That's exactly what I had in mind! He uses two air cylinders and has the spindle brake so he can turn the nut until it engages. That's been one of my problems with nut rounding happening when the impact wrench doesn't set the socket properly and then spins.
Or, now that the nut is a bit damaged, jams when down and then pulls out of the 3/8" drive and stays stuck to the draw bar nut. Eventually I'll have to replace the draw bar nut.
I don't have an encoder on it. Just one PPR pulse with hall sensor. I do have a sensor for socket all the way down.
I've also whipped up a drawing and G-Code for a spindle lock but haven't actually made it yet.
Here's a JPG of the assembly. The shape of the lock has changed a bit but you get the idea. Having a spindle lock will make even just manual operation easier.
And I had thought about using a DIP relay to switch in a different current limit resistor just as he did. But if I have a processor available that can do PWM or D/A then I have much better control over torque.
I've been in contact with H.O. with respect to his MicroChip PIC version of the HP_UHU micro-controller. To see about adding a torque mode motion.
I have some time. It will be a while before the planetary drive arrives. May turn out that 25:1 isn't going to be enough. I'll worry about that later.