One stepper motor does not change direction - drive needs reset

[waynec]

Well, I just got my new water cooled spindle installed, and loaded a file to test it. When running this file, the gantry suddenly racked and jumped the track.

As I diagnosed the problem, I first thought it was related to RF interference from the spindle. But when I run a program with the spindle OFF the program still jumps the track. I did order some shielded cable to reduce the chance for RF interference from the spindle cable. Cheap insurance.

Next, I ran the program with the X axis motors disengaged from the rack. (They are rack and pinion on an old ShopBot PR, btw). When watching the motors I found that one motor would not change directions, while the other one did.

I'll swap cables first thing tomorrow to see if the problem follows the swap. But what should I be looking for? Cable? Gecko? Motor winding? Do I also need to check the Mach 3 settings for these motors? Which ones?

Each time this sort of thing happens, I doubt the reliability a little bit more. I can't go and sell orders for product that I'm not confident this machine will cut out for me. Argh!

Thanks for any advice with this. I'm using old Shopbot geared motors - the 3.6 ones, and Gecko 201s think.

Wayne from White Salmon

[Gerald D]

For a motor to change direction, pin 9 (marked "DIR") of its gecko must get a change of voltage. You can probe a voltmeter there to see if the control board is providing this change of voltage, or if the gecko has gone faulty, or if it is just a bad connection. (there were some geckos with connector problems).

[bradm]

The other possibility is that one of the connections from the gecko to the stepper has gone bad. With only one of the two coils energizing, some steppers will run in only one direction.

[waynec]

Thanks both of you. I'll check the gecko pin 9, and the connections. I've checked connections hundreds of times, always thinking this is the fault. It hasn't been to this point. But I did just install a couple new circuit cards in the controller box, so its possible.

Could a change in Mach 3 cause this? Could one of the direction settings on either the A or X motor have somehow changed its setting? Maybe I somehow loaded an old version of my setup or somehow it glitched. I'm just wondering if software could cause this too.

Also, can I check pin 9 voltage with my old Simpson meter, or will I need a scope? If the voltage change is just a couple miliseconds long, I guess a meter won't be near fast enough. But if the voltage is held hi or low until a change is sent, I could detect it with a meter.

Anyway, here in the northern hemisphere in the US Northwest, we are having quite a winter storm. I've got over 30" of snow, and now freezing rain on top of it. As long as power stays on I'll have plenty of time in the shop to work on this.

Thanks for the quick replies, gentlemen.

Wayne from White Salmon

[bradm]

The dir signal will stay in a state for the duration of the motor moving in a single direction, so you should be able to measure it with a meter with a moderate size slow move (a foot at 2 IPS would give you 6 seconds to get a reading, for example).

[Gerald D]

Could a change in Mach 3 cause this? Could one of the direction settings on either the A or X motor have somehow changed its setting? Maybe I somehow loaded an old version of my setup or somehow it glitched. I'm just wondering if software could cause this too.

If you fiddled with "ports & pins" in the Mach3 "Config", you could certainly have disabled direction changes for one motor. Do the voltage check first.

[waynec]

I had this problem once before, and thought I had a bad Gecko. I ordered a replacement and that seemed to fix it, but I talked to Mariss at Gecko and he said that the Gecko was probably OK. Seems they have a current protection cutoff, but no indication that current limit has been exceeded. So my Gecko driver was doing what it was supposed to and tripping when a bogged motor caused a current overload.

I'm pretty sure that's what happened this time too. The connections all tested fine, but the problem of no reversing was still happening. When I removed power to the control box I allowed the Gecko to reset, because after this the problem disappeared and the motor started working correctly.

I tested this by running the same file in the air. It ran fine, without any errors. So I guess its good that the Gecko trips a current limit protection circuit, and bad that I didn't know that.

Thanks for the help. I'm impressed that you guys are able to reply that quickly with exactly the info I was asking for.

Happy Holidays to you both!

Wayne from White Salmon

[Gerald D]

Wayne, have you got a ShopBot G4 where the Gecko's stand up off the board without any heatsinking screwed to their backplates? How about a photo of the geckos inside your control box?

[waynec]

Gerald, I have an Ascension box which has the Geckos mounted to the metal chasis with heat sink paste. They don't seem to get hot that I can tell.

BTW, I ran the CNC for several hours today without incident, so I think the reset has fixed the issue. I'll get you an inside pic tomorrow.
Thanks for your quick help!

Wayne

[zetacnc]

Wayne,

I know there are a lot of people using Geckos and Machxx controlling them, and specially the "X" axis that uses two motor, one is the "master" and another is the "slave".

I had problems with these setup because time to time Mach3 loosed config (direction signal pin changed with no intervention) and the result is the same you experienced.

I solved just sharing the same direction and step signals to both drivers - in Mach there is only one "X" axis (no slave)...

[Gerald D]

Excellent tip Fabio, thanks!

I don't know if the G201 drives can easily be put in "parallel" with Wayne's controller. (The G203's are easy to parallel). Mike Richards, if you are reading this, comment please . . . . Wayne's Ascension has the Bob Campbell controller.

Wayne, you could ask Bob Campbell if it is okay to do it.

Rest of discussion moved to this thread:

http://www.mechmate.com/forums/showthread.php?t=1232 (http://www.mechmate.com/forums/showthread.php?t=1232)

[waynec]

Well, I've done it now. I'm trying to cut a sample sign for a pending job, and about 20min into the job, my old nemesis returns. One of the two motors quits reversing direction, causing and immediate gantry rack and failure.

This is like three or four times I've THOUGHT I've found the problem, only to find it again. The problem is the same as posted in this thread- one coil on one X axis motor quits working, so the gantry will go one direction, but not the other.

This time I started the same diagnosis procedure-- resetting the entire system, powering down for a full minute before restarting, and checking Mach 3 pin settings. All OK.

Next, I swap drives to verify that the problem is related to a drive, not to a motor. I swap one x motor cable for another at the control box. The problem is always isolated to a single Gecko 202 driver. So I start checking the connections again, this time at the Gecko driver plugs. With the control box open, I poke the connectors with a wooden dowel, and I saw a very tiny spark at the coil connection. I push it again, see the spark again. A third time and I get a larger spark and the Gecko power lite goes dead.

The first spark was tiny, but the motor worked and then quit working when I moved the connector. Then I got the larger spark and testing stopped. No blown fuse, but the Gecko would not reset, and is still dead.

I have TWO new G202s ordered, and I'll report when I get the new one installed.

My question- should I be getting intermittent connections when I poke the Gecko connectors? Not very hard pokes, mind you. I'm thinking maybe the last one was a bit too hard, anyway.

Thanks for the support.

Wayne

[Gerald D]

Gecko did have some quality issues with connectors - see my report:
http://finance.groups.yahoo.com/group/geckodrive/message/8924

And the response from Mariss:
http://finance.groups.yahoo.com/group/geckodrive/message/8933

[waynec]

Wow that's great news I guess. I'll go and check again to see what connectors I have. After reading the thread, I bet I've weakened the connectors by connecting and disconnecting them thru this constant cable chasing I've been engaged in.

I'll double check as you have to see if I'm getting volts at the screws but not at the pins.

Again, I'm tempted to just solder the damn wires to the pins on the Geckos, but I do want to be able to easily swap them if I need to. I'll try some new connectors. Maybe I can get Mariss to send some with my Gecko replacement order.

Gerald, thanks yet again for your help.

Wayne from White Salmon