Quote Originally Posted by irving2008 View Post
The drive current is unlikely to be the reason for missed steps. What optoisolators are they? More likely too much preload is stalling the motors or your parallel port is 3.3v out and BOB is expecting 5v signals.
Hi,

I check through the bearings yesterday and there were some bearings that were too tight indeed. Not sure what optical isolators are without opening the drive but the drive datasheet gives max 16mA per channel and the bob Schmitt gives a little over 7mA sourcing current.

I have a transistor system built to sink current from the ena-, dir- and step- such that I can wire the ena+, dir+ and step+ on drivers directly to 5v using the bob step dir ena to trigger the gates. Between the two I think I should have solved things but need to test it, I also ditched my mach3 machine and built a new rapid linuxcnc box that should help, my other machine was borderline. I scoped the output yesterday from the parallel port and it is putting out 5v.

The current sink arrangement was just confusing to me, I'm more used to working with n channel circuitry vs p channel I guess. the transistors gating the ground should solve things with minimal re-wiring and they are able to rise in 80-90ns and fall in 32ns so shouldn't impact timing.

thanks for the help, appreciate it, il report back when I get things tested,