On Thursday 19 November 2009, Chris Knowlton wrote: >My name is Chris and I am a CNC noob :-) > >I am setting up a 3 axis router and am getting along nicely, in the build >but since I am using random second hand steppers from a commercial printer, >I am having difficulties with the run time performance of the steppers. > >I have an Aerospace 4 axis controller that appears to be a pretty good > build (ebay store easysupply) but it has dip switches to select the step > configuration for each axis. What I am trying to figure out is: What do > I set them at? This board supports up to 1/16 microsteps. This router > will mainly carve pink foam for detailed casting patterns. > >Once I pick a setting for this, how does that translate to the axis > settings "Driver Microstepping"? Does 1/16 = 16?
Generally, yes. >The motors I have are minebea 23lm-c712-xxx. My understanding is that > these are 1.8 degree, bipolar steppers. They ohm out at 1.2ohms per > phase. I am driving them at the 75% current setting on the board, > supplying the board with 28VDC from a nice switching power supply rated at > 7.5A. On the face of it, that is good. In practice, maybe not. The problem is that these supplies definitely do not well tolerate a motor load that effectively uses the power supply as storage for unused motor winding energy when the current switcher in the driver turns the motors off at the set current. If the supply can tolerate a 4700 or more microfarad capacitor on its output, that would help, but many supplies cannot tolerate it and will shut down if good designs, or just go crazy for poorer designs. Here on this list, we have generally recommended a std, unregulated analog supply. My own, a junk box salvaged old Ampex with even the power transformer misswired in order to get about 28 volts, has a pi section filter, with 75,000 uf caps on both sides of the choke. Overkill by a factor of 3 or 4, but that is what I had. Sufficiently bullet proof that I have also used it as the supply for EDM machining at the same time it was driving the mill. I've since replaced the EDM supply with an 80 volt 5 amp rig, much faster, but gawdawful noisy, it makes my old ears ring and I won't let younger folks with good ears into the building when its running. But I can blow a hole through a 10" table saw blade with a 1/4" brass tube as the electrode, in about 8 to 10 minutes too. :) > I am using the default motor timings from the L297 default > selection because I haven't a clue what to set them to. The L297-298 chipset doesn't to my knowledge do any microstepping, perhaps that is your problem? But that conflicts with the 'aerospace' driver you mentioned above, and which I am not familiar with. Does it use this chipset? I tried to use them early on, but found they simply were not fast enough at switching, and the predictable result was converting a couple of them to slag, at which point I threw money at the problem and bought a Xylotex 3 axis kit. I've since bought a 4 axis too. Quite good drivers in this size range, for either the 262oz motors or the 425's. > My latency > setting is 10000 based on rounding the latency tool up to the nearest 1K. Better than mine by about a magnitude. So my small mill is best limited to about 12 ipm under cutting loads until I find a motherboard with suitably low latency's. >The symptoms are that the coarse feed moves are smooth and seem to work > fine (though with less torque than I expected). The fine g-code steps > just make the motors sit there and vibrate. Experimenting with the > stepmodes made the system make some really exquisite squeals and > vibrations, so I thought I might better ask a question or two before I > hurt myself :-) Generally, microstepping improves the torque, but at low speeds its by percentage points, not magnitudes. I actually lose torque at 1/4 step compared to 1/8 step. At midrange speeds, where the motors are still 'stepping' a step, then stopping till the next step, they will vibrate about the current step position, and at some speeds, this can actually cause the motor to forget which way its turning, or simply get confused and stall. An additional weight in the form of a flywheel with loose parts on the other end of the motor to absorb this vibration can easily extend the speed range to 2 or 3 times the original, un-damped stall speed. This is very important for full and half step lashups, somewhat less so at 1/4 step, and better yet at 1/8th. And I presume even better at 1/16th steps but mine quits at 8 microsteps. >Leadscrews are 2 start 16tpi (so effective 8tpi?) for the two axes that I >have working now. > >Thanks for your attention! > >ChrisK -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> "Well, it don't make the sun shine, but at least it don't deepen the shit." -- Straiter Empy, in _Riddley_Walker_ by Russell Hoban ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
