So I did some of the math today. Problem with the go-kart actually going is definitely gears. We’re waaayyyyyyyyyyy too low of a ratio at the moment. Sure, more power would solve the problem easily. However, let’s look at the math:

6000 RPM electric motor
20″ diameter tires
14:60 drive ratio (~4.28)

6000 RPM input / 4.28 motor:axle ratio = 1401.869 axle RPM; let’s call it 1402. So axle (and tires) are doing 1402 RPM at max motor speed (which is where DC motors run the best/coolest/most efficiently).

20″ diameter * 3.14159 = 62.832 inch circumference of the tire.

62.832 / 12 inches per foot = 5.236 foot circumference

1402 RPM * 5.236 feet/rev = 7340.872 feet/min

See the problem yet?

60 MPH = 1 mile per minute

1 mile = 5280 feet            DING-DING-DING-DING-DING! You should see the problem by now……

7340.872/5280 = 1.3903 miles/minute * 60 miles/hour = 83.419 miles/hour

We do NOT need to be tearing around at practically 85 miles an hour on a go-kart when the motor is running at its best! I’m not sure what to do about correcting this myself; perhaps others have ideas on how to just about double the drive ratio? What’s the best way to go from 4.28:1 ratio to something more like 9:1?

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