Reading the Rules Before You Buy Anything

"Playing a game is the voluntary attempt to overcome unnecessary obstacles." — Bernard Suits

Before you buy a single part, you need to know which document actually sets the rules for your event. It sounds like paperwork, but one clause about materials decides about half of your shopping list.

This is the step people skip. They read the model page, browse some parts, and figure the rules are a formality they'll sort out later. Then they lose a week arguing on a forum about whether a metal standoff is legal, when the answer was written down the whole time.

Find the document that governs

Events usually publish two documents, and only one of them is the actual rules.

• A construction specification covers how to build. Weight classes, weapon restrictions, safety requirements, sometimes weight bonuses. It's useful, but it isn't the final word on its own.
• A ruleset is what governs. In combat robotics that's usually a SPARC document, and the event's own page will say which version it follows.

The two can disagree, and when they do, the event's stated ruleset wins. We saw this firsthand. One construction spec offered generous weight bonuses for robots that walk or shuffle instead of rolling on wheels. The event that linked to it said in its own rules, "no weight bonuses for any robots." Anyone who planned around the bonus would have shown up overweight.

So read the governing document first and the supplement second. If you do it the other way around, you end up with confident answers to the wrong question.

The clause that settles your parts list

One sentence does more work than the rest of the class rules put together. COTS stands for "commercial off the shelf," meaning ordinary parts you buy rather than make. In SPARC's plastic class the clause reads roughly like this:

Commercial Off The Shelf parts can be made from any material. This includes components such as motors, electronics, axles, bushings, bearings, fasteners, and adhesives.

That line answers most of the "is this metal allowed" questions before you even ask them. Motors, the speed controllers (ESCs) that run them, receivers, batteries, every screw, standoffs, bearings, bushings, thread locker. All of it can be metal, because nobody running a plastic class expects you to print a ball bearing.

What has to be printed is the stuff you designed yourself: the frame, the weapon, the armor.

There's one limit, and it's worth reading twice. COTS parts can't be used outside their typically accepted function. You can use a bearing so a weapon spins. You can't bolt a chunk of metal on as a counterweight, a striking tip, or armor. Metal doing its normal job is fine. Metal quietly doing the frame's job is not.

Wheels usually get their own clause, since rubber and foam obviously can't be printed and obviously have to be allowed. Expect language that permits foam and rubber tires, and permits store-bought parts between the motor and the tire.

The rule that goes against everything else you've read

Post-processing of materials using techniques that enhance durability is not permitted. Disallowed processes include but are not limited to annealing, acetone soaking, and boiling of parts.

Annealing means baking a printed part in an oven to make it stronger, and everywhere else in the printing world it's normal, well-documented advice. Here it gets you disqualified.

It's also the first thing you'd think to try after your weapon shatters, and that's when you're least likely to go back and reread the rules. In this class, your only ways to make a part tougher are the print settings and the shape of the part, and that limit is the whole idea of the class.

Painting is generally fine, as long as it's just for looks.

No composite filament either

The list of allowed plastics is short and specific. Typically it's PLA, PLA+, PET, PETG, ABS and ASA, and nothing else.

Filaments with other stuff mixed in are specifically excluded, and the rules usually name carbon fiber PLA, glass-filled ABS and flexible PLA. These catch people because they sound like upgrades. They're stiffer and they print just like the plain version. Plain PETG is legal, but carbon fiber PETG isn't.

The lists also tend to say that anything that behaves like PLA+ counts as PLA+, whatever the marketing calls it. So a spool labeled PLA Pro or Super PLA doesn't get you anything extra.

Ask, and ask early

Every ruleset ends with some version of "robots may be disqualified at the event organizer's discretion if deemed to violate the spirit of the class," usually followed by an invitation to get in touch if you're unsure.

Take them up on it. Organizers would much rather answer an email in August than turn you away in September, and a written answer from them beats whatever the forums agree on.

Just ask early enough that the answer can still change what you buy. That's why this module comes before the one on shopping.

Five minutes before you spend anything

So the event's ruleset outranks the construction spec, the COTS clause decides what can be metal, and the post-processing and filament rules are the ones you'd break out of habit. Before you buy anything, check all of it:

1. Find the event's stated ruleset and version. Not the construction spec, the ruleset.
2. Read your class section start to finish. It's usually about two pages.
3. Write down the allowed materials list exactly as it's written.
4. Find the COTS clause and note what it rules out, not just what it allows.
5. Note anything that goes against normal practice, because those are the rules you'll break out of habit rather than on purpose.

The documents themselves

Bookmark these rather than trusting anyone's summary, including this one.

• SPARC hosts the standards most US events adopt. The one that governs your build is the Robot Construction Specifications, currently v1.6. There are four other documents there covering match rules, judging, tournament procedure and arena construction, but you only need the first one to build.
• Texas Robot Combat's rules page publishes TRC's own Construction Specifications, Match Rules, Judging Guidelines and Tournament Procedures. If you're competing with TRC, their documents override SPARC wherever the two differ, which is the same situation this module started with. TRC runs Plastic Ants as its own class alongside Open Ants and Open Beetles.
• Comet Robotics' Plant Series rules summary is a readable plain-language version of the plastic-class requirements, good for getting your bearings. It says outright that it isn't complete and may be out of date, which is the right way to think about any summary of a ruleset.
• Robot Combat Events is where most US events list themselves and take registration. Find your event there first, then get its ruleset from the event page rather than assuming.

One habit that pays off: when you find the answer to a rules question, save the exact sentence and the document version it came from. Six weeks later, when someone in a Facebook group tells you something different, you'll want the citation, not your memory of it.