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Topic: [SOLVED]-How big of a powersupply is requiered for 3 stepper motors... (Read 4275 times) previous topic - next topic

norbert1998

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?

norbert1998

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.

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.
Before you ask:
Did you really read and understand How to use this forum ?
AND:
Do you have already some solution or is a part of the problem sitting in front of the screen?  :)

norbert1998

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.

rpt007

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.
Before you ask:
Did you really read and understand How to use this forum ?
AND:
Do you have already some solution or is a part of the problem sitting in front of the screen?  :)

billcat

I've checked it, the motors rated voltage is 3A....Either way, the DRV8225 is not powerful enough for these motors.
I imagine you meant rated 'current' ..About 'powerful enough' , you may be right, or you may be wrong.  The drv8825 drivers will drive the 3a motors, and you may be surprised at how well. I've been running these drivers at 2.2amps (according to the current set adjustment on the driver) for quite a while now. But I am using both heatsinks and a cooling fan on them.  I'm driving two nema23 and one nema17 with this arrangement. All of my YouTube videos are of this very setup, if you can tolerate the poor quality vids :)
https://m.youtube.com/watch?v=2WCgwBhf8jw
cnc

Here is where it is suggested that these drivers can handle up to 2.2A with proper cooling.
https://www.pololu.com/product/2133
drv8825

Nonetheless, most of the previous replies of this thread provide very good, accurate info. You WILL get maximum torque and speed from your machine at max rated current of your steppers. So for a larger, heavier machine, the drv8825s may be insufficient.

I read so many negative things about the 'tb' drivers at cnczone.com over the last several years that I never bothered to 'chance' it with them; they may be fine.  I do have good experience with drives by Gecko, on a larger, heavier machine, but they'll cost you a bit.

rpt007

@billcat:

Quote
I read so many negative things about the 'tb' drivers at cnczone.com over the last several years
You are right; I think I mentioned that in one of my previous posts.
Most discussions are about insanely cheap Chinese TB6560 pcbs with 3-4 channels.

And: it turns out that besides of technical issues of the poor implemention of some pcb's (wrong dimensioning, wrongly placed opto couplers ..) that in lot of the discussions the newbie user are contributing to the problem (wrong wiring, no experience in how to limit the curent, removing motor wires while in operations etc.).

My first CNC control unit was a red pcb with 4 of those TB6560. After only 2 weeks of moderate testings the y-channel gave up and I installed the TB6600 based drivers instead, which now are operating since then (2 years). My newest project is based on GRBL/arduino and drv8825 and is working fine. The current is under 1A, so I don't use active cooling, but heat sinks.

So the drv8825 might work in this case, given that the whole motion setup allows for smooth gliding with low friction. I think, z-axis might be the most critical one to look at.
Before you ask:
Did you really read and understand How to use this forum ?
AND:
Do you have already some solution or is a part of the problem sitting in front of the screen?  :)

norbert1998

rpt007

I've been looking these variants:
Cheaper
Not that cheap, but still cheap
Both have free shipping to Hungary.



billcat

Yes, I meant current  :D
If I'm not mistaken, you're using belts for the X and Y axes while the Z axis is driven by a ballscrew.


I've found an equation for ballscrews (I've been searching for these equations, but Google wasn't willing to help me before, and now, without even searching for it, I've found it). It says that for, for example, a router like this one wighing about 4 kgs, with a ballscrew that has 3mm lead, I require 0.02122 Nm torque (for keeping up the raising of the Z axis).

So, this motors torque has to be enough for raising 4 kgs at max, according to the datasheet.

But, if the driver can make it a little bit more powerful (I don't know if it can), it should be enough. But, because I don't know the weigh it will have to move, for the Z axis, I'll have to use this motor.


Please, correct me if I'm wrong.

The equation is: Torque eqauls with linear force times lead divided by 2 times pi times ballscrew efficiency. (T=(F*l)/(2*pi*e))

But I might be able to use the linked nema 17 for the X and Y axes, if I'm not wrong.


#21(rpt007)

So, what should I use then? :D

MarkT

Do you mean, Mark, that I should use belts instead of ballscrews?
I never mentioned ballscrews (expensive), and if you read my posting again it is quite clear
that I mention belt drive only for laser cutters where the forces are much less.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

billcat

If I'm not mistaken, you're using belts for the X and Y axes while the Z axis is driven by a ballscrew.
That is correct:-)

I've found an equation for ballscrews (I've been searching for these equations, but Google wasn't willing
I once found a very comprehensive spreadsheet online for determining cnc parameters, torque,etc. I believe I have it saved on my pc at home. When I get off work today, and more importantly,if I remember, I'll see if I can find it and attach it here.


norbert1998

I never mentioned ballscrews (expensive), and if you read my posting again it is quite clear
that I mention belt drive only for laser cutters where the forces are much less.
I have one ballscrew which is about 30 cm long, that'll be good for the Z axis, and I figured I could use trapezoid thread with some kind of nut that fits it for the two other axes.

rpt007

Hi Norbert,

my findings:

* Driver:
I would prefer the slightly more expensive driver (2nd one) as I have more confidence in it, due to the way the whole thing is built. I've got exactly the same one from another source some time ago to use it in a test environment and it worked flawlessly.
Advantages of this driver:
1. it comes with optocouplers to separate logic controller (Arduino) from motor driver's electronics (I opened the case to have a closer look inside)
2. motor current is set by dip switches rather than fiddling around with a potentiometer, not knowing exactly what current you are measuring and when (stall, moving ..)

* Steppers:
There is a huge difference in your steppers regarding the torque (48 vs 270 oz in = 0.34Nm vs 1.9Nm)
My assumption is that the z-axis stepper will be quite a bit oversized whereas the x/y steppers imho seem to be too weak. At least you won't have much extra torque when it comes not only to move the axis but have to bring in some force while cutting material.

If I am not mistaken then your router will be in trouble when it comes to hard wood like oak.

My machine is way smaller than yours and it comes with NEMA23 on all axis. All motors might be a bit oversized on my machine (all of them come with 1.4Nm), but I like when the motors don't run at their limits.

My suggestion is, to get NEMA17 or NEMA23 for the x/y axis each close to or above 1Nm to be on the safe side, whenever your machine gets into rougher cutting conditions. The force which is need to cut hard material is higher than the force which is needed to move the axis.

Before you ask:
Did you really read and understand How to use this forum ?
AND:
Do you have already some solution or is a part of the problem sitting in front of the screen?  :)

rpt007

Before you ask:
Did you really read and understand How to use this forum ?
AND:
Do you have already some solution or is a part of the problem sitting in front of the screen?  :)

billcat

Thanks, billcat, I'd appreciate it :)



Your welcome, here it is. (attached)

I used the spreadsheet to help me design a larger CNC machine, demonstrated in yet another low quality video here:another hard to watch CNC vid     

*disclaimer1-haven't looked at it in quite some time, your on your own to figure it out!
*disclaimer2-I found it on the web a good while ago (don't remember where), hopefully it's ok to share

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