What is the realistic weight limit for Nema 23 steppers?

[Jeff0000]

I know they are rated in oz in, but not really sure what that actually means for me. I am looking at the 420 oz in steppers. Building a 4' gantry, and using R&P. Making my steel order I am realizing that my gantry all said and done is going to weigh like 350 lbs.
Going to Nema 34 is really going to blow up my budget, so just want to make sure this is still going to work, or if I need to rework my plan a bit.

Similar Threads:

• Nema23 weight limit
• Steppers: Nema 23 vs Nema 24
• Need Help!- tool weight limit?
• Nema 23 380oz/in max weight supported
• Question about steppers and gantry weight...?

[SteveWill]

Here a link to this question "How can we calculate the required torque to move a massive object by means of gear assembly?"

https://www.researchgate.net/post/Ho...gear_assembly2

1 HP = .746KW

[awerby]

That formula seems to have been written with regular induction or internal combustion motors in mind. With stepper motors, it gets more complicated, since the torque falls off with speed. The 420 oz-in rating is for the stepper at a standstill, which is when it generates the most torque. But when it starts moving, the effective torque goes down considerably. You'll have to look up the torque curves on the motors you've got in order to determine exactly what the torque will be at what speed, but off the cuff I'd estimate those motors are too weak for a gantry that heavy, if you want to do more than crawl along. You might want to look at aluminum for your gantry - steel will be fine for the rest of it.

[ger21]

The proper way to size your motors, is to pick target velocity and acceleration numbers, and work backwards to find the motors you need to meet those targets.

Weight, and gearing play a big role.

Nema 23's can probably move 1000lbs. The question is how fast do you want to move that weight.

Nema 34's will give you much quicker acceleration, which can be more important than top speed, depending on the application.

[Jeff0000]

Hmm, things are making a little more sense now.

I could probably run 34's for the x and then just 23's for the y and z right?

[hanermo]

A smaller Nema 23 driven at 1:3 with a belt drive is the optimal solution for low cost.
At 48V DC, a cheap chinese 2M542 drive, and HTD belts 1:3, 5/15 mm..

A 3Nm drive gives you about 600 kgf push at 1:3 and ballscrews.
This is a lot.
My table is over 200 kg, and vices etc easily 100-200 kg more.

Moved really well for a stepper system, when I still used steppers.

Because you only need a push force of about 2/3 total mass ie 400 kg or so in my case x 40-70%, the acceleration is high even at 1 Nm torque.
1 Nm from a 3Nm stepper is still available at around 900 rpm.
At 300 rpm at screw, a 5 mm screw still gives acceptable rapids.

Thus, the solution converges at around the same spot.
Cheap motors (30-40-50€), drives (40 -50€ € ish), couplers (belts (==20 per axle)).
Excellent acceleration, excellent resolution, excellent rigidity, excellent repeatability.
All for == 100€ / axis.

Rapids are the last thing you need to be concerned with.
If you need faster rapids, the next step up is ac servos, around 300€ / axis.

They cost about the same as Nema 34 high voltage steppers, but
accelerate 5x-10x faster, (0.02 secs to full speed vs 0.1-0.4 secs)
position 5x more accurately, 1/5000 vs 1/400-1/800
run 3-10x faster (3000 rpm typically), 34 sized steppers about 300-1000 rpm.

1. Yes.
2. Yes.
My experience points out the results in real world use with 400 kg+ mass on moving-table, linear rails.

3.
Well, yes, but..
size 34 wont run nearly as fast at top speed, as the torque falls off quickly,
Nema 34 steppers are much more expensive, and the high voltage drives are expensive.
System cost == 250 € or so, similar to 290 € for ac servos that are 5-10 better for similar costs.

Some new stepper-servos do run fast- but are likely at the same price point or higher.

I am referring to circa 50-80V AC servos, 5000 count, 3000 rpm, about 3-4 Nm peak torque (upto 3 secs).

1.
The proper way to size your motors, is to pick target velocity and acceleration numbers, and work backwards to find the motors you need to meet those targets.

2.
Weight, and gearing play a big role.
Nema 23's can probably move 1000lbs. The question is how fast do you want to move that weight.

3.
Nema 34's will give you much quicker acceleration, which can be more important than top speed, depending on the application.

[Jeff0000]

So because I have two nema 23's moving the gantry I really should be doubling the power of the stepper right?

[hanermo]

Not at all.
You limit is, and will always be, the torque at the high end rpm.

So, if You have 1Nm at say 800-900 rpm, with 2 steppers you will then have 2 x 1Nm at 900 rpm.
However, at say 1000 rpm, you will likely have about 0.2 Nm (0.5Nm), so the top speed is maybe 50 rpm better, say 950 rpm.

The torque drops off fast.
Thats why everyone uses servos on practically all commercial machines.
A stepper/servo hybrid is not option- these are recently available.

Steppers are cheap and cheerful and easy to use - but they have quite low dynamic range.
So they are either accurate, powerful or fast - but only pick 2 out of 3.

So because I have two nema 23's moving the gantry I really should be doubling the power of the stepper right?