Picture of The Simplest Speedometer.CHECK IT OUT!
This is my first item i am submitting in instructables.This is an Awesome thing found by me.But I feel sorry that I didn't put the image.Leave it,See the step by step instructions and you will be amazed!Do not put this article in any other websites I beg you don't do this without my permission PLEASE!.
Now,to the materials
Voltmeter (one which has a needle(analog))
A motor (from a toy car).
some wires(It should be big enough for your bicycle)
The one am showing is connected to a multimeter!
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Step 1:

First,you need to connect the wires to the motor.Now test the motor if it is working--Connect an LED to the motor and rotate the shaft.You should rotate in both directions because the LED wouldn't glow if current is passing throush the -ve terminal of an LED.after testing,you should remove the LEDs

Step 2:

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Now connect the motor in such a way that when the motor is rotated the voltmeter reads +ve. 

Step 3:

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Now remove the dial of the voltmeter and place the calibrated dial.You can do this on a distance-marked track.the formula for calculating the speed is Speed=Distance/time

Step 4:

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Now connect this calibrated speedometer to the motor and the item is ready!Now connect the motor to the wheels of a Bicycle.
How is it? Awesome? If it is good thanks.Here's the picture of an analog voltmeter.
You didn't use voltage to figure that out,only distance & time, that's my point. What does the meter do for you??
fahadshihab (author)  Lectric Wizard1 year ago
mark that speed there. I am saying that. You should calibrate the meter using the track, not calibrate the track using the meter.
fahadshihab (author) 3 years ago
I told clearly in this instructable that remove the dial of the voltmeter and place the calibrated dial
The only thing clear I saw was your lack of command of the English language.
How does the instantaneous voltage reading on the meter from a random motor relate to speed ??? Don't get it...
A DC motor generates a voltage if you apply a force on the shaft (ie turn it). This induced voltage is proportional to the speed at which the magnetic field is going through a coil of wire (and vice versa) Thus meaning the faster you turn the motor the more voltage it produces and the higher your speed.

However, speed is Distance over time. Instantaneous speed involves taking the Derivative of the Position Function or The Integral of the Acceleration function.
fahadshihab (author)  Nerdz3 years ago
you can connect the -ve terminal of the voltmeter to the +ve terminal of a rechargeable battery and connect the -ve terminal of the battery to the +ve terminal of the battery. so,while riding,you can generate electricity.
fahadshihab (author)  Nerdz3 years ago
See, the voltage produced by the motor is proportional to its rotational speed.So you can ride a bicycle on a distance-marked track.suppose I am going for a ride.its distance is 100m and I have covered 100m in 8.8sec.now use the formula s=d/t.So,100/8.8=11.36m/s.Now convert it to km/h.1km=1000m so d=11.36/1000 1h=3600sec so 1/3600. now divide.To divide,you should take the reciprocal of the second fraction and multiply.so,11.36/1000*3600/1=40896/1000.now cancel each other.so,40.896km/h.