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Saved by Amos Blanton
on November 16, 2011 at 12:45:51 pm

Pedal Power to the People!  and other alternative energy sources!


This site has been created for us to share information and designs on Pedal Power, based on experiences during the 2011 Occupy movements.

Please join and help us document the electrical and mechanical design.



Showing off the pedal power setup at Occupy Boston





FAQ (Frequently Asked Questions)


Q0. Are there any other good FAQs out there?

A0. Yes there are!  There are many other good FAQs on this topic on the net.  


The following is our own list of Frequently Asked Questions about building pedal-powered generators:


Q1. What design did you use and where can I get the schematics?

A1. Boston Occupy uses a generator design from the website http://pedalpowergenerator.com.  The plans cost $50.


Q2. How did you go about getting the materials?

A2. The materials for the Big Bertha generator in Dewey Square were mostly bought at hardware stores.  Others were scrounged from the local unversity.


Q3. What problems did you have in building them and how did you overcome them?

A3. A longer list of problems is below, including corrosion, getting a good charger for a small amount of money, communicating to people how much they've contributed.  etc. etc.  For now, the most we can do to overcome this difficulties is communicate them and share experiences about them.

Q4. What kind of motor do I use?


       The following video answers this question rather well.  Some additional considerations are written below.



For this kind of project, the best way is to find a DC motor.  Motors came in many sizes and shapes and varieties.  Almost all can be convinced to operate as generators, but the kind that will not give you a headache are DC motors.  

DC motors come in all sizes.  The smallest ones are used in little machines, toy cars, etc.  They won't be able to supply enough power for you.  The biggest motors are used in huge factories and are they size of a volkswagen.  They will be too expensive and heavy!  What is the sweet spot?  

The optimal size motor is based on the amount of power a person can pedal at.  For example, most people produce about 130-300 Watts while pedaling, so the motor should be capable of handling that much power.  Unfortunately, motors are usually not rated directly in Watts, they're rated in horsepower.  It's easy to convert:  760 Watts = 1 Horsepower.  Therefore, 130-300 Watts means about 1/4 to 1/2 of a Horsepower.  Unfortunately, motors are not even always rated in Watts or horsepower.  Often enough, you're only given voltage and current.  In that case, you can calculate Watts by multiplying current by voltage.  For example, down below I found a motor that runs at 23VDC and 50 milliAmps.  Multiplying those together we get 1.2 Watts.  That's way too low.   Now, where do you find a motor with 1/4 to 1/2 horsepower?

The web is full of sites that sell surplus DC motors.  You can also look for cool electronics surplus stores.  You see, DC motors are like screwdrivers....   They don't wear out until years and years of use, so people tend to keep them around without throwing them around.  They are valuable.  Often it happens like this:  Company A orders 5,000 motors from Company B.  Company B makes 5,000 motors, but since their factory is set up to make motors, keeps making another 500 motors.  Company B sells the original 5,000 motors to Company A for the premium cost.  Then Company B sells the extra 500 motors on surplus markets for less money.

Therefore, the surplus market is changing all of the time.  It's like watching the wind blow.  You have to watch for what you want based on specs and get what you can while it's available.  Our specifications so far are:  DC Motor, 1/4-1/2 HP.  Next, we're going to choose the voltage and RPM (Revolutions Per Minute, how fast it spins) of the motor.  Again, it is easiest when the motor you choose has similar specs to how its going to be used in the circuit.  Specifically, you need to anticipate how fast it's going to spin and declare that it should make about 18Volts at that speed.  So far, we've got DC Motor, 1/4-1/2 HP, and 18VDC.  What about RPM speed?

To anticipate the motor RPMs that you'll specify, estimate how fast the motor is going to spin.  For pedal power, we have several stages to work through.  1. The cadence, how fast a person pedals.  2. the gear ratio, what gear their bike is in.  3. the diameter of their rear bike tire, which drives the generator shaft.  4. the diameter of the wheel on the generator itself.  Wikipedia has typical numbers of these that we'll start with.  1. For example, "Recreational and utility cyclists typically cycle around 60–80 rpm."    2. Gear ratios range from 1.5 to 9.4.   3. Diameter of a bike tire is about 26 inches.   4.  Diameter of a generator wheel might be 2 inches.  Now, let's put these together.

I'm going to use the middle values of each of those ranges above.  We'll begin with 70 rpm for the typical pedaling cadence.  multiply by 5 to get a typical gear ratio, that's 350 RPM for the rear tire.  If the rear tire is 26 inches and the generator wheel is 2 inches, there will be a speed gain of 26/2=13.  350RPM *13 = 4550 RPMs.  That's the target RPM for your motor.

Now, our motor spec looks like this:  DC, 1/4-1/2 Horsepower, 18 Volts at 4550 RPMs.  We could either pay a company premium money to make exactly this motor for us, or we can go searching on the surplus market.  We may not find exactly these specs for the money that we are comfortable paying...   That's why I had to explain everything above, so that we'll know how far we can bend any of these specs.  For example, we chose 5 as the gear ratio for the person pedaling.  If we find an inexpensive motor that only makes 12 Volts at 4550 RPM, then we can choose to pedal the bike in a higher gear!  we compute with 5 as the ratio, but could pedal using 9, making the velocity 9/5 = 1.8 times faster or 1.8 times as much voltage.  In other words, a 12 Volt @ 4550 RPM can be run at 4550*1.8 = 8190 RPM to create 12*1.8 = 21.6 Volts!  That's a little bit too much, but that's okay, because we don't have to use that gear, we can use a slightly lower one.  Now, let's look at some actual motors.

I'm just going to simply google for DC surplus motors:  These are the first few websites that come up, but it changes all of the time:  

There are lots of motors there!  I'm starting with the last site on the list, eliminating any DC motors that have a "gearhead" or "gears" on them.  Also eliminating any "Stepping" motors.  Those are both for different applications.  Here are five candidates that we should look at:

12 VDC, 3000 RPM  This could be good.  Price $6.95.   It looks light it might be too small, but there's no way to tell from the picture

1400 to 4200 RPM, 130 mA brush-type motor, stall torque approx. 30 in/oz at 18 VDC.   Unfortunately, this one lists the current as 130 mA.  That is way too low for a useful bike generator.  We'lre for more like 5-10Amps.

24VDC/4325 RPM.  This one looks too small.  It's not specified (they don't tell you HorsePower) but I can tell from looking that it doesn't have enough power.

12 VDC motor; 4.5 Amps; Torque is 8 in/lbs; RPM= 3900  This one looks like one of the best so far.  it's a little under-powered though.  4.5 Amps * 12 Volts = 66 Watts.  We're looking for 100-300 Watts.

4.5 and 24 VDC with max sink current of 50 milliamps.  Current is way too low .

Anyway, now you get the idea.  

Try looking for other motors and ask the pedalpower@mit.edu list if you're unsure before buying.


Q5. From Philadelphia: "What about using alternators in the path Bike-to-Motor/generator-to-alternator-to-battery
Are there pros and cons to that method over this one?


A5. The pros are easy availability and high power (multiple bikes anyone?!).  The cons are more complicated electronics.


The question brings up the question of what kind of motor to use:  DC motor/generators or automobile alternators. 


Alternators are slightly trickier to use as generators.  The reason is alternators have no permanent magnets inside.  To make their electricity, they start with an electromagnet formed from an external energy source.  That electromagnet rotates rapidly against the field of another electromagnet.  It makes sense inside of a car, where there is usually already the battery power and the amount of material and weight should be low...  But if you have no battery charge to start with you can't use an alternator without some clever circuitry.  I think that's the main reason people prefer DC motors.  


Anyway, some people have done it, and I think this movement is all about investigating alternatives, so I'll look up some of those alternator-as-generator schematics.


Amos edit: I've heard that alternators tend to be quite inefficient as well, which is easy to believe as efficiency isn't usually a requirement in car electrical systems. Note that many have "cooling fans" which is a sign that they are designed to dissipate some power and heat through air resistance, something which you generally want to avoid for efficiency's sake. [/ end of Amos edit]


Here is a great video of a guy who built one.  He says the alternator costs $15 brand new at Auto Zone!  To get around the field problem, he uses a manual switch.  That's great, but tricky to teach people how to use!



This website teaches you how to modify an alternator to be used as a bicycle generator.  It has an excellent-looking stand for the bike, too!




I. Raw Power Generator   


Turns human pedaling into raw, unrefined energy.

     A. Bicycle            
        "typical" mountain bike or street bike.  Strong rear skewer preferred
    B. Mounting stand        
    C. Motor    


II. Power Refinery


    Turn raw, unrefined electricity into stable sources for AC or DC appliances.

    A. Chargers

        1. Storebought - e.g. NC25A -charge controller pricey and efficient but don't require attention. Big Bertha uses this at Occupy Boston.






        2. Simplest-Possible Charge Circuit - require few parts, but must be watched carefully



        3. Occupy Generator Schematic - open source, responds to needs of the Occupy communities



    B. Battery

        1. How to Select: Sizes, Prices and Useful life
        2. How to Use

III. Using Power 


Once you have refined power, it can drive the following:


    A. AC inverter -> AC Appliances

    B. DC peripherals at 12 Volts  

        1. Lamps
        2. Radios
        3. Amplifiers

    C. Common DC peripherals below 12 Volts

        1. Cell phone chargers
        2. Appliances < 1 Amp, Internet routers, "Wall wart" devices, a.k.a. "Black Box", "Power Brick," "Power Block"


Real-Life Problems Encountered


1. 12VDC cigarette light plugs popping out from vibration
-marine grade

2. Scumbag lights give false state of charge

3. People charging too fast

4. Skewers get bent b/c load is not on

5. Inefficiencies in coupling

   a. human error

   b. friction creating heat loss, wears tire out faster

6. wear and tree on front wheel

7. batteries draining too low

8. temperature problems
9. People "fixing" the wiring that don't understand how it works.

10. People replacing components that aren't broken, and or walking off with parts.

11. Corrosion

     After only about 1 month of service in the Pedal Power tent, we've already experienced a failure due to corrosion on Bertha. Below is a picture of what was our rectifier board. It was on the crate with the charge controller, thoroughly wrapped in electrical tape. There was no mechanical stress of any kind (that I know of) - just environmental.


The dark patches show where the copper has basically flaked off of the board as a result of corrosion. 

Bertha's tent has a couple inches of standing water on the downhill side. Thankfully, Dana put Bertha up on a palette so she's not actually in the water. But the air must be fairly moist more or less all the time. And, being outside in the elements, there must be plenty of opportunity for condensation as the temperature changes each day.

We recently re-wired everything to make it easier to swap different batteries in and out for charging, and I noticed that many of the bare wires in the charge controller seemed unusually corroded as well. It might be best to "tin" wires with solder the next time we do a rebuild, as I suspect that might keep the electrons flowing smoothly for a little longer.



Good Ideas

1. Lock bikes to generator
2. "Bike docking station"
3. Fitness center
4. Bike tires as V-belts
5. Mudshield
6. Treadmill form

7. Pennyfarthing as generator!!!




A Proposal for Standardizing Electrical Power






This diagram breaks things down into two categories: supplies and loads,.


Supplies - things you can plug stuff into to get power.  Examples include generators (pedal, wind, solar), and battery packs.


Loads - things that consume power.




Voltage 12 Volts


It would be useful to declare some standards - 12 volt being the first one. One could imagine a scenario where all the occupies agree on a standard and an interface for things that create power and things that use it. If OWS needs more power for an event, Boston can send them a few of their generators for a couple days, and / or vice versa. You get all kinds of emergence and unexpected benefits when you standardize the interface as a constraint and then let people innovate what's behind it.




Power Connector: Auto appliance adapter, a.k.a. cigarette lighter.


It has ends that look like this:



If we're using 12 volts, then we might as well use the cigarette lighter plug as the interface because there are lots of things that work with them out of the box. Aside from the many cell phone chargers, usb octopai, etc, you can get for your car, there are also a lot of cool electrical things made for RVs and boats, like coffee pots, slow cookers, refrigerators, and what have you. And marine grade 12 V cigarette sockets / plugs will actually lock in place.

This approach suggests we should focus our efforts in two places.

1. Make universal power regulators that can be used with (almost) any pedal generator

It doesn't take a deep understanding of electrical engineering to make a pedal generator: you just have to figure out how to turn a motor backwards. The difficult part is what to do with the unregulated, dirty, DC electricity that comes out of the generator wires in order to make it consistent, safe, and usable, so it can interoperate with all the things we might want to connect it to. Once a cheap power regulator is designed and made available, lots of people can then make pedal generators. They can order the assembled power regulator from sparkfun, or DIY it from plans made available, and then they're golden: hook up the two wires from the generator to the in, and then hook up the two wires for the out to a cigarette lighter socket. It doesn't matter that their generator looks or works differently than all the rest, as long as the output conforms to the standards.

A thumbnail first draft of a spec for the power regulator:
Contains a bridge rectifier so you can't pedal backwards and generate negative voltage
Takes in power ranging from - 30V to +30V and consistently outputs clean 14.5 volts ( which most 12 volt things can accept, and the extra couple volts are useful if you are charging a battery pack)
Consider using a largish capacitor so one can slow down pedaling or even switch riders for a second and still put out consistent power.

2.  Build Power packs with charge controllers

12 volts won't travel far on a wire without losing its oomph, and we can't put generators everywhere. So that means we need portable power packs to distribute power to where its needed on site. Batteries need charge controllers with simple interfaces to be usable by the masses. They should prevent over charge or undercharge, and they should tell the user when they are being charged or discharged, and approx. how much juice they have left. And it should make difficult to lick the terminals or short the leads, or otherwise do something dangerous.

User Stories

Here are some user stories of how I could imagine this working as we scale up:

The cook notices the light is getting dim, so the next morning someone takes the power pack to the pedal tent, where they charge it for an hour or so. They bring it back, plug it in, and the lights are good for another few days.
One of the people in the media tent needs to work on their laptop all night, so they go the pedal tent and "sign out" a power pack and and AC 120 volt inverter (and possibly leave some kind of collateral). The next morning they return both to the pedal tent coordinator, who places the power pack in the "dead" queue. Legions of healthy young pedalers stop by throughout the day and charge it and the rest of packs back up, under the watchful eye of the coordinator / pedal power team.




Trucker Blanket:

Cost: $27.88

Size:  58" x 27"

Electrical:  Current: 4.2 Amps  Volts (DC): 12    Watts: 50.4 





Simple Metal Stands to Hold Bicycles While Pedaling


A No-Welding Design for a Bicycle Generator Stand


This third attempt at a generator frame uses a mixture of materials.  It confirms the status of "superstrut" as stronger than previous materials.  Note that superstrut is only necessary in the A-bars of stand.  The remaining material may be made from less expensive material.  Note that this stand uses no welding!  It consists of about 10 sets of 1/4" bolt, washer, washer, nut sets.  The stand makes use of the pre-drilled holes in the material. This design was assembled by the MIT pedal power list at one of our first meetings in person.












An Earlier Simple Metal Generator Frame


This simple frame was designed and designed and built by Noah Vawter at MIT as part of the MADMEC competition around 2005.

It lifts the rear tire up to where it can rub against the generator motor.  With simple steel materials available

at some hardware stores it's easy to weld together. 


To make a make frame for an adult bike like this, plan to lift the rear axle off the ground 2 inches.  For 26-inch wheel, the highest part of the rear-wheel frame should 15 inches off the ground.  For a perfect 45 degree angle, the length of the base should be twice the height.  The four arms are all sqrt(2)*15 long, e.g. 21 +3/16 inches.  The two halves of the A frame should be at least 8 inches apart. 





It is crucial that the rotor the of Generator makes good contact with the wheel.  For this reason, it's good to be adjustable.



In this photo, you can see the simple adjustment mechanism to raise and lower the motor.

Note that heavy carriage bolts have wrench sockets welded to the ends to cup the rear skewer.




This was an experiment.  You can bolt this material together and chop it up with a hacksaw or angle grinder.

cost of angle grinder ~$100.  It's kind of wobbly though.  It's maybe useful for lightweight parts of the design.






Pedal-Power Hardware


These components are recommended based on specifications and cost. 



These diodes have been recommended for general use in pedal-power charger circuits.  They can all handle up to 10Amps and cost less than one dollar.  They have the lowest possible forward voltages for the price you pay.









Other sites we have been finding useful









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