Stepper motor troubles

Hello,
I have a homemade cnc router. It has three pacific scientific motors and drivers on it. The problem I am having is as follows: as the machine runs a program, the motors will lock up and start to hum. It usually happens when the z axis completes a movement and the x and y start to move.

I keep thinking that my power supply is not keeping up with the demand but it seems to happen no matter what speed I run the motors. I have had them as low as 200 mm per minute and they still do it. It happens randomly during a program run and does it on almost every program I try.

Any help is appreciated,

What controller are you using and how many volts/amps is your power supply?

Don

Quote:

---

Originally Posted by atwooddon

What controller are you using and how many volts/amps is your power supply?

Don

---

Don,

Thanks for the resonse. I am driving the router with Mach 3.

The motors are 7.5 amp bipolar motors that run at a max of 65vdc
The drivers run at 12-75vdc. All three axis are the same.

I am running this with a 36vdc 4.2Amp 150 watt power supply.

Thanks,
Jason

Hello,

your power supply is much too weak. Together your Motors can pull up to 22.5A but your power supply is just capable of 4.2A.

Christian

Quote:

---

Originally Posted by jchal3

Hello,
I have a homemade cnc router. It has three pacific scientific motors and drivers on it. The problem I am having is as follows: as the machine runs a program, the motors will lock up and start to hum. It usually happens when the z axis completes a movement and the x and y start to move.

I keep thinking that my power supply is not keeping up with the demand but it seems to happen no matter what speed I run the motors. I have had them as low as 200 mm per minute and they still do it. It happens randomly during a program run and does it on almost every program I try.

Any help is appreciated,

---

I am pretty sure you are experiencing stalling because of resonance. I had/have that too on my steppers. There are some fixes you can do mechanically; add a resonance damper like a flywheel or "hockey puck" for example (many other options too, do a search). Check these out for example:
[ame=http://www.youtube.com/watch?v=UJjivsVwSsQ]Stepper Motor Damper Test. - YouTube[/ame]
[ame=http://www.youtube.com/watch?v=mqCL7g4gwAU]Solving Stepper Motor Resonance Problem on CNC Lathe - YouTube[/ame]

Hub

Hub,

My motors definietly sound like the motors in the video. This may be a dumb question but what is resonance and what causes it?

I'm going to do a you tube search and figure out how to handle this.

Thanks

I wouldn't ignore Christian's comment on your power supply either. 150 watts is not a lot of capacity to drive a CNC machine unless you are going very slowly.

Resonance is basically a vibration that starts when the frequency gets just right for your machine. The dampers you see will basically stop the vibrations thru the drive system. They are simple to make and test. Hope that fixes your problem but I would bet on power supply first.

Don

Yes you should also check that you have enough power and I agree that your 36V/4.2A PSU is most likely not enough.
However I don't think that is your problem here.
Here is what happens if you don't have enough power:
- Not enough voltage: you loose speed
- Not enough current: you loose torque

Using microstepping might reduce resonance a bit. Are you using microstepping?
The fastest way to test if you have resonence, is to add a hockey puck or similar flywheel to your stepper. It's easy to attach if the motor has a double shaft.

Hub

I am using the microstepping settings. It is set to 25:1. My motors do not havea double shaft, so I'll have to get creative to figure out the resonanace issue.

Quote:

---

Originally Posted by jchal3

I am using the microstepping settings. It is set to 25:1. My motors do not havea double shaft, so I'll have to get creative to figure out the resonanace issue.

---

If you are using (AL) 'flex' couplings just add the flywheel to the coupling (motor side of the coupling). Just as an idea..
Hub

Hub,

When you say AL flex coupling, is that the same as a lovejoy coupling. Basically one half for the motor, one half for the shaft, and a rubber spider in the middle? I think that is what you are talking about. and yes I am using that. I'll give it a shot.

Quote:

---

Originally Posted by jchal3

Hub,

When you say AL flex coupling, is that the same as a lovejoy coupling. Basically one half for the motor, one half for the shaft, and a rubber spider in the middle? I think that is what you are talking about. and yes I am using that. I'll give it a shot.

---

Yes, that's what I meant. Sorry for the confusion.
Hub