Can't get accurate spindle speed for both drive gears using 424 with 407

[malcolmmp]

Hello,

I've got a Precision Matthews PM-940M CNC in the garage that I've been slowly getting to work with a PMDX 424 and 407. The original nMotion controller was pretty bad and didn't work with Mach4, so the 424+407 seemed like the right route. After some trial and error, I've got all the motors and limit switches running properly, but accurate spindle control still eludes me.

I' believe I have everything wired in correctly, and I can send M3 Sxxxx commands, and get the spindle running pretty close to the commanded speed, however, I can only get the speed accurate with the potentiometer for one of the two spindle gears. I wired in an optical sensor to the spindle for an Index signal on Input C, so Mach4 is reporting the spindle speed accurately. I assumed that the PWM output of the 407 would adjust based on the Index signal but that doesn't seem to be the case. Am I stuck with a spindle only calibrated for one gear? Or am I missing something or perhaps going about this the wrong way?

I'm attaching some pictures of what seems relevant. If anyone can offer any help or insight, I'd really appreciate it. I really like the SmartBOB hardware and software, and this is the only thing that I can't figure out.

If it's any help, the VFD is a Delta VFD015E21A.

Thanks!
Malcolm

[12strings]

I"m pretty sure the spindle speed control is "open loop" - i.e. there is no correction for measured speed not equal to commanded speed.

[malcolmmp]

Hi 12strings,

Thanks for the feedback. That makes sense if nothing is closed loop. It still leaves me mystified as to how one obtains accurate spindle control when there are different spindle gears. My mill only has two gears, but I know it's fairly common for other mills to have even more than that. I couldn't find anything digging through the Mach4 forums. I might have to register over there and ask some similar questions since it seems to be a little more active. Any ideas on how to get that working specifically?

[12strings]

You may be able to do this with a Lua script, but I 'm not sure.  I don't think you can replace the "S" command with Lua code like you can some of the M codes.  This would definitely be a question for the Mach4Support forums.