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Picture of Very Easy Cadence Meter For Your Bike <$12
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Cadence is the speed at which the pedals turn, measured in Revolutions Per Minute.
Inexperienced riders tend to pedal too slow which will put stress on their knees.

I always wanted to know how fast I was pedaling but I didn't
want to spend a lot of money to do it. Most experienced riders
have a Cadence of 70 to 90 RPM's. When I started using the meter
I found 60-80 to be my norm, but since then I moved up into the
70-90 range without realizing it.

Here is my solution for less then $12 and super easy to do.

Step 1: $10 Cycle Computer

Picture of $10 Cycle Computer
I bought this at Walmart, but many other
stores carry them. They are very accurate
and simple to use. They also turn on
automatically when the magnet passes
the sensor.

It will also record your maximum and
average Cadence plus the number of
times the crank turned. It will also
keep track of the time you are actually
pedaling. When compared with the time
on the speedometer it will tell you
how much coasting you did.

The only drawback is the meter only
reads to 99.9, but you can set it to read
1/2 and remember to double the reading.


 
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KevinK2129 days ago

This is a pretty ingenious idea! That being said:

You could get by with just one magnet, the speedometer comes with just one magnet because that's all that is needed. This would be better if you are stopping and starting a LOT.

You can get a cadence computer on ebay for around $5-$6

Benapain4 months ago

You can just mount 1 magnet, input 166cm or 1666mm as the wheel size, then when you read the speed just multiply by 10 so if you see 9,4 km/h you have a 94rpm cadence.

DanL15 Benapain2 months ago

I'm guessing more magnets would lead to more accurate measurement?... well this $20 piece of s*** PC I got from local store only goes up to 2999 (thousandth digit capped to 2), so I'll have to go with your way. Thanks for the tip bro.

balczezzz2 months ago

Hi,

I'm doing a bluetooth speed&cadence sensor based on a custom 9+ DOF IMU board. Everything including the code and 3D printing files is open-source and you can check it out here:

https://hackaday.io/project/5286-ble-intertial-mea...

kgtateddy7 years ago
i dont get why you use 5 magnets instead of just one..... like on the wheel can someone explain me??
BullN kgtateddy4 months ago

6 years later I hope this still helps:

It is because the computer only allows you to set the circumference of the tire between 1 - 9999mm, yet we need it to think the tire has a circumference of 16666.67mm. So if we divide 16666.67 by 2 we get 8333.335mm, but then it would have to spin twice as fast, so we cheat the system by adding a second magnet to make it think its spinning twice as fast.

On a road bike using 5 magnets is easier to space as the spokes do the spacing for us, but then you need to divide 16666.67mm by 5 which equals 3333.33mm and use that as your setting.

You can use as many magnets as you want provided you comply with the limitations of the computer you are using.

If you choose to use one magnet, you will have to set the diameter to 1667mm. this will have the effect of moving the decimal point so that 8.8km actually means 88rpm. Useful if you want to achieve a cadence above 99.9rpm.

See my comment below. I used one magnet stuck in the crank arm recess at the end of the left pedal. I programmed the cyclometer for a wheel size of 1667. It worked great. I ignored the decimal point for a direct reading of my cadence. I think the author used multiple magnets so the two display numbers would both be large, not the smaller decimal place number. He said the sun may glint off of the screen and make the smaller number hard to read. I did not have enough wire to reach the handlebar and mounted the display unit on my top tube near the headset. My body shields the display unit from the sun. It worked for me that way. I was concerned that magnets stuck to the caps of the chainring bolts could come off if I hit a big bump on the road. The recess at the end of the crank arm seemed like good insurance.
Benapain Phil B4 months ago

exactly...

For each revolution of the device measured (wheel or crank arm), the magnet triggers the computer that 1 revolution has been made, and it calculates speed from how many times per minute the magnet triggers it and multiplies by a formula.
each gear operates differently it can change the way it calculates the speed
BullN4 months ago

This is the best instructable EVER!!!

I am currently making my 2nd one and I ran into the problem of only being able to find a modern speedo that sets the tire circumference by the diameter (ie: 5" to 31").

I solved the problem the following way:

1. The magic number is 16666.67mm as 1 revolution per second will give a speed reading of 60km/h or 1km/minute which is equal to 1rpm.

2. As the speedo will only allow us to set the tire diameter in inches we need to divide the magic number by integers until we find a circumference that will most closely resemble the allowed settings. Eg: 31" = 787.4mm which gives us a diameter of 2473.7mm.

3. After trial and error I found that 16666.67mm / 8 = 2083.33mm. The diameter of a 26" tyre is 2074.7mm. This is the closest you will manage to get using the range of 5" to 31" tyres so I agree that this will not be the most accurate sensor, however the error will be extremely small between 0-99.9rpm that you wont need to worry.

4. Now we need to make the computer believe that a tire with a 26" diameter is spinning at 8 revs per second which will equal 1rpm of a tire with circumference of 2074.7mm. To do this we need 8 magnets. ONLY 8, NO MORE, NO LESS.

5. Place these magnets with equal spacing around the small ring.

6. The rest is the same as the guide above.

7. Set the computer to tire 26" and you're good to go!

NB: This is in no way as accurate as the older speedoes that allow you to set circumference in millimeters, but the margin of error using these exact steps is 0.414%. If you can get your hands on the older speedoes then I definitely advise that over this method, but this will work almost as well if you can't.

Vortexian4 months ago
I used it for more than a year before I found a good wireless Sigma with a cadence sensor.
(sorry, no photos - this construction is now history)
And I really appreciate, that the author decided to spread this simple and efficient lifehack.

The only difference in my design was a magnet and sensor mounting point. I used a magnet on the crank and a sensor on the chainstay (the sensor cable had a perfect length for that).
Aeshir4 months ago

bloody BRILLIANT

Dyers7 months ago

Black is the absence of light, but absorbs light readily - it's why dark things get hot in the sun. White is the presence of all light and reflects light - it's why light things stay cooler in the sun. Some things are treated to resist the damaging effects of UV light, and because black things are more rapidly damaged, they are more frequently treated. In my experience, even when plastics are treated to withstand prolonged exposure to UV, they still break down in a matter of years rather than decades.

m.p2 years ago
How to calculate de cadence in te crank arm with 1 magnet. The arm messures is 160cm
Not all chain ring bolts are steel, some are aluminum. Thus magnets will not stick to them. Realistically this whole thing cost you $22 after purchasing 2 computers. You might be better off (a little less complicated too) just buying a $45 cadence computer like this one: http://www.rei.com/product/751831

No sense reinventing the wheel!
Also this will allow you more handlebar space for lights etc. Especially since the above computer can be stem mounted as well.

Also using the hose on your bike, especially in the area of your bottom bracket/crank is not advisable. This could force water into the bearings and cause rust / corrosion.
If your magnet has a hole in the middle, you can run a zip-tie through it, through the chain-ring, around one of the spider arms or around one of the arms of the chainring if it is a pinned crank.
Sailor Bob (author)  thatcherthatch7 years ago
I agree with you the Cat Eye Strada is a nice computer, but I didn't want to spend anymore then I had to. I pulled another computer off of one of my other bikes to see if it would work and I liked it so much I think I'll keep it the way it is. I like the big readout you get, plus it shows your average Cadence which the Strada wont do. I did put a dab of rubber cement on the magnets to help keep them there. No problem they just peel off if needed. I find myself watching the cadence meter more the the speedometer though, it has really helped on the climbs. I don't think a lot of people want to spend $45 for a computer for their $100-200 bike but they probably already have a speedometer. This was just a cool project for #12.
JJJordan7 years ago
Dude, that's awesome, totally geek! I really appreciate it, but it is not as cheap as it looks like (you can get cheap cadence capable cycle computer for less than $40 herehere). But if you already have computer, than this might be your cadence meter... So it doesn't really worth it (except the tickle that you got your bike geeked by yourself) and is not reliable reliable - I think zip ties are one of the greatest human inventions.
Oh, and something else - if you want to have a heart rate monitor too, than your handle bar will look more like the Maltese Falcon dashboard'Maltese Falcon' dashboard

But I really like your "not in a box" style thinking.

P.S. I am not an expert, but I've heard that 90rpms is recommended speed for normal ride, about 100rpms is for sprints and uphills and 80rpms is when you want your legs to rest (at downhill or flat).
It depends a lot on the bike and purpose. On casual touring rides I usually pedal around 50-80 for most of the flats, and around 90-100 for hill climbs (sitting). On my old road racing bike, I used to pedal around 90-120, but would drop to around 40-50 for standing climbs. I am not a strong climber.
Using a pedal cadence meter will help you determine your optimal cadence for different situations, and the visible readout will tend to motivate you. It can also help you compile some basic data to see if you need shorter or longer crankarms or a different chain-ring selection.
hintss5 years ago
I have a bell branded cycle computer. the only thing is that it looks different, but the harness, sensor, and magnet that came with it look the ones that came with yours. It also has 2 buttons, and programs in exactly the same way, showing 2124 as default with 4 highlighted, and you also push the right button and push left to go to next digit. Everything else is also the same. Do you think one brand copied off another?
They are likely made by the same company in China and rebranded.
gdl12286 years ago
i have a question will it work on a go cart??? if so, what should i enter as a wheel size??
It can work on a go-kart, but you will need to mount the magnet on the wheel or driven cog. If you want to calculate ground speed, enter the number of MM of your wheel circumference (mark ground and tire with chalk and have someone push the cart with you on it, and mark 2 revolutions out, then divide by 2, for accuracy).
If you want RPM, mount the magnet on the driven wheel or gear and enter 2682 and select MPH. Ignore the decimal point.
Jodex gdl12284 years ago
It depends on your wheel's size.
Put 2682 into it for "MPH" It will read out your RPM (of the crank, with magnet on crank) as 5.5 MPH for 55 rpm. http://www.youtube.com/watch?v=qrL476g662I
karakris4 years ago
Hey, I've just purchased a cycle computer for less than $8.00 that shows wheel cadence, and the same bunch of other things. Just glued the magnet on the crank, and voila! No need for additional magnets.

I'm new to Instructables, so I don't know whether it's okay to post links. Just PM me and I'll tell you.
postg the link anyway...
I built with only one magnet attached to the crank arm. Set it using MPH and it can read in increments of 2 rpm by making use of the decimal. 7.0 = 70 20.0 = 200 etc. these computers only read in fifths of a mile per hour, hence it increments at 2rpms. but yes this idea works well, with the added benefit of tracking average cadence and max cadence.
and for the persnickety riders, 1magnet means less weight than 4 or 5 magnets :D
In order to do it this way, what wheel size do you have to set the comp. to? Also, what do you mean it increments at 2 rpms? You mean it won't count lower than 2rpm? (If so, who cares.) Or, do you mean, you have to divide your number in two? Sorry for being so dense, I (literally) have sort of a mental block when it comes to simple math.
Phil B7 years ago
I made one of these for a 2nd bike I have in the city where our children live. The magnet was stuck onto the inner end of the left pedal spindle. There was no recess for it to sit in. Somewhere I hit a bump and lost my magnet. Now I am moving the sensor a little closer to the bottom bracket and fixing the magnet more pernamently to the crank with electrical tape. It will also sit in a recess in the pedal casting.
Sailor Bob (author)  Phil B7 years ago
I stopped in at the local Family Dollar store to pick up another set of magnets to use on my comfort/trail bike. I have been riding rails/trails more lately because it's cooler and there is more shade. I glued the magnets to my road bike chain ring just to be safe and will do the same on the 2nd bike. I may just move the computer over to the other bike instead of buying another one. I have been using the Cadence meter for a month now and like you have noticed an improvement on my speed and time. I knocked off 15-20 min from my 22 mile trail ride without even noticing it. I looked back at my data and couldn't believe it.
I got 1/2" round ceramic magnets at Radio Shack. They are $2 for five (stock #64-1883). They save breaking apart the plastic or ceramic from a refrigerator magnet. I have also noticed that tired is tired. If I am fatigued, it becomes harder to hold a higher cadence, even in a lower gear. In the comment above I should have said the magnet will sit in a recess in the crank casting, not the pedal casting.
Sailor Bob (author)  Phil B7 years ago
Phil B7 years ago
This cadence meter has changed my riding for the better. If I ride hard, I can often do my normal 14.4 mile route in 60 to 65 minutes. Tonight I should have been a little tired, but I rode while trying to keep my cadence at 85 to 95 rpm. Sometimes it dipped to the high 70's. I found myself shifting earlier and more often than usual. But, my overall speed was higher and I did my usual course in 56 minutes and 47 seconds, which is my best time ever. And, I am probably do not feel as tired as normally.
Geordiepom7 years ago
Perfect timing for me. I just bought a similar unit and the magnet flew off the spokes 1st time out. Now I've seen this idea I can get either another meter and do what you've done or just fix the existing one with a fridge magnet. Thanks!
LightSpeed17 years ago
Ingenious adaptation of available cheap technology! Thank you for the suggestion. Locally, that bike computer from Walmart (I already have two) sells for under $9 each and is 10x more accurate than many models ten times the price since you can set it to mm circumference (others only do cm). I recommend it. Another alternative is to know what gear you are in and calculate the gear inches of the gear to determine the speed you have to maintain in that gear to be doing your optimal cadence. For instance, my third gear is 83 GI. At 90 rpm cadence, I am going 22.2 mph. If I am going slower, I am under 90 cadence. All I need is to memorize (or make a handy chart taped to my top tube) that number for each gear to have a guide. For 70 rpm, it is 17.3 mph. So to be in my range in third gear, I need to be going between 17 and 22 mph while pedaling. This way one speedometer is all you need. But you have to do the calculation and remember the ranges. Your method is easier to remember. Thanks for your instructable!
Phil B7 years ago
I did this and it works very well. I used one magnet and set the wheel size for 1667. The magnet rests very nicely in a little recess at the end of my left crank and sticks to the end of the pedal. I made a heavy wire attachment to hold the pickup coil in place. This attachment uses the water bottle screws on the seat tube.

I went for a ride this morning and memorized my speed, gear, and cadence reading. Then I fed it through the following formula and it shows the cadence meter to be quite accurate. Cadence = 336 x mph/gear in inches. 336 is a constant.
Sailor Bob (author)  Phil B7 years ago
Good Job

After I got mine setup I printed out a Cadence
gear ratio chart from here. You can cut it
out and tape it to your bike.
http://www.sheldonbrown.com/gears/
rseymour7 years ago
Cool, relatively easy hack. Thanks... added to my list of things to try.
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