> -----Original Message----- > From: andy pugh [mailto:bodge...@gmail.com] > > On Wed, 22 Jul 2020 at 19:33, Chris Albertson < > <mailto:albertson.ch...@gmail.com> albertson.ch...@gmail.com> wrote: > > > That said acceleration is related to speed. (acceleration) x (time) = > > (speed) > > example: (10 inch per second squared) x ( 0.5 seconds) = (5 inches per > > second) > > Also bear in mind that speed x acceleration x mass = power > > -- > atp Let's take step back to the original question One has a motor with a plate that says 3000 RPM, 226 oz-in, 7.8A continuous at 90V. The mill has a 5 TPI lead screw and a table that weighs 200 lbs. So the questions that I think were asked or what the discussion was about was: 1. Can you run this table lead screw at 3000 RPM if the Servo Drive can handle 7.8A at 90V. 2. If not what reduction ratio is required between motor and lead screw to run the motor at full speed. Jon Elson provided the numbers for linear force created by the lead screw pitch. (with some guessing at friction) and the form I created and attached with 1:1 ratio shows 600 ipm and and 2.2G acceleration.
In real life I have the second screen shot with 3:1 belt reduction and as is logical, speed drops by 1/3, Torque is multiplied by 3 so Acceleration also increased by 3 to 6.66G. If we divided 200 by 60 we get a speed of 3.333333 in/sec which, if the LinuxCNC ini file has LINEAR=inches, is used for MAX_VELOCITY. From the ini file documentation http://linuxcnc.org/docs/2.6/html/config/ini_config.html#sub:ini-variables However the document also says "The maximum acceleration for any axis or coordinated axis move, in machine units per second per second." There is no way that my motor can do 2556 in/sec^2. In fact 40 is a more reasonable number. So we can do as Andy suggests and just get to it by trial and error. But what's the point of any of this math if all we do is configure by mucking around until it sort of works. So either Jon Elson is horribly wrong with the constant linear force calculation to determine force required to accelerate or something else is wrong. I'm just trying to figure out how to calculate, knowing only the above parameters, what you'd plug into MAX_ACCELERATION as a starting point. I realize it needs to be tweaked since ball screw verses acme screw makes a difference. Static verses Kinetic friction makes a difference. So is Jon's calculation of Continuous Linear force correct? Something's missing but I can't put my finger on it. John Dammeyer
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