Power Racing Series, NFP

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====== Sprockets ======

Some sort of gearing is needed to transmit and transform the power from the motor to the wheels, as most electric motors (barring hub-motors) spin with too great of speed and too little torque to power a wheel directly. a Sprocket/chain system is the most commonly used way to reduce the motor speed and increase the motor torque via this gearing to transmit power into the wheels. 

As discussed in the Chain section, the ANSI #35 chain is the most commonly used size within the League. Sizing this type of sprocket to the typical context for Power racing includes a little bit of math. The [[https://www.bmikarts.com/Go-Kart-Gear-Ratio-Speed-Calculator |Calculator from BMI Karts is pretty useful for performing this math.]] Important data for using this calculator with a BOMA MY1020 motor:
  * "Drive Wheel Diameter in Inches" should be actual/measured, not just nominal off the sticker, for the most accurate calculation.
  * The "Rated Engine RPM" the standard "silver can" BOMA MY1020 motor is 4700 RPM
  * Adjust the Teeth on Axle value until you get a gear ratio/maximum RPM output that feels right.
  * For "Teeth on Clutch" the smallest #35 sprocket that typically fits on the BOMA MY1020 motor is a 9-tooth.

Aiming for 22/23 MPH on the calculator has proved acceptable for many middle-of-the-road karts.

Once you determine a calculated "teeth on axle" value for your prospective build, you can run it through the [[https://www.bmikarts.com/Go-Kart-Sprocket-Diameter-Calculator |BMI Karts sprocket diameter calculator]] to see what kind of ground clearance you'll have between the bottom of the sprocket and the pavement, since you must already know the diameter of your wheels in order to calculate the sprocket size.

It's good practice for your sprocket to not scrape too close to the ground, a rule of thumb is 3/4" clearance at minimum. More is better. 

===== Historic guide =====

This historic guide is preserved for posterity.

Common gear/sprocket tooth profiles:  

**#25 Sprockets** are the most common type of sprocket used on electric scooters, electric bicycles, electric pocket bikes and small electric go karts.

**#35 Sprockets** are the most common type of sprocket used on mopeds, mini bikes and full size go karts.

**8mm Sprockets** are the most common type of sprocket used on pocket bikes.

**Bicycle Sprockets** are used on standard pedal bicycles and electric bicycles, and typically correspond to ANSI #40N (narrow) chain size.


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**Useful References:**
  * [[http://www.smex.net.au/Reference/Ratios02.php]]  Determining the required gear ratio or maximum speed is not always intuitive. Many factors have to be taken into account. This page is particularly useful for electric or motor-driven locomotives w/javascript calculator.  
  * [[http://www.electricscooterparts.com/bicyclesprockets.html]]