What people continually get totally wrong with steppers is failing to understand that the maximum power is delivered at the corner frequency, and power output is constant above that.
If you have an application that needs to move at say 2m a minute and your stepper stalls, there seems to be some crazy logic that says to people "Oh, the stepper stalled because it was going too fast, I need to change the gearing so the motor spins more slowly" .. which is of course ass backwards. The stepper stalled because the power output of the motor was less than the power requirement of the machine ... to increase the power output of the motor, you need to spin it faster, not slower. Steppers motors are capable of excellent performance but they do need to be used correctly ... sadly, in most amateur applications they are not. If the corner frequency with your drive and voltage is at around 2000 steps per second and you are only ever delivering 1000 steps per second, you can never got more than half the mechanical power out that the motor is capable of. On Fri, 4 Feb 2022 at 17:13, John Dammeyer <jo...@autoartisans.com> wrote: > > > > From: Kenneth Lerman [mailto:ler...@se-ltd.com] > > The longitudinal travel is just over a foot, and it takes about 3-1/2 > turns > > of the crank to go that distance. I'm thinking around a second per turn > > would be about the maximum. So, that's 60 RPM. I'm thinking of a 1:6 > ratio > > on the timing belt pulleys, so that's 360 RPM at the stepper which is > > pretty slow. A full stepping rate would be 200 * 360/60 => 200 * 6 which > is > > only 1200 steps per second. > > You won't want to run full step. A minimum should be 8 micro-steps/step > to avoid resonance and loss of position or lockup. I'd measure the torque > required to move the table by attaching a lever to the hand wheel that is > say 1' long. Set it horizontal and start hanging weight onto the end to > get ft-lbs or ft-in until it turns. That's the torque required to overcome > static friction. Double that to choose your motor. > > Say that is 1 ft-lb or 192 oz-in. If you choose 3:1 for your reduction > ratio you get 600 oz-in. Look at the motor torque curve (they are all > different and if the supplier can't give you that buy one somewhere else) > and see where the torque drops below 400 oz-in. Say that's 180 RPM. > That's 3 RPS which multiplied by 2000 steps per rev for micro-stepping is > 6000 steps/second which achieves your 1 RPS on the handle. > > Or if you find it's 2 ft-lb or 400 oz-in choose a much larger motor like > 1200 oz-in > http://www.automationtechnologiesinc.com/download/9259/ > Notice the curve at 3000 half steps per second is about 3.2NM. That's > 12,000 steps per second (7.5RPS) with 8 micro-steps per step well within > the reach of even a parallel port controller and 450 oz-in. That's well > above the 1 RPS you need and even just 3:1 still gives you 1600 oz-in. > > My two cents... > John Dammeyer > > > > An alternative would be to provide more gearing, but I don't think it's > > practical to get more than about a six to one ratio in a single belt > > reduction and I'd like to avoid mechanical complexity if I can. > > > > Thoughts? > > > > Ken > > > > Kenneth Lerman > > 55 Main Street > > Newtown, CT 06470 > > > > > > > > On Fri, Feb 4, 2022 at 7:13 AM Chris Albertson < > albertson.ch...@gmail.com> > > wrote: > > > > > If looking for lowest cost solution you can us the old "Atom" computer > to > > > control the grinder as long as you do not need to run the mill and > > > grider at the same time. Get an Eiternet interface Mesa card for the > new > > > machine, You need two config files, just load the one for the mill or > the > > > one for the grinder. > > > > > > Then someday you buy a second computer you only have to move the > Ethernet > > > cable over. The best option is a newer version of the Atom. They > seem to > > > sell for just under $200. Finally Newegg.com always has many used oe > > > refurb PCs Used PCs sourced locally can be a cheap as "free" > > > > > > But 9ld PCs tend to burn up a lot of power. I am trying to get mone > to do > > > "wake on LAN" so it can not use power until I need to log onto it > > > > > > On Thu, Feb 3, 2022 at 6:52 PM Kenneth Lerman <ler...@se-ltd.com> > wrote: > > > > > > > I'm considering converting a surface grinder to CNC. To start, I'll > > > > probably just convert the longitudinal and transverse axes. > > > > > > > > I'll go with steppers for this -- I'm thinking NEMA-42 motors. > > > > > > > > My current Bridgeport clone uses servos and Jon Elson's hardware on a > > > > little Intel Atom Box. I'm thinking of using a Rpi for this. It will > > > need a > > > > minimal display/control panel when completed, but initially will > need a > > > > display with touchscreen or mouse and possibly a keyboard. In the > long > > > run, > > > > some buttons. and perhaps an mpg might be useful. > > > > > > > > I'd like to use a raw Rpi without adding special hardware directly. > That > > > > probably means using a USB or ethernet interface to control the > steppers. > > > > I'm thinking of using Mesa hardware. > > > > > > > > Can someone suggest the most cost effective way to do this? > (Although I > > > > have to admit, that after buying the timing belts and pulleys, the > > > > steppers, power supply, stepper drivers, ..., it's too late to be > really > > > > cost effective.). And the surface grinder only cost me $300. > > > > > > > > Thanks, > > > > Ken > > > > > > > > > > > > > > > > Kenneth Lerman > > > > 55 Main Street > > > > Newtown, CT 06470 > > > > > > > > _______________________________________________ > > > > Emc-users mailing list > > > > Emc-users@lists.sourceforge.net > > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > > > > > -- > > > > > > Chris Albertson > > > Redondo Beach, California > > > > > > _______________________________________________ > > > 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 > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
