The Most Useless Machine EVER!

And yet everyone wants one!!!?

AKA: The Ultimate Machine!

Get Your Useless Machine: Purchase Useless Machine Kits Here!

Update Oct 31, 2012:

“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.The Most Useless Machine EVER!

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

Useless Machine Kits are available from our on-line store. They have everything you need to build the Useless Machine including a laser-cut acrylic case.

Sourcing all the parts in one place can be difficult. If you don’t mind modding a servo then everything you need is at Newark/Element 14 and the parts are listed below.

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.)
RC Servo you can mod


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

First you will need a gear motor.

If you wish to modify a standard RC servo for your geared motor then follow this ‘ible:

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 diagram above indicates how you will wire the motor, microswitch 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.The Most Useless Machine EVER! schematic

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.


For more detail: The Most Useless Machine EVER!

About The Author

Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

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