[SOLVED]-How big of a powersupply is requiered for 3 stepper motors...

Hey there,

I am new to this whole Arduino stuff. I'd like to build a CNC machine with Arduino and stepper motors. I intend to use these things: Stepper motors (3x) Arduino Uno R3 CNC Shield V3 A4988 drivers (3x)

I am not sure if they would work together properly, so this is question no.1: Will they work?

Are these stepper motors powerful enough if I intend do use normal (for example M8) or "rare"(for example M8x0.35) Metric threaded rods as the rails for X, Y and Z axes? How fast will they be? Will I need to use rare threads or gears to change the speed of the motors?

And the last question is, how powerful power supply is requiered for this project, if I'd like to spend as few money on it (as well as the other components) as possible without taking big risks of failure? I think I should choose from these power supplies.

I have on old PC power supply which I could use as a temporary one.

Well, a lot of useful questions, but - if I would have to answer those in depth - that would be a l o n g post. Building a CNC machine from scratch isn't just a Sunday's afternoon walk in the sunshine.

Ok, let's get serious: - first of all: pls tell us what exactly you want to build, which means: - what do you want to do with your CNC -> will have impact on size, torque of xy steppers and dimension of the construction - what kind of router will be used (determines the load on the z-axis and thus the size/torque of the z-stepper) - do you have an idea about the friction of a metric m8 ? - what kind of linear guide(s) do you want to use ?

Let's stop here and wait for your answers before we go on.

You can calculate the mechanical advantage of a leadscrew very easily, but first you'll need to figure out the linear force that you want at cutter, which we cannot guess.

M8 fine would be a very great deal of mechnical advantage, but you would get glacially slow rapids.

What size is this machine going to be?

BTW standard metric studding is not a precision component, you might need to calibrate for accuracy and linearity of each such budget 'leadscrew'. Or source a higher quality version (stainless studding is worth investigating for this).

For sanity of rapids I'd recommend standard acme leadscrews with a more reasonable pitch (1204, 1003), and you'll have a much more accurate and linear machine. Unless its going to be tiny, but you can get miniature leadscrew, 0802, 0601 I think.

Don't forget stiffness - its not just about forces and torques, you have to check that the mechanical distortions of the machine under load don't reduce its positional accuracy below what you want.

As for motor supply, you have first to work out what speed you want and thus the supply voltage. You might want to check out other drivers that might run cooler or allow a higher supply voltage.

The old PC supply can only give you 12V, which isn't great. Remember slow rapids are ultra-tedious in a CNC machine, you spend all your time watching it move from one cut to another. In a laser-cutter they use belt-drive, not leadscrew, because you can (no cutting forces).

You may find some useful stuff in Stepper Motor Basics

...R

rpt007:
Well, a lot of useful questions, but - if I would have to answer those in depth - that would be a l o n g post.
Building a CNC machine from scratch isn’t just a Sunday’s afternoon walk in the sunshine.

Ok, let’s get serious:

  • first of all: pls tell us what exactly you want to build, which means:
  • what do you want to do with your CNC → will have impact on size, torque of xy steppers and dimension of the construction
  • what kind of router will be used (determines the load on the z-axis and thus the size/torque of the z-stepper)
  • do you have an idea about the friction of a metric m8 ?
  • what kind of linear guide(s) do you want to use ?

Let’s stop here and wait for your answers before we go on.

First of all, I need to say that the questions were written while the whole thing was a plan only in my head.
Last night (central Europe time zone) I talked about it with my father, and he told me that he has ballswrews in his workshop, and if he wanted to, he’d even found linear rails (the ones Google finds you first, if you search for, unfortunately, from mobile I cannot use links properly)

the tool I’d like to use will be a mini grinder of some kind.

I’d like to build something like this, but it might be built from metal instead of wood. I’d like it to be as big as a smaller desktop, at least.

For what purpose so I want to build one? I’m a student learning CAD/CAM, and this should help me greatly with understanding things before we even learn about them in school.

Do you mean, Mark, that I should use belts instead of ballscrews?

Thanks for your help :slight_smile:

Norbert,

I fully support your intention to learn in a practical environment rather than only listening to theoretical sessions at your school. Thus you know what you are talking about …

Another question would be: what is your budget limit?
You are talking about getting some stuff from your father; but there are still some investment (besides of time - don’t underestimate, this will be your most time consuming project ever so far) questions to decide.

I’d like it to be as big as a smaller desktop, at least.

So it will be in the range of, let’s say, 400 x 600 mm (outer measures), which will result into something like 300 x 400 (X x Y) mm working space.

If your budget allows, go for aluminum extrusions (pre-cut with very little tolerance).

As @MarkT said, take the ball screws rather than belt drives as you will need the force to cut (wood, aluminum, steel ??). I built a small CNC made of extrusions - but primarily I am cutting wood (soft- and hard wood, acrylic and sometimes thin aluminum). My machine has trapezoidal spindles, which for my needs is sufficient.

Currently I am busy with a new project, a very small laser engraving machine, which came as DIY kit, made of aluminum bars, driven by belts - as there is very little force/torque needed to move the lightweight laser around.

That said: if you are to cut something, I would go with the ball screws rather than belts, which might work, but a ball screw is the better choice. But you also have to consider, what kind of linear rails you want to use.

They start with simple tray sliders (I am kidding), bushings/rods and go to very expensive linear motion systems. Have a look here.
This site is a wealthy source for CNC newbies and experts as it covers most of the essentials for CNC’ing. You will find a lot of answers to your questions here with a systematic approach as it leads the builder through all steps and decisions.

Having decided for the mechanical driving/motion system you have to decide about the cutter (=load on z-axis). Only then we can talk about suitable motors for each axis, the motor drivers and the adequate power supply.

12V is just enough for my tiny laser engraver, but for your CNC we will talk about higher voltage as the discussion goes on.

rpt007,

The budget limit is a good question because I mostly have to pay for the electric parts as the metal parts, the screwrods and the rails are already in the workshop. I mean the boards, wires, motors and the grinding tool as the electrical components. I have about $50 to buy these(without the grinding tool and the PSU), but if it's really necessary, I could spend more on them. The grinding tool I'd like to buy is about 1.2 kilograms.

I meant a little bit bigger desktop, for example 1000*700, but I'm not sure about it, yet.

I also asked in our Hungarian Arduino topic about some things, but that topic is of course not as thorough as the Arduino forum. They suggested that I should try to buy a PSU of an older printer. They said that these PSU-s should be enough in Watts and give me higher Voltages.

You know the cnczone.com forum?

MarkT: You know the cnczone.com forum?

No, I don't. Should I try to ask it there?

As long as you don't know exactly what your specific requirements are there is no chance to get a serious answer on your initial question.

$50 might be a bit tight for a machine of that size with metal rails. For such a size I would go with NEMA23 size steppers which have at least 1-1,5 Nm or more to have something solid and strong. For the z-axis you should consider to have the strongest motor.

That might require at least a very good cooling of DRV8825's which I prefer rather than the 4988 drivers.

From a distance I would say, your PSU then should have at least 24V, better 30V and ca. 100-120W. But that very much depends on how good the linear motion system works (low friction ..).

You're right, I searched for all kinds of calculators for these rods and my conclusion is that I need stronger motors.

But are you sure that the drv8825 will be powerful enough to nema23?

I use something like this for NEMA 23s

https://www.amazon.com/gp/product/B00DFSF9GE/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

Hi Norbert,

But are you sure that the drv8825 will be powerful enough to nema23?

YES and NO. It depends, how much force / torque (and this results in current) is needed by your mechanical construction and while it is operated.

Nema is just a definition of the distance of the mounting holes of a stepper. It doesn't tell you anything about the accurate force/torque the motor can deliver.

Normally the wider the mounting holes are apart (which means a "bigger" NEMA number) the more power the motor has. But there are overlaps in power. You will find strong NEMA17 with close to 1Nm and NEMA23 with torque less than 0.5Nm.

If all of your axis (under operating conditions) only require 0.5Nm (max) or less, you can go with NEMA17. Given the size of your machine I would take the NEMA23 with at least 1Nm or more.

The downside of that is: there is no torque/force for free, which means that you need motor drivers which can deliver that current.

A drv8825 can go up to 1.2A/coil with proper heatsink (I would take an active fan plus heatsink). If your motor is able to deliver the required torque at that current (and - look at the datasheet - at a given RPM) then you are fine with a drv8825. It can also go with up to 45V of voltage. (I would go with 40V max = 10% less than the dat sheet tells you).

Voltage is important, as the dynamics of a motor increase the overall resistance (= ohm resistance of the coils plus increasing inductance as the speed goes up). Under these conditions the driver still has to deliver enough current so voltage (of the driver) is another parameter to look at. The resulting voltage at the motor coil is far less, so don't be confused when you find a coil resistance of your motor around a few ohms. Go for motors with low impedance (resistance and inductance values should be small as possible).

If you are exceeding the current of 1.2A/coil, you have to go with a stronger driver than the drv8825.

I purchased a while ago a TB6600 based stepper driver from a Chinese source. In some CNC forums the TB6600 are well respected, but some people seem to have troubles with the Chinese make. Anyway, when I follow the discussions it turns out that in 90% of the cases the problem sits about 40cm in front of the PC display .. That said: most of the issues result from wrong wiring.

My stepper drivers are working since the day I unpacked and installed them without any flaws, but I always stay about 10-20% lower than the specs would "guarantee".

The drivers were pretty cheap compared to others on the market. I got them for less than $15/axis 2 years ago.

So what are your next steps?

rpt007: Hi Norbert,

YES and NO. It depends, how much force / torque (and this results in current) is needed by your mechanical construction and while it is operated.

Nema is just a definition of the distance of the mounting holes of a stepper. It doesn't tell you anything about the accurate force/torque the motor can deliver.

Normally the wider the mounting holes are apart (which means a "bigger" NEMA number) the more power the motor has. But there are overlaps in power. You will find strong NEMA17 with close to 1Nm and NEMA23 with torque less than 0.5Nm.

If all of your axis (under operating conditions) only require 0.5Nm (max) or less, you can go with NEMA17. Given the size of your machine I would take the NEMA23 with at least 1Nm or more.

The downside of that is: there is no torque/force for free, which means that you need motor drivers which can deliver that current.

A drv8825 can go up to 1.2A/coil with proper heatsink (I would take an active fan plus heatsink). If your motor is able to deliver the required torque at that current (and - look at the datasheet - at a given RPM) then you are fine with a drv8825. It can also go with up to 45V of voltage. (I would go with 40V max = 10% less than the dat sheet tells you).

Voltage is important, as the dynamics of a motor increase the overall resistance (= ohm resistance of the coils plus increasing inductance as the speed goes up). Under these conditions the driver still has to deliver enough current so voltage (of the driver) is another parameter to look at. The resulting voltage at the motor coil is far less, so don't be confused when you find a coil resistance of your motor around a few ohms. Go for motors with low impedance (resistance and inductance values should be small as possible).

If you are exceeding the current of 1.2A/coil, you have to go with a stronger driver than the drv8825.

I purchased a while ago a TB6600 based stepper driver from a Chinese source. In some CNC forums the TB6600 are well respected, but some people seem to have troubles with the Chinese make. Anyway, when I follow the discussions it turns out that in 90% of the cases the problem sits about 40cm in front of the PC display .. That said: most of the issues result from wrong wiring.

My stepper drivers are working since the day I unpacked and installed them without any flaws, but I always stay about 10-20% lower than the specs would "guarantee".

The drivers were pretty cheap compared to others on the market. I got them for less than $15/axis 2 years ago.

So what are your next steps?

If I am not mistaken, the drv8825 is able to handle up to 2.2A, or at least it is written by the seller a on ebay. However, on Texas instruments website it says that the drv8825 can handle 1.8A as RMS and 2.5A as peak.

As nema23 i meant the average motor in that size standard, because I don't have an exact idea of which motor should I choose. I'm thinking on a 270oz-in variant for 10-15 bucks per piece.

Hi,

I wrote "1.2A/coil" which indeed should be peak and as there are always two coils, the result is 2.4A (max). If you go for 270oz that means in metric values 1.9Nm which should be more than sufficient for your CNC (provided for that the linear motion system is quite good).

I wonder where you would get those motors for 10-15 bucks/piece. The cheapest I found was $22.

Nevertheless, if you really want to do everything right from the beginning, then you should first build all the mechanics together, adjust and fine tune as much, precise bevels etc.

Then you can measure the friction exactly and calculate how strong your steppers have to be when they have to drive the router through your work pieces at a desired speed.

But theory is one thing, reality another one.

If you get those steppers, they should do. And then you have to decide for the drivers and power supply. Normally I wouldn't add all current consumptions of each single stepper.

They don't work too long all together, one or two are busy, the third one idle. So you might get along with the addition of all 3 stepper currents minus 20-25%, to have a little bit extra, when all 3 steppers should be under full load at the same time.

rpt007: Hi,

I wrote "1.2A/coil" which indeed should be peak and as there are always two coils, the result is 2.4A (max). If you go for 270oz that means in metric values 1.9Nm which should be more than sufficient for your CNC (provided for that the linear motion system is quite good).

I wonder where you would get those motors for 10-15 bucks/piece. The cheapest I found was $22.

Nevertheless, if you really want to do everything right from the beginning, then you should first build all the mechanics together, adjust and fine tune as much, precise bevels etc.

Then you can measure the friction exactly and calculate how strong your steppers have to be when they have to drive the router through your work pieces at a desired speed.

But theory is one thing, reality another one.

If you get those steppers, they should do. And then you have to decide for the drivers and power supply. Normally I wouldn't add all current consumptions of each single stepper.

They don't work too long all together, one or two are busy, the third one idle. So you might get along with the addition of all 3 stepper currents minus 20-25%, to have a little bit extra, when all 3 steppers should be under full load at the same time.

Hi,

I'm sorry, I misunderstood you.

So, you mean that I can use the cnc shield I linked here and the drv8825 or I'll have to buy the 6600?

I've checked it, the motors rated voltage is 3A, but I am not sure if it is per coil or altogether, the two coils. Either way, the DRV8225 is not powerful enough for these motors.

So go with a bigger one. My recommendation nowadays is a TB-6600 or ST-6600 based driver. I found some by asking Google "ST-6600 stepper driver" - price in Europe: 22€.

There are still TB-6560 out, but looking at the datasheet of the 6600, this is a better choice. The newest ST-7128 are out now, but I can't see the advantage which I could make use of compared with my 6600 based drivers.

rpt007: So go with a bigger one. My recommendation nowadays is a TB-6600 or ST-6600 based driver. I found some by asking Google "ST-6600 stepper driver" - price in Europe: 22€.

There are still TB-6560 out, but looking at the datasheet of the 6600, this is a better choice. The newest ST-7128 are out now, but I can't see the advantage which I could make use of compared with my 6600 based drivers.

The TB-6600s seem to be good, but I cannot find any ST-6600s (Google shows me only TB-6600s) and the ST-7128s are pretty expensive compared to the TB-6600s.

Will they handle the 3A-rated motors? I mean, I saw some guys using TB6560 for these motors and haven't complained yet; but I'm a little bit confused with the current ratings.

It seems that the ST and TB Versions are the same chips (one being produced by Toshiba = TB and one by ST = ST). Mightbe that Toshiba is the Original Manufacturer and the other one has a license or vice versa. I don't care.

Here is a link to a company, which carries those drivers. They go up to 4A max.

In the EU branch they are currently out of stock; but they have worldwide locations.