[sbalder]

My Viper 200 Servo Drivers arrived the other day and I have had the chance to work with them over the past 2 evenings. I thought I would post some of my experiences and I encourage others to do the same.

These will be for a Milltronics Partner mill that I am restoring. I am using the original DC brushed servos, made by SEM, rated 4000RPM at 140Volts and 11 Amps. One motor had a bad encoder, so I have replaced all encoders with 300-line units from US Digital. I have worked with several stepper systems before, but this is my first experience with servos and I am learning as I go.

I started by making a power supply and the necessary cables. Larken included all of the mating connectors for the board to make it easier (although I do wish they had included enough jumpers for setting all parameters on the board- c'mon they are like a penny a piece!) Salvaging transformers, caps, and a rectifier from the Milltronics hulk I built a power supply that runs on 120V and outputs a clean 86Vdc. This should give me about 2500 RPM or 250IPM as the mill is currently geared- well more than enough speed.

The instructions are adequate, but not exceptional. I'd suggest a few changes:
+Adding to the "connections" photo explanations of all the lights
+Better details on configuring the pc terminal program (including a screenshot)
+A true step-by-step set of setup instructions (or even an online video!)
+Clearer instructions on how to wire encoders with only one wire per channel

My testing: I hooked everything up, testing the low voltage control stuff first. The pc interface using a serial terminal works well and provides nice clear information. The default values in the drive were set way too high, causing an oscillation (I=6). I hooked a function generator up along with some switches to provide manual step and direction for testing. Upon first startup the motor shook violently, and I reversed motor connections per the manual to correct the condition.

I fumbled blindly through my settings, not knowing what is "normal". I wound up with P=700, I=1, and D=1400. This gave a strong motor hold at stop, a crisp stop from 500RPM, and no unwanted oscillation or humming. I've looked at current/response curves on different websites, but was unable to get my oscilloscope to pick up a clean trace. I'd like a slightly more scientific way to test my settings other than "that looks about right". A test point that I could hook my scope to, like in the Gecko drives, would be nice.

All in all, a nice product so far. I'll post more as I get more experience.

[Larken]

Wow, it didn't take long for you to get it running. I just mailed them last friday.
Have you got the mill moving with mach 3 yet?

Don't forget to connect the fault output back the the Estop, so it stops your machine if you overload it.

[sbalder]

Like I said, they were easy to setup so it really didn't take long to get them running on the bench. The mill itself is still in pieces completing the restoration so maybe another week or so. As for software I am sticking with TurboCNC for a couple of reasons.

Do my PID settings seem reasonable or are they too high? Also, is there a way to test or tune these setting that is better than "feel"? I tried to hook up a scope to measure current where it would do a single sweep when the direction is changed, but mine requires the external trigger to be on the same ground path so I couldn't make it work.

[Larken]

Do my PID settings seem reasonable or are they too high? Also, is there a way to test or tune these setting that is better than "feel"?

No, they seem about right. Did you change the L (looptime) parameter. This is the one that adjusts to the motors responce time.

I hope to have a software tuning program that displays error vs time soon.

What diameter are those motors ? size 42 or bigger ? I was looking to buy one of those mills for my shop years ago, but bought a Leadwell V40 instead.

[sbalder]

These servos are Nema 42, I believe. I moved the loop timing up to 5 and found 0 to be the best "I" factor.

Being a novice to servos I didn't think about using the servo error reading for tuning. I wrote a simple VBA application in an Excel workbook that reads the servo error 1000 times. While it is running I switch on the pulse generator (to start the motor spinning) and flip the direction a few times. Then it is simply a matter of plotting the direction change. Based on this I increased my Derivative 100 points and got what I hope is a nice pattern:



The servo error hovers around 70 while running. For fun and education I put in some deliberately bad parameters just to see what it would look like. Here's a P of 100 and a D of 200:





The curves look about the same, but the error hovers around 500!
Then I set a moderate P (400) and a very low D (100). Here you can the servo underdamped as it oscillates back and forth during a reverse:








Anyone who wants this spreadsheet please send me a PM.

[Larken]

So, your reading the error over the serial port? How many times a second? Does it do the HEx to decimal conversion ?
Are you getting a good comunication with low error rate. I program mostly in Delphi for the PC, but i don't have a good serial interface routine.

I am going to add a FeedForward setting soon to reduce running error. Without a Feed forward, a step/servo will produce a error proportional to speed.

[sbalder]

I am reading the error through the serial port. I moved the application to Visual Basic 6 so I could add time measurements and got an average of 47 milliseconds per reading with a standard deviation of 6 milliseconds. This is about 5 readings per second slower than just in the VBA Excel worksheet, so I am inclined to keep it the worksheet where I can get a solid 25 readings per second. This is not stunning resolution, but I think it is adequate for tuning purposes.

The program reads the returned text string, and parses it into the Excel workbook. Then I use the Hex2DEC worksheet function to convert the output into decimal. I'm most comfortable with graphing in Minitab, but obviously once this data is in Excel you can use Excel's graphing functions to make the same kind of charts.

As for the serial interface, I'm kind of a newbie at that kind of programming. I came across an ActiveX freeware control that is similar to Microsoft's non-free comm control called NetComm. Anyone using my application would have to have to download and install this control here:

http://home.comcast.net/~hardandsoftware/NETCommOCX.htm


I put the Excel workbook application here:

http://www.geocities.com/eba1972/ViperServoAnalyzer.xls

[DennisCNC]

How is this project going?

[sbalder]

I have had to put more work into the basic machine than I thought I would, taking nearly everything down to the castings for cleaning and refinishing. If this thing was any filthier the Discovery Channel would be featuring me on Dirty Jobs!

I'll have the basic machine assembled by the end of the weekend, all repainted and with servos, sensors, and lubrication installed. Then I can finish fabricating and installing the electronics!

[sbalder]

Wow how my life is passing me by so fast! I can't believe it was 6-29 when I last posted on this. I got diverted on several other projects and the work on the Milltronics mill took more effort than I thought. Anyway last night I finally finished the mill and got everything working! The Viper servo drives have performed well in initial tests, but the Y-axis was "jumpy" and weak at low jog speed only. Hooking the serial cable up I was able to adjust the parameters (mostly lowering the derivative) and got all 3 axes running.

This weekend I'll finish fine tuning and cut some test parts. I'll post a few pictures of the final setup.

[sbalder]

I got to work this weekend and tied up all the little loose ends on the mill project, such as calibrating each axis and cleaning up the horrible mess I have made in my shop! Anyway here are a few pictures of the completed mill/electronics setup.

[routerman]

Nice job, looks clean. What program is that running ?

[sbalder]

Nice job, looks clean. What program is that running ?

Thanks! The software is Turbocnc set to boot when the computer turns on from the USB drive. Once booted the USB drive can be removed and used to transfer files from the design pc.

Besides the fact that it is the software I started with, I have adopted the personal philosophy that cnc controls should be simple and embedded like the programming on my microwave oven. I've grown a hobby into a part time hobby business and I will be selling this machine. Keeping costs in line while still not limiting my customer base is important. With this setup the buyer is guaranteed a great working system with an easy to use interface. If they ever want to run any of the other pc-based cnc programs like emc, mach, camsoft, etc. all that is needed is to add a hard drive and operating system.

It's funny because the Windows-based programs offer some beautiful features that make the DOS environment of Turbocnc look quaint. But... the user interface of Turbocnc compared to the original controls on a Bridgeport Boss (or even the Milltronics Centurion V control on this machine) is like the difference between the Wright Brother's Flyer and a 747!

[bbrreid]

Nice looking job
I cant even get a reply from Viking.I want to upgrade my 4 Boxford lathes that have
SEM motors mt30e4-52 with Norwin drives which I did want to replace with the Viking but now having second thoughts after reading your post on setting them up etc.
I dont know much about electronics so what chance do I have getting them up and running.
I need one fixed ASAP for a long running job I am about to start and the Boxford would take the load of my Mazak lathe.
can any one suggest a good drive for these motors . 140v dc brushed.
spec at www.sem.co.uk

[sbalder]

I did want to replace with the Viking but now having second thoughts after reading your post on setting them up etc.

Instead if Viking do you mean Viper?

Anyway my post was not meant to discourage anyone away from these drives, but rather to show my experiences. Overall I am satisfied with the value of this product for the money and would/will purchase these again. I don't feel like they were significantly more difficult to set up than the stepper drives I have used in the past. With any step and direction type drive you need a power supply and a signal source. With servos you will also need an encoder properly hooked up and with these drives you will need a pc for tuning.

My philosophy on retrofits has been to rip nearly everything out and start fresh. There are other on this forum with good experience keeping older control electronics and fitting in new drives. In your case I would seek out someone experienced with the controls on your machine to see if step-direction drives like this would work. Good luck on your project!

[bbrreid]

Hi,
thanks for the reply,you are right I did mean Viper.
everything is in place power supply Heidenhain encoders attached to leadscrews, Mach3 ,
and busy playing around with Skyko cards and getting nowhere fast,the motors are ok the drives work sometimes but dont talk to Mach3 without the Skyko boards and I dont have time to fanny about with this its not my hobby I just want the boards plug them in tune them and start producing components

[Larken]

i cant even get a reply from viking.i want to upgrade my 4 boxford lathes that have

I reply to all my emails. Did you send it to [email protected] ?

Let me know if you need any drives.

Larry Kenny

[bbrreid]

Hi Larry,
yes I did but I may have made a typing error this is the basic email I posted :-
Hi,
I am in the process of upgrading my Boxford ACL cnc lathe which has
2 OFF SEM servo motors model No. MT30E4-52 info at
http://www.sem.co.uk/files/brochure/MT30E4.pdf
with old Norwin drives info at www.norwin.co.uk
I will be running it from a PC with Mach 3 software as the old ANC control has expired.
I have 4 machines for upgrade and need at least one up and running ASAP.
can you please advise and a price and delivery to
Dundee Scotland
Best regards
Brian Reid
[email protected]

[Larken]

What powersupply voltage are you running on the Boxford ACL cnc lathe ?
The Viper 200 is rated at 25 amps@ 180 volts.

I checked and didn't recieve an email before, but i received one from you today.

That link to the Norwin servo amps gave me an idea for a better mounting of my drives using a plate on the side for rack mounting. I will post pics of the new drive.

Larry K

[bbrreid]

Larry,
not at workshop today but I have some pics of the wiring for the machine here
http://www.cnczone.com/gallery/showphoto.php/photo/3667

I'm not very good with electronics. the Boxford is a 3 phase machine if you look through the drawings you may get an idea from them.
2 of the machines have a gearbox with a normal spindle motor the other 2 have
a large servo motor and drive. the machines with the gearbox have been updated to encoders which are on the end of the ballscrews the others have glass scales.
I woul like to start with the encoder machine first, I think this might be the simplest. I will gather more info on Monday when I'm back at work.
Brian