I modified the 1.7.1 version of the plugin a bit so that it sets RTS high when sending, and otherwise keeps RTS low for receiving, so that it behaves with dummy RS485 converters.
It's a quick hack, and I'm not sure if royaumedeole would approve releasing this, but if there's an interest in this, I can link it.

Awesome plugin and glad there are people like you who put time into this stuff!  I got it working and love the added e-stop trigger features!  Issue I run into is I have to engage an e-stop and then reset it before I can engage the spindle a second time.  First time works like a champ, second time it does nothing until I hit reset and then reset again.

Thoughts?  Would noise cause this kind of behavior?

I think the issue I mentioned before is the same as yours. I was finding on the first run, the spindle button in mach3 flashes for a couple seconds, the spindle does nothing, then it goes to estop because it cant detect any spindle movement. But then when you un e-stop it and try again it runs flawlessly. It has never not worked on the second try. This sounds very similar to your issue, and my "first time running" might not even be the first time, it may actually be the second time like what you're experiencing.

Ill have to check again, but from what I recall I think the VFD "clicks" like it received a signal, but the motor doesnt move at all. Until, like you said, it e-stops and you clear the e-stop, then it runs flawlessly

Seb: Do you have any idea whats going on? Maybe a variable in the code isnt reset after the first successful run or something?

I modified the 1.7.1 version of the plugin a bit so that it sets RTS high when sending, and otherwise keeps RTS low for receiving, so that it behaves with dummy RS485 converters.
It's a quick hack, and I'm not sure if royaumedeole would approve releasing this, but if there's an interest in this, I can link it.

How did you modify, do you have the source code?
Nosmo

While setting up this plugin, I had a problem getting the motor to even run. I played with it all day, only to find out my spindle motor burnt up. Now I don't know if it was caused by the plugin or if it was on it's way out beforehand. The spindle ran fine before the plugin was installed. I installed the latest version, as well as the C++ file and driver for the usb rs485 adapter. After the plugin install, It recognized the settings from the VFD and showed up after the install. It took me a while before I realized I needed to set a speed in the box first before I tried to turn on the motor. Once I did that, it ran, but very erratic. After a few tries to get it to run faster, it just died.

Long story short, after taking apart the spindle motor, with plans to rewind it, I found out that the Chinese 1.5kw water cooled motor is not a four pole motor. The VFD comes preprogrammed for four poles. The motor I have is actually a two pole motor. Now I don't know if that makes any difference, but I thought I would mention it, so others can check their VFD for the right set up. The VFD comes preset for four poles and should only make the motor run half speed. Set for two poles will make it run twice as fast.

Right now, I have my motor all ready for the rewind. I just got my wire yesterday and will start turning soon. Just for those wondering, my motor is over three years old, but only has 10 hours or less on it.

Don

Another issue is that the min freq has to be set otherwise if trying to run lower rpm will burn the motor out, it lacks sufficient inductance at any lower frequency.
IIRC it is PD011.
N.

Is there a particular RS485 adapter that is recommended? I have one of those cheap black USB ones ( http://www.ebay.com/itm/331071937819?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 ) and Mach3 runs unstable with it. I will lose steps occasionally. It gets worse with higher kernel rates. It does not happen if I disconnect the USB adapter and operate the VFD manually. I was thinking about getting a RS232-RS485 adapter instead. Is this a good one? http://www.ebay.com/itm/190380830801

Maybe it's not the adapter after all. I don't know. Here's a video showing the difference between having the plugin disabled, and enabled. That's the only difference between the two parts of the video. http://youtu.be/wOzXPzTsmVE

Check this one out. I have been using this one since 10/2013 and have not had any problems at all with my VFD and spindle. Far better than the black junk one, it went in the trash.
You will need a cable, it uses the same cable that is on my Dell printer. It has about a 1/4" or 5/16" square plug on one end and USB on the other.

http://www.ebay.com/itm/KMTronic-USB-One-Relay-Controller-RS232-Serial-controlled-BOX-/271361447833?pt=LH_DefaultDomain_0&hash=item3f2e671799

Sorry I listed the wrong interface ...............this is the right one

http://www.ebay.com/itm/KMTronic-USB-to-RS485-FTDI-interface-Converter-BOX-/271389457726?pt=LH_DefaultDomain_0&hash=item3f30127d3e