Gear ratio calculation question

In summary, the conversation discusses the specifications and calculations for making a scooter go 25mph with a motor. The motor has a power of 0.35 hp at 12 volts and 1.43 hp at 24 volts, torque of 0.47 lbf*ft at 12 volts and 0.97 lbf*ft at 24 volts, and efficiency of 70% at 12 volts and 76% at 24 volts. The motor also has a speed of 1260 RPM per volt and can operate at 12 or 24 volts. The weight of the motor is 11 oz and it has a 5mm diameter output shaft. The desired gear size for the motor is 0.39
  • #1
david90
312
2
I have a scooter with a 5 inch diameter wheel and I want to make it go 25mph with a motor that has this specs.
====
Power 0.35 hp @12v 1.43 hp @24v
Torque 0.47 lbf*ft @12v 0.97 lbf*ft @24v
Efficiency 70% @12v 76% @24v
Speed 1260 RPM / Volt
Voltage 12 volts or 24 volts*
Weight 11 oz.
Output Shaft 5mm dia x .75" long
Diameter 1.7"
Length 2.8" (from face)
Face Mount 2 M4 holes 1.14" apart
===
I use this equation to figure out the RPM of the wheel for 25mph.
RPM*(((D*3.14)/12)*60)/5280)=MPH
Calcuated RPM for 25mph is = 1680 RPM

i'm planning to use 17 volts, thus the motor rpm would be 1260*17=21420 RPM

Now I'm finding the gear reduction. 21420/1680= 12.75
5"/12.75 thus .39" is the required gear size that is attached to the motor.

Is the .39" gear size the diameter, radius or circumference?

i'm not using a sprocket because it is friction drive.

Are there any potential problems with this setup? Is my calculation correct?
 
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  • #2
This topic just arrived through a wormhole. Welcome to the future.

david90 said:
Now I'm finding the gear reduction. 21420/1680= 12.75
5"/12.75 thus .39" is the required gear size that is attached to the motor.

Is the .39" gear size the diameter, radius or circumference?
Since the 5" wheel is a diameter, the 0.39" must also be a diameter.
One problem I see is the high continuous RPM of the motor.
I would expect friction losses in the drive will damage the friction surfaces.
 

1. What is gear ratio?

Gear ratio is the ratio of the number of teeth on the driving gear to the number of teeth on the driven gear in a gear system. It is used to determine the speed and torque of the output gear in relation to the input gear.

2. How do you calculate gear ratio?

Gear ratio can be calculated by dividing the number of teeth on the driven gear by the number of teeth on the driving gear. For example, if the driving gear has 20 teeth and the driven gear has 40 teeth, the gear ratio would be 40/20 = 2.

3. What is the significance of gear ratio?

Gear ratio is important because it determines the speed and torque of the output gear. A higher gear ratio results in a slower speed but higher torque, while a lower gear ratio results in a faster speed but lower torque.

4. How does gear ratio affect mechanical advantage?

Gear ratio is directly related to mechanical advantage, which is the ratio of output force to input force in a system. A higher gear ratio results in a higher mechanical advantage, allowing for greater force to be exerted on the output gear.

5. Can gear ratio be changed?

Yes, gear ratio can be changed by using different sized gears in a gear system. This can be useful for adjusting the speed and torque of a system to better suit a specific application.

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