This project has given my students a lot of enjoyment- they love competing against each other to see who is the "fastest" or "strongest"... and then they discover that they are only putting out maybe 1/3 of a horsepower!
Step 1: Gather Supplies
Electric motor & drive parts
Covers come in handy later, but not necessary.
***NOTE*** You must make sure the motor in the treadmill will work as a generator!!! Hook up a volt meter to the wires coming from the motor and spin it BACKWARDS. If you can measure a voltage, it will work as a generator.
I was lucky enough that our school was throwing out a pretty nice one that wasn't working- something wrong in the control panel. Everything else was fine!
You will also need a large assortment of tools for this project which will depend on your treadmill. At the minimum you will need:
Layout tools- square, tape measure, ruler, scratch awl, markers, pencils, etc.
Welder and welding gear (hood, gloves, etc)
Cutter of some sort- plasma, torch, or even a hacksaw.
Duct tape. You never know, right?!
Other Supplies you will need:
2 digital multimeters (cheap ones run about $3.00)
A light or something else that requires about 120v to act as a load
Wire connectors and maybe some wire
Step 2: Destroy a Perfectly Good (or Bad) Treadmill.
Let the fun begin. If your treadmill is still complete, tear it apart. See Picture 1. We want it down to the bare frame, because we are going to cut a large section out of the middle and then weld it back together.
Once the frame is bare, it's decision time. You will need to decide how much of the frame you want out. I ended up cutting out about 48" of frame rail, leaving the rollers about 9" apart. Using your measuring tools and the square, be as accurate as possible and mark your cuts as shown in Picture 2. Once you have the marks, cut the rails as shown in Pictures 3, 4, and 5.
Step 3: Weld It Up.
You will want to spend some time making sure that the two pieces of frame are lined up. My treadmill had some fancy adjustments for the rollers, so it's pretty easy to get them parallel. Either way, look at Pictures 3 and 4 to see how I lined the pieces up.
Get it all lined up and weld it together! See Pictures 5, 6, and 7.
Once its welded, we can start putting it together.
Step 4: Assemble and Wire!
Wiring is pretty simple. From the motor, you need one wire going to the light bulb and another wire going from the light bulb back to the motor. You need to break one of these wires somewhere and put one of the multimeters in series (in line). This multimeter must be set up to measure AMPERAGE. The other multimeter is set up in parallel (across) and is set up to measure VOLTAGE. See Pictures 1 and 3.
Step 5: Finishing Up!
The rollers on my treadmill were very smooth and whenever we tried to pedal, the bike wheel would just spin out. I was hoping to take the roller to a machine shop and have it knurled, but time and money prevented that so I just spun the roller while lightly running the grinder against it to roughen it up. Once I had an even rough patch, I ground some deeper lines across the patch for even more traction as shown in Picture 1. Worked great!
Put the bike on! Using the two tie downs, set the rear tire on the rollers and put one tie down on the chain stays as far back as you can as shown in Picture 2. Make the tie downs as tight as you can. If you are having trouble with the wheel slipping, you can let some air out of the tire, make the tie downs tight, and then air the tire back up.
With the bike on you are pretty much ready! Make sure any covers are in place. They make a great mounting point for the multimeters- I just Duct taped mine on as shown in Picture 5. Told you it would come in handy!
Step 6: Pedal Like Crazy and Calculate Your Horsepower!
***NOTE***- Please be aware that this dyno has the capability to generate some serious electricity. Make sure your wiring is sound and that there is no way for an accidental electrocution.
It can be hard to get the dyno going- there is a fair bit of inertia between the rollers, motor, and the flywheel on the motor. Start by pedaling slowly and gradually build up speed until you are pedaling as hard as you can. Have someone keep an eye on the two multimeters and record the highest number seen on each of them.
Calculating the power generated is pretty simple: just use the formula P=Iv, where P is the Power in Watts, I is the amperage, and v is the volts. Using the numbers in Picture 2, we get P=.67 amps x 92.6 volts, which give us 62.042 Watts.
Converting Watts to Horsepower:
Converting is pretty simple. Just multiply the power in Watts by ..001341. So using our numbers from Picture 2, we get 62.042 Watts x .001341 which equals .08 Horsepower. Yup, less than a tenth of a horsepower!!! Just for the record, 1 horsepower is equal to 745.69987 Watts. Most of my students can hit anywhere from .3 to .5 horsepower with a little practice.