Title: It's All Quite Moving!

We didn’t always have motors. Before about 1870, we only had engines. There is a basic difference between engines and motors; engines convert heat into mechanical work while motors convert electricity into mechanical work.  During the Industrial Revolution everything ran on some form of James Watt's magnificent invention, the steam engine (1780), because mankind had not yet figured out how to generate electricity, but still needed some way to turn the shafts of their factory looms and newspaper presses.  Indeed, the Steampunk aesthetic itself that we espouse at Wackenhammer's harks back to those days and envisions a Jules Verne-inspired present and future where neither electricity nor the internal combustion engine were ever invented and so the world and all its myriad devices still run on that quaint form of power conversion, steam.  Steampunk has also retained Victorian fashion into the bargain, but that is another story.

Steam machinery has gradually been replaced by more efficient, cleaner, more reliable and less complicated technologies.  Diesel engines have run our trains since about 1930.  Cars have been made with gasoline engines since about 1920. Starting around 1870, electric motors have come to run everything else.  Engines require a constant supply of fuel (coal, petroleum), which is burned, producing nasty exhaust. Steam engines also require a vast quantity of water.  Motors simply take in electricity and produce work quite cleanly in a compact, simple  and reliable package that is extremely easy to control. There is no fuel or water to store or pipe about and no exhaust released.  Of course we use them where we can!  The great irony is that nearly all our modern electricity is produced by generators turned by giant engines which are generally based all or in part on...you guessed it...steam.

Unfortunately, our Treadwall game will not use any steam-driven components.  It will use motors.   But what kind of motors will we use?  Motors these days come in many different flavors, shapes and sizes. A typical motor has a set of magnets positioned around a spinning shaft that is itself surrounded by coils (windings) of copper wire wound around an iron core.  When electricity flows through the wire the iron is turned into an electro-magnet.  This attracts or repels the surrounding magnets.  By energizing the coils in the right order around the shaft it can be made to turn.   A basic motor choice is AC or DC power which determines how the electricity is commutated into the windings. AC motors count on the fact that the voltage changes direction.  DC motors use a pair of brushes to put the current into a particular set of windings that changes as the shaft spins.  See  this excellent reference for more info.

The strength of a motor is basically proportional to its size, tiny motors vibrate your cell phone, while gigantic motors drive a streetcar along its track.  A motor's size and design will determine its speed-torque characteristics.  That is how fast it turns in Revolutions per minute (RPM) and the force it can exert.  Torque is expressed in units like inch-pounds.  A 10 inch-pound torque motor can push 10 pounds around at the end of a 1 inch lever or 1 pound at the end of a 10 inch lever.   Speed and torque can be traded by the use of gears.  Gears will reduce the speed of a motor but increase its torque by the same amount.   So you can have a very fast motor that is weak or by adding a gear box you can have a slow motor that is very strong.  A gearmotor is a motor with a gearbox attached for just this effect. Small motors tend to spin so fast (1000’s of RPM) that they are not very useful without a gearbox.  

The picture shows a number of motors.  The largest one at the bottom left is a windshield wiper motor.  I happen to like this motor very much.  Since it is a car part, it is readily available on the surplus market for about $20.  It is a 12V gearmotor that has torque in the 15 foot-pound range at 30 RPM.  This makes it an ideal motor for my animatronic projects.  The tiny motors bottom right are DC toy motors and could be used to drive the wheels of a battery operated car.  Since the motor is ungeared, it runs very fast with low torque.  Your toy car will go fast but will be easily stopped by your thumb on the wheel.  The motor left center with the long shaft is a 12V DC gearmotor, with a 2 RPM, 5 ft-pound output for about $15, the cylinder is a small DC motor, the square box is the gearbox.  The flat motor center right is a so-called timing motor as they are used in washing machine timer applications.  They are geared 120V AC motors that go 2-30 RPM but are very low torque even though it is a gearmotor.  All of these motors share the characteristic that they are free-running, you plug them into the appropriate voltage and they spin.  With a DC motor you can even choose the direction of spin.  

For the Treadwall game I am going to use two kinds of motors that have the advantage that the computer can precisely control their rotation.  The stepper motor shown upper right with the colorful wires has its coils separated, so that the computer can choose how to energize them.  By doing so in the right order, this motor can be placed precisely at 200 positions over 1 rotation.  This allows the speed and direction of its spin and the number of times it turns to be very precisely controlled.  A stepper motor can be identified by its having 4, 6 or 8 input wires instead of 2.  Stepper motors are complicated to drive and usually require a driver circuit.  The nice people at Polulo sell this motor for $15 and the controller for another $5.   Two of these motors will be used in the game to turn a 5 ft long screw shaft each.  A nut on the shaft will move up and down as the shaft is turned.  In this way the computer will be able to control how far the nut moves up and down the shaft very precisely.  A little man glued to the nut will indicate the climbing height that the game player has achieved.

The other motor I will use is called a servo motor.  The rectangular box on the top left is one of these.  They are always in this standard form factor.  They always have 3 wires: power, ground and control. Control is done by a series of pulses in a format called PPM that the computer can output.  This motor does not spin.  The servo has internal gearing and circuitry such that the shaft will only move over at most half a circle (180 degrees) range determined by the pulse width present in the control signal.  This type of motor is often used to steer Radio-Controlled (RC) cars, boats and planes. It is a remarkable package and can be purchases at hobby suppliers like ServoCity for $5-$100's depending on the speed-torque rating. I plan to use a small servo to display a simplified clock to show the game participant how much time he has left to climb.

Hmm....Maybe steam would be simpler...

-Otto