Reality check please

[pk7639]

Hi, I've just bought a 6DOF robot arm that I intend to drive with EMC.
I have a reasonable background in small machine conversions and fabrication (My CNC Adventures), have done a lot with Mach3, and am comfortable building the PWM amplifiers.

This will, however be my first implementation using EMC so there are some things I'm unsure of.

Can anyone
A. Confirm that a Mesa 5i20 card can generate 6 pwm outputs, read 6 encoders and have some IO left over?

B. Suggest what level of PC processing power would be appropriate for closed loop control of 6 axii?

Many thanks in advance

PK

[chester88]

A 5i20 ( with firmware SVST8_4 down-loadable) can have 8 encoders and 8 pwm and will have 24 I/O points still available.
Since you are probably not going to use the 7i33 card ( DAC and encoder filtering )
you could set this same firmware to have 6 encoders and 6 pwm with 36 I/0 points.
but don't you need an encoder for MPG jogging?
Other combinations are possible - Mesa stuff is very configurable.

I assume you mean processor speed. More important is latency.
Not all computers have good latency you really need to check the actually equipment you want to use. there is a latency test that comes with EMC.
Here is a user made list of equipment with latency figures:
EMC Documentation Wiki: Latency-Test
Now after latency is good then more processor speed may help the response to non realtime stuff like the screen controls etc.

There are some videos of robot arms with EMC:
EMC Documentation Wiki: Videos

Welcome to EMC.

Chris

[chester88]

I might add about latency figures.
The number to compare is the max jitter of the base thread (25us)
Most of the docs talk about this number in respect to software stepping.
You using a hardware card so can get away with more latency.
Under 100Us of jitter is usable but well under 50 should be quite possible.
Note there are tricks to fix some latency problems. read the page i posted link to.

[pk7639]

Thanks, but that only seems to relate to generating accurate step and direction signals.

In my setup the mesa board will just be getting it's PWM registers updated and it's encoder registers read. Most, low end, servo drives update their PWM output at aout 1-2 KHz. Surely all EMC has to do for me is update 6 PID loops at aout that rate?
PK

[chester88]

Latency is important either way. Just less so for servos.
EMC reads the encoders from the Mesa card calculates the trajectory calculates the PID and then outputs to the Mesa card for pwm.
This must be done in a regular, consistent cycle.

Thats why I said the latency numbers could be _much_ higher then what is recommended for software stepping.

[Zig]

I have just upgraded the CPU ( Athlon XP ) from 2000+ to 2500+ on an EMC /Mesa 5i20 combination.

It is driving a gantry system with linear motors ( iron cored and coggy).

The difference in performance of the motors is noticeable. Their motion is quiter and smoother ( at 8000mm/min and 3000mm/s/s)

The faster cpu is giving me an improved latency figure and the screen is much more responsive.

SO You do need good latencyfigure and good numbercrunching performance.

I have just acquired a HP xw6000 dual Xeon 3GHz machine ( second hand for under $200.00 ) whihc is giving exceptional altency typically under 5000 ns with odd excursion up to 15000ns. Hope to see some improvement in linear motor performance.

[ftkalcevic]

I'm using emc to control my lathe - 3 axis servo, 5i20, 7i33, 7i37. I'm using an intel D945GSEJT, which has a 1.6GHz atom processor, in an M350 case.

It all runs fine.

I'm in the process of upgrading my router (6 axis - x, y1,y2, z1,z2, a) using a similar set up - same board and case, with 5i20, 7i33, 7i37, 2x7i40 (each axis has a different type/brand of motor). I've only got one axis moving at the moment, but I expect (hope) it will be fine.

[pk7639]

Thanks for the feedback. I'm on the way to getting it going:
I have the 5i20, a shuttle PC (latency counters both run around 9000nS)
I've done a design for the PWM amp based on the SA57 driver IC, parts should be here tomorrow.

Don't suppose anyone could point me at the doc that has the pinouts for the 50pin connectors on the 5i20 when running the 8 servo, 4 step/dir firmware???

TA

PK

[ftkalcevic]

On the mesa website, Mesa Electronics, you can look at their hardware manuals to see that.

The manual for the 7i33, http://www.mesanet.com/pdf/motion/7i33man.pdf, shows the 50 pin connector when used for a servo (4 servos - pwm + encoder + enable)

The manual for the 7i32 (stepper card), http://www.mesanet.com/pdf/motion/7i32man.pdf, shows the same pin out, so I don't know how the connector maps for a stepper driver.