If you drive two steppers for a X-axis then build a torque dependent e-stop in case one goes limp. You do not want to destroy your setup while one stepper is locked for some odd reason (pick one of 10,000) and the other one is happily pulling things apart. With a setup like the machine pointed out but more robust you will be in servo territory. Expect to switch form steppers to servos at one stage. I know... this is just what you want to read lol.
Rainer
 

yeah, not what I want to read at all.  If I do go servo it'll be a long time from now.  Already invested in all the stepper hardware.

Hmm, torque dependent e-stop.  Do you have a link for that kind of part?

Barry 

I'm curious too. Just what is a torque 'dependant estop' and what would you use to trigger it ?

Tweakie.

uhhhh i think my roland operates on similar principal for finding its home.. its controller board registers a high peak in the motor "voltage/ampage/wattage??"  when it slams the table into a stop.... basically measuring when the stepper stalls and sends a signal to stop driving it and then marking that position as "home"  thats good for about 0.3mm accuracy as a "home" position measurement... i hate my roland...

What made me curious is that from my experience stepper motors (unlike dc motors) do not draw any more current when they are stalled than when they are running (assuming that the driver is still sending current to the windings). Now I wonder how Roland detect the stall.

Tweakie.

lemme ask my guy.. who likely is on this forum too as he has mach controlled mills too.. hmm lemme serach my other forum.. may find info there too.. hang ten

ok .. he calls it  "current sensing"

i post a quote .. excuse me mark for quoting you here without checking with you first

Quote

"Current sensing, used by Roland to indicate a MDX-15/20 limit has been reached, is a recognized method, but is widely thought to be a poor trade-off in performance for economy. If you do accept the trade-off, then the rough design of the stops is still ... ermmm ... stunning"  and "When they collide, the stepper current goes skyward, the MDX electronics sense this and shut down the homing cycle. Then the MDX moves off the stop (a different Y amount by a matter of 4mm depending on whether it's acting as a mill or a scanner) and says to you "I'm in the VIEW position!" so you can then UNVIEW the unit and watch it go an exact distance to 0,0."

and this from Ken .. mwaaaaaahahahaahaha

Quote

"If I am understanding things right, are you saying the "faux limit switch" is actually two hard metal pieces that crash into each other and stall the motor out?
If so, why in the world didn't roland invest a few pennies into some cheap micro switches or even a few dollars into some proximity type switches to avoid homing and zeroing problems?"


so basically i went from a mill that crashes 2 plates into each other and registers a motor stall as a homing signal to a Minitech with 1 micron accurate Omron switches...   you think im happy???


Betcha Ass I am!!

Thanks for going to all that trouble Chris.

Tweakie.

no trouble dude.. i used to have a life, regular sex and party and all that stuff.... but then i bought a mill.. now i have a keyboard glued to my fingers and wax dust in my hair.. and i look a little like a deranged mental asylum escapee with bad dandruff...

no trouble at all!

Heh, I'm right there with you Chris.  I'll post some more picts this weekend.

Btw, a question was asked before what toolpath generator to use.  After some research and talking to friends, I think I'll use linuxCNC for toolpath, and Mach3 for controlling.

Barry