Motor torque…..do I need more?

[RoxanaPS]

When and why would it be desirable to have increased motor torque? I’m not sure what the benefit would be for the disadvantages may be to go either way. Thanks.

[Richards]

Motor torque depends on the load being driven. A small motor that can spin fast (3,000+ RPM) can be connected directly or to a gearbox. The torque increases depending on ratio of the gearbox. The speed decreases at the same ratio. For example, a 5:1 gearbox would increase torque 5X but it would decrease speed by 5X (disregarding the loss due to inefficiency). A large motor might not be able to spin as fast as a small motor, at least if the motor is affordable. It would also require more power.

I start with the weight of the load that I need to move and the speed that I want to move the load. Next, I look at the friction caused by the construction of the machine. Does the machine have ball-screws or rack and pinion or something else. Does the machine have linear rails with ball-bearing blocks or is it just metal to metal with a thin coat of oil? Then, I go online and use the motor-sizing software that various vendors have to see what size motor would be required.

After seeing what size motors are recommended, see if other motors would work if gearing were added.

[CNCMaryland]

Your existing motors are not powerful enough. Period. The gear reduction helped in terms of boosting the torque, however, as you have learned, and as physics go, increasing torque results in a decrease of horsepower(speed). By adding the gear reduction you can now only go so fast.

A stepper motor can only spin so fast. While I do not know the calculations for rack and pinion, I will demonstrate the concept using a ballscrew.

Let's say the Max RPM is 3000. You have a 5mm pitch ballscrew as well. Therefore 3000x5mm = 15,000mm/min max. I can try all I want to go 20,000mm/min, never going to happen, and more likely it will fault.

In short, you have reached your limit. Now you need a more powerful motor.

[CNCMaryland]

https://www.omc-stepperonline.com/ts-se ... cl57t-s30a

[ShawnM]

Another problem is that he has now been told by the manufacturer of his hobby, extruded aluminum frame router, CNC4Newbie, that his machine the way it's currently configured is capable of 3000 IPM, which is TOTAL BS. They have never seen his current configuration, motors, drives and software and have not done any mathematical calculations to support their BS. Now Rob has it in his head that his machine should move 4 feet a second for rapid moves. It's simply impossible with this machine, that is if you want to actually cut anything.

A bigger stepper isn't gonna help him, they simply cant spin fast enough and still produce enough torque to actually cut anything at the crazy speeds he wants to go. Large format, industrial routers that cost in the hundreds of thousands of dollars dont move that fast. There's absolutely no reason to go that fast and remember you still cut at 100-300 IPM and Vcarve a little faster.

I explained to him what a planetary gearbox will do to his torque and speed and he got advice from someone to buy 10:1 gearboxes. Not sure why as that just killed his speed again.

He made some dip switch changes to his stepper drive (it has a few settings not found on other drives) that he thinks fixed the stalling issue and he had it running great at 500 IPM rapids. Then he of course wanted to go 4 times faster and then it broke down again. He's chasing his tail here.

I've really tried to help him but there's really nothing more than can be done when you try to exceed the physical and mathematical limits of a machine.

[CNCMaryland]

200ipm rapids is totally good enough if you ask me. If he can get reliable use of the machine at 200ipm, then take it and go make parts.

[RoxanaPS]

https://www.omc-stepperonline.com/ts-se ... cl57t-s30a

Thank you. I am going to order this motor. I have discovered that my Y axis can still run very fast even with the planetary gears installed.

[CNCMaryland]

https://www.omc-stepperonline.com/ts-se ... cl57t-s30a

Thank you. I am going to order this motor. I have discovered that my Y axis can still run very fast even with the planetary gears installed.

It's worth a shot dude. And I know you don't want to hear this, but I'm still betting hard on there is something binding. I assume with a rack system when the machine is powered off, you can by hand push the axis. Not sure, I've never had a rack system, but I wouldn't see what not.

I would 100% be checking this. I would 100% be adding grease to the linear rail bearing blocks/carriages. I would 100% be lubricating the rack as well.

You have to see at this point that your issue no matter what you do is the same, there is something wrong with the linear motion of that axis.

In that video you posted the machine would move almost to the middle of the machine and it would bind there. If that is always the point of the problem, I'd be looking, measuring, etc.

[Jerminator96]

Extruded aluminum frame? Wonder if it's flexing in the middle of the span with torque applied? You wouldn't be able to tell pushing it by hand, necessarily.

Maybe chuck a pencil in the spindle and tape a sheet of paper on the table, set Z to just touch the tip of the pencil, run full speed and see if it draws a straight line or if there's a "hump" when it stalls?

[Sword]

Just for comparison sake, I run NEMA23 439 oz-in closed loop motors on a 4' x 8' rack and pinion machine, with 5:1 planetary gearboxes and 24t pinions. I have plenty of torque to cut anything at a reasonable/recommended feed rate and the max rate is set at 1200ipm. The only time I've faulted the drivers, is when I stalled my spindle with a 1.25" bowl cutter going too deep and fast upon entry into the cut.

Edited to say....steps/rev is 3200, and turns/in is 1.326291. Edge quality on hardwoods are excellent, and 3D/Vcarve toolpaths work great as well.