The Decisions Before the Build

"Ever tried. Ever failed. No matter. Try again. Fail again. Fail better." — Samuel Beckett

Before you buy a single part, you'll make three choices that look like matters of taste. Plastic or metal. A robot that pushes the other one around, or one that spins a weapon. A kit out of a box, or a robot you piece together yourself. Each has a pretty clear answer for a first build. The reasons matter more than the answers, though, because next season your situation will be different and you'll want to make the call again on your own.

All three come back to the same idea. When you're starting out, the number of tries you get matters more than how good any one try is.

Plastic or metal

Most events split the small robots into two groups. In the plastic class, the frame and the weapon have to be 3D printed plastic. In the open class, anything goes, including aluminum and steel. The open class sounds like the serious one, and it's natural to assume that's where you should aim.

Start in plastic anyway, and not as a consolation prize. The reason is what it costs you when something breaks, and something will. If a printed frame cracks, you start a reprint before bed and it's done in the morning. If a metal frame bends, you're ordering material, waiting on shipping, and asking yourself whether it's worth fixing at all. Over one season a plastic builder might go through five or six versions of the robot while a metal builder gets through one, and every version teaches you something the last one couldn't.

Plastic also isn't a detour. A plastic robot and a metal robot in the same weight class are basically the same machine with a different frame. The motors, the electronics, the battery and the layout all carry over. So printing first is how you find out your layout is wrong before you pay someone to cut it out of aluminum.

There's also the matter of who you'd be fighting. The open class at most events is full of people with machine shops and several seasons behind them. A first robot in that bracket tends to have a short day.

A pusher or a spinner

Robot fights are scored on damage, aggression and control, and there are two broad ways to go after that. A control robot, usually built around a wedge, wins by getting underneath the other robot and shoving it around the arena. A spinner carries a fast-spinning disc or bar and wins by hitting things hard.

There's a good case for each. Driving decides more matches than weapons do, and a wedge that keeps getting under its opponent will beat a spinner that keeps missing. Judges also reward a robot that controls the fight, even when nothing breaks. And a pusher usually survives to the next match, which means more time behind the controls, and practice time is what actually makes you better.

The case for a spinner is simpler. Spinners are more fun to build and a lot more fun to watch. If you're building with a kid, that matters more than it sounds, because a kid who isn't excited won't want a second season.

You don't have to pick forever. Keep the body and the drive the same, and make the front end a piece that bolts on. Run one setup at your first event and the other at your second. Comparing the two across a season will teach you more than guessing right on day one.

A kit or your own build

A kit is a box of parts that are known to work together. Building your own means taking a published design, printing it, and choosing every part yourself.

A kit takes care of the part of the build you'd learn the most from. Putting a robot together isn't the hard part. The hard part is the fifty small decisions before that, and a kit makes them for you. You end up with a robot that works and no real idea how you'd design the next one.

Building entirely from scratch has its own cost, though. Most published designs give you the shape of the robot and not much else. The parts list might just say "38mm wheels, approximately 10mm wide," and then you're the one stuck figuring out which wheel that is. Sourcing a Build That Has No Parts List is all about that problem.

For most people the answer is somewhere in the middle. Use a published design for the printed parts, and buy the electronics as a bundle from a combat robot shop. Those bundles look about the same everywhere: two small geared motors for the wheels, one speed controller that runs both, a radio receiver, a battery and a power switch. Some include the weapon motor and its controller too. Everything in the box is picked to work with everything else, so you're not guessing at whether the electronics will talk to each other.

We ran straight into the problem with that. Parts that work together won't necessarily fit your robot. A published design is drawn around specific parts. The motor pockets fit one motor, the wheel wells fit one wheel size, and the bearing seat fits one bearing. The shop that put the bundle together has never seen the design you downloaded, so a box of perfectly matched parts can still be the wrong size for your chassis.

So do things in order. Pick the design first and buy the parts it was drawn around, or pick the bundle first and find a design built for those exact parts. If you choose both separately and hope they line up, you can lose a month finding out they don't.

What the three have in common

In every one of these, you're giving up a little top-end performance to get more tries. Plastic over metal, a swappable front over a fixed one, a published design over a blank page. It's not a beginner's compromise you grow out of, either. Plenty of experienced builders work this way on purpose, because the person who gets five tries at a decent design usually finishes the season ahead of the person who got one try at a great one.

Whatever you decide, write down why and keep the note. Next season, when things have changed, the reasoning is the part you'll want to look back at.