On 15.02.13 09:02, John Kasunich wrote: ... > Make the pulleys as big as you have room for - that helps you > three ways: > > 1) the belt tension needed to transmit a given torque goes down > > 2) there are more teeth engaged between belt and pulley. That both > increases the ability of the belt to transfer torque, and it reduces the > possibility of slip (which could show up as backlash) > > 3) if there is any movement (backlash) between belt and pulley, > a given amount linear movement results in less angular rotation > of the shaft. > > Regarding backlash, it might help to work an example with > numbers: > > Suppose you have a 5 thread per inch ballscrew, and are > using a 3" diameter pulley to drive it. The circumference of > the pulley is 3 x pi = 9.42 inches. It takes five revolutions > of the pulley for the axis to move one inch. That means > 5 x 9.42 = 47.12 inches of belt movement to cause one > inch of axis movement. So any backlash between the > pulley and the belt is reduced by a factor of 47 before it > gets to the axis. If a belt tooth is 0.005" smaller than the > groove in the pulley, then in theory the belt could slip by > 0,005". Divide that by 47 and you get 0.000106" at the > ballscrew.
John, I read that last night before going to bed, again today, and I'm going to add it to my notes. It's the good oil. ... > One more thing - keep in mind that the rated torque of a > stepper is at zero speed, and you can't load it to even half > that level and expect to get much speed out of it. If you are > calculating your belt tension and bearing loads based on > stepper rated torque you are being very conservative. Most > stepper machines run at one-fourth of the rated torque, or > even less. The motor torque graphs confirm what you say, but your words are easier to understand. Many thanks. Erik -- You got to learn three things. What's real, what's not real, and what's the difference. - Terry Pratchett, _Witches Abroad_ ------------------------------------------------------------------------------ The Go Parallel Website, sponsored by Intel - in partnership with Geeknet, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials, tech docs, whitepapers, evaluation guides, and opinion stories. Check out the most recent posts - join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
