Introduction
Today we are going to build a modified version of this snakebot.
Take a look at your materials and make sure you have all you need: batteries and holder, wheels, motors, three switches (two large and one small), a circuit playground board, a crickit board, bolts for attaching the crickit to the circuit playground, cardboard for the body, and a USB cord.
You’ll also need access to double-sided tape, a small screwdriver, binder clips, and a hot glue gun- these are available in the lab.
Assembly
You can do the following tasks in any order. Since you are sharing tape and glue guns with the rest of the class, you might skip ahead while you wait for materials to become available.
Mounting the Playground to the Crickit
You should have a packet of six long spacers and twelve screws. You are going to use these to attach the playground to the crickit board. The circuit playground is the “brain” of the robot, and the crickit is the central nervous system. These brass spacers are the nerves- they are carrying information from one board to another. But in order to do this properly, they have to be aligned correctly. If you look at the crickit board, you will see that there are six screw holes in the center and these are labelled. You can match these labels to six of the holes on the edge of the circuit playground.
Follow these directions to attach one to the other. Note that your crickit has a mounting square on the backside, so it looks a little different than the one on that page!
Attaching the front switches
These switches are going to make the front bumpers or “whiskers” of your snake- what tell the bot when it has collided with an obstacle. Take the largest piece of cardboard and turn it so the black markings are facing up and in the front. (The wheels should be on the bottom now, if you did those first):
Place the two large switches so they are opening outwards, like so:
Make sure the corner of the switch is lined up with the corner of the cardboard, it can even hang over a bit. Glue the switches in place with hot glue. Be VERY CAREFUL NOT TO GET GLUE ON THE METAL SWITCH.
Now place the small switch on the center line. The switch has a little metal pin- you can use this to anchor the switch inside the cardboard. Make sure the two wires are on top, like so:
Now glue it in place- I found it worked well to put a dollop of glue on the pin and then press it into the cardboard again.
Now it should look like this (ignore the wheels if you haven’t added them yet):
Attaching the wheels and motors
Your motors each have two axles. You are going to use the “outside” axles- that is, the ones opposite where the wires come out. Attach the two wheels to the outside axels of the motors, like so:
Now turn your cardboard so that the large black squares are facing up (the switches are now on the bottom, if you did those first).
Cut two squares of double-sided foam tape and put them on the squares:
Now peel the protective layer off the tape and align the motors on top= with the wires facing towards the notches, and making sure the wheels are clear of the cardboard:
Now pull the wires through the slits in the cardboard carefully, so they emerge on the other side:
Mounting the Brain to the Body
**The previous tasks can be done in any order, but you must do all of them before proceeding.**
Turn your bot wheels side down. Put a large piece of tape in the center of it.
Put the batteries in the battery holder and close it. Note that the battery holder has an on/off switch- you want to make sure this is facing up! Peel the other side of the tape on the bot and put the battery holder on it with the word “open” facing down and the on/off switch facing up. Try to center it between the wheels and make sure it is clear of all of the switches:
Now put a piece of tape on the middle of the battery holder:
Note that there is a mounting square on the back of the crickit – peel this off:
Stick them together, orienting the barrel of the crickit to the back and making sure the on/off switch on the battery is visible. The crickit will likely be off-center:
Finally, put a large binder clip on the back of the bot to keep the cardboard from dragging.
Putting on the bumpers:
Now you need to attach the cardboard bumpers to the switches. The long cardboard pieces go on the sides, and the smaller one in the middle.
This is delicate, as you don’t want to get too much glue on the switches or they won’t work right.
Make sure the binderclip “tail” on your snake is folded correctly- it should prop the back end up a bit:
Put a thin line of glue on the metal strip of the switch and hold the cardboard in place.
Make sure it is roughly parallel with the ground but isn’t dragging:
Attach the other long piece on the opposite side:
You may need to trim the cardboard after attaching it to keep it from dragging- that is alright!
Now attach the center one in front of the other two. Put a little glue on the metal switch (TAKING CARE TO AVOID THE RED DOT!) It will be angled out slightly at the bottom:
Let the glue completely cool, and then check that the bumpers work by pressing on the cardboard until you hear a “click” of the switch engaging. It should spring back once you let go.
Wiring it all up
Now it is time to attach everything together. First, attach the motors to the screwblock terminal marked “motor.” There are four wires from the motors, a red and a black from each. Place them in the outer four holes of the screwblock with the red wires on the outside and the black on the inside (you may need to loosen these with a screwdriver), then use a phillips head screwdriver to tighten it back up:
Now wire up the three bumper switches. First, look at each switch and note it has two wires- a light wire (yellow, red, orange, or white) and a dark wire (black, grey, brown, or blue). The “light” wire is the power wire and the “dark” wire is the ground wire.
These are going to plug right into the big black box labeled “signal I/O” (that means signal input/output.) Now look at the “signal I/O’ box, and note that it has a grid of holes on top of the box. These are labelled in three columns (signal, 3.3 v and GND) and in numbered rows. The wires from the switches will go into these holes- the “light” wires into “signal” column and the “dark” wires into the GND column. Each numbered row of holes will be dedicated to a switch- that is, make sure the two plugs from the lefthand switch (on YOUR left) are in row 1, the two plugs from the center switch are in row 2, and the two plugs from the righthand switch are in row 3. Here is a photo:
That is hard to see, so here is a wiring diagram- here, the “light” wires are all green (this diagram has the wrong kind of switches but ignore that):
Finally, plug the barrel from the battery into the back of the crickit:
And that’s it!
To turn it on, make sure the “on/off” switch on the crickit is set to on, then put it on the ground and turn on the battery switch. There it goes!
Optional fun
Make a tail!
You can link together pieces of cardboard with binder clips and pipe cleaners to make a little tail!
Decorate!
You can draw on the robot body, or use any of the materials available in the lab, to personalize it.
The Code
So what makes the bot run? The circuit playground you got in your kit came preloaded with a program written in a language called Circuit Python (basically regular python, honestly). If you are interested, you can follow this guide for what the bumper code is doing, or this general guide for getting started with circuit python. The playground express actually has a bunch of lights built in, so if you wanted to add lines to the code to make those blink in fun patterns, you can see how to do it there.
Cyd Cipolla 