Especially for these high level matches, I think a PTC check immediately after a match is warranted. This would ensure that nobody is adversely affected by the check, and that no alliance is competing unfairly with modified motors.
Agreed! We both voted that they should not do checks before matches. I think they should have teams bring there bots to inspection right before lunch/after alliance selections to test the motors, and give them time to cool off, or they could be done after matches. I will say though that in my division (spirit division), they were good about not checking bots right before matches.
-Harrison and Luke, 4951H
They definitely could have been, not coincidence. All that torque going into stall is an issue for those gears.
We normally have a âturboâ drive button to help drive overheating. It puts out either 70% or 100% power. For your issue above, you could place it in 70% power for the PTC test and tell the ref you did. The PTC will take longer to trip, but you will decrease the stall torque to the gears that can shred.
The thing is with canned air, it only cools down the motor it doesnât allow the PTCs to resolidify. As far as I know the ptc is just a casing for a conductive chemical that breaks the circuit when it melts. I donât think cooled air will resolidify the bond, the PTC has to convert from a liquid to a solid. If you spray cold air the PTC will likely be (at least partially) melted; this could cause less ampage to reach the motors, and hurt performance. By spraying with any sort of coolant youâre just lowering the temperature of the motors to make them less likely to trip, not allowing the PTCS to fully recover.
note: I donât know that much about PTCs, what I say is just my understanding.
This wikipedia article is well sourced and a good read on how the PTC works:
PTC Checks always rekt me.
This is the important part from that article:
It looks like even if you could cool it down all the way with the coolant spray, it still wouldnât be the same and it could be significantly different. How close it is to being the same probably depends on the PTC.
Add my name to the list. While we didnât make it to elims, the PTC test during inspection broke a motor completely, to the point where it still wasnât working 3 hours after the testâŚ
We were also checked during the qualification rounds at one point, right before a match⌠I guess I donât need to say that we lost the matchâŚ
Something that people have to understand with this is that if teams are given a lot of time between testing and a match, and if somebody is really trying to cheat, then that is more than enough time to swap motors. This is why I advocate for a post match test, rather than a pre-match one.
Are they going to have legitimate motors 20 minutes before every match, then switch out their motors right before the match stars just to skirt around this? That seems like it would be very tiring and very suspicious to me.
I think a post-match check does make a lot of sense, though.
Well according to previous posts, people are asking for an hour of time between check and match. Iâm not saying that people will do that, but if a team is really trying to cheat, then I am sure they would be willing to do something like that. Swapping motors isnât very hard either.
I think they should give us the option of running the stall test or showing them the PTC. In our bots, the motors are zip-tied to the mount for easy change and replacement. We could pop it off quickly and show the PTC and the lack of shorting. They could even apply the current right there at the PTC to see it trip. It would still need to cool down, but at least it wouldnât have any chance of shredding gears.
Secondly, if their cortex is driving this test then it should not be putting out 100%, thatâs not really fair to the internals of the motor.
BTW, we applied a constant 3A to all of our motors, 60 of them, and then sorted by length of time to trip and an oscilloscope trace for good down to bad. We had a range of 0.25 seconds up to 6.2 seconds. With one never tripping. We took that one apart and found a short to the pad right next to the PTC. It came that way. Some of the new ones were < 1 sec trip, pretty bad. So, the numbers where all over the place, but repeatable.
Thatâs a nightmare scenario. I wonder how the officials would handle that. Would you be DQed for something that is clearly not your fault?
Thatâs not good! That would mean functionality of the PTC isnât tested during manufacture.
No, I think the 6.2 would still be legitimate for them. They just want to see a trip in a reasonable amount of time.
It may have been, more like a solder splash/ball. Some faults like this only show up or go away when a board is flexed, temperature cycled, etc⌠Although one thing I am sure it wasnât was dendrite growth, at that amperage it would have popped the dendrite right away.
Iâm concerned with the PTC that never tripped at all.
Iâve never seen as low as 0.25 seconds, sounds like the wrong part was installed.
For new forum members, a link to an old thread discussing the 4A PTC in the cortex.
I like the idea that was stated in the original post saying that tamper resistant methods could be put on motors after they pass. If a colored zip tie was used, it could be placed between the attachment points of the motor and around the top. I do not believe this would allow a motor to be tampered with as the zip tie would have to be cut.
Please add us to this list, we were given this test 30 seconds before preforming our quarter final match and lost due to our robot preforming sluggisghly there after. I wouldnât mind this so much if they tested the opposing alliance but they only tested ours putting us at a drastic disadvantage.
PTC checking needs to be done to prevent cheating, but the current system is flawed (obviously). Weâve all seen how badly motors run when the PTC trips, so what they are doing isnât really good. I see a few possible solutions:
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PTC check right after a match. Have the fields set up so that they canât leave without going through PTC inspection.
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PTC check in the morning or at least 15 minutes before matches start. And PTC check all the motors, and mark all of them with a paint pen, with a line going all the way around the motor or something, that way itâs obvious if they changed anything. I think the ziptie idea would work well with this too, for another layer of security.