Need Help!- Nema 34HST9805-37 and DM860A Driver

[Dan911]

Really hoping some1 could explain this and give a possible solution other then replacing motors. I get a bad vibration in motor between 70-75ipm any speed below or above the motor runs very very smooth.

I'm using these motors and drivers with the CNCRP R&P system. They seemed to work very well, I was able to get 1100 ipm before stalling, I have it set at 800ipm with acceleration set to 80. When jogging 100% the motors run very smooth.

I noticed this problem after installing a hand controller and doing some air cuts when the motor is more likely to run at this speed (70-75ipm). I tried different motor and driver(same models though) and microstepping settings with basically the same results.

Any help will be really appreciated,
Dan

[aarongough]

I believe you may be encountering what's known as 'mid-band resonance'... There is a certain speed for all motors where their effective torque drops dramatically. Normally you can accelerate the most past this speed with no problems, but if you run at that speed constantly then the motor's performance will tail off and it may even stall.

Try to work out roughly what speed the motor is running at, then try moving the gantry the length of the table at that speed... What happens? It my well stall as soon as you try to hold it at that speed...

I'm not an expert on this, but that's the first thing that comes to my mind.

[aarongough]

For more technical info on mid-band resonance have a look at this page:

Support

Click the 'Step Motor Basics' button, then the 'mid-band Instability' button.

[Dan911]

Thanks for reply/help Aarongough, the speed this consistently happens on was between 70-75 ipm microstepping set to 1/8, setting it to 1/16 caused the vibration to start at 100ipm, setting it to 1/32 didn't seem to make a difference from 1/16. I did set my jog to 12% so I could maintain the speed with motor vibrating to see if I was losing steps and it didn't seem like it was but can't be sure, but it never stalled.

Thanks for the link, it's allot to take in, but will be reading through it for sure.

Thanks again,
Dan

[aarongough]

Hey Dan!
No worries.

If my understanding is correct then mid-band instability simply causes an oscillation (back and forth motion) in the motor, when the motor is spinning at a certain speed... This oscillation takes time to build and and grow in magnitude until it finally overcomes the motor's ability to keep working which results in a stall.

The time that it takes to build up depends on the specs of the motor and the specs of the drive, there is no real information around though about what exactly that time will be, you have to learn through experimentation.

The time may be as long as 10 seconds though from what I'm seeing on the Geckodrive site... This means that unless you have a long section of travel you may not ever be able to make the motors stall because they don't have a long enough run at the 'critical speed'...

I'm not really sure what to suggest as far as solutions go. One suggestion would be to buy and try a Geckodrive on a single axis and see if the problem persists. Their drivers have a built-in electronic damping system that is supposed to stop mid-band resonance from happening and in my experience it seems to work well.

(I'm not affiliated with Geckodrive in any way, I'm just a very happy customer)

I have also seen people attaching mechanical 'dampers' to the drive shafts of their motor. Basically the principal is that the extra rotational weight makes it harder for the motor to oscillate... I have no experience with how well this works (or whether it works at all) though.

Here is a video of someone demonstrating mechanical dampers:

https://www.youtube.com/watch?v=UJjivsVwSsQ

I'm not sure that it's a terribly valid test though as the second run is at 185IPM, which is larger than the critical speed he had already established of 115IPM...

[Dan911]

Mechanical dampers isn't a option these are single shaft steppers.

I cannot begin of how disgusted I am with this 4 axis kit from China.

1. Originally purchased with a TB6560 board, after some research and valuable information on this forum learned this board wouldn't work well with motors so decided to purchase 4 DM860A Drivers from same company.

2. Once build began I realized shafts were longer than normal 34 nemas and needed to modify for K2 slide and R&P system.

3.Shafts are 14mm not 1/2 so needed new coupling and pulley's with custom boring.

Now all said and done these motors are actually useless since this is happening at speeds that are most commonly used when cutting.

Just wish I took the first $500.00 lost and bought a new kit here in the States.

Thanks for the info aarongough and giving me a opportunity to vent,
Dan

[aarongough]

Hey no worries Dan!
In a way I'm just glad that the hundreds of hours I've spent researching and mucking about with CNC makes me able to help others! :-p

I highly recommend the Geckodrive drivers. I only have experience with the G540 which is an integrated 4 axis board... I'm not sure if that has enought capacity ro run your Nema34 steppers (probably not), but I know that their other driver boards do.

Their best and biggest drivers are about $150 each, they can run 80V at 7 amps which should be more than enough to drive your big Nema 34 steppers.

I'm sure that's bad news at this point, but at least you have a decent idea where the problem may lie.

I would say you should try running some actual g-code through your machine and see what the results are like. If it only spends very short periods of time at 75IPM as it's accelerating toward 800IPM then all the worry may actually be for nothing!

[Dan911]

Originally Posted by aarongough I would say you should try running some actual g-code through your machine and see what the results are like. If it only spends very short periods of time at 75IPM as it's accelerating toward 800IPM then all the worry may actually be for nothing!

When air cutting with G code with a feed rate of 200 was when I realized I had a problem. Just jogging at 100% the motors sound great. I did air cut some G code with a feedrate of 500ipm and I never heard any vibration but in reality I'll never be able to cut at that speed.

I think my problem are with my motors though and not the driver. I already replaced a motor with 1 I purchased from CNCRP on Z, and the driver controls motor fine without this problem. The drivers specs are same as you described above 80V and 7.8amps.

Thanks again,
Dan

[aarongough]

Hey Dan,
It may be that the problem is with the motors, but having the motor on the Z work is no guarantee of that as it usually won't be travelling anywhere near the speed or distance that the X & Y are...

I would move that motor to one of your other axes if it's of a suitable size and see if that fixes the problem, if it does then you have a definite solution there!
-A

[ger21]

I think my problem are with my motors though and not the driver. I already replaced a motor with 1 I purchased from CNCRP on Z, and the driver controls motor fine without this problem.

The resonant frequency can vary greatly between motors, even with the same drives. Larger motors are more likely to be affected.
It's unlikely that something is wrong with the steppers.

As suggested, Geckos would probably fix the problem.

Unfortunately, a lot of people are getting sucked into these poorly matched kits on Ebay, thinking they're getting a great deal. Instead, they have to spend more money to get a good working system.

I'm not sure that it's a terribly valid test though as the second run is at 185IPM, which is larger than the critical speed he had already established of 115IPM...

Since it's my video you linked to, I'll comment.
Without the damper, it wouldn't run any faster than 115ipm, and was stalling at that speed. Most of my cutting is done between 100-125ipm, and it's still running smoothly.
The resonance on my router occurs at almost all rpm's. If a setscrew on a damper happens to come loose, it'll stall almost immediately.

[aarongough]

Originally Posted by ger21 The resonant frequency can vary greatly between motors, even with the same drives. Larger motors are more likely to be affected. It's unlikely that something is wrong with the steppers. As suggested, Geckos would probably fix the problem. Unfortunately, a lot of people are getting sucked into these poorly matched kits on Ebay, thinking they're getting a great deal. Instead, they have to spend more money to get a good working system. Since it's my video you linked to, I'll comment. Without the damper, it wouldn't run any faster than 115ipm, and was stalling at that speed. Most of my cutting is done between 100-125ipm, and it's still running smoothly. The resonance on my router occurs at almost all rpm's. If a setscrew on a damper happens to come loose, it'll stall almost immediately.

Haha, trust that Ger made the first video that comes up when I type 'stepper motor dampers' into Google!

After the explanation the 115IPM -> 185IPM thing makes sense, my 'science alarm' went off when I initially saw that the target speed had changed :-p

Thanks for lending your expertise as always Ger!

[Dan911]

aarongough, thanks for your very helpful info/links. The motor I purchased from CNCRP did work, but I would prefer to go with the Gecko drivers like you suggested since it would be a cheaper way to go for me. The motors I'm using have a lower amp rating so replacing motors would also mean replacing power supplies. Ger21 has me a little concerned with putting the probably in Italic though...LOL Guess I'm going to have to research and think this through before I throw any more money away.

Ger21, obviously you are right about these poorly matched kits being sold, but after some goggle searches on this, it's not only the kits from Ebay that people have this trouble with. This infuriates me! As far as I'm concerned basically these drivers company's are selling are paper weights. I could except tolerating some vibration because of buying a cheaper model, but from what I understand is most likely it's missing steps which make these drivers garbage.

Once again thank you both for your valuable info and only hope this thread helps some other newbie starting out in this hobby like myself from making the same mistake.

Dan