[beezerlm]

Hi,

I have a dell optiplex 620 (actually 3 of them I got on ebay) and i have disabled hyperthreading in the bios.

On my first test, I opened glxgears, played a video file, and opened firefox all in seperate pages. then I opened the latency test. My base jitter hovered around 11,000 after a couple minutes of running. But if I close the video file and reopen it my jitter jumps to about 29,000.

This computer is going to be dedicated to my machine only. It will not be connected to internet or used for anything else. Should I still base my results on the 29,000 jitter?

Also, I have a couple gecko gx320's I was going to use when I was planning on using Mach 3, but I am considering having the PID loop run directly throught the EMC2 via external IO hardware (Mesa?) Any thoughts on this?

Thanks!!!!

[chester88]

Try getting rid of the on board video. You have any old video cards lying around?

steppers using PID is possible and has been done with EMC. Personally i can't see the point. Or did you mean servos with PID now that would different.
using a board like Mesa will allow you to have higher step speeds regardless if you try PID or not.


Chris M

[beezerlm]

Thanks Chris,

1. Yes I was planning on using servo's

2. Do you have a recomendation on a video card that would work well with my gx620?

3. How does mesa or pico hardware increase the step rate?

Thanks!

Brandon

[jmelson]

Thanks Chris,


3. How does mesa or pico hardware increase the step rate?

Brandon

With the Pico Systems Universal Stepper Controller, EMC tells the board what step rate to produce, and the board counts out the time between pulses from a 10 MHz clock, so the step pulses are timed with 100 ns resolution. Since this clock is different from the CPU clock, the steps are counted and the position is sent back to EMC. This allows you to go to 300,000 steps/second or more.
Also, you can use encoders on the motors so missed steps can be detected.

The Pico Universal PWM Controller has no steps at all, it sends a pulse of varying width to the servo amplifier to control motor speed. You can run brush DC or brushless motors with this system.

I think the Mesa hardware works in a very similar way.

Jon

[chester88]

What John said, he is Pico.
calculating the trajectory is done less often (servo period) then calculating the software stepping rate (base period). With a hardware stepper ( Mesa or Pico card) then EMC just has to calculate the trajectory and lets the card calculate the step pulses.

I don't have a recommendation for video cards though EMC doesn't need fancy ones.
If you have some, just try them. I'll see if I can dig up someone else's recommendation.

What are you going to control?

[beezerlm]

What are you going to control?

Well, I have a Kearny and Trecker Milwaukee-Matic Series Eb, a Moore G18 jig grinder, a bridgeport mill, and a custom built machine for dressing shapes in grinding wheels. All of these machines are in need of a control. I have done a couple retrofits with mach 3 but I am not a big fan of the windows environment for cnc control so I thought I would give EMC2 a go!

So your saying If I use Pico hardware I don't need to pay much attention to the base thread? I think my servo thread was around 15,000. Would that be sufficient to use external stepping hardware?

-Brandon

[samco]

15000 is awesome for external servo/stepgen.

sam

[samco]

^ 15000 is pretty damn good for software generation also.

Love your K&T here is the latest video (don't know if you saw it)


[nomedia="http://www.youtube.com/watch?v=39q6kvrSBSk"]YouTube - Kearney and Trecker CNC running simple program. (tool changing and everything)[/nomedia]

sam

[beezerlm]

Samco,
I did see that video. Very nice Job. I like the rigid tapping. Do you need encoder feedback running straight into emc2 in order to sinc the spindle and Z axis? Blue and Maze......Michigan fan? How much travel does your IIIB have? I think my EB is 24 x 24 x 24.

I was taking a guess at the servo thread number I could be way off. I will check when I get home tonight and see what it really is. Feel like I have been spinning my wheels on this whole latency thing........ I can't wait to get to the fun part!

As for Pico hardware, what advantage does PWM provide over the typical step/direction signal? I am not afraid to spend some money on some good hardware if it will improve the overall integrity of the system. I have only used Mach3 with gecko or viper drives so this stuff is new to me.

-Brandon

[samco]

The K&T is X38,Y36,Z24. The table indexs in 5deg increments.

we are not using step/dir - we are using analog amps with encoder feedback feedback to emc.. (I need 40a drives for the k&t.) I can 'tune' the servo loop for each axis within emc using halscope. (think of it as emc's oscilloscope)

Jon E of pico systems could probably explain why it is better. (than step/dir)

if you go with an external interface - both pico and mesa have good hardware. (I am using mesa - I know people using pico) They seem to be the best supported bang for the buck.

sam

[beezerlm]

Yea I was way off. My servo thread number is about 40,000. Will that work ok with an external interface?

[beezerlm]

After running some numbers, I may not need external hardware for the "Wheel dressing machine" I am building. I was planning on making this machine my first EMC2 project because it is only 2 axis servo, and needs I/O for spindle,coolant, limit and e-stop only. Its almost ready for the electronics to be installed.

Ok, so with my base thread jitter landing at around 29k, I can figure my the step rate for my pc at 1/(29us x 2) = 17,241 steps per second. I have a 500cnt/rev encoder (times 4 from quadrature)=2000steps per rev. Therefore, I can feed 17,241/2000 = 8.62 revs/sec -or- 517 revs per minute. 517 times my lead of .07874" = 40 ipm. Is this calculation correct????? I can live with 40 ipm on this project. I don't really need it to be any faster. most of my feeds will be 3 to 5 ipm with an occasional rapid movement at the end of each pass. I have some .020" precision lapped diaform diamonds in a special holder i will be using to contour the 14" diameter grinding wheel.

I will definately want faster feeds on the other machines - 100ipm minimum

[beezerlm]

Ok, I ordered a 7i43 board to handle my I/O (through parport). I guess it doesnt make much sense to have encoder feedback through EMC2 with step/direction drives. Now I just have to wrap my head around HAL. I can't wait until I understand EMC2. It seems very powerful.

[photomankc]

Just to make certain, is this the PC you are using?

Dell OptiPlex GX620 Desktop PC - Intel Pentium 4 3GHz, 512MB DDR2, 40GB HDD, Combo, Windows XP Pro (Off-Lease) at TigerDirect.com

I have a smaller form factor version that has no expansion ability at all and the servo thread latency on mine is really bad. 320,000. The base thread is actually livable at around 19,000 to 21,000 but the servo thread is rather bad and I want to use the PICO board to get 3 axis plus spindle and charge pump in one board. Since the servo thread is what it is tied to I'm thinking this PC is not really what I want to stick with. If the bigger brother has that low of a servo thread I don't mind springing for one at $150.00

[beezerlm]

Photoman, Yes I believe it is. I think mine have 1gb ram and 80gig hd but I don't think that will make much of a difference. I have attached a pic of the 2 that I am not yet using.

[photomankc]

Perfect, thank you! I got the SFF GX620 for free so I can hand that down to my daughter. It's a shame though, it's very quiet, nice and compact, and had a parallel port but it uses a laptop MB it seems to me and that servo thread latency just can't be corrected so far.

[jmelson]

Just to make certain, is this the PC you are using?

Dell OptiPlex GX620 Desktop PC - Intel Pentium 4 3GHz, 512MB DDR2, 40GB HDD, Combo, Windows XP Pro (Off-Lease) at TigerDirect.com

I have a smaller form factor version that has no expansion ability at all and the servo thread latency on mine is really bad. 320,000. The base thread is actually livable at around 19,000 to 21,000 but the servo thread is rather bad and I want to use the PICO board to get 3 axis plus spindle and charge pump in one board. Since the servo thread is what it is tied to I'm thinking this PC is not really what I want to stick with. If the bigger brother has that low of a servo thread I don't mind springing for one at $150.00

This may not be as bad as it seems. By PICO board I assume you mean a Pico Systems Universal Stepper Controller? With that, you don't use a base thread, which releases a LOT of CPU resources for the servo thread. The UPC doesn't use a "charge pump" it has a dedicated hardware E-stop circuit, with a watchdog to command E-stop if the computer stops talking to it.

Jon

[photomankc]

The servo thread is bad no matter what you do. And when I talked to the Pico systems guy, I didn't like terms such as 'on the edge' and 'maybe you'd be alright'. Seems like that little guy is a lost cause. Got the new bigger GX620 hooked up and the base thread is running great. I can hear the difference in the way they sound at high speed.

The base thread goes to about 24,000 when I just hammer the crap out of the box and the servo thread is about 30,000. MUCH improved. The normal just sitting there and doing not much else base thread is around 12,000. Seems cool to me, I don't do anything else on it when it's running the machine so I'm not sure I need to worry about what the jitter is when I have 2 GLXGEARS and 25 firefox sessions open.

I rebuilt the system with a 64GB Solid State Drive and it's now 22 seconds from power on to desktop. Kinda nice. Also figured less heat and nothing to mechanically fail. She does need a new PS fan though. It's not sounding healthy.