Need Help!- I can only get 30 ipm out of my motors.

[stagefivedrift]

Hello. I hope someone can help me with this.

I've built the driver board from Tom McWire on instructables.com. I'm using Mach 3 and Vexta, Nema 23, 1.8 degree, 2 phase motors. It's set at 2000 steps per inch for the 1/2-10 acme screws. If I leave the feedrate at 30 or below, it works perfectly. No matter what I do, if I turn the feedrate over 30, all the motors will do is hum with increasing frequency per advance in feedrate. I think I've tried everything possible including the kernel speeds and everything.

Is it possible that the driver will not handle going over that speed? If so, I've just wasted alot of time and money.

Does anyone know if these are capable of running 100 ipm or better?

http://cgi.ebay.com/3-Axis-12-36V-3-...item2a0397a729

http://cgi.ebay.com/4-Axis-CNC-Stepp...item2a038075d0

Any help would be greatly appreciated.

[beone]

on my machine-using xylotex board and motors- I was limited to 30 ipm reliably. I eventually changed to 1/2-10 5 start--2 turns per inch- and can now run 200 ipm no problem. course I can only cut about 60 to 100 without burning bits.
Dave

[ger21]

What voltage are you running at now?

[stevespo]

I can't speak to your specific driver board, but it seems unlikely that you'll get 100 IPM speeds with the 1/2-10 acme screws you're using. Most steppers are not going to achieve 1000 RPM unless you really up the voltage and the boards you're looking at are kind of limited in that respect.

My guess is that you're hitting some mid-band resonance at the 300 RPM mark and you might be able to solve that with some type of stepper damper. Search CNCzone and you'll find some nice (simple, inexpensive) designs that could help with this.

Steve

[stagefivedrift]

My power supply is 18v, 25watts.

[ger21]

25 watts is probably too small, and 18V is too low for high speeds. At 24V, my Z axis with 1/2-10 is only reliable up to about 55ipm. Speed is proportional to voltage.

However, a 25watt supply is only 1.4 amps. My steppers are set at 2.3 amps each. A 24V, 5amp power supply might give you better performance, but there's no guarantees, as I'm not familiar with the drives you're using.

[stagefivedrift]

Thanks Gerry and everyone else. I've used a 14v, 3amp supply and it did the exact same thing. Time to find another supply. I robbed this one out of a printer for testing anyway. I'll try the damper idea too.

Any thoughts on those other boards I posted?

[irving2008]

Originally Posted by stagefivedrift Thanks Gerry and everyone else. I've used a 14v, 3amp supply and it did the exact same thing. Time to find another supply. I robbed this one out of a printer for testing anyway. I'll try the damper idea too. Any thoughts on those other boards I posted?

Firstly, is the stepper driver to which you refer this one? http://www.instructables.com/id/Easy...-and-Driver-ci

If so then sadly, your driver, power supply and motor combination simply doesnt have the guts to go faster. Increasing the voltage on that driver will have very little effect on your motor speed, all it will do is increase the heat generated by the circuit. What is happening is your motors are stalling as they simply dont have sufficient torque at the higher step rate to move.

Do you have a datasheet for the stepper motors? And how are they currently wired, Unipolar or Bipolar?

If they are the motors I suspect they are then you need (for 3 motors) at least a 5amp supply and 24v (120W) but the driver you have simply won't cope with that.


To get significantly higher speeds than 300rpm, which is where you are now, you need a much better matching of driver and motor and a better understanding of what torque/power is needed to drive the screw. You could increase the pitch of the screw, from 10tpi to 5tpi which would double your speed, but would also double the torque required so your motors would stall earlier so it could be self-defeating.

The boards you have listed will be better than the simple driver you have now, but may not be compatible with your stepper motors. And again, if they are the motors I suspect, you wont get a huge improvement. You should not run these boards above 24v (despite what it says in the advert) as they tend to go bang as several people have discovered the hard way. Doesn't make them a bad board, just not as good as they make out.

[stagefivedrift]

Yes, that's the one.
The motors are- http://cgi.ebay.com/CNC-Mill-Router-...item5ad534c082
They're unipolar. I've got a 24v, 10A power supply at a friends house but, if what you're saying is true, I'm probably just wasting my time.
I'm not looking to cut at 100ipm. I would just like to be able to jog at or near that speed. I have a 9'x5' table and it takes forever at 30ipm. How much better do you think one of the other boards would be, if any, or can you recommend a good but affordable driver setup.

[dertsap]

Originally Posted by stagefivedrift can you recommend a good but affordable driver setup.

people have had lots of success with these boards , http://www.hobbycnc.com/

[TOTALLYRC]

Originally Posted by stagefivedrift Yes, that's the one. The motors are- http://cgi.ebay.com/CNC-Mill-Router-...item5ad534c082 They're unipolar. I've got a 24v, 10A power supply at a friends house but, if what you're saying is true, I'm probably just wasting my time. I'm not looking to cut at 100ipm. I would just like to be able to jog at or near that speed. I have a 9'x5' table and it takes forever at 30ipm. How much better do you think one of the other boards would be, if any, or can you recommend a good but affordable driver setup.

Here is great drive to run up to 4 axis, has a built in breakout board, and 0-10v analog output for a vfd when you get there.
I think it is very affordable.

http://www.geckodrive.com/product.aspx?c=3&i=14469

Capable of running 50v and 3.5 amps per drive it comes preassembled and ready to rock. They also have an xml file since your are running Mach3.

I know some people will say it is expensive and no disrespect intended, but how much money did you save by building it yourself the first time now that you have to replace it to get the performance you need?

My take on jog speed is that anything over 30 secs full travel is agonizingly slow. I personally think that 15 secs full travel is about the lowest I would shoot for. Even wire EDM machines which work at very slow speeds have a pretty quick jog speed.

Mariss at Gecko is a big fan of the vexta pk?? series of motors and IIRC correctly says they are some of the smoothest he has ever run. I bought several based on his recommendation and am awaiting installing them on a machine.

A quick email or call to gecko with the motor numbers in hand will get you all the info you need. I believe they are one vacation right but check the website for details.

Mike.

[irving2008]

Originally Posted by stagefivedrift Yes, that's the one. The motors are- http://cgi.ebay.com/CNC-Mill-Router-...item5ad534c082 They're unipolar. I've got a 24v, 10A power supply at a friends house but, if what you're saying is true, I'm probably just wasting my time. I'm not looking to cut at 100ipm. I would just like to be able to jog at or near that speed. I have a 9'x5' table and it takes forever at 30ipm. How much better do you think one of the other boards would be, if any, or can you recommend a good but affordable driver setup.

Well those steppers are not the ones I suspected, they are better, but are being run at a fraction of their capability with those drivers. These are 2.8Nm 4A, 12W/phase steppers but you are driving them at around a fifth of their capability. So the good news is that there is scope for improvement by using a better driver.

The bad news is that changing the driver alone won't dramatically help. I am sorry to say this but basically you have a bad mismatch between driver, motor and leadscrew. For a 9' bed, and assuming the screw is near ful length of the bed, 1/2-10 is just too small a diameter and fine a screw. Assuming it is just supported both ends in simple ball races the maximum linear speed before whipping occurs is around 22ipm, so another reason your steppers are stalling is that the torque required to turn the screw faster is rapidly increasing due to the increased frictional losses of the screw pushing sideways against the nut. If you try to run this screw faster you will get all sorts of nasty problems including poor surface finish and massive wear in the nut. If you were to improve the bearings to be a fixed bearing at each end, holding the screw in tension, you could increase the critical speed to 47rpm before whipping. At this speed you would need a bipolar chopper driver capable of around 2A/phase with a 24v or better voltage.

To get above 47ipm without the screw whipping you will need a screw of 0.75" dia, 0.2" pitch, supported in a fixed bearing at the motor end and a sliding bearing at the far end. A screw of this size over that length has more inertia and demands more power from your motor. Some calculations show with such a screw your motor would stall at 70ipm assuming you are fully driving it which means you need a 50v bipolar driver capable of at least 4A/phase driven from a 40v power supply able to deliver around 8A continuously, 10A peak (for all 3 motors). That would be the limit with these motors.


Another thing you might want to consider is changing the drive mechanism from screw to roller-chain as per the 4' x 8' blacktoe v2.1 design