Introduction: Lego Generator

Picture of Lego Generator

I was screwing around with some of the motors from my old Lego Mindstorms kit, and discovered that when two motors were directly connected to one another the spinning of one would cause the other to spin too. It was obvious once I realized what was going on, but still strange to see the other motor spinning without being connected to anything but the other motor.

Step 1: Parts

Picture of Parts

The only things really needed to do this experiment are the motor and the power wire connector. To demonstrate on a second motor you need a second motor, to measure the voltage you need a multimeter, to demonstrate on an LED you need an LED, etc. A rubber wheel is also a good idea because it will be easier to grip then the axle coming from the motor.

Step 2: Procedure

Picture of Procedure

Connect the power wire to the motor, put the wheel on the motor.

If you are demonstrating on another motor:
-connect the power wire to another motor with a wheel on it.
-spin one of the wheels and notice how the other wheel will spin
-to get the wheel to spin in the other direction reverse the polarity of the wire connections by unplugging the square connector and plugging it back in facing the other direction

If you are demonstrating on a potentiometer:
-connect the square power piece on the end of the wire to the 2 leads from the potentiometer
-set it to 20v dc and spin the wheel as hard as you can, from just running it on the desk the highest I generated was 19v
-optional: connect the motor to a dremel or a power drill and see how much voltage you can get it to generate

If you are demonstrating with a LED:
-connect the square power piece to the LED (I used the same LEDs that were used for the throwies)
-spin the wheel, the LED should light up, if not check polarity

Step 3: Potential

Picture of Potential

This experiment has huge potential for many different projects. It can be attached to almost anything with motion, in order to generate electricity.

The perfect project for this would be a bike light. Unfortunately, since I am away from most of my parts and tools, I do not really have the opportunity to test it it out. Hopefully someone reading this will further experiment with it seeing what interesting things they can make.

Multiple motors can be used, to create either more amperage or more voltage, depending on how they are connected.


mpnb402 (author)2010-09-03

you should put one of those motors at each wheel it will make it 4 wheel drive. and what motors are using

BobQDobbs (author)2007-12-18

I'm 38 yrs old and have never had a car drivers' license. Excuse me if I'm off here - and please correct me. It has always puzzled me why there are no magnet generators installed on every wheel that spins on every vehicle that travels - cars - bikes - trikes - shopping carts?. Now I know I'm getting a bit hyperbolic but - really - why is this energy wasted. Another thing I will just throw out there is if we could use capillary action (or some other currently overlooked action) to raise water above sea level we could harness the power of it's descent through big pipes (think flushing the toilet) to drive turbines. Nice post sir.

knektek (author)BobQDobbs2010-02-17

they dont use them in shopping trolleys because people can jack/steal them.

godofal (author)BobQDobbs2010-01-03

ever ride  a bike with the dynamo (for the lights) on?
ul notice that ul have to kick harder, so, more energy used, for less energy output.
on a car, this already is being used for things as the battery (for starting the engine, lights, dashboard, etc) but the energy that is needed (gas/diesel) to generate other kinds of energy (elektricity) is equal, but mostly a bit less since theres a small resistance from the wiring.
so, it would actually wasting energy...
i already thought of  that, and its a nice experiment :)

btw, if ul make this experiment (with that lego thingies) large enough, ul notice that the second engine is *slightly* spinning slower...

junits15 (author)BobQDobbs2009-08-26

its like one of those free energy machines, they don't work =)

hoihoi151 (author)BobQDobbs2009-08-09

because driving the magnets would effectively slow down what ever u are moving and more energy would be needed to move it. thus being completely pointless

Techno23 (author)BobQDobbs2008-07-17

That's how all hybrid cars work now, I beliebe - when they're free-rolling the momentum charges the batteries.

sheepborg (author)Techno232009-07-28

only when brakes are applied plus it is not set up to collect on every wheel if there where 'good' enough batteries and enough of them it would be beneficial to collect power from every wheel btw: alternator is only from the engine spinning (as for you hoihoi151 I am 14 years old)

ramses (author)Techno232008-07-29

they use the turning of the wheels to generate electricity only when the brake pedal is applied. that is why they don't do much better than normal cars on the freeway; you dont break much

catprog (author)BobQDobbs2009-06-02

there is a big generator attached to the wheels through the axils and gears called an Alternator

Noodle93 (author)BobQDobbs2008-01-15

Because to create this electricity it is adding extra 'load' to spin. Thus, slowing down the effectiveness of the fuel per kilometre.

killrsheep (author)Noodle932009-01-18

I second that simple yet completely correct explanation, bcuz of that you gould need a sort of engaging, disengaging system to activate/deactivate when accelerating/braking plus 4 that size it would probably have to b a non magnetic generator, not to go into much detail its uses electromagnetism adn well it get more complicated from there on thus it is used in modern Eco-friendly cars with "regenerative braking systems" but still present technology offers a very poor cost/benefit factor in these kind of stuff

Noodle93 (author)killrsheep2009-01-19

Yes. Now I have the correct terms! "This" energy is not being wasted. We are combusting chemicals into kinetic energy (movement). The kinetic energy is making us move forward (or reverse for that matter). For every reaction we make there is an equal reaction, but it's efficiency is never 100%. If it was 100% we would have perpetual motion, which defies the laws of physics. Now if we did your suggestion, the process would this be: Chemical Energy (fuel burning) to Kinetic Energy (the pistons moving, the wheels turning) to Magnetic Energy (an magnet moving in and out of a coil etc.) to Electrical Energy (electrical charge) The more reactions, the more energy wasted in undesired forms. Whereas kinetic energy is not an undesired form.

hoihoi151 (author)BobQDobbs2009-01-11

no offense but that is the most ridiculous thing i have ever heard. ok where would they store this electricity and how would they transport it off the shoppin cart or item of choice? and its really expensive for very little electricity. also raising water above sea level isnt as easy a turning on a tap. and ur now what 39 or 40. GET A DRIVER LICENSE. what is stoppin u from driving?

Jaycub (author)BobQDobbs2008-08-12

How would you get the wick to release the water when using the capillary effect?

Stanislaw (author)BobQDobbs2008-07-29

that is essentially how the alternator works

qolque (author)2009-12-14

Glad you boys are experimenting, learning on your own.  There's not much that's revolutionary here, it's essentially the same process as water spinning a turbine/generator in a hydroelectric dam, and sending the power over miles of wire to a home where a circular saw runs.  One motor spinning the other.  The key is you figured it out by yourself!  Experimenting is what moves America forward!  I played with LEGOs myself as a boy, even though they've come a long ways since those years.

So don't let the naysayers and their insults get to ya.  Even if they are right about limited application of this particular trick (DC power loss over wires of any length, no perpetual motion due to friction/heat loss), it doesn't mean there aren't discoveries to be made.  Critics don't invent and they don't get patents either!  They just get frownier and more bitter and sarcastic. 

So keep it up with the experimenting!  Thousands of engineers the world over are doing similar work

cantrell8 (author)2009-08-07

I wonder if this would work with any motor?

sheepborg (author)2009-07-28

at the fastest I can spin the mindstorm motor it puts out the equivalent of between 2 and 3 AA batteries

sheepborg (author)sheepborg2009-07-28

Edit : at normal (slowish) speeds it puts out 1-2 AA batteries worth

joey2542667 (author)2007-05-12

what you can do is you can make a much bigger one and use it on a electric car! I should get a padent!

JakeManes (author)joey25426672007-11-01

the energy created would equal the energy exerted. So its like using a gas generator to power a light to power a solar panel. And its patent. And electric cars have been patented.
But if you dont believe me, do some searching here:

joey2542667 (author)JakeManes2007-11-02

oh, ok i guess that wouldn't work... Oh well. Hey, should i post some of my office weapons?

wheatstone (author)joey25426672009-06-07

you too! lol

JakeManes (author)joey25426672007-11-05

depends if they are already posted.

joey2542667 (author)JakeManes2007-11-10

no none of em' are posted. I have two that I can think of but one the ammo is juniper berries

wheatstone (author)JakeManes2008-09-18

there you go again perpetual will never be equal. one cannot destroy energy but rather transform it! Your loss is through heat!!!

joey2542667 (author)wheatstone2008-09-18

lol, are you talking to me or Jake?

wheatstone (author)joey25426672009-06-07

Put a hat on!

L-A (author)2009-05-26

That's an old trick that (if I recall correctly) originated from a japanese lego bot builder, who made walkers you controlled by turning a motor alternatively left and right. It's good for making a steerable car, too.

lucianoabcd (author)2007-10-11

I tried this with a 3V-motor and I can't get any reading in the multimeter when set to voltage, and only a few microamperes in current mode. The shaft was moving very fast in my trials (I attached it to a wheel on my bike and rode it) and I know that the motor works ok (I mean as a motor), so which do you think the problem is? Can it be the fact that the motor is not a steeper motor? Thanks!

rotf101 (author)lucianoabcd2008-12-26

i got the same problem with a small 3v generator found in hand-held fans. i attached it to my bike and even at top speed, it put out only about 1v. then i found out that 3v of power from batteries turns the axle far faster than my bike, thus the lower output. the efficiency of the generator can also affect the output. i decided to find myself a 10v generator often found in higher-end r/c cars. it doesn't put out 10v, but it puts out enough to power a bike light.

sooraj619 (author)rotf1012009-03-16

can u say which motor i should buy to generate a 3v

killrsheep (author)lucianoabcd2009-01-18

nah its ok if its not a stepper motor as long as it uses magnets to generate the magnetic field inside, it could also be what the guy below me said maybe you are not puting enough rpm's through the axle

Sandisk1duo (author)2008-05-23

wow! those are really efficient motors!

rotf101 (author)Sandisk1duo2008-12-26

that's the first thing i noticed!

Sandisk1duo (author)rotf1012008-12-27

too bad that they are around $20 a piece

rotf101 (author)Sandisk1duo2008-12-27

oh wow...i think it's better to invest in higher quality RC motors. those 10v things are really nice

Sandisk1duo (author)rotf1012008-12-27

psh... forget your RC motor, go invest in the stock market, it's been going up and down for the past few months

rotf101 (author)Sandisk1duo2008-12-28

haha. i have a couple stocks: apple, google, baidu. none of them are looking too pretty since i bought them

rubikmaster911 (author)2008-10-13

Hold on if i conncet a motor leads to a led and rotate it, the led will work?

that's the point

Thelonelysandwitch (author)2008-10-25

I did the same thing and hooked one to the wheel of an old bike and theother to the chain. I rolled down a hill and went where I wanted to go for like 10 blocks.

not-killerk (author)2008-10-19

me and my friend took apart a microwave, and the turntable motor is a high speed motor (well this one n e way) just gear down big time, so i was holding onto it, and my friend spun the spindle and i got this MASSIVE shock. it hurt, and then we attached it 2 a drill and hooked it up to a multimeter and it generated 200 volts!! it was crazy, but then we got carried away and ripped the teeth off the gears lol.

minime110 (author)2008-07-29

I build micro scale lego cities, and this is perfect for supplying and routing electricity to LEDs in the city models, thanks for the Instructable.

hi111 (author)2008-07-09


southqaw (author)2007-11-12

Cool, I've actually tried this before. Only I used a crank that used gears, I geared it so that the crank handle was attached to a large gear and a small gear was attached to the motor shaft. So that each turn of the handle equaled several turns of the motor shaft.

javapda (author)2007-11-08

Where can you get the motors? Is there a spec number?

Yerboogieman (author)2007-11-01

when i took apart my RC helicopter i had 2 motors and tryed one out and it worked the same

dogsrcool2me (author)2006-10-22

motor+cap+5v regulator=charged ipod

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