# Society of Robots - Robot Forum

## Mechanics and Construction => Mechanics and Construction => Topic started by: yatsu86 on July 25, 2007, 10:23:55 PM

Title: wheel diameter and rpm calculation problem
Post by: yatsu86 on July 25, 2007, 10:23:55 PM
ok if you would use this formula to figure out wheel diameter then u could use it for finding a rpm right

example
3 ft/s = diameter * pi * 100rpm
3 ft/s = diameter * pi * 1.67rps (rotations per second)
diameter = 3 ft/s / (3.14 * 1.67 rps)
diameter = 0.57 ft, or 6.89"

real
3 ft/s= 3" *pi *rpm
3 ft/s= 9.42*rpm
rpm= 3 ft/s / 9.42
rpm= 3.18 ft/s or 19.12 rpm

but if u check the math it is not right or did i do my math wrong.

checking
3 ft/s = diameter * pi * 19.12rpm
3 ft/s = diameter * pi *.318rps (rotations per second)
diameter = 3 ft/s / (3.14 * .318 rps)
diameter =3.00 ft, or 36"

admin edit: Changed the subject 'i have a ?' to something more useful.
Title: Re: i have a ?
Post by: hazzer123 on July 26, 2007, 04:15:40 AM
You have to be careful with your units on this.

36"/s= 3" *pi *rps
36"/s= 9.42*rps
rps= 36"/s / 9.42
rps= 3.82 rotations per second.

Try to use the same units of length and time throughout your calculation.(eg. inches and seconds)