@jjneeb had one for a while on his Mach 4 setup.
Make sure your homing is as consistent as it can be.
On their discord server they have sections for Mach 3, Mach 4, and Centroid. You might look there for more info/help.
Thanks Eric, Yeah I did exchange a few messages with him, watched his videos and asked a few questions and he was very kind and helpful and I really appreciated it. I couldn’t ask him for more! I also spent quite a bit of time with Dereck from Rapid Change on zoom calls but together we couldn’t figure out how to wire it in properly. It was really just a matter of figuring out which I/O ports were which and what type of relays and settings were needed. Truth be told, it’s not Dereck’s fault. 20 years ago I designed and built a 5x10 machine myself that I used commercially for many years. In starting the business up again I decided to just buy the Avid Pro this time because A, if I were to build a new one it would have been pretty much the same, and more importantly, B - for medical reasons I just don’t have the mental energy anymore to do the problem-solving. And that right there is why I need help if I’m going to be able to get this ATC going. Like, step by step instructions. 
I don’t want anyone to take from this that the folks at Rapid Change aren’t helpful or knowledgeable. They are. It’s just that they didn’t happen to have an Avid machine at their disposal and that the info they needed on the circuitry was a little deeper than what was in the Avid docs available. I’ve been hoping that a bunch of people would have done it by now and there would be a forum or that something resembling an idiot guide would be out there somewhere.
I used Mach 3 on my first machine. This was quite some time ago. There was this guy who was on CNC Zone forums named Gerry who made these screensets that had all kinds of useful code imbedded. I bet you that would have been helpful for the issues you describe. The MTC routine was complete and easy to edit. Thanks Gerry if you’re out there!
We have full schematics available for both Mach and EX controls right here:
Rapid Change should be able to easily interpret these and give you step by step instructions. This is exactly what these schematics are meant for.
Which rapid change model do you have? I got one with a retracting lid, and a ir sensor. The retracting lid moves correctly but I currently have it off the machine as it was more hassle than value. If you forgo the retracting lid the most you need to wire up is the sensor.
Yeah Dereck and I were able to get the retracting lid working on mine. at least, for sure it was moving. It would move every time I turned the machine on. I just looked it over and I don’t see a model number on it anywhere. If my memory serves correctly we couldn’t get the IR sensor working . I honestly don’t remember what (if any) other I/O it has. We didn’t get to a point where any functionality could be tested.
I found that I had an incredible amount of noise on the ir sensor line. I wound up having to increase the debounce settings on mach 3 and smooth stepper. If you are a brave sort of guy you don’t even need the ir sensor. If you go that route you need to be prepared to hit emergency stop any time there is a too change, or modify the script for a visual inspection that the tool has been removed.
Send me an email in a week (I’m out of town this week) and let me know what you got working and what is not working. I can’t remember how much documentation I sent you and how far we got with this (I talk with a lot of people on line and can’t remember the details of each one 
).
jim