Kstep and Minarik Spindle Drive

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MadTooler
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Joined: Thu Nov 08, 2018 11:57 pm

Kstep and Minarik Spindle Drive

Post by MadTooler » Thu Nov 15, 2018 3:03 am

I am trying to use Kstep to control an older Minarik DC motor drive to control my spindle on an older Sherline mill. I attached the manual for the drive. See pages 11 and 12 for reference.

The drive needs 0-10vDC signal.

After a lot of head scratching, I discovered the drive seems to suck a lot of power from the signal, resulting in only about half of the 10v output.
When I do not have the drive attached, Kstep does what it should. Looking at the drive, I think it may have some isolation circuitry that is power hungry.

Testing with a 9v pack of AA batteries has no problem getting the spindle up to near full speed.

Does this look like I will need to make a FET driver to drive the drive, or do you have a another solution that is not as redundantly redundant :roll: ?

Thanks again for a really slick series of products.
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TomKerekes
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Re: Kstep and Minarik Spindle Drive

Post by TomKerekes » Thu Nov 15, 2018 2:17 pm

Hi MadTooler,

KStep’s Analog output basically has 1K Ohm output resistance so should be able drive that input designed for a 10K Ohm potentiometer directly.

You might disconnect KStep’s Output from the drive and check the voltage with a voltmeter to see if that is the problem.

How do you have it wired?

Post the program you are using to control it.

What are you commanding?
Regards,

Tom Kerekes
Dynomotion, Inc.

MadTooler
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Joined: Thu Nov 08, 2018 11:57 pm

Re: Kstep and Minarik Spindle Drive

Post by MadTooler » Thu Nov 15, 2018 11:22 pm

I did disconnect it from the drive and the voltage output from Kstep was correctly at 10v. Kstep and my code seem to be functioning properly (using your example code with my spindle settings and also have output 255 directly to pwm for confirmation).

When I have the drive wired, the voltage output is essentially 1/2 what it should be. The drive does run with variable speed at and below 5v output, but obviously only half speed max.

I will double check wiring before I post any diagrams, but I believe it is wired correctly. As I noted earlier, disconnecting the drive leads from pins 6 and 10vgnd and supplying them with a 9v battery with the same polarity does drive the spindle near full speed. That said, I hear that same response from so many of my customers before I have to correct the way they have wired their robots. :D

After I double check all, I will post code and diagram.

Would altering the duty/freq of the pwm help if this is a current issue?

Thanks.

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TomKerekes
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Re: Kstep and Minarik Spindle Drive

Post by TomKerekes » Fri Nov 16, 2018 12:16 am

Hi MadTooler,

Here is the circuit.
IsolatedPWMtoAnalog.png
As you can see it has 1K output resistance. I'm surprised the drive seems to have 1K input impedence to divide the voltage in half. You might try your 9V battery through a 1K to see if it has the same problem to prove this.

Would altering the duty/freq of the pwm help if this is a current issue?
No. 255 would be 100 % on with no frequency.

If it is a current drive issue a simple tranistor follower should allow it to work.

Did you try to compensate with the sig adj pot, or other pots?
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Regards,

Tom Kerekes
Dynomotion, Inc.

MadTooler
Posts: 20
Joined: Thu Nov 08, 2018 11:57 pm

Re: Kstep and Minarik Spindle Drive

Post by MadTooler » Fri Nov 16, 2018 7:38 pm

I made a basic follower circuit with a 2222a NPN transistor and a 4.7k resistor. Maybe I need some other components, but this worked. Here is the schematic I followed (image from wikipedia):
follower.png
The circuit seems to work well. If it should have further components please advise.

Turns out my 10v supply is actually a 9v supply. Not sure if that has anything to do with the issues. I will be replacing it soon.

Also, I am not connecting to the 10k pot connectors on the drive. That is internally powered by 3.4v (actual measurement) and requires 10k to function. The 10k pot is also being used as a manual override when switched per the supply pins on the drive. I have connected kstep to the 10v analag signal line on the drive. That is where I have been assuming needs the higher amperage.

Some working data: Directly from the 9v supply measures 9.33v. At the pins 5-7 on kstep it measures 8.95v. I forgot the output on pin 6 when at full, but it was near the 8.95 if not exactly the same. After the follower, it was about 8.33 (.6 volt transistor drop). The Minarik drive has an input adjustment that allowed me to set the 8.33v as full speed, although I will be getting a new 10v supply that will probably result in closer to 9.4v signal.

So I know, what are the min/max voltage and current limits for the analog output on kstep?

Thanks again.
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TomKerekes
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Re: Kstep and Minarik Spindle Drive

Post by TomKerekes » Fri Nov 16, 2018 8:04 pm

Hi MadTooler,

The optocoupler limits the voltage to 35V. The transistors are rated for 0.3A but the 1K resistors limit the current to much less.
Regards,

Tom Kerekes
Dynomotion, Inc.

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