Servo - April 2010

Now comes the most exciting time of the entire build process. That first time you flip on the power switch and bring your machine to life. It’s a great time to be alive, isn’t it? Wouldn’t it be great to stay alive?

That first time you flip the switch is exciting, but it’s also the most dangerous time in the build. Over the past several weeks, I’ve watched builder after builder posting videos on You Tube.com of their robot’s first weapon test. A little robot, six pounds or less with aluminum, steel, or titanium spinning at 5,000, 10,000, even 30,000+ RPMs sitting on the floor with little or no protection between the bot and builder. I cringe and grit my teeth waiting for a loose screw or random nut (that was dropped on the floor and forgotten a mere two hours ago) to ricochet around the room. I further cringe as the video continues with the inevitable test hits. I’m a nervous wreck after 40 seconds of video.

Don’t get me wrong. I’ve done FIGURE 1. A storage trunk, a.k.a., the basis for a robot test box.

FIGURE 2. Create a rectangular opening in the trunk.

34 SERVO 04.2010

the same thing, and I’ve lived to tell about it. My whole perspective changed the day my vertical spinner “gyro’ed” over upside-down with the blade at top speed and struck the concrete driveway I was testing on. Pieces of concrete shot at me. I was fortunate I was not hit. That single event was a huge wake-up call. “HEY, 10,000 RPM IS REALLY FAST. HOW ‘BOUT WE TRY NOT KILLING OURSELVES NEXT TIME, HUH?” I’ll give you a breakdown of how to build a small, simple test box that you can use to spin-up those nasty weapons, hit stuff, practice driving with the weapon on, and not DIE. Here’s the best part: The whole thing can be built for under $100 and in less time than it takes me to find a pair of matching socks in the dryer.

You will need the following items/tools for this project: a storage trunk (see Figure 1; they can usually be found in department stores for $20 in late summer when college students are going back to school); a 14”x 28” piece of polycarbonate sheet 1/4” thick or greater; one 8’ long 2”x 3” piece of lumber; a box of wood screws; some string or lightweight chain; a drill; a hole-saw or spade bit; and a jigsaw. If you have a particularly nasty robot, you can pick up a sheet of Medium-Density Fiberboard (MDF) for additional reinforcement (described later).

The process for building this box FIGURE 3. Polycarbonate sandwiched between the lid and the 2” x 3” piece of lumber.

is so simple it practically builds itself. (Okay, it’s not that easy, but you could build a robot to build the box for you.)

Altering the Trunk

You have your trunk sitting in front of you. In theory, you could throw the bot in there, close and lock the lid, and call it a day. But unless you’re a dolphin, it’s hard to drive your robot via sound. The first thing you need to do is create an opening in the top of the trunk so you can see in. Driving a bot via looking at it is so easy, a caveman can do it. Measure in about 2” from each corner of the trunk; the dimension isn’t super critical, so don’t stress over it to much. Break out your trusty (or rusty) drill and spade bit/hole-saw and create a hole in each corner. The holes are for the purpose of starting the jigsaw. Next, break out the jigsaw and run a straight line between the holes forming a rectangular opening in the lid (see Figure 2). Now you could throw your robot in there and test, but the test box offers about as much protection as a tissue in a hurricane. (From experience, that isn’t much protection at all).