Stepper motor stalling at 15 IPM

[Mindcore]

Hi, some may remember me in my quest for what steppers to get.

My machine has been completely rebuilt, lead screws and all, and I'm very happy with it.

My problem is, I can't get my motors to go above 15 IPM without stalling.. whether they are on my machine or not.

I'm sure the link won't last, but this is basically the kit I got http://cgi.ebay.com/4-Axis-Nema-34-s...item3f009bdb97

except my motors are 740 oz-in as opposed to 872.

I'm running 2400 pulses per rev. max speed 15, acceleration 1 in Mach 3

if I go to 17IPM or higher they stall after a second, over 20 IPM stall out instantly.

24VDC pus, rated at 14.something amps @ 120VAC.

What in your experience should I be looking towards? is my PSU not enough for those motors? do I just not have a clue how to set them up?

I'm lost, and considering my mill is 4X8 I'm getting too old to wait for it to get from one side to the other

Any help or pointers is much appreciated.

If more info is needed, let me know what that is and I will find it.

Thanks

Mike

[Mindcore]

Some additional info on my motors

Step angel ( 1,8° )

Rate Voltage(6.27V)

Rate Current (1.65A)

Phase Resistance (3.8 Ω )

Phase Inductance (24 mH)

4 wire motors

Holding Torque (740 oz.in)

[Mindcore]

I'll continue my conversation as I go.

Went through every setting on my controller, it was set to 75% current. Changed it to 100% - no change

Set the stepping from 1/2 to 1/8th no change.

Set Buffer to slow, to 50% to 75% no change.. seriously do those dip switches do anything at all?

I adjusted my voltage set screw from 24VDC to 29VDC ( maxed out ) and the motor at top speed went from shuddering to baby butt smooth. So, no increase is speed, but that little bump in voltage was the only noticeable change.

I, in my supreme newbiness is sure that my "kit" is mismatched and my steppers are far to big for my driver, and after reading the horrors of max voltage ( 36 ) on those boards, I'm not going to attempt to pump anymore in.

Next step.. gearing. It's all I got unless I buy new drivers..or new controller.. or... back to the beginning of not really knowing what works with what.

ah well.. carrying on.

[ger21]

Basically, you got ripped off. Or, you got what you paid for. Take your pick.

To get maximum performance from those motors, you'd need to use 155 Volts.

And with larger motors, even at their maximum performance, they won't spin as fast as smaller ones.

Need more info on your machine to give you a better recommendation. But seriously, those motors aren't good for much. And a 24V power supply probably wouldn't be any good if you had the right motors. Depending on your machine, it's possible that a 48V G540 package with 380 oz motors would far outperform what you have. It costs about $600. But, it may be that you need even more power, which would be bigger motors, Gecko G203's, and possibly an even bigger power supply.

Give us some more info on your machine.

[rowbare]

Mike,

Those motors are horribly mismatched to your power supply. The generally accepted formula for stepper motor voltage is sqrt(impedance) * 32. With your 24mh motors the ideal voltage works out to ~150v. As well your motors' rated current is really low so to get any kind of power you need the higher voltages. You are probably getting about 150 oz-in with your power supply.

bob

[Mindcore]

Thanks, you pretty much confirmed my suspicions and math.

Trying to balance torque ratings, power, etc. I thought I was erring on the high side by going with more powerful motors, neglecting the step up in power to match.

As I mentioned I get the same performance whether my motors are on my machine or not, at low speeds they move everything just fine. It's an all aluminum build based on no plans, just piecing things together with the materials I came across. V bearings running in channels, 5TPI screws with HDPC? ( cutting board ) nuts.

Slaved dual X axis, with a cutting surface of 47" X 90"

Average speed on the X and Y is 15 IMP and 30 IPM on my Z. ( no load )

I guess my question to you guys is..with what I got am I better to:

Gear it? ( when it's running at low speed there's nothing I could do to stop it from moving, enough torque to pull me off my feet )

Keep the motors and get a new higher voltage controller and PSU

or get smaller motors that better match my controller, since I think my machine runs pretty smooth.

What do you think?

[ger21]

If you get them to spin faster, you're going to have a problem with the screws whipping. Are they 1/2"? The cheapest thing might be to gear them about 3:1 or 4:1.

I wouldn't spend the money on better drives and power supply, as the motors are not good for high speeds. And similarly, from what I've read, the drive probably won't drive smaller motors all that fast either. Either way, you'll be spending a few hundred more for a small gain in performance.

Depending on how much weight your moving, an 8' axis is really too long for inexpensive screws. It really needs at least 1" diameter or bigger. A better choice is rack and pinion. Guys building Joe's hybrid machines are getting up to 1000 ipm with a Gecko G540 package and rack and pinion from www.cncrouterparts.com

Bottom line is how much do you want to spend? Might be better off to re sell it on Ebay, and use whatever you can get on a better system. You'll probably be out less in the long run.

I also recommend doing a bunch of research. Read through the threads here, and see what everyone else is using.

[Mindcore]

My screws are 1/2"

Thanks for the opinion of replacing one component or the other. I had a similar thought.

I don't mind spending more money on it, I've invested enough as it is, and more then enough hours into it that putting more into isn't a big deal. I'm not rich, so the lower I can go the better of course. Perhaps selling the parts ( which I got a good deal on as far as advertised price goes ) is probably best.

Believe me, I've done a lot of research, I've spent a few months reading the forums, and to be honest, it's still not straight in my mind, and there are only about a million combination's it seems.

I was so concerned about having enough torque to move my big machine that I over compensated in the wrong area. If in fact I'm only getting 150 oz-in at the moment, it would seem that it's plenty of power to run it.

I guess a well matched 240 oz kit would suffice, but that nagging feeling to get the 400's are still there.. but even with the name brand kits do I still run into the same issues? case in point...Probotix has a 400 oz kit running at 40volts, and looking at the motor spec with that kit, it want's 60? so why buy the 400's if I can't ever use it?
"realizations based on my latest experience"

I'll check the gecko stuff and do some comparisons.

I'll also try gearing this week and see if I get satisfactory results in which I'll live with it for a while.

I built the machine because I want to use it's functions, the fun of building it was an added bonus, but ultimately I just want it running.

[rowbare]

Your motors are your weak link. There aren't a lot of drives that run that kind of voltage.

A gecko G540 with Keling 381 oz/in motors is a really nice combination. Those motors are tuned to take full advantage of the G540's capabilities. Keling also sells a 387 oz/in motor, that one works well but the 381 is the better choice. There is also a larger motor that happens to work well, I forget the exact specs but it is a motor in the 640 oz in range that needs 50v and still delivers about 450 when derated. Crevice Reamer describes it in several of his posts.

Where are you located?

bob

[Mindcore]

Thanks, I was just looking at a similar kit, forgot about keling, I studied their site pre-purchase before. I'll take a look again.

I appreciate the help Bob, and Ger.

I had another thread before and everyone was helpful as well. I either didn't follow the advice, or I know more now then I did before.

I'm just north of Toronto.

Now that I get what you're talking about, that's just a stupid voltage to be running at. Argh I wish I posted before I bought, but I suppose I don't mind the school of hard knocks either. I expect to be an expert when I'm finally done with this

[RomanLini]

Something's not right. You said you are running 5 TPI screws and it is stalling at 15 IPM? That is 0.25 inches per second.

So it is stalling at just over 1 motor revolution per second? That is well BELOW the top speed (ie PSU voltage) issues as mentioned by others.

It's probably an issue with the primary resonance of the motor, those size 34 motors have a lot of detent torque especially when they have magnetics optimised for the high holding torque figures they claim and troublesome bipolar wiring. You might be able to stick with the 29v PSU and try a mechanical solution like adding flywheels to the motors or build resonance dampers which are in a thread here somewhere. Also check drag and mechanical load on the machine etc. Once you get the motors through that primary resonance at 1.2 RPS there should be some usable performance up to a few revs per sec (maybe up to 60 IPM) although you won't get real good high speed performance because of the PSU issue.

[ger21]

I use 60" long 1/2" screws, 4 turns/inch. I'm limited to 150ipm due to whipping. My guess is you'll be lucky to get 100ipm with those screws, due to whipping.

The Gecko G540 package with the 381 oz steppers are the best package, but your screws will be the limiting factor. You really need to go to 2 turns/inch, or rack and pinion at that length.