Newsgroups: comp.robotics
Path: brunix!news.Brown.EDU!qt.cs.utexas.edu!cs.utexas.edu!sdd.hp.com!saimiri.primate.wisc.edu!zaphod.mps.ohio-state.edu!uwm.edu!src.honeywell.com!The-Star.honeywell.com!umn.edu!mmm.serc.3m.com!mmc.mmmg.com!timbuk.cray.com!hemlock.cray.com!kilian
From: kilian@cray.com (Alan Kilian)
Subject: Re: RPM -> Speed
Message-ID: <1993Feb16.115634.16762@hemlock.cray.com>
Lines: 26
Nntp-Posting-Host: poplar18
Organization: Cray Research, Inc.
Date: 16 Feb 93 11:56:34 CST


A lot of people have complained to me via Email that I used
the constant 3 instead of PI in my RPM to Speed equation.

Sorry. I'm not in school anymore and I cannot measure
motor RPM, wheel diameter or linear speed within 4% anymore.

4% of a 10 RPM motor is about is about 1/2 a rev-per-minute.
4% of 5.5 inches is about 1/4 inch (There I go AGAIN)
   and most of the wheels I use squash at least that much.
4% error in a 165 feet-per-minute robot is 8 feet.

Actually I have never met a motor that maintained a set speed
to within 4% over even a slight load.

I was amazed, dazed and ablaze to find out just how many people
care about a 4% error.

I'll be more careful to quantify the approximations in further postings.

                      -Alan "Cripes!!!" Kilian

-- 
 -Alan Kilian           kilian@cray.com 612.683.5499 (Work) 612.721.3990 (Home)
 "It is a little hard to tell the difference between a machine that doesn't
  work and a machine that doesn't exist." -Martin Walker quoting someone else
