How to calculate velocity ratio, input and output speed

A basic review for my students. Using a Lego model I identify the input (driver) and output (driven) pulleys. I then calculate the velocity ratio (VR) and the output speed from a known input speed.
VR = driven / driver
Output speed = input speed / VR

[@butchyboy69]

Thanks for posting this video. You have saved my dumb self some trouble.

[@animaloverload7465]

I'm designing a waterwheel powered rock tumbler and this is exactly what i needed. How big do I have to make the wheel to turn the barrels? This video helped a lot!!!

[@ANONYMOUS33322]

Thanks so much I'm doing tech homework

[@ramboofc1301]

This takes me back to when sweet and innocent

[@py-sk4dn]

Clear and precise

[@jackf498]

if you need to calculate a driver/motor wheel size to drive a driven wheel at a specific rpm
...divide motor rpm by the needed driven-wheel rpm=velocity ratio
...then divide the driven wheel size by the velocity ratio=needed driver wheel size.
.............(an example for a needed 900rpm driven wheel speed with a driven wheel size of 250mm and a 3650rpm motor speed)
motor 3650rpm/900rpm=4.05
driven wheel size 250mm/4.05= 62mm driver wheel size needed for 900rpm driven wheel speed.

[@ghafarabcd]

Amazing calculation. I may still need your help with some calculations . How may I contact you please ?

[@amelliamendel2227]

So does this mean I can use teeth on the the pulley for that math. Like a stepper motor with 20 teeth driving a pulley with 80 teeth on a g2 timing belt would be 20/80? How does torque effect it? Does the length of the belt or the distance from the center of the pulleys make any difference?

[@PizzeyTechnology]

Good questions!
Teeth, radius, diameter, circumference can all be used to calculate velocity ratio.
In your example it would be VR = driven / driver = 80 / 20 = 4
The motor would rotate 4 times for every 1 rotation of the output pulley.
The ratio is not affected by torque or distance between centres.

[@amelliamendel2227]

@@PizzeyTechnology Thank you very much. I'm building a scara robot. I found a turntable at home depot for $4 bearings are expensive. I also found out that 5/16 rods are close enough to 8mm to work. I'm using a threaded rod instead of a lead screw. I got 4 stepper motors for Christmas.

[@PizzeyTechnology]

I had to look up SCARA - so it's a robotic arm you are making? Is this just for fun?

[@a-iatelier1113]

Thank you Sr.

[@PizzeyTechnology]

You are welcome

[@ramboofc1301]

8 out of 8 would recommend