Birthday serial number #26 - Round Rock, Texas
 

As I mentioned in another thread, I've been lurking for more than a year.

Well now I am ready to start to build the MechMate. I plan to start with the kitchen table project for the basic check-out of the control hardware and software.

For the kitchen table project, I have:

3 OM Vexta motors (explained below)
1 PMDX-122 BOB
4 Gecko G203V (standard) drives
2 test power adapters (12VDC, 24VDC (as a test Power Supply as suggested by Marcus))
Mach3
PC running Windows XP


Regarding the OM Vexta stepper motors, I got the chance (Ebay) to purchase 3 OM Vexta stepper motors for $125 total, including shipping.:D
I know, I know, Gerald's warning about USED motors that you don't know the history of. But this was too good of a deal not to give it a try.

These motors are removed from a parted-out ShopBot.
One of them is a PK296A1A-SG3.6 which we all know pretty well based on this Forum. Two of them are A6497-9412KTG's. Most of you know this is the "custom" motor built for ShopBot that is described as "similar" to the PK296A1A-SG3.6. I will possibly get two more similar steppers from the same source at a similar price. Could happen. May not. If I don't get them, I'll purchase a new PK296A2A-SG7.2. I know, I know Gerald's warnings about mixing motors. But this was too a good of a deal to pass up.

So, now to some questions. I have the OM datasheet for the PK296A1A-SG3.6 plus the experience of this Forum, so I know how to wire it. However, the A6497-9412KTG only has 4 wires, not 6. The wire colors (colours) are Black, Green, Red and Blue. From the PK296A1A-SG3.6 wiring diagram, I could assume that the Black/Green is the A coil and the Red/Blue is the B coil. Is this correct?

Gerald, have you worked with the A6497-9412KTG? If yes, do you have a "specification"? I could not find one on the OM site, with a Google search or on the CNCZone forum. Also, are there any concerns you would have using this motor for the MechMate? I plan to build a 50" X 100" table with a standard Z slide.

Regards,
John

See Mike's post here.

We have used a lone A6497-9412KTG on the z-slide of the original MM without problems for a couple of years. (It was bought used from ShopBot at $175. The state of the used motors in that batch made me vow never to buy used again). See the pics in this thread.

I opened that motor the other day. See this thread.

To make a long story short, you need to drive your G203V's at just below their voltage limit of 80V.

Thanks, Gerald

Can you confirm that Black/Green wires are the A Coil and the Red/Blue wires are the B Coil for the A6497-9412KTG stepper motor? I don't want to release any "magic smoke.":eek:

Is your reason for running the Gecko 203V's at near 80 Volts to maximize the torque, at some sacrifice of top speed for the 4 wire stepper motors?

I have considered a scheme that would provide 2 power supply voltages to the Gecko's. The voltages would be approximately 39 VDC and 78 VDC.
Thus the 4 wire motors would be run at 78 VDC and the 6 wire motors would be run half-coil at 39 VDC. I know there is a risk of messing things up when using multiple voltages, but do you think the difference in performance of the 6 wire steppers run at half-coil would be significant.

Regards,
John

OM have standard wire colours across all their motors. I didn't release any smoke.

If you calculate out the voltages you need, that match the inductances of those motors, the answer is always higher than 80V, irrespective of the coil choices. We ran at 75V and the motor didn't get hot.

A half-coil PK296A1A has an inductance of 7.7mH, which relates to a voltage of 88V. (Hope you are not confusing it with a PK296A2A). Greg J runs his PK296A1A motors on 70V.

Gerald,


You are right:
I was confusing the two types. A2A versus A1A. :confused:

I was thinking ahead to the PK296A2A-SG7.2, if I end up having one (or more...in case one of my used ones fails) in my configuration.

I will proceed with an Antek toroid transformer with 2 x 28 VAC secondaries. Wired in series they will give me about 78 VDC. If I later move to PK296A2A-SG7.2's, I can re-configure the secondaries to parallel and 39 VDC output.

Regards,
John

The problem with the PK296A1a-SGxx motor wired FULL COIL is voltage. When wired full coil, the inductance is about 30.8mH which equates to 177VDC maximum voltage. The Gecko power supplies can only handle voltages up to 80V, so most of the potential of that motor is wasted.

The Gecko G203v is designed to work best with motors having induction in the 0.5 to 20mH range, so, with the G203v, that motor will run rougher than it would with a G202.

Because some of your motors only have four conductors, you will have to wire the motors bipolar series (full-coil). The Black/Green conductors are the A-coil and the Red/Blue conductors are the B-coil.

Wiring the motor full-coil at 78V will significantly reduce your top speed, but they will work very well to get you started. After you've made a few thousand parts, you should have enough generated income to buy some PK296A2A-SG7.2 motors and a suitable power supply to optimize your MechMate.

Thanks Mike,

I was hoping you would wade in. I appreciate your input.

So, next I plan to see if I can get the motors to turn using Mach3, the PMDX-122, and the Gecko's. Of course there will be no load on them at this point.

Is there a way to put a load on them before I get them on the MechMate...which is still some time off?

I noticed that some folks have wrapped a paper towel or rag around the shaft and applied pressure with their fingers (I think it was you when you were checking current draw under various conditions). I know this isn't a scientific load test, but would the hand-applied load be enough to discover some problems that would not show up under no-load conditions. Or is it enough just to know they turn, go fast, go slow, reverse, etc?

Regards,
John

John,

A quick and dirty way to load down a stepper motor is to install a V-belt pulley onto the shaft (2 to 5 inch diameter) and then just wear a heavy leather glove as you use your fingers to squeeze the pulley. I turned down a V-belt pulley on my small metal lathe to get a smooth fly-wheel type drum that is easy to grip with a gloved hand. Because it is smooth, I can gradually increase finger pressure until the pulley stalls.

Be careful anytime you use your fingers. A geared stepper can produce a lot of torque, and you don't want to find out how much torque a bone can handle.

Success!:D

I got a motor turning via Mach3-PMDX-Gecko-Stepper. No heat and no magic smoke...at least so far.

I was held up for an hour or two because of a sequencing problem. I had started Mach3, configured it, then powered up the PMDX and Gecko. I was getting no motion. In fact, Mach3 was not responding when I attempted to jog. Then, I shut down Mach3, brought it back up and it worked. Apparently I needed to power up the PMDX before bringing up Mach3.

I'm still a babe-in-the-woods with regard to using Mach3. So the only thing I've done is jog. I'm going to have to dig into Mach3 a bit more to get beyond slow jogging.

Regards,
John

Okay, so I learned a little more about Mach3 and G-Code. I wrote a little G-Code routine to let me turn the motor in either direction. I can vary the feed rate and loop the routine so it runs continuously.

So far, I have run the motor very slow like 5 inches per minute and up to 500 inches per minute. The motor is from a ShopBot and has the pinion gear still on it. The pinion gear is 34mm(1.34 in) in diameter. I wrapped some duct tape around the gear and tried to stop the rotation with my gloved hand.

At 5 inches per miinute, I could NOT stall the motor. At 500 inches per minute I could stall it with medium-high pressure.

I haven't done much tuning. Also, I'm using 1 amp and only 30 volts. I'm still just checking things out. I have yet to build my power supply.

Does this sound like a properly functioning motor? Remember, my motors are used and have an unknown history. So, I'm trying to validate that the motors are working.

Regards,
John

That motor sounds healthy.

Now is a good time to tune your G203 to the motor (adjusting the trimpot). Read the G203 manual to find the simple procedure.

Thanks Gerald. I'm starting to develop some confidence in those used motors.
I'll do the Gecko tuning you suggest.

I have a question on an entirely different subject.

I'm working on the design of my Control Box. I would like to post the schematic once I'm done. I have, of course, downloaded the PDF Drawing files which include the schematics. But, it's difficult to modify the downloaded PDF. I've got a PDF to DXF converter. It converts the PDF but the text is not text, it's just bits. So, I've had to go to each line of text and replace it with AutoCad text. Very tedious. Even after I've done the clean-up, the conversion back to PDF is only somewhat satisfactory.

I've tried to locate the DXF or DWG versions of the Drawings without success. Did I just miss something?

Is it possible to download DXF or DWG versions of the drawings? I don't actually need them all. Just 10 70 115 and 10 70 130 are needed. I would prefer DWG versions so that I have a better chance of a "clean" version when I convert it back to PDF format for posting.

Regards,
John

The tuning of the geckos may change with power supply voltage and current resistor (I don't know if it will), but it is far better to set it while the motors are off the machine.

Sorry, but I am not planning to release drawings in other than pdf. I have far too many layers that need to be hidden before releasing.

Gerald,

Thanks for the additional tip on tuning the motors.

As for the DWG/DXF version of the drawings, I can clearly understand the issue.

I do have an additional question regarding the conversion of the AutoCad drawing to PDF. I used the DWG to PDF selection on the AutoCad Plot menu.
Is that what you use, or have you found a better, or more useful tool?

Regards,
John

Plot to Adobe PDF - it makes smaller files than the freeware PDF makers.

Progress: all used OM Vexta Motors have been tested and work fine. I'm moving on to construct the Control Box. I've received most of the components and I painted the enclosure today (MechMate blue, of course).:D

I have a question regarding mounting the Control Box.

My MechMate will float out in the floor, not next to a wall. Power is buried under the concrete and available right next to the MechMate site. Dust collector ducts too.

My question is whether to mount the Control Box on a post like, for instance, JR did, or to mount the Control Box under the MechMate table like, at least, Hugo and David (Taiwan) did.

I know Gerald has expressed concerns about the Control Box being mounted under the table due to concerns of dust and dirt and accidental bumping into it.

What has been the experience of those who have mounted the Control Box under the table?

Are there additional issues that you can identify?

This is an important decision for me now, because my enclosure has an end plate. If I mount the enclosure on a post, I want the end plate on the top. If I mount the enclosure under the table, I want the end plate on the bottom.

Any help would be appreciated.

Regards,
John

Hey John,

Another thing to consider when choosing the control box on the wall or on the machine is cable length/cost.

The main reason I mounted mine to the table is an extreme lack of wall space in my garage/shop. The cable length vs cost took second place but the lower cost certainly didn't hurt

Hope this helps.

Greg

If you mount the control box under the machine, be sure that it faces out. My Shopbot has the controller facing in. Lying on my back on a cold concrete floor every time I decide to change something is hard on these old bones.

Suggest you consider end-plate always at bottom. If on a post, you can make a thicker end-plate and weld that to the post.

Don't look at the control box mounting in isolation . . . . You also need to figure where your PC, keyboard and mouse are going to go. They could all go on a "post", but they cannot all go under the table....

Thanks to you all for your input. Gives me plenty to think about.

Greg,

See Gerald's point regarding location of the PC...

Greg, what did you do with your PC, Display, Keyboard & Mouse?

Gerald,

Regarding the end-plate...
Why "always at the bottom?" I'm not planning on routing cables through the end-plate on the top. If mounting on a post, the end-plate presents an uneven surface. It is off-set to the back, so if I terminate the post on the end plate, there would be an out-of-balance situation.

Just trying to understand the logic.

Regards,
John

In factories and on ships I have always noticed the end-plate on the bottom. Suppose that is the point where leaks develop? Okay, water leaks shouldn't be an issue, but for me it will just feel odd to see a plate on top.

The post doesn't have to go to the center of the plate, and the top plate of the post can be bigger than the original end-plate.

Gerald,

Thanks for clearing that up.

Regards,
John

Currently my computer sits on a desk next to my laser. At some point in time I plan on building computer cabinet similar to David's.

The Control Box is complete. All steppers (3 for now) work from Mach3 via the computer printer port through the control box, PMDX-122 and the Gecko's.
Attachment 3305
The above photo includes the the steppers and the 3 24 VDC Contactors to be used for turning on the Router, Dust Collector and Vacuum Hold-down. I decided to go with Contactors rather than SSR's after reading about the heat generated by the SSR's. The Contactors will be mounted on the table (in the case of the Router) and next to the motors of the Dust Collector and Vacuum Hold-down. Just need to run a 2 core, 24 VDC cable to each Contactor.

Below, the three panel indicators on the right of the front panel are for the Router, Dust Collector and Vacuum Hold-Down. The keyed switches below the indicators are for "test." Keys to be removed in normal operation.
Attachment 3306 During testing, the 3 Contactors have been turned-on by Mach3 via the M3, M7 and M8 commands.

The Control Box includes 78 VDC power supply to the Gecko's, a 12/24 VDC power supply for the PMDX, E-Stop Circuit and to power the 3 Contactors as well as a Relay Board to control the Router, Dust Collector and Vacuum Hold-Down.
Attachment 3307


Below, in the upper right hand corner, there's room for a 2nd PMDX-122 for a future expansion to 4 axes.
Attachment 3308 The 3 yellow boxes in the middle of the picture are the relays on the Relay Board built to switch on the Router, Dust Collector and Vacuum Hold-down. They are controlled by signals from MACH3 via the printer port and PMDX-122.

Below, the Gecko's are mounted as per forum recommendations. The space to the left is for a possible future 4th axis.
Attachment 3309 In the bottom left corner is an AC outlet, accessible from the bottom side to plug in the computer, monitor, etc.

Hope I haven't bored you with this. I'm so happy to have reached this point. Now on to the "table."

Regards,
John

Very nice and tidy! Look forward to the rest of the build.

That is excellent John!

Thanks Justin and Gerald.

Welded up the Y-Car last evening. Kinda sloppy welding job. Clean-up needed. But seems level and sound. Followed Gerald's welding sequence and happen to have a piece of granite on-hand to make sure it was level and at right angles. Of course the test will be when it's riding on the Gantry and the Z-Slide is attached...down the road a bit.

Bill Tolbert and I are going to Houston for steel on Friday. They have good prices and have some "seconds" on-hand especially for the Main Beams.

Regards,
John

John, I've just noticed your collection of hammers partly shown in the one photo! :eek: They will come in useful for aligning the rails. :D

I have found a good selection of hammers helps my 'attitude' when debugging electronics. ... That may be why some of my electronics projects don't fair to well :)

In post #27, I said that Bill Tolbert and I were going to Houston to get steel on Friday...at the time I meant Friday, 16-JAN-2009. Well, make that Saturday 24-Jan-2009.:D

Here's the trailer loaded with TWO MM's at the Steel Yard

Attachment 3437


John on the left., he's smiling because we've already unloaded his steel. ...................................Bill on the right, don't know why he's smiling, still have to unload at his house

Attachment 3439Attachment 3438

I don't know if these two are going to qualify...NO FACIAL HAIR!:( But, hey, full heads of hair up top. Does that count for anything?:D

Regards,
John