Introduction: The Most Useless Machine EVER!

About: Frivolous Engineering is the end result of a hobby that got out of hand.

And Yet Everybody wants one?!!???

AKA: The Ultimate Machine! AKA: Leave-Me-Alone-Box

We manufacture the Best Useless Machine Kit out there:

"Weird Al" Yankovic Sez:"I never realized till now how much I needed one of these."

AS SEEN ON TV! Make Magazine's amiable editor-in-chief, Mark Frauenfelder demonstrated The Useless Machine on the Colbert Report!

Useless Machine Featured in Vol 23 of Make Magazine!

Thanks everyone for all the cool comments, suggestions and all the videos! Keep 'em coming.

Step 1: Background

Also known as The Ultimate Machine: Claude E. Shannon built the first one based on an idea by Marvin Minsky.

After seeing a video of such a machine I just had to have one of my own.

The only design I could find uses a PIC microcontroller but I consider this to be overkill (not knowing how to write code for micros may have had some influence on my humble opinion...).

Additionally, the microcontroller version really doesn't shut itself off. It's circuit remains powered even when the switch is in the off position.

Knowing a little bit about servos and basic electronics, I felt sure that I could build the machine using a simple analog circuit.

My main goal however was to have the machine REALLY turn itself off.

The machine in THIS instructable accomplishes that!

Step 2: How Does It Work?

Inside the box is an geared motor powered by double A batteries and two switches: a toggle switch on the top of the box and a micro-switch inside. That's it.

The switches are positioned to be limit switches for the motorized arm. The toggle causes the motor to reverse, while a micro-switch powers down the circuit when the arm finishes retracting back into the box.

When idle, the circuitry is fully powered down. The toggle is “Reverse” direction, and the micro-switch is being held in the off position by the servo arm.

Keep in mind the micro-switch is wired up so that it works completely opposite from a normal switch like you would find in a doorbell. By using the common pin and the normally closed pin the micro switch is “OFF” when it’s button is being pushed.

When a person turns the toggle switch to the forward position, it also provides power to the motor causing it to rotate the arm towards the toggle switch.

As the arm moves away from it's off position it releases the micro-switch providing the backup power needed for the motor to retract after the toggle switch is turned off.

When the toggle gets switched “OFF” it actually reverses the motor’s direction. The arm reverses direction returning towards it's 'OFF' position. When the arm runs into the micro-switch it stops.

The toggle switch needed is a Dual Pole, Dual Throw (DPDT) toggle switch. This type of switch is actually a pair of switches which operate together (Dual Pole) and both are On-On (Dual Throw).

Step 3: More Details

When I originally published this instructable I used a standard RC servo and a simple control circuit using a 555 timer in the photo above.

Compukidmike was quick to point out that by modifying a continuous rotation servo (basically just using the the servo as a geared motor) and using the same switches it wouldn’t require ANY control circuitry.

Much simpler and just about any geared motor or a modified standard servo can be used. Start looking through your junk pile because Useless Machines have even been made from CD/DVD drives.

So you have a choice. Step 5 is the easy method.

If you prefer to use a standard unmodified servo then follow steps 6-9

Step 4: Parts

Frivolous Engineering buys parts from Newark/Element 14 & you should too!

Here's the parts you need to build the Useless Machine:

Battery Holder 2-AA Cells (Note: 3 AA's or even 4 AA's will work, faster, maybe too fast )
DPDT Toggle Switch
SPDT Micro-Switch (Just about any with 3 pins and a lever should work.)

Gear Motor

Or you can modify a standard RC servo for your geared motor:

If you use a Parallax continuous rotation servo there is no need to modify the gears, but you will have to modify the wiring to the servo's motor.


The servo I modded is a JR Sport ST47. It's a standard size servo with a torque of 55.0 oz-in.

Stay away from any of the micro-sized servo’s. A standard size servo with at least 4-5Kg/Cm torque will work in most cases. Keep in mind that the toggle switch and arm length are some of the things that will determine how strong a servo you’ll need. Most of the standard servos should do the job.

mrrigsby reports that a toggle switch from Radio Shack, catalog # 275-636 works.

He also pointed out that it's better to use "4 fresh alkaline batteries--with 4 rechargeables, I couldn't depend on having enough power to always throw the switch."

Step 5: Wiring Diagram

The diagram above indicates how you will wire the motor, micro-switch and battery pack to the pins on the toggle switch. This is called 'Dead-Bugging' and is a prototyping method from way back.

It's a very simple circuit but it's easy to mess up the wiring. Follow the directions carefully or purchase the Useless Printed Circuit Board from us to speed up and greatly simplify the wiring process. And a cool LEDs to the circuit too.

Wire the gear motor to the indicated pins.

A short length of wire connects opposite pins on the toggle.

Another wire connects the other outside pins on the toggle and this wire has the microswitch in-line.

The battery pack goes to the other remaining pin on the toggle.

If you find that the motor is running in the opposite direction from what is needed, simply reverse the wires going to the motor.

tydarby posted the great graphic below, showing how wire up a modified servo . The pins to use on the micro-switch are the common (C) and normally closed (NC). Nothing should be connected to the normally open (NO) pin.


Batteries: The original parts list used a 4 AA holder but you may find that 4 batteries driving the machine makes for way too fast operation. Blink, and you'll miss it.

In most cases you should be able to get away with just 2 or 3 AA batteries, making the overall action more slower, and more visible.

Keep in mind that the our kit only uses 2 AA batteries.

More on Motors:
I originally chose to use servo's because they are available almost everywhere, and are standardized, but you don't have to use one. Just about any motor should work, as long as it's geared down, and has enough torque to flip the switch.

The more salvaged parts you use, the better.

Keep in mind that another reason for using a geared motor is to prevent bounce-back from happening when the machine shuts off. Without the gearing, motor wouldn't keep the arm pressing down on the micro-switch while it's off. The machine's arm would just keep hitting the switch, turn off then on, then off, then on....

The next couple of steps show the original way I made my machine. If you're building one using the information above, then SKIP the next 4 steps and jump to step 10.

Step 6: Original Design Using 555 Timer

For ease of construction, I highly recommend going with a modified servo or a gearbox motor instead of using the 555 timer circuit show below. There is almost nothing to be gained, or any improvement of operation of the machine using this circuit and a standard servo.

Some drawbacks in using the timer circuit are: you have to use a 4 cell battery pack. It won't run on any less voltage. This will ensure that the servo will run very quickly, sometimes too fast in my opinion. Using a modified servo, you can use 3 or possibly even only 2 cells, making the machine run at a slower, more spookier speed.

Another drawback of using the 555 timer version is placement of the mechanical parts are limited due to a standard servo only having 180 degrees of rotation. Using a modded servo or gearbox/motor will allow easier design and placement of the parts.

The only advantage with using a standard servo and the circuit is that just about any servo can be used, and if it should break or wear out, replacement is simple.

But when pondering the concept of the Useless Machine, perhaps going with the most complicated version is the aesthetically superior choice.

Note: if you need more rotation from the servo, change R3 to 10K.

sirus20x6 edited the 2nd schematic putting the pins in order.
colin55 provided the 3rd version.

All of the schematics are basically the same circuit, just arranged differently.

Step 7: Original Parts List

If you wish to build the more complicated, yet cooler dead bug circuit this is the parts list:

Revised Parts List Feb 27, 2010 , including the digikey part numbers.

Servo 900-00005-ND

Battery Holder 4-AA Cells BH24AAW-ND

NE555P Chip 296-1411-5-ND

C1 0.1 uF Capacitor 478-1831-ND

R1 220K resistor CF1/4220KJRCT-ND

R2 27K resistor CF1/427KJRCT-ND

R3 15K resistor CF1/415KJRCT-ND

D1 1N4148 Diode 1N4148FS-ND

DPDT Toggle Switch 450-1533-ND

SPDT Micro-Switch EG4544-ND

Cost: around $25.00

Step 8: Breadboarding:

If you're going to use a standard servo and 555 timer, it's best to test things out first on a breadboard. The photos show exactly how it's wired up.

Also, if soldering isn't your thing, then this can be your finished, working circuit. Just keep in mind that it's very easy for wires to be accidentally pulled out.

Step 9: Dead Bug Circuit Construction:

The circuit has very few parts so instead of making a circuit board or using a prototyping board I just soldered most of the components directly to the appropriate pins on the 555 chip.

This method of prototyping is called Dead Bug construction.  As the name implies, the finished results aren't very pretty and often resemble a dead bug.

You’ll need a fine tipped soldering iron, steady hands and basic soldering skills.

Keep in mind that you don’t have to dead bug the circuit.  Prototyping or perf board can be used for the final circuit, or just keep it on the half-size breadboard that you tested it on.

Step 10: The Box

I don't have much skill in wood working so I was fortunate to find a ready made box at the Dollar store. 

Also, you can get really fancy wooded cigar humidors that make for a great box.

The box you use need only be big enough to fit a battery pack and servo.  The one I used was about 5x4x3 inches.

I removed the latch that came with it.  The lid was carefully cut down the middle and the hinges were move from the back to the side.  A hole for the toggle switch was drilled in the other part of the lid about an inch from the cut side.

Step 11: Putting It All Together

I’m finding this part very difficult to explain, so if you’re having trouble understanding things, let me know…

The micro-switch will only shut off power when the toggle switch is in the OFF position.

Before you start installing the parts in the box, you'll want to make note of the direction the motor turns and in which position of the toggle switch is off.

Mount the toggle-switch and now you can align where you are going to mount the motor and design the shape of your arm.  Design the arm so that when it's in the off position, it will hold the micro-switch OFF.   You may need to build a stand-off for the micro-switch.

Before you put in the batteries, manually move the arm to check that it will rotate between hitting the toggle, and hitting the micro-switch.

If you are using a standard servo and 555 circuit the idea is the same.  The only thing to keep in mind is that the servo arm can only rotate at most 180 degrees.

Once you have the parts installed and aligned there is some fiddling.

Power up the circuit but leave the arm off of the servo.  Flip the toggle to the ‘on’ position and the servo “axle” rotates to the on position and will then stop.

Now take the batteries out of the circuit and flip the toggle to the "OFF" position.  Now put the plastic actuator (with the wooden arm) back on the axle so the ‘hand’ is touching the toggle switch.

Put the batteries back. The servo will return to it’s “off” position.

Now you can see if the arm is fully retracted back into the box.  I had problems with the arm sticking up to high, not allowing the lid to fully close.  Or having the arm hitting the bottom of the box.

At this point I had to tweak the shape/dimensions of the arm.

Once I had the arm switching the toggle, and retracting back into the box I mounted the micro-switch so that when the servo is in the "OFF" position it is holding the microswitch down.

At this point you should have a working Useless Machine.