Friday, July 20, 2012

Motorized Balancing Toy


Materials:
• Annealed steel wire (bailing wire)
• A hobby motor
• About a 2' solid core copper wire (we like to use twisted pair telephone wire for this)
• AA battery
• Wide rubber band or inner tube slice
• 1'' x 6'' wood dowel
• Small piece of wood (1/2' x 4 x 4'') for a base
• Small piece of foam core
• Popsicle stick
• Steel washers

Tools:
• Scissors
• Pin nosed players
• Small wood saw
• Hot glue gun


This project addresses two basic mechanics concepts, center of mass and torque. In order to get the toy to balance you have to find the center of mass of an asymmetric object, the motor wire and battery.  Because the toy is essentially a beam you're dealing with an issue of torque.  That is to say the twisting force on the toy will be equal to the weight of whatever is at the end of the wire (the motor or battery) and how far the motor or battery is from the balance point (the center of mass).

When it comes to powering the toy, you also have to deal with issues of torque.  The main difference being the force comes from the propeller not gravity, so the size and shape of the propeller are a determining factors. Less obviously, the torque force the propeller can put on the whole toy (which effects how fast it will spin) is determined by this pushing force and the distance the propeller is from the pivot point on the wire. This is similar to how the effect of the weight differed based on its distance from the balance point. This is to say that the further the motor is from the pivot point as compared to the battery the faster the the toy will spin.  If you added a lot of extra weight to the motor so it balances much closer to the pivot point than the battery you would get a very slow spinning toy. Even though the propeller's pushing power would be the same its torque would be greatly reduced. Although this project has an electrical component it focuses primarily on achieving balance and the right spinning speed not the circuit. That said, we consider this a mechanics project not an electricity project.             


The first step in creating your balancing toy is to wrap one end of an about 14'' piece of annealed steel wire around your motor so it is held securely.


Next, put a broccoli rubber and or inner tube section on a AA battery and slip the other end of the wire under it like so.


Find the balance point of the three pieces, you can do this by holding the toy on one finger and sliding it back and forth until it balances as seen above. Note the balancing point is not going to be in the middle of the wire, as the battery is heavier than the motor the balance point will be closer to it than to the motor.


Next add a divot in the wire for the toy to pivot on. Placing both thumbs at the balancing point bend the wire up into a shallow "V."


About 1/2'' from the center of your "V" bend the wire back down.


Do the same thing on the other side.


You should end up with something that looks like this.


Try to balance your toy on your finger again. The angle of the wire and the position of the battery will probably need some adjusting to get it to balance straight.  Note that the motor and battery are a little below the bottom of the pivot point, this is critical to prevent the toy from tipping over.


Next, make a propeller by cutting a diagonal oval out of the side of a cup or bottle and use a pin to poke a hole for the motor shaft in the middle.


 Wire up the motor and batter, using some small gauge solid core wire. We like telephone or network cable wire for this as they come in pretested pairs. Strip both ends of the wire, twisting one end onto the motor terminals. Twist the wire around the annealed steel wire until you reach the battery.  Then slip the wires under the rubber band the motor should start spinning.


Finally, add a stand and some decorations.  The stand consists of a 1'' dowel with a divot in one end (to hold the toy) made by twisting and pressing a Phillips head screw driver into the dowel and then hot gluing it onto a 4''x 4'' piece of wood.  We also decorated the toy by adding some plane wings using foam core and a Popsicle stick in this version, but making it look like anything that flies gives a cool effect.  Note that the decoration will add weight to the motor side so you may need to slide you battery further out or add some washers to re-balance the toy.  The biggest challenge is getting the speed right. Typically these toys will initially spin absurdly fast, getting them to slow down can be achieved in a number of ways. The simplest way is to reduce the size of the propeller in order to lessen the spinning force. Alternately, you can move the battery further out by twisting on more wire (and counterweighting the motor appropriately) in order to increase the torque necessary to get the whole thing to spin. The slowest speed would be achieved with a toy weighted so the battery is further from the pivot than the motor and a small propeller.    

Here's a couple videos of the motorized balancing toy in action.




Thursday, July 19, 2012

Scribbling Machines










Materials:
• Skewers
• Dowels
• Popsicle sticks
• Clothes pins
• Cups
• Cardboard tubes
• Pipe cleaners or wire
• Masking tape
• Rubber bands of various sizes
• Straws
• Hobby motor
• Annealed steel wire
• AA batteries

Tools:
• Hot glue gun
• Wire cutters
• Wire strippers


Scribbling machines are simple drawing machines which use a small motor to move a pen or pens around a pad of paper to create interesting patterns.  The idea of scribbling macines is not a new one in our experimentations we've found that having a restricted pool of material to build with creates more interesting patterns and more importantly machines that are truly adjustable. Adjustability is valuable from a an educational perspective because it encourages iteration and an understanding of how changes in form effect changes in movement.



The most important element of a scribbling machine is motive power, this consists of a hobby motor,
 two telephone wire leads (fine solid copper wires), a AA battery and a rubber band to hold the wires in place on the battery. Broccoli rubber bands work well to hold the wire on the battery, but they can be hard to find so we tend to cut up old track bike inner tubes to make our own rubber bands.  There are a couple of options to get the machine to move around the paper. Sticking a section of hot glue stick on the motor shaft to make a counter weight will create a vibrator.  The amount of vibration can be adjusted by centering the motor shaft more or less in the glue stick. We found wood screws work well to make a pilot hole in the glue stick. The other option is direct drive where the motor shaft or a wheel is in direct contact with the pad of paper.  The former makes more jittery chaotic patterns, where as the second method can make more Spirograph like drawings. In general we consider this to be a mechanics projects not a electricity project, as it is the motion of the machine not the circuit that is the focus of the activity.


Apart from that, there is no specific way to build build a scribbling machine, outside of the goal of making a structure to attach a pen to the motor. The activity itself is really adjusting the machine and figuring out how different changes in form effect the quality of the drawing and then taking that information to adjust the characteristics of the drawings. Here are a few models we tried out:



This is a very simple configuration, a toilet paper roll with clothes pins as pen holder claws and the motor/counter weight and battery attached on top. Originally it didn't have the skewer, but it did not produce very interesting drawings. Adding the skewer reduced ground friction and added some simple height adjustability which made for more interesting drawings.    






This version has a pen on one side and motor and battery on the other with a bottle cap skid in the middle. Because of the position of the motor this model can be configured as a vibrator or a direct drive by making the glue stick just long enough to touch the paper which makes for a really bouncy energetic motion (as seen below).  Changing the position of the bottle cap skid is another way to change this machine's behavior.    






This model is particularly jittery, with the pen coming in and out of contact wit the paper, as no part of its pipe cleaner structure is very ridged. Although the battery skid can't be moved the wire part of the structure can be bent and adjusted in an infinite number of ways to change behavior.






This is a direct drive model where the motor shaft is directly in contact with the paper.  It tends to make circular spiral patterns as the motor and pen rotate around the clothes pin skid. Adjusting the pen height and angle and moving the center skid around can change the pattern produced dramatically.  



Further experiments:

• Try separating the motor and pen with something flexible (sting or wire) so the pen gets dragged around.

• Confine your scribbling machine to a pen, pieces of wood or a cardboard box with no top or bottom works well and will lead to a higher concentration of line where the machine hits the walls.   

• Tether your machine with string to a point with a string and a thumb tack, this has a similar effect as the pen, with the bonus of the string possible changing length over time as  it wraps around the machine or the tack.

• Tether two machines to each other with string. Will they work together, fight each other, of orbit in some new combined motion?

Sound Automata



Sound automata is a modified automata mechanism designed to make a series of sounds instead of animate a scene or character. We've separated the material needed for the mechanism for the automata and the noise makers in order to make things clearer. While this a good starting place there is really no limitation on what material you can use especially on the sound making side.


General materials for the automata mechanism:
• A small bottle or large plastic cup
• Foamcore or Cardboard
• Skewers, chopsticks or 1/4'' dowel 
• Straws: standard and jumbo
• Popsicle sticks  


Materials for making sound:
• Annealed steel wire
• Rubber bands, clothes pins (these make good springs if you need something to snap back)
• Cups, cans and cardboard tubes (can be simply hit or have something stretched over them to make a drum, alternatively they can be cut into smaller pieces).
• Bottle caps
• Washers
• Nails
• Hot glue sticks


Tools:
• Scissors
• Hot glue gun
• Pine nosed pliers with wire cutters
• Utility knife


The base for our sound automata is the bottle (or cup) and diving board structure used in the our large automata, a foamcore base can be added if needed. The main difference is that that we've used both sides of the crank, and in some models (see the drop hammer) multiple items on one side.


Here is a simple example of a noise maker.  We have a short length of cardboard tube with a steel end cap, it's been glued to the diving board and slots have been cut in the bottom so as not to muffle the sound.  Several washers on a cam driven wire arm are raised and dropped to make a vaguely cymbal like sound. Different combinations of strikers, objects to be hit can make a wide variety of different sounds



Sound automata specific mechanisms:


Ratchets:



In this case a piece of plastic cup has been glued into the inside of the automata cup so it hits a wheel with multiple skewers attached which pluck the plastic when turned.




This version uses a Popsicle stick with a plastic cup hinge and rubber band. when the crank is turned the Popsicle stick is lifted by a series of dowels glued on a bottle cap. There is a piece a annealed steel wire attached to the Popsicle stick that hits the tin lid in the back of the automata when the crank is turned.

Drop Cams:






A Drop Cam, sometimes called Snail Cams because of its shape, results in a slow lifting motion and quick drop which is good for striking something.  Because of the steep drop Drop Cams can only be turned in one direction.  Eccentric Cams, a wheel with an off centered hub, like the ones we generally use for automata lift and drop at the same rate and can be turned in both directions.


Drop Hammers:


This is a very simple way to hit something below the crank. It is just a bottle cap with a piece of wire stuck through it off center with a loop on the back so it can move freely. When the crank is turned the wire ends up laying on the skewer until it is vertical at which point it falls faster than the turning bottle cap striking what's below. After it strikes it drags along the surface until it ends up laying on the skewer again.



Trip Hammer:




Here's an example off our original drum machine sound automata, which employes trip hammers.

Rotary Hammer:



This mechanism is somewhat unrelated to the others, based on a  vertical shaft connect to a weighted friction gear with a pivoting wire hammer spinning on top. 


(Theoretical) Scrubber/ Brusher:

We're still trying to figure this one out, the general idea is to use some sort of a cam or crank to move something back and forth to scrap or brush a surface.  



Sunday, July 15, 2012

Diving Board Automata




Materials:
-Foam core or cardboard
-A plastic cup, or bottle
-Jumbo straws
-1/4'' dowel
-Bamboo skewers
-Material and accessaries to create the scene to be animated

Tool:
-Utility knife
-Hot glue gun
-Wire cutters/ pin nose pliers



We made automata several different ways in the past and eventually settled on this one, which we call diving board automata. The main structure consists of some sort of container with a  piece of foam core sticking off the top like a diving board. The container can be a cup, yogurt container, soda bottle or any other shortish food containers which serves to hold the crank shaft. The diving board holds the mechanism and the scene to be animated. This is a distinct advantage over micro automata because the mechanism is easily accessible if it needs repair or adjustment.  


First poke 2 holes in the bottle about 2/3 of the way up. Wood screws work well for this as you can use them to drill into the plastic  Optimally, the holes should be straight across from each other and just big enough to fit a skewer so it can spin freely.


Next make the diving board, an about 3''x5'' piece of foam core. This will be the platform on which the object to be animated will be built. In order to cut the hole in the board take the lid off the bottle and press the mouth of the bottle into the center of one end of the foam core.  Use a utility knife to cut out the imprint and then use a screwdriver or pen to stretch out the hole until the board will just fit the top of the bottle. Position the foam core over the 2 holes in the bottle and tighten down the cap to hold it in place. If you want to use a cup simply glue the diving board to the top of the cup for this step, this will make a simpler, but somewhat less stable automata.


 Use a screw to poke a hole in the end of the board.  This hole will hold a straw and skewer for the cam and friction gear automata or a wire for a crank slider mechanism.


We've made a simple crank wheel by hot glueing a bottle to the end of a skewer and then adding another small section skewer to the side of the cap to form the crank.


Here's the automata with the crank inserted and a handle and straw spaces added to keep everything in line.


Here's the completed crank slider mechanism with a long piece of annealed steel wire attached to the crank and a piece of foam core added to prevent the wire from slipping off. Adding a small piece of straw or another piece of foam core between the crank wheel and the wire is a good way to keep the wire from slipping back and fourth.



Alternately, you could add a cam instead of a crank slider for a straight up and down motion.  If you used a simple wheel instead of an eccentric cam you can make a friction gear in order to get a spinning motion.


Here's the cam with the follower wheel installed and lever arm to modify the up and down motion (there's a video of this below). Note that the addition of an arm did make the arching motion the builder wanted but is not a necessary part of the cam mechanism.   Note that we added some sand to the bottle to help keep it steady. If you make a cup based automata you will be unable to add sand for stability but you can simply glue the whole thing onto another piece of foam core or cardboard to make a foot.


Here are a few finished examples:
                                                                                                 


This bottle based automata uses the cam mechanism shown above for an up and down motion.


Here's the same automata as seen from the back, a screwer and several straws have been used to get an arching motion from the original straight up and down motion.


This bottle based model uses the more complicated crank slider mechanism, using thin wire to constrain the wings to the diving board to get the flapping motion.


Here's a cup based crank slider mechanism this time with the top of the head constrained to the diving board to make the mouth open and close.


 Here's a side view of that same mechanism.

Micro Automata



Materials:
• Wide clean plastic cup or clear solo cup.
• A straw
• Skewers
• Bottle caps
• Foam core
• Tape


Tools:
• Scissors
• Hot glue gun
• A wood screw
• Phillips screw driver or pencil

Automata meaning self operating machine typically consisted of a clockwork statue or scene and were first created centuries ago in Europe and Asia.  They were in many ways the direct ancestor of what became electro mechanical robots.  For our purposes automata are a good way to explore machine's function of converting one form of energy and motion into another.  They are also a way to teach simple mechanical problem solving skills.


Micro automata were the first in our series of attempts to simplify cardboard automata. The basic idea was to avoid building the box by putting the mechanism inside a clear plastic container.  Mechanically they are very simple. They have a input shaft with a crank coming out the side and an output shaft coming out the top with a mechanism in the middle to convert the motion. Here is a good basic model to start from to which more features can be added.


 First you use a wood screw to poke a hole in the side your cup about half way down and big enough for your skewer.


Insert the skewer and mark the position of the second hole so the skewer is parallel to the top of the cup.  When inserted this skewer is the input shaft.


Make a hole in the center of the bottom of the cup using a wood screw.


Use a phillips screw drive or pencil to widen the hole until a straw will fit tightly in the hole. Note that the straw has to be big enough for your output skewer, so size your straw and hole accordingly. With the straw sticking about 1/2'' into the cup hot glue it in place being careful not to melt it.


Prepare the output shaft, by glueing about a half skewer into a bottle cap (a round piece of foam core or card board works too)


At this point you have to decide what you want your output and whatever you build on it to do. You can either poke a hole in the center or off center in the bottle cap for the input shaft. Making the hole centered will result in a friction gear which will spin the output skewer when the crank is turned. If you put the hole off center you will get a cam and follower, the output skewer will go up and down when the crank is turned.


In this case we went for a friction gear resulting in a spinning output.


Here are the two parts assembled into the cup. Note that you have to put the output skewer in first and then add the input shaft below it.  


The final mechanical step is to add a crank and some spacers to keep the input from sliding around, a bottle cap or a foam core square can be used to make the crank. You can use tape flags or cardboard/ foam core washers to keep the crank shaft from sliding in and out too much.


The final and most important step is to use the mechanism to drive a puppet or scene, below are some examples we built:





This version used a simple friction gear to turn a horizontal rotation into a vertical rotation. 



This version uses a cam which has been placed of the edge of the follower making the bee go up and down and circle the flower slowly. If the cam were placed in the center of the follower it would just go up and down.


This version uses two offset cams to get the birds to go up and down and back and forth around the tree.

Mechanics Projects

Mechanics is the science of motion and includes things like the science of falling and gravity, of mechanisms, of pressure and of aerodynamics. Sound is also technically included in this category though we've separated it for clarity.   We have a number of mechanics projects which we will share in the next batch of posts, but we wanted to take this opportunity to highlight some of great mechanics projects created by other institutions.


Drawing Board:


This is an Exploratorium Science Snack we particularly like, which records the pendulum motion of a suspended platform to create what is called a harmonogram. We sometimes call this a pendulum drawing machine, because the drawings it makes are a record of the motion of a pendulum swinging in 2 dimensions. The drawing created illustrates conservation of energy, the conversion of gravitational potential energy to kinetic and back again, which attempts to maintain the motion of the board and friction between the pen and paper, as well as the in the ropes which slows the board down.     



 Stomp rockets:


This is another activity derived from a Exploratorium project called Bottle Blast Off. The basic idea is to make and optimize paper stomp rockets for maximum flight distance. When we do this activity we usually start by launching a finless rocket, students can choose to use their paper long or short ways to make different length tubes and then test them. Having a few extra sections of pvc pipe to roll the paper onto will produce rockets that travel farther as they will fit snugly onto the lunch tube. Optimally you want to roll the rocket as tight as you can while it can still slide off the tube easily (contrary to the original instructions). Next, we add fins letting students chose the number and position of the fins and test until the rockets fly well. Finally, you can add some weight to the nose, 2-4 pennies work well, to increase the rocket's momentum and test again. You can also test things like adding nose cones, and the difference launch angles have on flight distance or adding small wings to make a rocket glider which is hard to achieve but cool when it works.

The launcher is just  a piece of 3/4''x18'' pvc pipe duct taped to a length of vinyl tube (3') and then to a 2 liter bottle.



A well built stomp rocket, where the tube is rolled tightly can fly over 200 feet. This can makes avoiding obstacles more challenging than expected.



Wind Tubes:






Wind Tubes (which are also an Exploratorium invention) are basically vertical wind tunnel into which you can place various objects and watch how they interact with the stream of air. Think of it like miniaturized indoor sky diving for cut up paper and food containers. When we work with wind tubes we usually give the simple prompt to chose some action spin, tumble, float and then try to make your object do that action. Being this explicit is not really necessary, wind tubes are engrossing and people, kids or adults will typically be more than willing to spend a lot of time with an object until it flies how they want it to.

Wind tubes are a powerful teaching tools capable of implicitly giving people pertinent insights on aerodynamics as they modify their objects and correlate form and behavior in the air stream.
Following wind tubes with an activity like stomp rockets is a good way to apply some of the phenomena seen during wind tube experimentation.