[Jonathon]

Hi Fella's
Iv'e just completed the build stage of my router, Its dimensions are 1500 X 1500 using wiscarver linear bearings and 5mm pitch ball screws. I'm using RTA HGD Drives at 50v 6 amps, 3.5Nm 34 frame steppers.The Y-axis uses two srews coupled to one stepper in the middle and has no problems but the X-axis Stepper is directly coupled to the lead screw. When doing an arc there is an chatter at the identical spot and same very low feed each time. Im running Mach2 and I have tried everything. I realise that this is more than likely a resonance problem , what can I do.
Jono.

[ger21]

If it's a dual shaft motor, they make dampeners to help eliminate resonance. Or increase or decrease the feedrate to avoid the resonant speed.

[Jonathon]

They have only one shaft, I have tried different feed rates but because the motor still has to slow right down when doing an arc it still does it, I thought I might change it from direct drive to a belt to isolate the vibration.

[H500]

Do your drives have a microstepping mode? That helps immensely.

[Jonathon]

The drives have Full Step , Half Step and Quarter Step , they are set on 800 steps.

[bunalmis]

Add extra friction.

[Jonathon]

Ok, so I got home keen to try all these ideas and I decided to take the motor off the screw and there you go it still does it. On all drives on every LPT output and with every motor, it still chatters. So here is the thing, It only happens at 500 steps per second within 20 steps either side.
I have only tried 1 PC and its a laptop, tomorrow I will try another PC.
Any ideas?

[ger21]

Different drives

[jcc3inc]

Sir:
There are viscous dampers made for steppers; these are meant to minimize the resonance which a stepper exhibits. You might peruse the various stepper motor companies sites to find these. Since you are working with 1/4 step, you can't go any smaller with your setup.

Regaards,
Jack C.

[Jonathon]

FIXED!!!
I wired my motors in parallel and it fixed the problem.
Thanks for the ideas guys.
Jonathon.

[H500]

FIXED!!!
I wired my motors in parallel and it fixed the problem.
Thanks for the ideas guys.
Jonathon.

Can you explain what you mean by wired in parallel?

[Jonathon]

The stepper motors im using have 4 windings, 2 windings per phase (8 wires), the phase windings were wired in series first for high torque, But this was causing the motors to resonate at 500 hertz. So i then reconfigured the motors in parallel. Must be somthing to do with the controllers, maybe series raised the voltage too much. ?

[kywoodwrkr]

Jonathan,
Can you post a simple drawing of what you speak?
The motors I have are eight wire.
4 power, 4 ground.
The pairs are:
Black-Black/white
Orange-Orange/white
Red-Red/white
Yellow-Yellow/white
This is a step angle of 0.9 degrees.
Did you combine yours originally so as to create a five wire?
or a four wire?
Or??
Thanks
DaveP

[ger21]

8 wire motors can be wired 3 different ways. Bipolar parallel, which gives the best high speed performance, but possibly a little less low speed torque. Bipolar series, which will give you full torque at low speeds, but the torque will fall of more rapidly than bipolar parallel. Unipolar, which will give you only about 70% of the motors rated torque.

Bipolar series and parallel basically just wire the 4 coils either parallel or series to make 2 coils.

[Jonathon]

DaveP.
Here is a bit of a diagram. Fisrt i wired them in series, then I combined two coils together on each phase so halving the steppers resistance. So they are wired in parallel, as colors go, motors will vary. Are the 4 ground wires all connected to each other, if so it sounds like they are unipolar motors only.
Jonathon.

[H500]

I think I understand what might be happenning. When you wired it in bipolar series, you probably did not reduce your rated current in half. The motor would probably run pretty hot and you would end up with a much higher low speed torque. So, when the rotor steps, it snap into position with a much greater force and this is likely why it resonated.

[Jonathon]

Yeah thats right, Like they say, "The answer is always in the last place you look." THE INSTRUCTION MANUAL !!
I didn't reduce the current, and so the motors were cogging.
But if it had have worked first time think of all this stuff I wouldn't have learnt.

[santiniuk]

Jonathon,

I suspect I may be in the same trap but hopefully one of the guru's will advise me.

My Steppers are rated 4.5A 2.5V - They are 8 wire.

I have wired them as bipolar series and use the Picstep boards to control them.
I am current limiting to 3A as this is the maximum rating the picstep will drive.

The motors run really cool but I also have a resonance noise at certain low feed rates.

Can someone advise what current I should run these at. I am using a 34V supply.

Thanks

[H500]

Santiniuk, In bipolar series, the current needs to be 1/2 the rated value, which is 2.25 amps in your case. With 3 amps, you're actually overdriving them. I suspect that they will overheat if you left them at standstill for about half an hour.

Since you have an 8 wire mot, I suggest that you use bipolar parallel instead and set the current to 3 amps ( or as high as the lmd18245 will allow) You holding torque will only be 2/3 of the rated value, but your high speed performance might be substantially improved.

Make sure you wire bipolar parallel properly, or you will kill your controller as soon as you apply power.

[santiniuk]

H500,

I really appreciate this information, thanks.

I will try the parallel arrangement tonight, Hopefully it improves things.

I suspect the reason I have not noticed the motors getting hot at stand is that the picstep code switches off after a preset time.

Thanks.