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David Butcher: PPPM Alternative: Pedal Generator Using Your Bicycle

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Many visitors to my pages ask if there is a way they can use their own bicycle to generate power instead of building the Pedal Powered Prime Mover. It is definitely possible, and in fact, there are examples all over the Internet of pedal generators constructed from bicycles, stands, and various collections of parts. (There are no examples I know of with daily riding/power generation logs - that should tell you something...) They all provide the benefit of using a bicycle, which is already assembled, in combination with a training stand, which can be purchased in most bicycle shops or online.

One small drawback with this design, especially when powering larger loads, is that the "flywheel" effect of the bicycle and generator is not large enough to smooth out the power, as it is in the PPPM. An Ultracapacitor or battery is required to help keep voltage constant, unlike the PPPM, which can be pedaled directly into larger loads with minimal voltage fluctuations (although an Ultracapacitor makes this task much more enjoyable). Watch the light pulsate in this video to see what I mean:

http://www.youtube.com/watch?v=mgRFPpZGx8Y

You don't want that. You want a large flywheel like the PPPM.

A more significant drawback is the space required for this style of pedal generator. Most of these "training stand" designs attach in some way to the rear wheel of the bicycle, and many of them extend a bit (up to a foot) past the rear of the bicycle. You may wish to try this for yourself - pull your bicycle into the house and see how long it is. Now add another foot for the generator! It's going to require almost as much space as a small sofa! The PPPM design fits in a space two feet wide and three feet long. It's an important point to consider if your pedal generator will be in your living space. In fact, before you go any further, go get your bicycle and put it where you expect to generate power. Add an extra foot past the back tire for space for the generator. How is that working for you?

Perhaps the largest drawback is you are wearing out at least one tire and ALL of your bicycle drive train! (Not to mention your rollers...) Why not build the PPPM and wear it out instead of your expensive bicycle? The PPPM has no hubs, chain, derailleur, or tires to wear out. The crankset is "bulletproof" because it was designed for bicycle moto-cross. The one part that does wear can be replaced for less than two dollars. Don't stress your carbon fiber or titanium bike for an indoor workout. Use your bike for bicycle rides!

Nonetheless, there are times when a bike in a training stand approach makes the most sense. To power the lanterns in the tree at the Big Chill in England in 2007, for example, I "invented" a training stand design on the plane flight over, and built the 15 pedal generators needed at the festival site over the next several days (with help!). The designs worked well enough, but the installation was outdoors where I had all the space I needed, and my goal was simplicity and durability, not efficiency. If that's your goal as well, read on...

I believe the "Big Chill" design presented here is one of the easiest to build. It does not require any special parts, machining, or welding. It is assembled with simple hand tools, and it is rugged enough to withstand public use.

  1. The training stands used for the 15 pedal generators were similar to the Minoura Mag 850D-LW Dial Trainer.
  2. The generators were Razor Scooter 250 Watt motors - with the cog belt pulley - NOT the chain sprocket.
  3. Everything else was basic - wiring, screws, hinges, and lumber.
  4. Most designs I see on the Web for "training stand generator" devices are made out of metal. I used wood rather than metal whenever possible, because:
    • It's easier to work with than metal
    • It's less expensive than metal
    • It's more green than metal

The base of the Big Chill pedal generator bicycle conversion system ("BCPGBCS") is made of a sheet of plywood and two 2x2s (that's two inches by two inches by eight feet) boards.

I used full-size (4 foot x 8 foot) sheets of plywood, but (3 foot x 6 foot) pieces would have worked just as well. Since a full sheet is needed either way, I just used the full sheet.

The boards are screwed UP from underneath the plywood. I used three inch deck screws with quarter inch flat washers under the screw heads to keep them from pulling through the plywood. Three days of brutal riders did not break any of the bases, so I have confidence in the design. Once the screws are in, the base cannot be placed on anything that could be damaged, like a hardwood floor, unless you put padding under the base to protect the floor from the screw heads.

Here are some drawings to review. The boards are 96 inches long, and they have each been cut into four pieces (side views):

|------------ 5 feet 4 inches (64 inches) ---------------|--- 14 inches ---|- 6 inches -|- 6 inches -|
Add a hinge between both of the 64 and 14 inch pieces. The 14 inch pieces will need to flex UP towards the rear tire of the bicycle. Pretty much any old hinge will do.
FRONT                                                                   BACK
                                                       HINGE
|------------ 5 feet 4 inches (64 inches) ---------------|--- 14 inches ---|
Add the training stand. The 2x2s are side by side with about two inches of space between them, enough for the bike tires to fit between them without touching them. The wood pieces rest on TOP of the training stand and hold it down onto the base. Screw three inch deck screws up from underneath your plywood base into the two long boards. Screw one of the two short pieces crossways under the front end of the two long boards to hold them level. Screw up into the cross piece from underneath the plywood as well. The long boards will not be touching the plywood because the front cross peice and the training stand will be holding them up away from it. That's correct.

                                               /\
                             Training Stand ->/  \
                                             /    \
                                            /      \   HINGE
|------------ 5 feet 4 inches (64 inches) -/--------\----|--- 14 inches ---|
|_| <- Cross Piece                        /          O
--------------------------------------------------------- <- Plywood
 ^                                                 ^   ^  <- Deck Screws
Add a six-inch-square piece of 3/4 inch plywood across the ends of the 14 inch pieces to serve as the motor mount. (Tim Siddall, http://www.electricpedals.com/ made this suggestion. Thanks for this idea, Tim!)

                                               /\
                             Training Stand ->/  \
                                             /    \              Motor Mount
                                            /      \   HINGE      ---------
|------------ 5 feet 4 inches (64 inches) -/--------\----|-----------------|
|_| <- Cross Piece                        /          O
--------------------------------------------------------- <- Plywood
 ^                                                 ^   ^  <- Deck Screws
Screw the scooter motor to the motor mount. Pry off the end of the toothed pulley. Press a skateboard wheel onto the pulley. Screw two brass screws into the gap between the pulley and the skateboard wheel, 180 degrees apart. Clamp your bike, flex the motor up to the rear wheel, and test. For short-term tests, use a bungie cord to keep tension. For permanent use, consider a spring. Bungie cords weaken over time.

Watch this video to see the design of the base.

Once the generator is built, then what? What can you power? Play with the PPPM Circuit Builder to find out.

If you are interested in seeing more details on this page, press the button below. It will activate a voice synthesizer that will say "I am interested" - that's all. If I am within earshot, I'll become inspired and add more to this page.

The bicycle generators for the Big Chill worked out pretty well. A number of design decisions were made to limit the amount of power they produced to simplify the electronics and ensure they would be reliable in the face of a crowd of 30,000+ festival-goers. None of the generators produced more than 50 Watts of power, as this was the limit of the incandescent bulbs in the lanterns in the tree. I'm certain this design could produce more than 50 Watts, but it's not terribly efficient. If you want ultimate efficiency, go back and review the PPPM through this Learn More link. It will beat any bicycle design.

More Movies...

Bicycle Generators at the Big Chill
Bicycle Generators at the Big Chill

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