to be irrational or even unscientific:

When it is most important, and at the worst possible time, everything that can go wrong will go wrong.

However, there is a sound science behind it. The catch is that it is mostly in the field of human psychology.

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This is similar to how CGI is. Bad CGI is bad CGI because you notice it. If you don’t notice the bad CGI in movies the producers are successful at making the CGI fit in, but they will never be praised for it because nobody notices that it is CGI. In terms of Murphy’s law, it is only applied whenever a bad thing is noticed.


Unless everything goes wrong at competition’s so much you do notice when nothing goes wrong.


Oh boy. I have way too many of these stories.

  1. We don’t meet our alliance partner until 2 minutes before the match, we get flipped over within the first 10 seconds of driver control and our alliance partner gets stuck on a ball
  2. Every single autonomous ever
  3. Last year our arm fell off in the middle of a match
  4. Our robot fell off a table and our driver sliced their hand open catching it
  5. At one competition, an axel snapped in half and someone almost set the robot on fire
  6. We used motor coolant on our v5 motors and then they didn’t work properly for the rest of the competition
  7. We made it into the first place alliance and then our alliance partner and us had severe connection issues and lost
  8. Our chain fell off of our drivetrain and then one side of our robot wasn’t driving

last year we were in the last finals match, this win WOULD bring us to state. Suddenly, my robot stopped in the middle of the field, looking down at the controller I saw the LEDs on my controller go red.

my battery had died


Early in the Starstruck season one of our senior teams was practicing the day before the competition. Robot’s center of gravity was a bit too high and about every 20 min of practice they would grab one too many star and accelerate too quickly resulting in the robot tipping.

I suggested they add some weight on the bottom of the robot, to which the team driver/main builder replyed that he understands the problem and will drive carefully if robot carries a lot of game objects. As he continued practicing, we accepted his reassurences, and went on to joking with other team members about the robots tipping over.

Someone made a funny prediction that if robot falls once every 20 min then, statistically speaking, you could expect it to fall every 10th match at tomorrow’s competition. No one, including me, took this very seriously.

Next day the 10th match was finals and, sure enough, the robot tipped over and fell the first and only time during the competition.


Did a scrimmage with our local teams, and we had added one extra rubber band on each side of our puncher. Little did I know, those rubber bands converted the puncher into a cannon and consistently shot over the top flags from the back of the field. We tied our first match and lost two more quals because of it. I fixed it by bending the ball-retaining bars (just some 1x’s above the puncher’s “barrel” to stop it from flying out of the intake) so the ball would hit them and redirect; I call it the “muzzle break”. We ended up getting to finals with that beautiful thing.


At our state championship, our alliance and our team were holding some decent ground against the other alliance. My team had put a few caps on high posts and was playing good defense against the opponent’s descorer, and there was a bit of back and forth action with flags. However, somehow our alliance’s drivetrain broke 30 seconds before the end of the match, losing us most of the flags. We tried to make it up, but had to give up defense of several high-scored caps, and our flywheel didn’t stand a chance against the new flags. To add salt to the wound, the other alliance knocked off all of the caps we had worked so hard to score on the poles.
At the very least, we had an epic parking battle, with my team coming out on top. We had a whole 6 points for that match.
Oh, and the match right after we lost 36-0.
And there was that time our drive train snapped within 5 seconds.


The wheel system which we spent 2 hours working on and checked at least four times before competing lost 3 bolts, 3 screws, and a plate kept falling off no matter how many times I bolted it. Moral of the story: prepare for every eventuality.


During the NbN, by the end of the season our flywheel was performing very well. It couldn’t beat the rate of fire of the best punchers, but was almost as fast, extremely accurate and, unlike punchers, could score reliably from almost any location on the field. Everything, including the ability to high-lift alliance partner was working great the week before the States. So, what could go wrong?

The day before the States we decided to re-tighten all screws and re-lubricate all axles and gears, including 393 motors’ internal gears. Flywheel’s accuracy relied on a single IME connected to one of the motors.

At the States it took several qualifications with extremely degraded flywheel accuracy, before it was tracked down to white lithium grease making its way onto IME’s encoder gear and interfering with the optical reader. Even after taking care of the grease, there were still some issues of flywheel starting misbehaving mid-match, most likely due to the static related IME resets. The school that held the States that year had much dryer and hotter air than any other event we attended that year.

On top of that our sister team, that we planned to alliance with and practiced lifting, had added a few extra pieces of steel to their robot the last day before the competition, making their robot just slightly heavier that ours could lift.

Overconfidence makes you blind to the things that are obvious in the hindsight.


Once in a match, our autonomous (somehow?) drove itself onto a cap while trying to park, and though this had never happened before, just decided to be, and we were unable to move for the rest of the match except to spin around in circles.


At our state competition we had our blue autonomous not work a single time only on one field. We tested it on practice fields, it worked, tested it on the skills field, it worked. But never on the comp field. Lost two matches for it. Still won state though, back auton worked fine.

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Our auton worked on the practice field, but on the first match, it did not move back enough, and it crossed the line instead of going on the platform.

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Our entire robot burnt out during elims in states. We got three balls stuck inside us while we couldn’t move.
and we lost. couldn’t get the balls out.

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During a starstruck

  • The team programmer accidentally left a kill command in the auton code. This resulted in the robot stopping if auton wasn’t ended early.
  • Our claw got caught in the opposing team’s lift (which had nylon rope on it) and tipped over.
  • We kept losing equipment to ESD, the total amount of damage was around $1,500.
  • Our power expander came unplugged, and it was powering the left half of the drive

During In the Zone

  • We accidentally drove the robot off a table at an event, which snapped the 3D printed claw and resulted in us frantically taking the claw assembly apart to repair it (VEXU).

During Turning Point

  • We pushed a team off the center platform then parked, the team’s small bot then attempted to push us off, but tripped/flipped their robot over a cap they just tried to flip.
  • My Choo-Choo catapult has bent or destroyed every piece of metal it was originally made of. This consists of 3 bent C-channels and 2 sheared screws. The whole system was replaced with custom machined metal and steel.
  • Someone over-tightened the cap claw at an event I couldn’t go to, which is powered by a single action cylinder and resulted in the claw not being able to open.
  • A team was complaining about how we didn’t spray our field with anti-static, they claimed they lost 6(?) ports at our event. That team placed very poorly at our event, but placed very high at another event.

Every Year

  • TSA manages to amaze me by how consistently they can break our boxes. The amazing thing is that we ship our bots through commercial-only channels and the boxes still end up super beaten.

During the final at states, our intake managed to get 2 balls stuck between our puncher and intake for the first minute. We could not get it out for some time. @Azeem7830C will know.

That’s happened to me, luckily I had it happen in practice so I made a plan for when it happened, I had a catapult so I was able to go half on and half off a platform to tip the ball in

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