> -----Original Message----- > From: Thaddeus Waldner [mailto:thadw...@gmail.com] > Sent: July-22-20 8:43 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Calculating table acceleration. Was: Need help with > Bostomatic BD18-2 to linuxcnc > > Start with a 226 oz in > > / 16 = 14.125 lb in > > 5 threads per inch is the same as a belt pulley with a circumference of 0.2 > inches > > since our unit is in lb in, we need to go from a pulley with diameter of > Pi, to diameter of .2 > > thus our final force is 14.125 * (pi/0.2) = 221.875 pounds (poundal?) force > > divide that by your mass of 200lb and you get > > 1.109 g > > 1g = roughly 32in/s^2 so > > 35.69 in/s^2 > > This is close to your ballpark guess of 40 > > Did I make a mistake anywhere? >
1 G is 32 ft/sec^2 or 384 in/sec^2 and that's where it falls apart. Based on real life the acceleration value is out by a factor of about 100. And I don't understand why " since our unit is in lb in, we need to go from a pulley with diameter of Pi, to diameter of .2" It could well be that Jon Elson's explanation of linear force is incorrect. John > > > On Wed, Jul 22, 2020 at 5:24 PM Nicklas SB Karlsson < > nicklas.karlsso...@gmail.com> wrote: > > > On Wed, 22 Jul 2020 11:29:36 -0700 > > Chris Albertson <albertson.ch...@gmail.com> wrote: > > > > > I don't see any relation between max acceleration and max speed. > > > Acceleration is determined by (1) the mass of the table and (2) the > > > torque the motor can produce while speed is determined by the max RPM > > > of the motor. > > > > Mostly agree though as torque usually depend mostly on current there will > > be a resistive voltage drop at higher torque which will reduce speed at > > higher torque, speed reduction is usually small. For example series > > connected DC motors and induction motors made for direct will reduce speed > > so there are exceptions but do not expect these are used as servo motors > > anyway. > > > > Change gear ratio and use motor with same power different speed may change > > acceleration due to rotor inertia. > > > > > It is very easy to buy a tiny motor with low torque that spins very > > > fast. Or you can find powerful but slow motors. Multiplying the > > > speed by three to find acceleration, if it works is just a > > > coincidence. The factor could be 0.5 or 10. > > > > High torque motors usually need a gear box or will become heavy. This is > > because flux and current is multiplied to get force while there is choice > > between current or flux in electric motor air gap, there is an optimal > > choice then either air gap area or diameter need to be increased. Magnetic > > materials will saturate then flux get high enough while conductor losses > > increase with current. > > > > > There are two whys to go. A mechanical engineer would start with a > > > requirement for a certain speed and a certain acceleration. His boss > > > would give him those goals and then he would select a motor and drive. > > > The other way used by most amateurs is to just buy a motor that > > > "seems right" and then test it to see what speed and a certain > > > acceleration you can get from it. > > > > Not sure the boss will ask mechanical engineer about speed and a certain > > acceleration and then give these as a goal to the engineer. It is common > > boss read economics and contract but then it come to technical details odd > > things may happen. > > > > > > Nicklas SB Karlsson > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
