Plexiglass limit - rationale

lets not assume
lets assume they use 4’’ for the width (im being generous )
does anyone have an exzact count of cubes and breaks in their system or the vevo
we can math this out

I have a 2 stage tray with lexan backing. If each strip was 2/3 the current size then yes you would have enough for 3 stages.
However, if all strips are 5.5 inches or wider and span the length of the 35 hole c channel, then they are probably using too much

lets map it out

Honestly this seems awfully like a witch hunt.

There is (supposedly) a team, somewhere on the other side of the world from where I assume most of us are, that may or may not be using slightly too much polycarbonate.

Why would you all care? You will likely never compete with this team. You will likely never have any interaction with them. “Exposing” them on the forums here does nothing to help anyone.

Let the inspectors in China (and everywhere, really!) do their jobs. Have trust in the teams to follow the rules. None of this affects you, so you have no real reason to involve yourself in this potential dispute that may have happened between a team and an inspector that are on the other side of the world from you.


I don’t think this is about any specific team at all, no one mentioned any team number. All we’re saying is that trays take up a lot of polycarbonate which can be frustrating due to the limit. To make this more productive I guess is what would be the most effective use of poly carbonate and how would you ration it effectively.

People were simply contemplating the ethics behind going over the limit even if it is slight. In general this will affect everyone even if it isn’t directly because there are teams that follow the rules exactly while there are others who don’t. Just because no one gets caught doesn’t make it okay.


That seems like it’s mentioning a specific team, or set of teams, to me. While @OscarMNOVA12’s comment wasn’t bad in and of itself, subsequent calls from other community members to “map it out” and “math this out” in reference to the amount of polycarbonate on some Chinese team robots, presumably in order to catch them breaking the rules, seems pretty witch-hunty to me.

That being said, the rest of your post I completely agree with. Going over the limit is bad. We need to find ways to build our designs within that limit. But I don’t think we should be taking it upon ourselves to try and “expose” teams over rules violations that we have nothing to do with.

I mostly just wanted to steer the conversation away from this kind of behavior, considering there’s been quite a bit of what could be considered anti-China bias/viewpoints on this forum before.


If we don’t do it then who will? At competitions, you are allowed to question the legality of a robot on the field. Maybe a team is considering this design or something; I think it should be talked about if they feel that because other teams have gotten away with it then maybe they can too. I want to discourage this kind of culture.

Also, it is not just Chinese teams though they have pioneered the three-stage trays so as of now it is mainly the chinese teams that are used as examples. I highly doubt an inspector has gone out of their way to measure how much polycarbonate is on a robot, rather they eye ball it or ask the team (at least that’s what was done for me). No one is exposing any team in particular, nor was any match specifically pointed out. I do think that it is worth calculating the area of polycarbonate on a three stage tray for future reference. This way you can build accordingly.

Assuming you use a full-length c-channel (35 holes) and go 14 holes wide (7 inches across counting the holes that’ll be mounted to the tray “rails”) (the comfortable sizing for a tray intake), the area comes out to be 119.52 square inches. Multiply that by 3 and you get 367.5 square inches. ( 17.5 in (full length c-channel) * 7 in (14 long c channel) * 3 (three stages)). According to rule the legal amount is 288 square inches (12in x 24 in).

So yes, it is over the limit assuming they used those dimensions which I believe to be reasonable. A cube is 5.5 inches across therefore this design leaves you with 12 holes to work with or 6 inches, essentially .25 an inch on either side of the cube in an ideal scenario. Correct me if I’m wrong.

A solution to this problem: zipties. I’ve seen a Chinese Finals match of a really good 3 stage tray robot that used zipties for the backing of their tray. It seemed to work well though there wasn’t any close up or anything. Regardless, zipties can be a good supplement to the polycarbonate limit. I highly suggest you look into using zipties, otherwise consider an aluminum plate or standoffs maybe. Zipties are the lightest however.


The reason I mentioned China is because that is where the majority of match videos with tray bots are from, so it’s where we get the best look.


Read A

This has been covered in the thread before, some just use “plexiglass” to collectively refer to the vex-legal plastics

But then people would search for and buy plexiglass instead of lexan so we should try correcting them even if they mistakingly say it. I have found a team or two at my competitions in the past who puts plexiglass on their robots by mistake likely because someone said Plexiglass instead of Lexan to them.


And even then, Lexan is just one brand of polycarbonate.


our robot uses exactly 2 of those tray segments… plus about 1/3 of another one… oops… might want to look into those zipties.

okay so I did the math and we use exactly 278.88 square inches, give or take a few. so we’re good, but close.
(I’m not looking at my robot right now, so I’m going by if what you say is true).

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Polycarb is also useful for other applications so you’d only be doing yourself a favor to find an alternative for trays since it uses practically all of the allotted polycarbonate. You could probably use polycarbonate on the first stage and then rest could be zipties mainly because it would best align the cubes (giving them a flat surface to square themselves against) and in theory they’d follow that alignment up the intake.

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What other uses for polycarb are you thinking of? I can only think of the tray backing

Flaps on the side of the bot to prevent pushing

Increasing the legal amount of polycarb is long overdue.
More polycarb leads to more creative designs and less copy bots.


There are a bunch of small things that poly carb is useful for, particularly the custom parts you can make from bending and cutting it. Anything from custom gussets, protection or decoration.

I have a question. If polycarbonate is used as a non-functional decoration, is it legal? You can add stickers to it and things of that nature. Namely, a polycarbonate plate like the one on the back of this robot: (448x Goofy bot) Would it be considered non-functional even though it sort of protects the back of the robot?


If it’s sole purpose is decoration, the piece should not count towards the limit.

If it’s deemed to be protecting the back of the robot, I don’t think it’ll count as non-functional.

That said, I think the polycarbonate allowance needs to be upped.