[cncprogramer]

I have built my own cnc router. I am using Nema 23 425oz stepper motors run from mach 3. My issue is I can not get the axis's to move smoothly. Every thing jogs nice and smooth but as soon as I run the roadrunner program that is sent with the mach 3 software. The machine jerks and the motors have like a humming sound. I know that I can tune the motor in mach 3 but there is something that is not right. Anyone with any Ideas?

[James Newton]

Sounds like a question for the MACH3 forum.

[awerby]

Have you actually done the motor tuning?

[cncprogramer]

I have tuned the motor's. I am new to this forum. Did not know that there was a mach3 forum. Wrote some long hand g-code with just straight lines. Everything worked just great. It seems like it may be the short quick moves that are causing this problem. Hoping to work on it some more this weekend.

[aarggh]

What drivers, and power supply are you using? Some of those 425oz/in steppers have horrendously high inductance and will run pretty crappy.

The formula for working out what DC voltage to supply the steppers is (32 x (sqrt inductance in mH)), in other words, if your steppers have an inductance of 10mH, square root is 3.16, multiplied by 32, equals 101VDC required to optimally power the steppers.

If your PSU is very much lower than say 48VDC, but your inductance is high, this will cause all sorts of issues with acceleration, at the very least.

cheers, Ian

[SteveWill]

In mach3 there is ( Config, General Config) a Motion Mode and a place to chose Constant velocity or Exact stop, guessing Exact stop is checked.

[cncprogramer]

This is what the power supply paper work said. I am not the best at figuring out how the setting up of motors and what to use or power supply and drivers. I bought it all thru ebay. t
This is all a different language to me. I could use all the help anyone can give me.
Input Voltage 90-132VAC and 180-264VAC /
Input frequency 47~63Hz /
Output Voltage 36v /
Total Current 10A /
Volute adjustable range 36V±10% /

[James Newton]

aarggh, I just noticed your signature line: "It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!" LOL... that made my day.

[awerby]

That's a pretty standard 36v power supply. I doubt it's your problem, although your motors might run better if they got more voltage. What are the specs on your motors, particularly the voltage, inductance and amperage?

[cncprogramer]

This is the description that I was given when I bought the kit off ebay.
Model GB23H2112-30-4A
Shaft Single Shaft (Diameter:8mm; Length:21mm)
Rated Voltage 6.0VDC
Rated Current 3.0A/Phase
Step Angle 1.8°±5%
Phase 2 Phases
Phase Resistence 2.0 x (1+10%)Ω/Phase
Phase Inductance 7.5 x (1+20%)mH/Phase
Holding Turque 3Nm (Approx. 425 Oz-in)
Positioning Turque 600gf.cm
Insulation Resistence ≥ 100MΩ (500VDC
Insulation Class Class B
Weight 1.6Kg/Piece

[aarggh]

aarggh, I just noticed your signature line: "It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!" LOL... that made my day.

Yeah, probably none too subtle, or maybe too subtle depending on the view, my daughters real big on faeries and the whole idea of when someone stops believing in them a faery dies, so the analogy seemed appropriate for the crappy blue box controllers out in the wild!

cheers, Ian

[aarggh]

This is the description that I was given when I bought the kit off ebay.
Rated Voltage 6.0VDC
Rated Current 3.0A/Phase
Phase Inductance 7.5 x (1+20%)mH/Phase

Ideally those steppers want around 85VDC to perform optimally, so 36VDC is going to make somewhat noticeable differences with speed and torque, but more importantly, you haven't mentioned the drivers your using?

Also, if the PSU is one of the common Chinese variety, I'd take the 10A figure quoted as being somewhat optimistic, assuming the drivers your using can even deliver the required 3A per axis sustained?

cheers, Ian

[awerby]

Yes, those motors have way too much inductance to run well on 36 volts. But if you gave them 85v, then you'd probably fry your drives, although you might look up the specs to see how much voltage they're rated for.

[cncprogramer]

Would I be better off sizing down on the motor for the axis to move smoother. I bought the 425 because I was worried that the weight of the axis's would be to much for smaller motors to run.

[aarggh]

Would I be better off sizing down on the motor for the axis to move smoother. I bought the 425 because I was worried that the weight of the axis's would be to much for smaller motors to run.

I would consider different steppers myself, you'll find the commonly available 280oz/in ones which usually are around 2-3uH, are much better, and will actually perform far better than the 425oz/in you have. The 425's would only be good at quite slow speeds. Slow enough to not lose so much torque they're useless that is.

cheers, Ian

[RCaffin]

Sounds very much like you have set the machine to Exact Stop in config. it does that. Try Constant velocity instead.

I don't think any of the hardware 'fixes' will do anything for you.

Cheers
Roger