LinuxCNC generated resolver output

You only need two analogue pairs. (the third pair is the excitation).

But therein lies the problem, it is likely that the drive samples the output somehow synched to the excitation. If it samples at the peak then that's all fine, but it might not.

What hardware are you using?

The bldc HAL component can be coerced into producing sine/cosine outputs at 120 degrees to each other. This might or might not work with the resolver inputs.

Alternatively a simple custom HAL component can calculate the two 90-degree phases.

The simple answer, though, would be to add a resolver to the motor. Does the drive output quadrature encoder signals by any chance? Many do.

Do you plan to use rigid-tapping? If not then you could simply remove the encoder.

You can pick up resolvers pretty cheaply on eBay (example: www.ebay.co.uk/itm/331998862516 ) though be aware that that might be a 400Hz item and probably isn't brushless. I have one of those in a box marked "£1500 firm price")

lamandesigns wrote:

As far as the controls, I am running 6i24 with 7i48 and another 5 or 6 different cards through the 6i24 as well as serial.

So, the good news is that you do have analog outputs to generate the simulated signal with, so that's a good start.

And chance of piggy-backing a resolver on the existing encoder?

I think the first thing to do would be to see what the excitation signal is out of the drive. (Frequency and voltage) so you know what you are dealing with.

There are some resolvers with a large through-hole: www.ebay.co.uk/itm/1628502898

But it might be more expedient to mount a 1:1 belt drive:
This is the one I mounted for my lathe spindle: photos.app.goo.gl/89usAYUfWn9bkWp38

Tamagawa seem to have pretty much cornered the market. Muirhead / Vactric used to make them for the aerospace market, but those tend to work less well in CNC applications.
You need to know if the drive is expecting a single-turn or multi-turn resolver. Often a 4-pole motor will have a two-cycles per rev resolver, and so on.
(You can achieve that with a single-turn resolver and gearing if you use the belt-drive approach).

Be careful on eBay, quite a lot of people seem to think that it is reasonable to try to sell the outer part of a built-in resolver without the inner rotor.

The ones I am talking about are where they have taken the resolver off of the motor and not noticed that they left half of it behind. A number of the BRX ones on eBay have photos where it isn't clear whether the inner spool is present or not.