Build a Bike Dyno- Calculate YOUR HORSEPOWER!

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Introduction: Build a Bike Dyno- Calculate YOUR HORSEPOWER!

What do  you do with an old, broken treadmill that's taking up space?  Hack it up and convert it to a Bicycle Dynamometer!  What, you may ask, is a dynamometer?  Well, simply put its a machine used to measure power output- usually of an engine, but in this case, its measuring the power output of YOU!  How much horsepower do you put out?!

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!

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Step 1: Gather Supplies

Get all your stuff together.  The big thing, obviously, is the treadmill.  You don't need it to be complete, but you should at least have:

Frame
Rollers
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.
Wrenches
Screwdrivers
Welder and welding gear (hood, gloves, etc)
Grinder
Cutter of some sort- plasma, torch, or even a hacksaw.
Wiring tools
Electric Tape
Duct tape.  You never know, right?!

Other Supplies you will need:

2 digital multimeters (cheap ones run about \$3.00)
Some Tie-downs
A Bicycle
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.

I was originally hoping I could just put the rear tire on the track of the treadmill and pedal, but the small contact patch of the tire put too much pressure on the board underneath the track so it wouldn't spin.  I ended up removing all of the track parts and sectioned the frame to shorten it so the bicycle tire sits right on the rollers.

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.

Here's where the big tools come in to play.  Now that the frame is sectioned, we need to clean up our cuts using the grinder- see Pictures 1, 2, and 3.

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!

With the frame done, we can put the motor, drive, and rollers back in.  See Picture 2.

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!

Almost there!  Just a few things to help make this a little easier.

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!

With everything hooked up, we are ready to generate some electricity!

***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.

Calculation Power:

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.

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11 Discussions

Hi im planning to build one of these rigs for a university project testing a 2 speed bike. Do you think your multimeter can pick up gear changes?

In your last picture you are not using the tension cords to tie the bike down. Is this true? does it work without them without slipping?

Theoretically you can use this method to calculate the horsepower of anything that spins. That said, if it was me doing the testing I probably wouldn't put anything on it that would have more power than the electric motor in the treadmill originally put out.

could you use this to measure the power of a scooter or a small motorcycle?

As I recall, there are some AC motors that don't work (easily)... I only used the treadmill motor because I had it, it was free, and it worked. Very simple to test- hook up a voltmeter to the motor and spin it- if it generates electricity, it will work.

Fantastic Idea! I was going to use the same dynamometer principle to measure the output of a small 2 stroke piston engine I have. But, I need to know, does any kind of AC Motor do or did you use the treadmill motor for a specific purpose? For example, can I use a squirrel-cage motor? maybe I need some excitation current beforehand?

I can see that the final project is quite simple, guess any working generator will do the trick, am I right? can I use a car alternator or anything like that?

Yes, you should be able to use any type of generator. I have seen a few bicycle powered alternators, but I'm not sure how the wiring would work. The nice thing about using a treadmill is that you already have the rollers. You could put an alternator on the bike in place of the back tire, but I don't know how "accurate" that would be for calculating to-the-ground horsepower...

This is a great project, especially to give students some fun hands on science! I wonder if the original display on the treadmill would work if you hooked it back up (and maybe reverse the connections)? Then you'd be able to see your speed. Since you're handy with a welder, it be a great addition to construct a bicycle trainer style mount to secure the rear axle in place. Well done!