6 axis DMM servo setup

If you have PCI slots then it is hard to suggest anything other than the 5i25 + 7i77 combo from Mesa.

store.mesanet.com/index.php?route=produc...83_87&product_id=120

To use the DMM tech servos make sure you get the DYN4 drive as that has a +/-10V interface compatible with the 7i77.

You _could_ use a 7i76 and the step-dir interface to the servos, but that isn't quite so flexible and the 7i76 only supports 5 step/dir channels.

The 7i77 spec is here: store.mesanet.com/index.php?route=produc...83_87&product_id=120
The PCI plug-and-go kit is here: store.mesanet.com/index.php?route=produc...83_84&product_id=214

But you might get things faster from: mesaus.com/index.php?route=product/produ...ath=69&product_id=79

0jw wrote:

I am going to be using 4 of the DYN4 and 2 of the DYN2 drives.

If you are committed to the DYN2 then you probably need to use step/dir or quadrature. The DYN2 has a 0-5V + direction analogue input, but rather scarily it runs at full-speed if this terminal becomes disconnected.

the DMM-Tech DMB4350-8B Breakout Board has a hard slave that frees up an axis that makes it appealing to me.

I would normally advocate keeping as much control "inside" LinuxCNC as possible.

I don't know if the DMB4350-8B is putting out a ±10v so iv sent DMM an email asking.

It doesn't, it is a digital board for step/dir and doesn't do anything clever. If you are using a 5i25 then you should look at the 7i76 daughter board, that has a whole bunch of IO pins, spindle control and 5 stepper channels, for not a lot more than the DMB breakout.
The 7i77 is a servo-version, that also has lots of GPIO pins that the DMB does not.

I'm curious as to why someone would choose analog ±10v to the drives over using steps?

In this case, because the 7i77 has 6 analogue outputs fro servo drives and the 7i76 has only 5 stepper channels. But also +/- 10V analogue works well when the position loop is being closed inside LinuxCNC. It is much easier to tune your system when you can see inside the PID calcs. This fits with the policy of doing as much of the clever stuff in LinuxCNC as possible.

I'm more than a bit confused on all of the analog ±10v, torque,velocity,position servo modes and how that all ties into step/direction, A/B phase quadrature or CW/CCW from the port.

The easiest system to tune is normally a servo drive in velocity mode (velocity loop closed inside the drive) and the position loop inside LinuxCNC. To an extent it doesn't matter that much whether the velocity command is analogue voltage or pulse-stream, though I am not sure that the DMM drives support pulse-stream velocity mode.

Every time I try to look into the A/B phase quadrature I just come up with encoders but in the DMM manual this has to deal with the steps going to the drive with 2 step pins at "90° phase differential". Id think this would have a faster response as it has the shortest Pulse duration.

Yes, though in practice you are always moving very slowly when you change direction, so it probably makes little practical difference.

0jw wrote:

If I close the loop sending the encoder out signal from the drives back to the pc would this then be using RTC?

RTC? If you mean "Real Time Control" then the answer is yes.

I also hope to find a way to run some nema 17 and nema 14 as the 4th and 5th for a different setup where I need very small motors. I haven't came across any industrial servos in this size range other than some pricey Maxom dc motors.
Could I use a 5I25+7I77 and a 5I25+7i76 on the 2 PCI slots so I could run servos and steppers?

You can run a 7i76 _and_ a 7i77 from one 5i25. Or for a bit less money use a 7i78 for the stepper channels.

0jw wrote:

This is leading me to think I should be using position servo mode.

In velocity mode LinuxCNC would send velocity commands to the drive to put the machine into the commanded position.

So. if the machine is where it should be, velocity command is zero.
If the machine is to the left, velocity command is slow right until the position is correct.
If the machine is a long way right, the velocity command is fast left.

For easy PID you want the commanded quantity to be a time-derivative of the feedback.

So, for a position servo system it is nicest to send velocity commands, for a pid-controlled velocity you want to be commanding acceleration (or torque)