Current Reduction, HobbyCNC - Mach3

[gacrwell]

The HobbyCNC controller has a current reduction feature, that works independently on each axis. After 10 seconds (the time can be altered by changing resistors) of no step activiy on an axis, that axis will go to 50% current.

The question I have is, is this something that you normally want to do on the axes independently? If you're doing a long straight or constant depth cut (2.5D axis router), do you really want an axis to go to half current while the cut is still in progress? I suppose with a 10 second delay, it really doesn't happen that often during a cut - normally the reduction would come on when the machine is idle. But still, wondering...

And one reason I wonder is that I notice that Mach3 has a currentH/L output, but I never found out much about it in the documentation. Since it's only a single pin, it is necessarily intended to perform a current reduction for all axes simultaneously. Is there any information on how this output operates? I presume it reduces current when all axes are idle, and since it 'knows' the code that's running, it can idle them immediately when a pause or end of a program occurs. I also assume that it brings the current up some time before an initial step (how much time before?).

The HobbyCNC instructions suggest that you might want to reduce initial acceleration, so as not to miss a step when starting at half current, since the current won't go full until sometime after the first step. If Mach3 were doing the current controlling, this shouldn't be an issue.

It doesn't look like it would be difficult to modify the HobbyCNC to use the Mach3 current control pin, if it works like I think it does.

Gary