Turn an Exercise Bike Into an Energy Bike

Why pedal a stationary exercise bike for exercise? Put all that sweat equity to good use while getting into shape. Turn you exercise bike into a power generator to run lights, a TV, stereo, blender, etc. Recharge a 12V battery or drive appliances directly. This is an excellent educational tool for science and technology classes. There are several options for how you design and build it. I'll show you how to build this one and point out other options along the way.

Here's a list of parts you'll need to get started:
- exercise bike, with cast iron flywheel or rubber tire type
- DC motor or generator with magnets, 12Vdc or 120Vdc recommended
- 1/2" plywood, 3/4" will also work
- 6' - 2"x 4" pine lumber
- 4' link belt (or fan belt)
- 1/4" Lag bolts
- assorted screws
- 3/4" water pipe and end caps
- screw band
- wire DC volt meter
- DC amp meter
- 14 ga. wire
- 2' of 1-1/2" PVC pipe
- 1-1/2" sheave (pulley)

Tools you'll need:
- jig saw
- hand saw or chop saw
- router (optional)
- drill and bits
- hacksaw
- file
- wire cutters and strippers
- screw driver
- socket set and ratchet
- carbide cutter
- vise grips

Step 1: Prepping the Exercise Bike

I prefer to use Tunturi or Vitamaster exercise bikes for conversion. They are well built with a heavy flywheel and good bearings. The frame is solid, but the handlebars may wobble a bit on some models

Start prepping you exercise bike for conversion by removing unnecessary equipment. Most exercise bikes have either brake pads or a web strap that rides on the perimeter of the flywheel. This one has a watt meter hooked to the drag brakes.

On this model, you'll also need to remove the rubber banding from the perimeter of the flywheel.

Step 2: Turn a Groove on the Flywheel

The flywheel needs a groove to receive a drive belt. Some models have a wide shallow groove, others have a narrow, deep groove. The easy way to do this is clamp a carbide-tipped square shank cutting tool in a pair of vise grips and hold it securely against a base with the tip against the fly wheel.

Have someone pedal the exercise bike while you gradually turn the metal groove to the desired width and depth. This can take a little while, especially if your human motor is out of shape. Take your time and take light cuts.

An approximate width and depth as shown in the second picture will work adequately. Test fit your belt periodically to ensure you are getting an appropriate fit.

I like to use a link belt available from numerous sources, one of them being Woodcraft.comWoodcraft.com. It's easy to add or remove links to get just the length you want.

Step 3: Creating a Base for the Generator

There are many ways to mount the generator. I created a base and an adjustable cradle for the generator.

Cut a piece of 1/2" birch plywood large enough to hold the generator cradle reach the frame of the exercise bike on each side of the flywheel. Drill a hole for a 5/16" T-nut which will be used to fasten the cradle. Cut and screw 2x4's to the base on the underside the plywood.

Attach 2x4 boards to the bottom of the base using glue and screws. Lag bolt the cross piece 2x4 to the ends of the other 2x4's at the front of the base.

The two long boards need to have the ends cut to match the angle of the exercise bike frame. I chose to use a U-bolt to attach the base to the frame by drilling a series of small holes to create a slot for the U-bolt tang. An easier way would be to drill a 1/4" hole through the frame and into end of the 2x4's. You could use a lag bolt or a machine bolt into a cross dowel nut.

I chose to attach wheels to facilitate rolling the energy bike around. Because I used 1-1/8" x4 boards rather than 2x4's, I needed to add wood to support the wheels as shown in the picture.

Two of the boards need slots cut in them for the pipe section. You can drill and jigsaw slots or use a router for this task.

Step 4: Making the Generator Cradle

Cut two pieces of 1/2" plywood to fit the diameter of your generator. Cut slots in the cradle base by drilling a series of small holes close together. An 1/8" router bit could also be used to cut a slot.

Glue and screw the two sides to the cradle base.

Step 5: Assemble the Parts

Attach the base to the exercise bike frame. If you attached wheels, make sure the base is level when attached to the frame.

Attach the generator cradle to the base. Insert a hard sheet of plastic such as Plexiglass or clear acetate between the base and the cradle. This will help the cradle slide easier for adjustment. Lay the generator in the cradle and insert the 1"x8" pipe section through the base. Insert the 18" pipe strap through the slots, around the pipe and around the generator. Tighten the strap to hold the generator to the cradle. Insert a 5/16" by 1" T-bolt through the slot into the T-nut.

You may find you need to cut a piece of angle iron or strap and attach it between the base and the axle for the flywheel to make the assembly more rigid. (See the second picture).

Place the link belt around the flywheel and around the 1-1/2" pulley on the generator. Add or remove links as necessary to get the length correct. Slide the cradle assembly back until the belt is tight. If you reach the end of the adjustment slot, take another link out of the belt.

Attach the 12V power jack (a regular out let is recommended if using a 120V generator). Radio ShackRadio Shack catalog # 270-1556 is shown in the picture.

Step 6: Build a Meter and Light Display

This display has 3 switched light sockets, a switched outlet, and two meters. It is 24" tall, 8" wide, and 5" deep. Use 1/4" birch plywood to build the box with 3/4" x 3/4" pine for the internal frame. Drill holes for the sockets, switches, and meters.

I used 3/4" x 5" pine for the top and bottom with holes drilled for a 1-1/2" PVC pipe. After installing and wiring the meters, switches and sockets, install the pipe. After the pipe is in place, the top piece of 1/4" plywood is installed. Drill a 1-3/8" hole in the bottom plywood and attach. This will hold the PVC pipe captive.

Step 7: Start Pedaling Power!

With the meter display plugged in, starting to pedal should start to deflect the volt meter. If the meter moves the wrong way (negative), reverse the leads connecting the generator to the 12V socket. Screw in an incandescent and a compact fluorescent.

If you're using a 12V generator, you'll need to use 12V rated bulbs. These are available at most RV centers. If you use a 120V generator, you'll need to use resistive loads or appliances with magnets in the motors. Many compact fluorescents will work on 120Vdc, but not all.

If you find that you have to pedal to slow or too fast to get the desired voltage, change the size of the pulley on the generator. A larger pulley will turn the generator more slowly and generate a lower voltage for a given pedal speed.

I added a smaller handlebar for smaller kids. An 8-year-old on frost sugar pops can crank out an amazing amount of energy, over 200 Watts!

Have fun pedaling different DC appliances. Read a book with pedal-powered lights. Hook a 12V TV to the Energy Bike. Make your kids pedal if they want to watch TV. They can rest during the commercials. If you have a laser engraver, make a side plate with a picture of an Energy Bike cranking out lighting bolts!