"DoN. Nichols" wrote:

On 2010-07-09, Karl Townsend wrote:

But how does the control tell the drive what speed to use, if the
drive is in torque mode?

I do not quite understand this.

i

The control is smart, the drive is dumb. The control only tells the drive
what to until the next refresh. The control looks at actual position vs.
command position, acceleration, etc. and makes a decision for how much
motion till the next refresh to solve the positioning problem. The dumb
drive just gets a voltage and does what its told.

In which case, it is possible for the computer acting as the
control to lock up (BSOD for Windows) just after issuing a command for
high torque, leaving the motor running quite rapidly until it hits a
stop.

Less likely to happen with the linux backed EMC, but still
possible if there is a hardware failure in the computer.

This is where watchdog timers come into play. I presume the I/O boards
Iggy is using have such a feature since the ones for Mach3 do. The
watchdog timer monitors a signal from the PC that is supposed to cycle
continuously as the program operates normally, if the signal doesn't
cycle in a second or so, the watchdog timer times out and forces an
E-stop.