Good day all.
I’m in the process of building a CNC but there are some things I’m unsure about and would like to ask for some assistance.
I purchased 3 x DRV8825 stepper drivers and got my code working and tested the system with old Nema 17 steppers obtained from old floppy drives. The problem is, these motors are quite weak and I would like to get stronger, more suitable steppers in my final build.
There are 2 or 3 stepper motors that I have in mind, but I do not know which one will perform the best in terms of accuracy and performance. Essentially I would like to make PCB’s with the CNC, as well as ordinary cut outs such as wood and aluminum. So it requires good accuracy.
Which would be best between the motors below? (Using the DRV8825 driver)
NEMA 17 http://www.hobbytronics.co.za/p/576/nema-17-stepper-motor
specs: 4.8kg/cm - 0.9 degree, 4 leads
Step Angle (degrees): 0.9
Motor Length (mm): 48
Rated Voltage (V): 2.4
Rated Current (A): 2.4
Phase Resistance (Ohms): 1.0
Phase inductance (mH): 1.8
Holding Torque (g/cm): 4800
Rotor Inertia(g/cm3): 68
Detent Torque (g/cm): 260
Weight (kg): 0.36
NEMA 23 http://www.hobbytronics.co.za/p/578/nema-23-stepper-motor
specs: 56mm 9kg/cm - 1.8 degree, 6 leads
Step Angle (degrees): 1.8
Motor Length (mm): 56
Rated Voltage (V): 3.6
Rated Current (A): 2
Phase Resistance (Ohms): 1.8
Phase inductance (mH): 2.5
Holding Torque (kg/cm): 9
Rotor Inertia(g/cm3): 300
Detent Torque (g/cm): 400
Weight (kg): 0.7
Will a 6 wire stepper have good accuracy with the DRV8825 driver?
Should I be looking at other steppers rather?
Also, would a 24V supply be enough? Or is that too high?
I’m somewhat confused with stepper motor selection after reading various forums and will greatly appreciate some advice in selecting the best option for a stepper motor). I actually have so many questions, but will stick to the basics for now
Thank you in advance.
Both of the stepper motors you are considering have rated currents that are outside of the range that the DRV8825 can deliver without additional cooling. They should still both work with the DRV8825 if you set the current limit to around 1.5A per coil, but you might consider using a stepper motor that is more appropriate for this driver. For example, we carry several NEMA 23-size stepper motors that have a more appropriate rated current of 1A per phase.
I would not expect the number of wires to affect the accuracy, and you would only be using four of the six of the wires, anyway (leaving the center tap wires disconnected).
As for your question about the power supply, 24V would work fine as long as you have the current limit set correctly. Using a higher voltage than what a stepper motor is rated for will let you achieve higher step rates. You can find more information about this in the first FAQ on any of our stepper motor product pages.
Thank you so much for your advice and recommendations.
I think I will go with the Nema23 stepper and run it at 1.5A. I’m struggling to find local suppliers with 1A stepper motors (No stock).
I’ve also found a 36V 350w PSU with a 12V 1A and 5V 0.5A rails, I’m sure that will do the trick .
This thread helped me out to choose a NEMA 23, but I got mine from…http://www.motionmarketplace.com/marketing/stepper-motors/.
It works Great and Thanks!
I agree with Frank as far as this thread being helpful to me, but I would like to add another source for more information and where to get stepper motors:
motioncontrolguide.com/learn … tor-guide/
Can we use DRV8825 for driving Nema 17 stepper motor ?
The DRV8825 carrier can handle 1.5A per phase without additional cooling. If your NEMA 17 stepper motor has a current per phase rating equal to or less than 1.5A, it should work with the DRV8825.
i have a Fujikoki unipolar Stepper Motor with 5 leads and connected it to the drv8825. It works perfectly. I just reduced the phase current by a factor of 1/sqrt(2) and it works.
But why cannot be the DRV882 used for 5-leads-unipolar Stepper Motors? The “com”-Leads are internal connected together an thats why only 5 leads are comming out. So why can it not be used as an 6-leads-motor with bridged com-leads (Intern)?
In full step mode, without current limiting and no load, a five lead motor should work perfectly with a two phase driver. The two center taps are always at about the same potential so no current should flow.
However, if current limiting is employed and a load is in place, then there is a possibility of current flow between windings. How that will affect operation is difficult or impossible to predict, but it is hard to imagine how this could lead to better performance.
Try it and let us know how it works.
Why is it that important that it runs only in full step mode?
Today i tried to run the stepper motor with load. The stepper motor controls an expansion valve. So i took pressure on the valve with 5bar, 10bar and 15 bar. It worked without any problems by driving it.
Now i want to know if i can set other step modes. Is it a big risk?
The timing and voltage levels between the phases is very different in microstep than full step mode, but you can certainly try it and see.
I am new to this forum, but I want to show that a 5 wire stepper can be driven by a bipolar motor driver. You will need to connect the fifth wire to + ve terminal of the power supply and set the motor current to it’s rated current.In this configuration the N channel Transistors/ Mosfets are inactive because they are shorted fifth wire going to + ve terminal.This is not harmful to circuit.Only four P channel Transistors/ Mosfets are active and act as a uni-polar driver. Current chopper circuit is also active. Less heat is generated and motor works fine.
[quote]You will need to connect the fifth wire to + ve terminal of the power supply and set the motor current to it’s rated current.[/quote]This is undoubtedly a bad idea and not to be recommended. The MOSFETs are not shorted to the + terminal, because there are inductors in the motor circuit.
I do not believe that Shantaram knows the internal circuitry of the driver chip and is in a position to make an informed recommendation.
Actually N Mosfets are bypassed by connecting the fifth wire to +ve Terminal.This is practical experience. This works fine.
Imagine that there are no N channel Mosfets in the circuit.
[quote]Actually N Mosfets are bypassed by connecting the fifth wire to +ve Terminal.[/quote]No, they are not. There is a motor winding in between, in which large voltages can be induced. Are you confused about N versus P MOSFETs?
If you want to use a five wire unipolar stepping motor, the safest and best approach is to use a unipolar motor driver. “It worked for me” is not a good reason to recommend a dubious practice to others.
Please see the attached schematic on hoe to connect 5 or 6 wire motor to bipolar motor driver.I am using this technique since only L298 was available as bipolar stepper motor driver.
Looks complicated! This is what I’ve been using for unipolar stepping motors, and it works very well. Replace the NPNs with logic level N-MOSFETs for truly superb performance.
can we use nema 17 2.8v stepper motor driving by a4988 ?
motor voltage 2.8 and we use wihch voltage ?
I see you have posted a similar question elsewhere on our forum. We have answered your question in that other thread.
So I have to adjust voltage to give me 1.5A per phase.