Troubleshooting a Gecko

[waynec]

I have an older shopbot that I've upgraded to the Ascension 1000 controller. I'm having an intermittent problem with one of the X motors not working.

When I switch with another G202 in the Ascension box the motor starts working. This leads me to believe that cabling and such are OK, and that the Gecko G202 is likely bad.

Is there a way to confirm this other than swapping G202s in the Ascension? The G202 looks physically OK, no funny smells, no escaped smoke, nothing that tells me its fried.

Argghh. What is the fastest repair? A new G202?

Thanks for input from anyone with experience with bad Gecko drivers.

Wayne from White Salmon
waynec@gotsky.com (mailto:waynec@gotsky.com)

[gary_n]

I have had the same problem, the Z driver. At fist I thought it was heat, and added an add'l 4 3/4 X 4 3/4 fan, blowing right on all the drivers. I'm sure that helped, but did not solve the problem. My Z driver quit would and after changing channels with the Y driver, both Y & Z would work. This went on for a few days. We had some pretty high temps. at the time. I finally wound up ordering another gecko 202 driver. It is due tomorrow.

[cnc_works]

Wayne, I have an Ascension box and had exactly the same problem. The off side X driver would intermittently quit, usually on long rapids. It would continue working after recycling the box. I replaced it and have had no problems since (a year and a half or so).

Donn

[weslambe]

I've had problems with my 202's on my home built machine since the day I got it running. That's been almost a year.

I've sent the Gecko 202's back for inspection and each time they come back as testing good.

My problem was that my x drives would quit intermittently. Cycling power on the control box would start the drive again for some period of time.

A friend sent me a couple of 201s since he has a good idea that the 202 has issues. I replaced the 202s on the x axis with the two 201s and then ran a sign job. The job ran for 59 minutes then the Y axis failed for only the second time in a year.

I am getting a whole new control box on loan to try it out.

I've also been talking with another shopbotter who is having problems with his 202's. He is of the opinion that Mach is causing the problem.

Check out www.warp9td.com (http://www.warp9td.com) This is a link to a company making a pulse controller that works between mach and the controller bypassing windows.

I think there are lots of people having problems with these drives

[richards]

Contact Shopbot and ask about their V201 controller card. It allows you to use SB3 software with the controller of your choice.

If used with Gecko G201 or G202 stepper drivers, you would only have to invert the step and pulse signals with a 7404 chip (or something similar). The V201 card can drive the Gecko G203v stepper drivers directly.

I've been using the card for several months and it has handled everything that I've thrown at it.

[bill.young]

Hi all,

For you tinkerers that want to find out more about the V201 controller card, we've put some information in a wiki at http://shopbotdev.pbwiki.com/

Wikis are always a work in progress but Mike Richards has done a great job of supplying content to get it started...many thanks to him.

Bill

[gskinner]

Did not know Shopbot had a controller they sold separate from there systems.
Can someone give me an idea of what the V201 controller costs?
Those of you that have used Shopbot software and Mach software what one do you prefer?

[richards]

I run Shopbot software on my PRT-Alpha and on the V201 controller board at the test bench. I run Mach3 software on several other test setups.

Without a doubt, the Shopbot software is easier to use. The SB3 software easily handles Input and Output instructions so that you can control various attachments to your machine. The SB3 programming language is more like other programming languages so that you can call another cut file from within a cut file. You can use labels and GOSUB routines for peck drilling, circular pocket drilling and all other specialized tool paths.

On the other hand, Mach 3 has the ability to cut an arc with the Z-axis being one of the active axes. However, to get some of the features that are built into SB3 with Mach3 I've had to resort to writing a custom code generator. It's not difficult, but without programming experience, it's not something that everyone would feel comfortable doing. Very simple operations like turning a spindle on via software and detecting a Zzero plate are more complex with Mach3 than with SB3.

If you're familiar with computer languages, SB3 is more like BASIC and Mach3 is more like Assembler Language.

As for the cost of the V201 board, give Shopbot a call. Ted Hall and I talked about pricing at the Maker Faire in California earlier this year, but I don't know what the final figures are.

[weslambe]

I just replaced all of my 202s with 201s. My machine hasn't had a fault using the 201's yet but I am still doing air cuts to be sure. I am a couple of hours into the air cuts. Using the 202's I would have faulted in about 20-30 minutes max.

[richards]

The Gecko G202 is an upgraded version of the G201. The G201 is an older design. Every designer that I've talked to chooses to use either the G202 or (more likely) the G203v.

The G202 shuts itself off if it gets too hot. There is no LED to notify the user that the G202 had overheated, so some people would assume that the stepper driver was flaky when it was just doing exactly what it had been designed to do. The only way to reset a faulted G202 is to turn the power off and then on again. However, the real solution is to mount the G202 on an adequate heat sink so that it doesn't overheat.

I've been running four G202 stepper drivers for over two years under the most harsh conditions imaginable. Those four steppers are mounted on a $20 strip of aluminum that is 3/4-inch thick. The G202s have never faulted on me.

I've had similar success with the G203v stepper drivers; however, I have them mounted on a 1/2-inch thick piece of aluminum and they have never faulted on me either. The G203v has the added feature of an error LED so that you would know if the G203v needed to go through a power cycle.

The only problems that I have ever had with any of the Gecko stepper drivers and the Oriental Motor stepper motors has been bad connections. I've been careless a few times and screwed the terminal down onto the insulation on a wire instead of on bare wire. A quick continuity check with a meter has always found that problem. That, of course, was totally my fault.

[weslambe]

I agree with your points Mike. I have a 1/4" thick plate of aluminum that covers the entire back of my control box and the geckos are attached to it using the white electrical conductive compound from Radio Shack. It looks like the zinc that swimmers used to put on their noses.

The problem was that the drives never got warm let alone hot. The new 201s get pretty hot so I have a big fan on them until I can figure out another way to keep them cool. But, I ran a whole job without them quitting. That's the first time in a year.

I've gone through the troubleshooting process meticulously. Every lead was checked and tightened then re-checked. My power use was recalculated and I determined that I needed more dc amps so I added another toroidal transformer.

Maybe the 201s are more heat tolerant. If that's the case then the 202s flaw may be in it's enhancement. I would rather run a little hot than not run at all.

If buying a portable air conditioner and venting it directly into the control box would have solved the problem then I would have done that a year ago.

[Gary Campbell]

Mike, Wes...
If keeping them cool is the only real problem, have you considered liquid cooling? There are tons of computer based LQ parts, hoses, radiators etc out there that are dying for someone with a cnc to modify into a heat sink.
Gary

[richards]

If the cause of the fault is temperature related, and not some intermittent short-circuit, the junction of the MOSFET is the only point that you have to be concerned with. The top of the case can be cool to the touch, but if that junction temperature rises above a pre-set level, the G202 stepper driver will shut down. That feature was added because many people fried their G201 drives by running them too hot.

The heat-sink compound needs to be used very sparingly. If used in the correct proportion, it helps transfer heat from the device to the heat-sink and it fills the small irregularities between the two pieces of metal. If too much is used, the compound actually becomes an insulator and keeps the heat from transferring properly.

The proper way to check a G202 for temperature caused faulting is with an oscilloscope. Mariss has posted photos of the 'scope pattern that you should be looking for. (www.yahoo.com (http://www.yahoo.com) -> groups -> geckodrive).

The time to trigger a fault is very short, 3.1uS, so the "event" can happen long before you're even aware that an error condition exists.

Here's two quotes from that document:

"The short-circuit protection responds in 3.1 microseconds and disables the MOSFET half-bridge
driver IC’s. These take an additional 400 nS to turn off the MOSFETs, for a response time of 3.5
microseconds. In that period of time current reaches a peak of 44 Amps before decaying."



"Cruel Experiment Department: We have a G202 that has been wired with a continuous short-circuit from a phase output to ground (worst case) that has been operating continuously at 80VDC since May 20. The protection circuit re-tries once a second and has accumulated 2.5 million short-circuit shutdowns since it began. It is checked every few days and it still functions normally."

[waynec]

Thanks all for the great info and help. I installed the new Gecko 202 last night, and its working fine. I did a test cut that went well over an hour with no faults.

I also checked temperature by feel, and felt no difference between the other functioning drivers, so I assume there is no temp issue. But I'm not convince the heat transfer goop is applied correctly, so I'm thinking I'll get some more and redo the bond. I think its probably thicker than it need to be.

I did notice that the new 202 has a brighter LED than the other axis drivers, maybe 2x as bright. Is that an indication of more current flowing? Is this a problem?

Also, when I install a new driver do I need to recalibrate my X axis?

Thanks again for the all the great info.

Back to getting the job done.

Wayne

[richards]

Two days ago, I posted a question on the geckdrive forum on yahoo.com about replacing a G202 with a G201. Mariss Freimanis, the designer of the Gecko products, quickly responded (in part) with:

"The natural migration path is G201 to G203V. The fatal flaw of the G202 is it doesn't have a FAULT indicator. It shuts down when it "sees" an over-current but gives no indication to the user."

Just a few minutes ago he posted again with a more lengthy summary of the causes of the G202 faulting. In this response, he has some observations about the characteristics of some larger stepper motors:

"The G202 was our first drive to have short-circuit protection. It is a rudimentary circuit compared to what is in the G203V but it works properly. The fault threshold is fixed to 8A at 50C and any current artifact past that threshold lasting longer than 3 microseconds will trip the fault latch. The temperature compensation is intentionally biased towards lowering this threshold to 6A at 90C.

What causes false tripping of the protection circuit?

This can happen when a motor is driven into saturation (current set > motor rated current) or the power supply voltage is excessive for the motor's inductance (V > 32 * SQRT mH). Also there are some high-torque motors that have onsiderable inter-winding capacitance which causes unusually large amplitude current 'ringing' on the 20kHz switching edges. Finally, inadequate heatsinking can combine with any of the above. Simply put, the G202 is very picky about any limit excursions.

The G203V uses a more sophisticated approach. It can afford the complexity because it uses a CPLD. Currents greater than threshold (I -8A) are integrated with time before application to the fault latch set input. By analogy, the protection circuit functions like a slow-blow fuse; minor over-currents take longer to trip the circuit than major over-current events. This approach seems successful because there are no "faulting problem" reports at all on the G203V.

The G202 is an older design and is limited by what can be done with discrete logic ICs. The G203V is a much newer design. It uses a CPLD which allows far more circuit complexity with room left over for future improvements.

Mariss"

[waynec]

So Mike, is the G203V plug compatible with the G202? That is, can I just unplug one and plug in the other? Or do I need to rewire?

And, should I be replacing the G202s with the G203V. I prefer not to wait till I have a problem, because the downtime can be expensive. If there is clear improvement in reliability of the G203V, I'll bite the bullet and upgrade before I have probs.

Thanks for your input, BTW.

Wayne

[richards]

Wayne,

The G202 and the G203v have one major difference. The G202 uses 5VDC as its common data signal and expects the step pulses to be 0VDC. The G203v is just the opposite. It uses 0VDC as common and expects the step pulses to be at least 2.5VDC but not more than 5VDC.

Some break-out boards (I'm assuming that you're using Mach3) support either polarity of signal. The PMDX-122 boards that I use on my test bench work with either the G202 or the G203v.

If your board only works with the G202, then you can add a 7404 chip that reverses the polarity of the signal. That chip has six circuits, so you would need two chips if you use four motors (four step signals and four direction signals).

There is another difference between the G202 and the G203v. The G202 was designed to handle motors with inductance ratings up to 40mH. The G203v was designed to handle motors with ratings up to 20mH. As far as I know, the 3.6:1 geared motor supplied with the original PRT machines had a Bipolar Series rating of 30.8mH. That same motor, if wired half-coil has a rating of 8mH; however, many or all of those motors only have four conductors exiting the motor housing, so they can only be wired Bipolar Series. To modify a G203v so that it can handle 40mH only requires a resistor change, but the resistors are little surface mount units that are hard to replace without specialized equipment.

[cnc_works]

Mike, I have an Ascension box with the G202's as well. As I mentioned earlier, I did have one misbehave and haven't had any trouble since. However, forewarned is forearmed, so do you have any specific knowledge regarding adapting the board in the Ascension box to use the G203?

Thanks for your excellent analisi (?) of the situations, I can even occasionally understand some of it.

Donn

[richards]

Donn,

I don't know which break-out board is used in the Ascension 1000 box ( including manufacturer and model number so that I can look for support documentation on the Internet). If I had that information I might be able to make a recommendation about replacing Gecko G202 drivers with G203v drivers.

I believe that they used a board manufactured by Robert Campbell, but I don't know for sure. The last time I looked, the Ascension web site was not functioning, so I have no contact information for anyone who sold or distributed the Ascension 1000 controller.

[jhicks]

check warp9td web site for a solution to lost steps, how and why it works.
:-)

[waynec]

I installed the Gecko, and now I'm getting some wierd jerking on the X axis on direction change. Its a Yaw motion, and looks as if the two motors are not totally synced, like one motor changes direction more slowly or with less force than the other. When I reduce speed its better, but is still noticeable at any speed.

Also, the new Gecko G202 LED indicator light is considerably brighter. Is this a problem?

I can't tell if the jerking on change of direction is due to the new G202 or some other controller or motor problem.

I'd appreciate any suggestions! I'm passing up jobs because I can't rely on this to be accurate.

Wayne
White Salmon, WA

[richards]

Wayne,

I don't know how your X-axis is wired. Sometimes the coil on one motor has the wiring reversed, i.e., Black/Green on one motor and Green/Black on the other motor. Sometimes the opposite polarity is handled internally by the software or the break-out-board. In any case, both motors should respond within a few microseconds of each other.

Carefully check the Direction signal wiring connections. A dual input oscilloscope would let you compare the two signals. I just checked the X-axis and the A-axis with my oscilloscope on my test bench. Those two axes are slaved via Mach 3. Both G202s on my bench receive the direction pulse simultaneously. If you don't have an oscilloscope, some break-out-boards have an L.E.D. indicator for each output signal. If yours has those L.E.D.s, just compare the two direction L.E.D.s. You should easily see any lag.

One other thing to check is the current limiting resistors on both G202s. Verify that the current limit resistor is correct for both stepper motors. It is easy to have a 10X factor difference. Check the colors carefully. Usually the third band is either Red, Orange, or Yellow. Verify that the colors on both resistors match each other.

The brightness of the L.E.D. is a function of the amount of current passing through the L.E.D. and of the luminosity of the L.E.D. If you have the same voltage going to both G202 stepper drivers, then I would guess that Gecko used L.E.D.s with different luminosity on the newer G202.

[jnbish]

Mike can I borrow your oscilloscope?
and maybe $100.00?

[richards]

Jeff,

I'd be honored to lend you anything that I have. If I had $100, it would be yours.

(For those who don't know Jeff Bishop, he is a great friend, who lives just a few miles away, and an expert with a Shopbot. In the short time that he's had a PRS-Alpha, he has done things that I can't even begin to understand.)

[dana_swift]

I have a dual trace 60mhz Tektronix for sale if anyone is interested-

Dana