Two designs for a shaker motor-powered toy that can evolve into all sorts of fun.

BUILD TIME: 30 MINUTES
DIFFICULTY RATING: BEGINNER

This month, we’re winding back the complexity a bit. We’ve had a few complex projects over the last few issues and even last month’s wireless power project would have been a bit difficult for the youngest or least experienced makers. Therefore, we’re changing things back to something that involves only a few electrical connections, but lots of creative options and various end-uses.

The Bristlebot is a name seen in many online posts regarding these simple creatures. The idea behind them all is simple, and is so widespread we have no idea who the original inventor is. The same goes for the Peg Pests. The idea of the two is the same, however. A toothbrush head or a peg is used as the basis to mount a coin battery, some LEDs, and a small shaker motor. While we bought this shaker motor, they can also be recycled out of old, unwanted mobile phones.

After building your toy the way you want it, there are various options for playing with them, including races, robot battles, and obstacle courses. We’ll present one of each. They’re a great thing to do in a group, so if your friends make one too, you’ll have a lot more fun.

Warning

This project uses coin batteries. Young children can easily swallow these, and cases have been in the news over recent years where this has put children in hospital. It has even been fatal. Be careful with these batteries and make sure your adult keeps a close eye on them. When not being used, put them somewhere safe.

Additionally, there are two LEDs used per BristleBot or Peg Pest. While we have specified a part number, it’s really up to you. You can choose 3mm or 5mm LEDs (although 10mm ones may be a bit big to work well) and you can choose any colour you like. You can also get fancy, and choose flashing LEDs or even something more advanced, like a colour-changing LED.

Any of these are available from the regular retailers, but the part numbers we list are basic 5mm red LEDs. You could also check out www.ledsales.com.au, for a great range of interesting LEDs. Be aware of minimum order value, but this store has things no one else does, at a retail level at least. We have used their red and blue flashing LEDs, and flickering flame LEDs on some of our Bots.

A NOTE ABOUT LED selection:

Some LEDs will not work well for the BristleBots or Peg Pests. Certain examples, particularly blue or green, or any with driver circuits built in, need above 3V to run. The coin battery with a motor attached may not run these LEDs.

ADVICE AND INSTRUCTIONS

We encourage you to read all the way to the end of the article before you build. Not only will you then have a better feel for the overall picture as you build, but we sometimes discuss options or alternatives that you will need to have decided on.

You will need some basic hand tools for most builds. Small long-nosed pliers and flush-cut side cutters meant for electronics are the main ones. Materials like tape or glue are mentioned in the steps, too. We always produce a tools materials list if you have to go shopping, but anything that is lying around in most homes is just stated in the steps.

As always with Kids' Basics, we avoid soldering to make the build more accessible to more people, but having an adult around can still be helpful. You won't need any particular skills besides being able to identify components at a basic level, and even then, we help as you go along. If, for example, you don't already know what a resistor is, you'll probably be able to work it out from the photos and description in each step.

We do provide a schematic or circuit diagram but this is just helpful if you already know how to read one. Don’t stress if you have never learned, but take the chance to compare the digital image of the breadboard layout (which we call a 'Fritzing' after the company that makes the software) to the schematic and see if you can work some things out. You can make this project from the Fritzing and photos alone.

While you browse the photos, you may see some with the bots posed in action, but without batteries. Unfortunately, bots move so much they end up blurry in photos, so we had to stop them.

The Build:

TOOLS & MATERIALS (See Text for details):
Toothbrush
Clothes Peg
Hot Melt Glue Gun and Glue
Double Sided Tape
Blue Tac

Electronics Parts Required:	ID	Jaycar	Altronics	Core Electronics
2 x Shaker Motor	-	-	JA0070 #	ROB-08449
4 x LEDs of Choice	LED1,LED2	ZD0152	Z0860	-
2 x CR2032 Batteries	-	SB2522	S4999B	-
1m Red Hookup Wire	-	WH3010	W2250	-
1m Black Hookup Wire	-	WH3011	W2251	-

# Different shaped item

Having an adult with you for this build is recommended. We’ll be using a fair bit of hot melt glue, and at times a sharp blade. This last one has to be done by an adult, but it's for some of the craft options so you may be able to avoid it. Have a look around for your materials first, and collect everything you will need to make your robot before you start. Additionally, there is one bristlebot and one peg pest in this build. If you’re only building one or the other, scroll along until you find the beginning of the one you want.

Step 1:

Take a wooden or plastic peg and glue two LEDs to the side of the back.

Step 2:

Under the peg, twist the two long legs of the LEDs together, and the two short legs. Make sure there is a gap between them.

Step 3:

Glue the shaker motor to the top of the peg, between or just behind the LEDs.

Step 4:

Twist the black or blue wire from the shaker motor to the short legs of the LEDs. Twist the red wire to the long legs.

Step 5:

Strip the ends of a piece of black hookup wire. Twist one end around the short legs of the LEDs and glue the other so that it sits in the jaws of the peg. Make sure you glue the end into the recess in the jaws.

Step 6:

Strip the ends of a piece of red hookup wire, and repeat step five for the long LED legs and the other side of the peg jaws. Make sure you glue at the end of the wire and toward the middle, so the bare wire is free as a battery contact.

Step 7:

Straighten out three paper clips. You can also use any firm wire like tie wire. Bend them into shape to be used as legs. Make sure the ends curl over to hide the sharp bit.

Step 8:

Glue the middle leg onto your peg pest, then one under the jaws of the peg at the very end. Also, glue one toward, but not right at, the front of the pest peg, which is where you put your fingers to open the peg.

Step 9:

Cover the connections to the LEDs, motor, and hookup wire carefully with hot melt glue. If these are uncovered and not stuck down, they will move with use.

Step 10:

Insert a coin battery and make sure the motor shakes and the LEDs light up. If nothing happens, check your connections. Make sure the battery is touching the wires properly. If the motor shakes but the LEDs do not light, turn the battery over.

Step 11:

Have an adult cut the head of a toothbrush. You can use a hacksaw or cutters for this, but make sure you sand or file the end to remove sharp objects. Alternatively, cut it with a hot knife if your adult knows what one is and how to use it.

Step 12:

Strip enough of the black or blue wire of the shaker motor that you can make a coil.

Step 13:

Place a piece of double-sided tape on the back of the toothbrush, and mount the shaker motor to it. Carefully place the wire coil on the tape, too.

Step 14:

Stick a coin battery to the tape so the smaller circle touches the coil of wire and the ‘+’ sign faces up. Touch the red wire to the upper side of the battery to make sure the motor works.

Step 15:

Slide two LEDs of choice onto the coil battery beside the double-sided tape, with the short leg under the battery and the long leg on top. Make sure they light up, and if they don’t, swap which leg goes over and under.

Step 16:

Tape the red motor wire and the upper legs of the LEDs to the top of the battery with masking tape. Your BristleBot should now be lighting up and buzzing around.

HOW IT WORKS

As usual, you don’t need to know any of what follows to make your Bots, but if you like science, read on. Note that because Kids’ Basics readers come from so many ages, from the youngest school years and up even into adults beginning their electronics journey, it’s hard to write an explanation for everyone. We’ll try to find middle ground.

We have used electric motors several times in Kids’ Basics but we have never delved into how they work. They’re a fairly critical part of this design, but in a future issue, we’re going to make an electric motor and will describe their operation then. For now, we’ll see why the motor shakes. Before we do, however, some readers may have noted that we have used LEDs here without current-limiting resistors. LEDs are diodes constructed for their ability to emit light, and that comes with certain compromises.

Most PN junctions (the chemical combination diodes and many other electronic components are made from) do not have enough internal resistance to limit current through themselves to safe levels.

This means that, if given the correct supply voltage, most LEDs will pass more current through than they are rated to handle, reducing their lifespan. The exceptions are LEDs with internal resistors, or internal drivers (although some of these still need resistors). However, LED production has come a long way.

Most modern LEDs will still last hundreds of hours running like this connected to a 3V battery with no resistor. While resistors remain recommended for most applications involving LEDs, the difficulty of adding them, in this case, does not bring enough benefit when the LEDs will still outlast the toy.

Shaker motors are a very specific device. They are designed to provide feedback in situations where touch is a useful sense with which to give a person information. If you’ve ever used a keypad on a touchscreen device where there is a slight feeling when you press a key, this is usually a shaker motor like the ones used in these bots. This is one form of something called ‘haptic feedback’ where a device you are interacting with gives some sort of information back to the user to show that their input has been received.

Shaker motors use some of the most basic laws of physics. There are two ways of building them, but we actually have no idea which one is used in this project. Some shaker motors use a motor with a weight offset on its shaft. These are called ‘Eccentric Rotating Mass (ERM) motors.

These produce a very strong vibration but are not always compact. However, in recent years, they have been made very compact indeed, including into micro coin packages like these, as is the other type of motor. Both use Newton’s Laws of Motion, so let’s look at those.

Newton’s First Law of Motion

An object at rest will remain at rest, and an object in motion will remain in motion unless acted on by a force.

This means that an object sitting still will remain so unless something makes it move, but it also means that things want to keep going in a straight line once they are moving, and not stop. In the real world they are stopped by things as slight as air being moved out of the way, although this on its own may take some time to slow an object. Any other friction from surfaces sliding together also slows things down, like the bearings in a motor.

Newton's Second Law of Motion:

Force equals Mass multiplied by Acceleration

The amount of force something can exert is defined by its mass (how much matter or ‘stuff’ there is in it) multiplied by its acceleration, which is its change in speed. Weight is the term used to describe how much the force of gravity pulls something here on Earth, and it depends on how much ‘stuff’ (mass) there is so we often hear and see the terms mixed up. While you don’t need the maths to understand these motors (you’ll get that in early high school if you haven’t already) just know that the heavier something is for a given speed, the more force it exerts. The faster a given mass moves, the more force it exerts when it slows down or the more force it took to get it to that speed.

Newton’s Third Law of Motion:

Every action has an equal and opposite reaction.

This is the one we hear quoted all the time, often to justify social behaviour rather than physics. It means That if there is a force in one direction, there must be an equal force in the opposite direction.

Eccentric Rotating Mass motors use a weight attached to a motor shaft in such a way that most of the mass is to one side of the centre. When the motor spins, the mass wants to move and keep moving in a straight line, which means outward.

This is Newton’s first law of motion, but it turns into Centrifugal Force because the mass is attached to the motor shaft and cannot move outwards, only around. When this happens, a point called the ‘centre of rotation’ is created, in the middle of the mass and the shaft it is attached to. Note that it is in the centre of mass, which means the most weight, not the distance. In the mass drawn here, most of the mass is at the outside edge so the centre of rotation is more than half-way from the shaft.

Because the centre of rotation is not over the shaft, and Newton’s Third Law says that for every force there is an equal and opposite force, the motor wants to move as well, opposite the mass and around its centre of rotation. However, the motor is attached to the device, usually a phone but in our case a toothbrush or peg. The result is that the force is transmitted to the device and the whole thing moves slightly.

The other type of shaker motor is the Linear Resonant Actuator (LRA). This is closer in operation to a speaker than a traditional motor, and the forces are even simpler. It consists of a coil of wire around a magnetic core, with a spring underneath. When the coil has current going through it, the core is pulled or pushed (depending on coil placement) against the spring.

When the current stops, the spring pushes the core upwards. Some more sophisticated versions have two coils, one to push the core and one to pull it. In both cases, a tiny circuit is needed to switch the current on or off or change which coil (and in which direction) it flows through.

Build designs vary. Some LRAs are built with the free-moving core impacting on an upper surface, while others have it fixed to a flexible surface. Some have coils under the core while others are around it. The interaction of forces involved, and therefore the combination of Newton’s Laws that applies, varies. What is the same is that all of them involve Newton’s Third Law where a force is exerted in one direction by part of the device, which creates an equal and opposite force in another part of the device.

When observing your BristleBots or Peg Pests, if they show a pattern of moving in circles, they are probably using ERM motors. If they have no pattern to their bussing and move any which way, they’re probably LRA motors.

USING YOUR BOTS AND PEGS

BristleBots and Peg Pests can be used in several ways. Of course, you could just watch them do their thing and buzz around, and push them away from or into things. However, there are some more structured things you can do. In each case, you may need to ‘shepherd’ your bots around, because sometimes they just headbutt obstacles or spin in circles. This is best done with a stick like a skewer or ruler. Be careful to use this only to steer your bot, and not push it. Your friends will call you out pretty quickly if you do!

BUILDING AN ARENA OR TRACK

Arenas or tracks are useful for all of the following ideas. They can be made from any flat surface and need to be surrounded by walls. These can be anything you have at hand to form edges: Books, either flat or propped up; cardboard boxes or sheets of cardboard cut from them; wood if you have any around; toys like slot car sets or toy race tracks; or anything else you can think of while looking at the photos.

OBSTACLE COURSE

Obstacle courses are great fun. The idea is that you create a track full of things to navigate around. It can be a long narrow track or an arena. After you define the sides of your area, fill it with different obstacles from around you. Anything will work. You can race one bot against the clock and better your time, or race against friends. Agree on a start and finish point and use a pushing implement only to turn your bots around and not to steer away from obstacles. If you prefer, make it harder by not using the pusher.

RACING

Set up a track, either straight, round, or curved and straight like a car racing track, and line your bots up at one end. Using the pusher to keep them straight(ish), whichever bot crosses the finish line wins. You could do this solo against the clock, and you could also avoid the pusher for extra chance or difficulty.

BATTLE OF THE BOTS

This one needs an arena. Two or more bots are placed in the play area, and allowed to push against each other. You can set up rules like a line down the middle and a certain amount of time that one bot has to push the other into a certain side. Or, you can set up things like small ramps or objects for the bots to ride up over and possibly tip over. The winner is the last bot standing in that case.

WHERE TO FROM HERE?

There are probably many other things you can do to put your bots to use. The biggest avenue for further development is craft. You can decorate your bots with colour, cardboard, jiggly eyes, paper wings, pipe cleaners, or anything else you can think of.

We have done this for some of ours in the photos but it is so variable we haven’t tried to describe it. The best way is to gather some materials first, then once you look at them, the ideas will probably flow.