Compumotor OEM750 settings

[BrassBuilder]

I have a two Compumotor OEM750 drives that I am trying to figure out the switch settings to go with my Pacific Scientific PowerPac hybrid motors. Here are the ones I am having problems with:

Resolution (Steps per Revolution): The default is 25,000. There are a lot of choices between 200 and 50,800.

Waveform: Default is -4% 3rd Harmonic. There is also -2, -6, -8, and -10% to choose from.

Automatic Standby: Default is Full Current. Others are 75, 50, and 25% current.

Current Loop Gain: Default is 8. There are 1, 2, 4, 16, 32, 64 to choose from too.

My motors are:
N33HCHJ-LNK-NS-00
N32HCHK-LNK-NS-00

All advice is appreciated!

Thanks!
Mike

[derekj308]

Hi BrassBuilder

Those motors you have could twist the arm off a gorilla!

A few questions to get started.

What controller are you using (Mach3, SmoothStepper, ... ?)
What mechanical resolution would you like to achieve eg 0.05mm?
What is your maximum linear speed of each axis (rapid) that you want to achieve?
What gear ratio are you using for each drive?
What pitch ball screw are you using?

Your answers will determine how the drive is set up.

The OEM-750's have current limiting resistors. You don't have to match the maximum current rating of your motor to the resistor selection. You can go smaller to suit your power supply full duty cycle current rating. The great thing about the OEM-750's (and 650 and 300) is that they are current controlled. This means you can use a high input voltage on your drives (75V max on Parker OEM drives) and get an extended torque curves in comparison to lower voltages. The OEM-750's will work b/w 24 and 75 V input voltage.

If you haven't already downloaded a copy of the manual it is linked here http://www.compumotor.com/manuals/OE...tire_Rev_B.pdf

Cheers

derekj308

[BrassBuilder]

Originally Posted by derekj308 Hi BrassBuilder Those motors you have could twist the arm off a gorilla! A few questions to get started. What controller are you using (Mach3, SmoothStepper, ... ?) What mechanical resolution would you like to achieve eg 0.05mm? What is your maximum linear speed of each axis (rapid) that you want to achieve? What gear ratio are you using for each drive? What pitch ball screw are you using? Your answers will determine how the drive is set up. The OEM-750's have current limiting resistors. You don't have to match the maximum current rating of your motor to the resistor selection. You can go smaller to suit your power supply full duty cycle current rating. The great thing about the OEM-750's (and 650 and 300) is that they are current controlled. This means you can use a high input voltage on your drives (75V max on Parker OEM drives) and get an extended torque curves in comparison to lower voltages. The OEM-750's will work b/w 24 and 75 V input voltage.

I'm using Mach3.
Mechanical resolution....I'm not sure what that is...
Max Speed: I'm not too worried about going "fast." I prefer to run the motors at a slower axis speed and not too worried about it zipping along.
Gear Ratio: I was going with direct drive on both axis. Is this bad?
Pitch: I only have one ballscrew. It is a Thompson, but I can't remember the pitch. I haven't bought the other one yet.

I did not realize all of this would come into play on these settings. Is there a good "middle ground" to get me started? Default settings?

I'm just setting these up right now in test mode as my breakout board and parallel cable didn't show up yet.

Will it be a big deal if my other ballscrew is a different pitch?

Mike

edit: I have the manual already. I read it over before I bought the drives.

[derekj308]

The mechanical resolution is the smallest increment of movement you require. For example if you have a mechanical resolution of 0.1mm you can never achieve a dimension of 10.12mm or 28.37mm. You could only get 10.1 or 10.2 and 28.30 or 28.40.

You need to make a decision on your maximum speed. A starting point would be to choose the maximum feed rate you will use and then double that for a rapid rate. Rapid rate is often overlooked when designing a machine but is important to consider if you want to have half decent cycle times.

Direct drive is OK for your application.

Measure the pitch on your screw. Its probably 5.08mm (0.2").

It doesn't matter if your other screw is a different pitch.

derekj308

[derekj308]

What power supply do you actually have, what is the full duty cycle current rating and what is the voltage output?

[BrassBuilder]

Originally Posted by derekj308 What power supply do you actually have, what is the full duty cycle current rating and what is the voltage output?

I have this one from Antek:

http://www.antekinc.com/details.php?p=213
http://www.antekinc.com/pdf/PS-5N56R.pdf

It is a 56V, 8.9A power supply.

I'm thinking the ballscrew was either .2 or .5 pitch. I'll look for that this afternoon. The pitch is how far the ballnut travels on one turn of the ballscrew, right? If so, that should be easy enough to measure.

I'll check my mill for the speed I am running it right now. I'll put the lathe up a little faster than that.

Can't I set the feedrate through Mach3? If so, can I set the drivers at a higher feedrate than I really want and then adjust it in Mach3?

I was going to set this up in test mode this afternoon. Can I just use the default settings on that? The amp default is correct for my motors.

For a little more info. I was going to use Keling C10 break out board with this.

Thanks for the help!

Mike

[BrassBuilder]

Here is more information:

The pitch of the ballscrew is .2

On my mill, I am running the X and Y at these settings (this is from the Mach3 motor config settings):

Velocity inch per min: 21.186
Acceleration inch/sec: 12

The Z velocity is at 7.878.

I would like to boost the lathe up a little higher.

I would like to go to .001 on the mechanical resolution if possible.

Any other info I can round up?

Mike

[BrassBuilder]

WooHoo!

I got one motor running in test mode!

I figured out the Current Loop Gain (that was easy once I found the numbers I needed). But I do have a question on the next motor.

The current loop gain is the Motor Inductance divided by power supply voltage and then multiplied by 364,000.

My power supply is 56V but my motor is 35V. Do I still want to use the 56V for figuring out the current loop gain? I know it says power supply voltage, but I want to make sure before I start wiring.

And will the OEM750 automatically adjust the voltage for the 35V motor even though I have 56V going in?

Thanks
Mike

[derekj308]

Hi Mike

I think your power supply will be just fine. Even though your motors are rated at 6.1A and 5A the output of your PS only being 9A is still OK because the chances of both your drives both drawing enough current at the same time above and beyond 9A is slim given your application. That said, to be on the safe side you can limit the amount of current your drives will draw by selecting appropriate value resistors for the current limiting resistors. The chart is on pg.11 of the manual. I think selecting 5A on the carriage axis and 4A on the cross slide axis seems to be a good starting point. This would mean you would need to set the dip switches on SW3 (refer pg.16 to : dip switch 7 to OFF, dip switch 8 to OFF. This will set your current limit range to be 2.5A to 7.5A. You would then select a 6.8kOhm resistor for the current limiting resistor for the carriage axis drive and 11.5kOhm for the cross slide axis drive. Make the 11.5k by soldering a 1.5k and a 10k in series. Make sure to cover the exposed leads in heatshrink. Now your two drives are set up with a current limit of 5A and 4A.

The next set up is the resolution. All of the questions I asked up front are to assess what resolution you can actually achieve. The limiting factors for microstepping and resolution are the maximum output frequency of your controller (in your case its Mach3), the pitch of your screw and the gearing (if present, not in your case)

Since Mach 3 is capable of outputting 100kHz of each axis we could base our calculation on 100kHz but it may not be necessary to run the controller that hard.

For example, you require 0.001" mechanical resolution. Your stepper motor has (I am assuming) 200 discrete steps per revolution without any microstepping from the OEM-750 drive. With a 0.2" pitch this means that with NO microstepping you can achieve a mechanical resolution of 0.2"/200 steps = 0.001". If you used 10 micro steps per step this would mean you would have 200 * 10 step per revolution which equates to a mechanical resolution of 0.2" / 2000 steps = 0.0001". I think you would be pretty happy with that. This also means that your controller needs to output 2000 pulses per revolution. If you want a feedrate of say 30 inches per minute this equates to 30/60 inches per second = 0.5" per second. 0.5" per second with a 0.2" lead screw is 2.5 revolutions of the screw per second. 2.5 revolutions of the screw per second is 2.5 * 2000 = 5000 pulses per second which is 5kHz. Mach3 is capable of 100kHz. You have plenty of overhead. For your application I would set the pulse frequency of Mach3 to 25kHz and run rapids of 80"/minute which would equate to 13.333kHz. Your feeds can be anything equal to or under 80" a minute.

Assuming there is no backlash in your system you should be able to achieve achieve your desired mechanical resolution of 0.001".

The setting you should use in Mach3 for 'Steps Per' in the Motor Tuning And Setup tab for 10 microstep i.e. 2000 microsteps per motor revolution is 2000 * (1"/0.2") = 10000.

Your screw rpm (and hence your motor rpm since you are direct driving the screw) to achieve a rapid rate of 80" per min is 80"/0.2" = 400 rpm. Stepper motors make very decent relative torque at this speed and the torque will only increase the lower the rpm is i.e. under feed which is where you want the most torque.

I think that 10 microsteps is a good start for your system. On SW2 this means you would set dip switches 2,3,4,5 to OFF,OFF,ON,ON respectively.

The complete settings for SW2 is

1 ON (anti resonance on)
2,3,4,5 to OFF,OFF,ON,ON respectively (2000 microsteps per revolution)
6,7,8 to ON,ON,ON (default waveform, very rarely is this needed to be tweaked)

The complete settings for SW3 is

1,2 OFF,OFF (25% standby current. Try this and if you don't get any unwanted movement all is good otherwise try 50, 75 then full. The point of starting low is to minimize the amount of heating up the motor does whilst it is not required to be moving.)

3 ON (Automatic test set to OFF)

4,5,6 (Current Loop gain - use what you have calculated.)

7,8 OFF, OFF (current range selected as 2.5A to 7.5A)

You will need to set the two trimpots on the top of the drive to remove any offsets between the two phases. This is just trial and error starting with the trimpots in the centreish position and tweak until you minimize the vibration coming from the motor. Use a stethoscope if you are a doctor otherwise use a quality screwdriver as a poor mans stethoscope. Refer pg44 and 45.

WARNINGS

DON'T forget to put the current limiting resistors in.

DON'T operate the drives with the cover off. It is a PITA to be removing all of the wires while you are tuning the drives whilst setting the dip switches but it is safer for you and your drive.

DON'T turn the drive on without the motor connected. Although I have accidentally done it before as have a few of my friends and gotten away with it, it is not good for the drives.

DON'T put any heat sensitive parts near or above the heatsinks.

Especially in your case with high current motors DON'T run the drives without BIG heatsinks and use thermally conductive paste between the mating surface of the heatsink on the drive and the BIG heatsink. If you can afford a cooling fan blowing across the heatsinks and exhausted out the case, even better.

ANSWERS TO YOUR Q's

Yes the OEM-750's will take care of the voltages being supplied to your motors. Remember they are current controlled so what the drive is trying to do is maximize the voltage supplied to the motor without going over the current limit set by the current limiting resistor. Doing this extends the torque curve of the motor without frying it.

Use the 56V input voltage for your calcs on current gain as per the manual.

Tweak your acceleration in Mach3 by changing the accel value to achieve a gradient of about 60 degrees on the tuning graph and tweaking up or down from there to see if the motor 'stalls' or not.

If you need more help feel free to ask.

I think I just broke my keyboard


Cheers

Derek

[BrassBuilder]

Thanks Derek!
That helps immensely. I got both motors tested in test mode and I installed the current resistors before I started. I also made sure to put both covers back on before I ran the test. Both motors did the test just fine. I'm going to be out of town all week, but I am still waiting for the breakout board and the parallel cable anyway. I won't get any more done to this until next week now.

I have a huge tower computer case that I am putting all of my electronics into (including my KB DC motor controller). I was going to make some custom mounts for the OEM750s and mount them where the CD-ROM/DVD drives normally mount. I was not going to use a heat sink on them though, but if I need a heat sink, I can rethink my plan. However, with that, I was also going to use the computer power supply to power 2-3 large diameter 12V cooling fans mounted in the case to get air flow going.

Mike