Mesa 7i43 + 7i29 (x2)

A friend and I have taken on the task of reviving a dead CompuMill 2500. The controller and motor drivers need to be replaced. The motors themselves are all fine and are 100V DC servos with 500 line encoders. EMC2 will be the controller (obviously, since I"m here ).

We were just about order the CNCDrive Dugong step/dir drivers when I started reading about closed-loop systems. Since I've got working DC servos and encoders, I have a feeling I'd be doing myself a disservice not to go closed-loop (p.s. thoughts on this subject welcome!)

Anyway, I'm a newbie at all of this motion control stuff, but here is what I think should work:

Does that look feasible? Or am I way off base?

Andy and John, thanks for the input!

John, the original drives are +/-10v, though we aren't sure the condition of them right now. But thanks for the suggestion of the 7i33TA; considering how cheap it is, it's probably worth getting one and trying it out.

Regarding FPGA cards, do you (or anyone) have any strong feelings on the 5i20 verses the 7i43? Obviously the 5i20 has 24 more I/O but is also twice the price. Both seem to be fully supported by EMC2. Do you really need more than 48 I/O?

Understood - I'll do some more research on that particular topic. It does look like the specs of the 5i20 are better overall.

The original drives are Baldor equipment (UM3015-100). The motors are trickier, as their internals don't match the label on the outside (not even close). According to Baldor, they are a custom job so were probably rebuilt at some point, but do have both an encoder and a tach. But apparently the mill worked when the controller died, so I would think the motor/driver combo are matched for each other. The tachos were attached to the drives.

Actually, I'm glad you mentioned tacho feedback because I haven't wrapped my head around that yet. Where do tachometers fit into the whole equation? I know they generate a voltage based on speed, but how is that information used?

The 7I43 will be slower than a 5I20 but for a normal CNC servo system running at a 1 KHz servo thread the difference will be negligible
The 7I43 also requires a parallel port that can be set into EPP mode either by the BIOS setup (motherboard ports) or by EMC/linux (plug in cards)
Motherboard parallel ports are by far more likely to work with the 7I43 due to this setup issue, and the fact that the most common PCI parallel port cards (NetMOS based)
do not implement EPP correctly

If you can save the original motor drives you are better off.
You can do a crude test of the drives with a 1.5V battery connected to the +-10V inputs, the drives should run at 15% of full speed
and you should be able to reverse the direction by reversing the battery.

If you use a 7I33TA or 2 7I29s, you will have 24 I/O bits free, you will need to determine if this is enough for all your remaining I/O

Peter Wallace

Thanks for clearing that up, Peter.

If I may, another thing I'd like details on is where the encoders are connected. Mine are differential encoders with normal and inverted channels (A normal, A inverted, B normal, B inverted). Where are these actually connected? In looking at the manuals for both the 7i43/5i20 FPGA and the 7i33/7i29 boards, they all seem to mention encoders, so I'm a little confused.

BigJohnT wrote:

In the case of the 5i20 + 7i33TA you need a 50pin cable to connect the 7i33 to the 5i20 (and one cable for each 7i37TA). Your encoder inputs connect to the 7i33 and the drive +-10v also connects to the 7i33.

So to be clear, the encoders connect to the 7i33, which sends encoder data to the 5i20, which passes it along to EMC2, and that's how the loop is closed?

*whew* I need a diagram or something.

Actually, that's not a bad idea. Do I understand it right for my specific setup?

http://yeup9g.bay.livefilestore.com/y1p73zlDJwEeLpE7L7pfpUb3E3-8K-ally9g7Tunm3gl0E8Kde4Uf3EwYFuc0EMZ_qh6QqdEBHTWMAp_FJCyq6m4zmHMDGtfo2K/diagram.png?psid=1

BigJohnT wrote:

btw, the 50 pin cable is not the ones you find in your computer junk drawer that used to connect your hard drive up.

Of course not.