"I am about to order a 4-axis controller and four 305oz-in steppers (hobbycnc.com) with a 32Volt unregulated power supply."
I would not recommend this kit (unless you do the mod below)....I have the hobby cnc pro and it finally works correctly after I had to modify the circuit to let Mach 3 control the motor current.
Thank You Gary!!
http://www.cnczone.com/forums/showthread.php?t=49043
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The problem:
So, why is the HCNCP's timer set for ten seconds? I suspect the reason for that is because the timer-sync function has been bundled with the current reduction function. Remember, the timers for each axis are independent, so, if there is no activity on one axis, it could go to reduced current while another axis is in motion. Due to a total lack of experience in such matters, I can't say for certain, but it seems to me that you would always want all axes at full current while any are in motion. And, I believe this is the reason for the '10-second' timer on the HCNCP: If any one axis is idle for ten seconds, it's likely that all cutting and motion has ceased, and it is OK to reduce the current.
That's probably a pretty good assumption, so why is it a problem? Well, the issue is, that it is the step pulse that triggers the timer, turning off the sync and restoring full current. That step pulse also goes directly to the driver chip, which immediately starts the commanded step, and that action doesn't wait for the timer/sync/current functions to return to a normal operating state.
So, what happens is, you have an axis that functions normally most of the time, but when it has been idle for ten seconds, it stalls when attempting to begin motion again. This apparently happens because the current ruduction or sync functions have not really turned off when the step action starts. The common suggestion is to "reduce the acceleration" or "reduce the step rate", which is an attempt to slow down the initial motion to allow the circuit to 'catch up'. Apparently this is inadequate in some situations, or the driver software doesn't support it; regardless, it's what's technically known as a 'kludge'.
The difficulty in diagnosing this problem is that it manifests itself differently on different systems; and all systems are different: Different motors, screws, nuts, lubrication, cables, masses, voltages, currents, etc. Some will never see an issue, while for others it appears to be a persistent problem. In testing on my own system, it's pretty easy to set up a step rate and acceleration that will jog reliably when there are no delays between jogs, but which will nearly always stall when attempting to jog after a 10 second idle time. This can be nearly always fixed by reducing the acceleration, or, by disabling the current reduction (placing J4). Since the problem is fixed by disabling the current reduction, we can be pretty sure that sync is not a part of the stalling problem (disabling current reduction does not affect the sync function). The question is though, why, should I have to live with reduced acceleration all of the time to accomodate this single problem case, or, why should I have to forego the temperature reduction advantage of a reduced current control to get back that acceleration?"
http://www.cnczone.com/forums/showthread.php?t=49043
Hope this helps,
Robert
