[jasonlg3d]

We recently upgraded our DIY machine from 170 oz/in motors to 425 oz/in motors. With the lower torque motors we could not get the ipm speed nessecary to cut wood (80 - 110 ipm). Thinking that our motors were the problem, we upgraded them to the larger ones mentioned above. Actual motor details here.

With new motors in place, we still have speed issues. They are actually slightly worse with the new motors than the old. I'm wondering now if our controller is the issue. We are using the TB6560AHQ drivers implemented in this board.

The motors are 200 steps / turn at 1/2 micro stepping = 400 steps/turn
The lead screw is 12 turns / in.
So total turns per inch = 4800.

We began trouble shooting by completely removing the motors from the machine and just driving them with no load. I could get the motors up to 110 ipm with very slow acceleration. At that speed, I could just tap the dampener (a rubber hockey puck) with one finger and get the motor to stall. I would have expected these motors to be much more robust than that. When hooked to our y-axis, the best i can do with no stalls is 40 ipm and fairly slow acceleration.

Could this be a driver problem? Perhaps lack of sufficient current? We would greatly appreciate any help as this is devastating our progress.

[doorknob]

Do you have the motor connected with a "bipolar parallel" hookup or a "bipolar series" hookup?

Either way, you are limited by the TB6560 to using a maximum voltage of perhaps 24 or 36 volts, whereas with a different driver you could use something closer to 80 volts to get improved torque at a higher maximum speed (for a bipolar parallel hookup).

(The motor specs do not include a torque vs. speed curve for comparison purposes, however. What are the specs of the motor that you used to use?)

[jasonlg3d]

They are Bipolar-Series. Would having only 24V really limit our speed to such a low number? That surprises me given the popularity of the Toshiba drivers. I've been looking at the calculators here. I can't make sense of what they are telling me for max speed. If I use the data from the datasheet I posted earlier. The calculator says a max RPM of 22. Which is absolute nonsense. :drowning:

[doorknob]

With a bipolar series hookup, the winding inductance is substantially higher (by a factor of 4) than with the bipolar parallel connection, and so the driver voltage required for best speed will be substantially higher (and way outside of the capabilities of the TB6560), and the torque would be expected to drop off with speed sooner than with bipolar parallel.

So the first test that you could do would be to rewire one of the motors for bipolar parallel (and set the current to the proper amount via the DIP switches on the board) and see whether that gives you a speed boost, and assuming that it does, your next step would be to try a better driver with a higher power supply voltage.

[jasonlg3d]

So it seems we basically picked the worst possible way to wire our motors for our machine. We don't need more torque we need speed. I wonder now if our original motors would have worked. Oh well check that cost up to educational expense. I think the other thing we did wrong is our lead screw pitch is too small. 12tpi may have been too fine. We will rewire the motors over the next day or two and report back. Thanks so much for the help.

[ger21]

425oz motors are a bad choice for any driver not capable of using 80V, as they have high inductance which = slow speed. Couple that with 12tpi screws, and you have no speed.

.....................given the popularity of the Toshiba drivers

They're popular because they're cheap, not because they're good.

If You're looking for speed, you have everything wrong.
1) Cheap drives.
2) High Inductance motors
3) Low power supply voltage
4) 12tpi screws

It's possible to get decent speed from 24V, but you need the other components to work together.
I use 250oz motors with a Xylotex on 24V (wired biploar series due to the current rating), and 1/2-8 2 start acme screws. I can get up to 190ipm.

For a router using acme screws, best performance will come from screws with 2-4 turns per inch.

One other issue you may be seeing is resonance. My machine was almost unusable due to resonance issues until I built some dampers.

[jasonlg3d]

Thanks for the reply Gerry. We have received a big education over the last couple of days. I see now that you are right when you say we did it all wrong. I'd like to say I wish we knew all that before we started, but seeing the effects of our misjudgments makes the lesson that much more memorable. After a boat load of reading and researching we have come up with the following game plan.

Budget is most definitely an issue at this point, I stupidly mowed over the money tree sapling that had sprouted in my backyard. Still kicking myself for that. That said, we are going to try to get to 110ipm by spending the least amount of money possible. First thing we are going to do is re-wire the motors from bi-polar series to bi-polar parallel. That should give us a boost. I don't know how much. Can any of you give us an experienced estimate on that?

Secondly, we have already ordered a new lead screw for our x axis. This one is at 8tpi, which i realize is not as good as you suggested but it was cheap. If any of you have a great resource for buying those things please let me know.

Once these two upgrades have been made, we will test and see what kind of performance we have.

One last upgrade we are also considering is to increase our power supply from 24V to 36V. This is a fairly cheap upgrade ($60) but we will hold off on that for now.

When we started this project we had a very small budget. The controller, power supply, and motors all came as a bundle. I see now that the controller is pretty pathetic, but short of slapping down another $250, that is what we have to work with for now.

I'd say we would go back to our old 170 oz. in. motors, but they only take 24V max and they are single shaft, which leaves no room for a dampener. We have added hockey puck dampeners to our current motors, so far I see no difference in their performance, but that could be a lack of speed, or a lousy damper.

Thanks to you guys again for being so helpful. We'll keep this thread running as we progress. Maybe someone else can avoid some mistakes we made because of it.

[awerby]

...we are going to try to get to 110ipm by spending the least amount of money possible. First thing we are going to do is re-wire the motors from bi-polar series to bi-polar parallel. That should give us a boost. I don't know how much. Can any of you give us an experienced estimate on that?

[Here Stepper Motor Connection Options is a handy chart that quantifies the performance boost you can expect by going to parallel over series wiring. There are also some wiring diagrams there.]



I'd say we would go back to our old 170 oz. in. motors, but they only take 24V max and they are single shaft, which leaves no room for a dampener. We have added hockey puck dampeners to our current motors, so far I see no difference in their performance, but that could be a lack of speed, or a lousy damper.

[What makes you think those motors can only handle 24v max? The nameplate voltage on stepper motors isn't any indication of max voltage; usually they want about 25 times the rated voltage. The voltage for a stepper is best calculated using the formula: Optimum Voltage = 32 x (square root of the inductance in MH). There's a thread here on the Zone where all this is hashed out in more detail: http://www.cnczone.com/forums/steppe...selection.html

I think that your original motors will probably perform better than the new ones, even without the hockey pucks...]

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[jasonlg3d]

I have seen that graph you linked. Problem is there are no units so I don't know if that performance increase is to scale.

I'm basing that 24V rating on what I remember the datasheet says for those motors. I'll try and dig it up and confirm it. Also, the smaller motors are only 4 lead, so they cant be wired in parallel. (Perhaps they already are, again will try to find that datasheet).

We do plan on building a 2nd machine in the future, so all of these lessons will be put to good use eventually.

Thanks again for the help.

[automationtechinc]

if you use a G540 stepper driver with a 48V, 7.3A power supply
you will get a lot of speed
Automation Technology Inc. | Stepper Motors, Automation Technology Inc