On 31 March 2013 07:31, Gregg Eshelman <[email protected]> wrote: > So, yeah, no servo drive available to us mere mortals is going to be able > to out-accelerate gravity.
This doesn't add up. Any Z-axis capable of lifting the head can out-accelerate gravity. All that is required is for the force exerted by the actuator to be greater than the weight of the parts being moved. (I do mean "weight" here, the mass of the parts x little-g) There is a little more to it than that, as the motor inertia becomes much more relevant under acceleration than under constant-speed (or stopped) conditions. Taking the example of the 1kW motor here: http://literature.rockwellautomation.com/idc/groups/literature/documents/pp/mp-pp001_-en-p.pdf It has a peak output torque of 7.9Nm and an inertia of .000078 kg-m2 (kg-m2 = Nms2) So, the motor itself can accelerate at a rate of 100,000 radians/sec2 = 16000revs/s2 If we have a 500mm length of 20mm x 5mm ballscrew rigidly coupled then that adds a further 0.000041Nms2 to the system http://www.gg-powertransmission.com/ball-screw-drives/ball-screws/ So now the system can accelerate at 10000revs/s2 = 52m/s2 = 5g. That doesn't tell us very much, other than that this system can't accelerate any payload whatsoever at more than 5g. However, at 2.5g we have 4Nm of torque "left over". That's 5kN on a 5mm pitch screw, enough to accelerate a 200kg payload at our stipulated 2.5g. -- atp If you can't fix it, you don't own it. http://www.ifixit.com/Manifesto ------------------------------------------------------------------------------ Own the Future-Intel(R) Level Up Game Demo Contest 2013 Rise to greatness in Intel's independent game demo contest. Compete for recognition, cash, and the chance to get your game on Steam. $5K grand prize plus 10 genre and skill prizes. Submit your demo by 6/6/13. http://altfarm.mediaplex.com/ad/ck/12124-176961-30367-2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
