  ### Author Topic: Wheel and speed  (Read 4024 times)

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#### ScubaCap

• Guest ##### Wheel and speed
« on: March 01, 2008, 18:06:03 PM »
Ok i really do not know if this is maths or geometry.

Suppose we have a motorcycle with a wheel diameter of 75cm.
Now we have a sensor that will count the number of wheel turns.
Each wheel turn has 8 points for the sensor to measure and so he will send 8 pulses

The question: How can we calculate the speed (in Km per Hour) having these? Is there something else that we need to know?

#### kam

• Hero Member
•     • • Posts: 1849 ##### Re: Wheel and speed
« Reply #1 on: March 01, 2008, 20:14:51 PM »
well.
The diameter is 75 cm. To calculate the peripheral you must multiply the diameter by 3.14.

p=R*PI (for your example the p=235.5 cm)

In every wheel turn, your bike will have comer p centimeters. For every p centimeter, the controller will have receive 8 pulses. So, for every pulse, your bike will have cover p/8 centimeters.

So, you only have to measure the mSec (this may change according to the range of speed you want to cover and the bits that you have available to measure) from one pulse to another.

Example
Suppose that one pulse to the other had gap of 100mSec. This means that in 100mSec your bike covered 235.5/8 cm = 29.4 cm. you measure cm per mSec but you want Km per Hour. To convert cm to km you need to divide by 100.000 and to convert mSec to Hours you need to divide by 3.600.000. The final number will be:

Km/h = (36/time [mSec])*29.4 =>Km/h = (36/100)*29.4 = 10.58 Km/h

So you do not run so fast...   If the delay was 50mSec, the speed would be

(36/50)*29.4 = 21.1 Km/h and that's a little bit faster #### ScubaCap

• Guest ##### Re: Wheel and speed
« Reply #2 on: March 02, 2008, 16:20:54 PM »
I really thank you kam.
This is very good explanation. And i can change some parameters to your formulas to fit my needs.
Thanx again!