Motors Stuttering only at low speeds

I'm retrofitting an old Dyna Myte 2400 mill using a cheap TB6560A 4 Axis driver board and I'm finding that my motors stutter at low speeds.

When I run the stepper at max velocity = 0.2in/s and max acceleration = 1in/s2 everything works great. But when I try testing it at a velocity of about 0.05in/s the stepper stutters. Is this a common occurance? Like am I supposed to set up some minimum speed in my configuration or someting?

If not, how do I go about trouble shooting this? I'm not sure where the issue is here. Right now I'm using these values:

Step Time: 50000ns
Step Space: 1000ns
Dir Hold: 1000ns
Dir Setup: 50000ns

I have microstepping off (i.e set to 1) and a scale of 10160.0 steps/in. This stepper is a little odd in that it only has 100steps per rotation. Base Period Max Jitter (based on the latency test) is set to 13266ns.

If anyone has any advice it'd be much appreciated.

Thanks!

Hi

Your timings are probably out and your base period is probably hopelessly optimistic

Use the timings here as a starting point
linuxcnc.org/index.php/english/forum/49-...ler-a-variants#23828

I would suggest you set your base period to 30000 at least to start with.
I usually recommend tripling the figure to start with and tuning down when everything is running

Your current one maybe theoretically OK, if you did really rigorous testing, but leaves no leeway for error whatsoever and the slightest burp will cause lost steps.

regards

EDIT:
As Rick says below, without microstepping the steppers will not be smooth at low speeds, especially with 3.6 degree steps
Assuming your gearing is in conventional realms, it should give you double the scope for micro-stepping
ie x2 will only bring you to the same as x1 for a normal motor

But when I try testing it at a velocity of about 0.05in/s the stepper stutters. Is this a common occurance?

Not sure what you mean by stutters, do you mean you are losing steps or that the motors are noisy? It is not uncommon for stepper motors to have a narrow low rpm range where their movement is rough.
If after checking all your settings as ArcEye suggest.
Double check that the amps are not too high and microstepping may help smooth the movement.

Rick G

Rick wrote:

But when I try testing it at a velocity of about 0.05in/s the stepper stutters. Is this a common occurance?

Not sure what you mean by stutters, do you mean you are losing steps or that the motors are noisy?
Rick G

Oh what precisely is happening is the motor will sporadically change direction. Like it will go a quarter rotation back, than forth, than maybe move a half a rotation forward, and then reverse a quarter again. It looks very random.

Hmm, I guess I can up the microstepping on my x and y but my z doesn't seem to have a enough torque to move up without full steps. If my motors do have some narrow RPM range I need to avoid, how do I ensure my gcode doesn't put the motors in that range?

Thanks!

That sounds more like under power, have you tried adjusting your settings as ArcEye suggested?

Rick G

Well after letting this project drag for a bit I think I figured out a way to tease out if my issue is the step/timing settings or the current.

After following ArcEye's suggestion for settings, I hooked up a cheap little stepper to my drive that's rated for 1.8 A, and low and behold! It works just as the documentation implies it should. I clearly have some top speed, but no real minimum speed (I tested it at a speed of .01in/s and the little guy still moved reliably).

So my theory is if the board can run a smaller 1.8A motor just fine, but creates strange errors when I try running the mill's 3.6A motor, the current must be the issue. I don't have much experience with steppers though, so if you guys could let me know if this sounds right to you it'd be much appreciated! Thanks =D

My guess would be that the drivers are just not suited for your motors.

I have never had a stepper with 3.6 degree segments and doubt that many exist.

All the driver calculations for interpolation of steps etc will be for 1.8 degree segments.
It makes kind of sense that at low speed it starts falling over.

If new steppers work well, it may be either find a driver that works with the old ones or just upgrade the steppers to new ones.

regards

a few things to ask
what voltage and current are available to your steppers
have you changed the stepper motors ? as i doubt the motors are 100 step

it's more likely your step and microstepping are incorrect
can you give details of your ballscrews also