Home CNC with Arduino III - Electronics

Introduction

At last it is time to look, in detail, at the part electronics of the Homemade CNC with Arduino Root 3.

The electronics are fairly straightforward, but what can be misleading is that there are many possibilities.

In this article I will tell you how I did it. Why I have made the decisions I have made and I will give you tips for selecting components.

My premises, when choosing the components, were as follows:

• Components powerfulthat do not limit the possibilities of the machine.
• Components versatileThe use of the most materials is possible.
• Components reliablethat they don't break down at the first attempt.
• Components economicin line with the rest of the CNC machine.

We will divide the electronics into several groups, as each of them can be different and it is possible to combine different groups to get what we want and meet our objectives.

The groups we will discuss separately will be:

• Engines step by step
• Drivers of the CNC engines
• Controller CNC
• Feeding
• Milling machine, spindle or spindle of the CNC

Stepper motors

The engines for the CNC will be one of the most important decisions The choice we make and the rest of the electronics components will depend, to a large extent, on this decision.

Although there are different types of motors that we could use, such as DC motors, stepper motors, servomotors and many others, in this case we are going to decide for stepper motors.

The reasons that have made me decide in favour of stepper motors are as follows:

• It is one of the most economical options (servo motors are better, but one of them costs several times as much as a stepper motor).
• They have a very good power/weight/size/consumption ratio electric.
• They are very resistant
• They do not require mechanical adjustments
• Do not require too many drivers special and expensive.

Once we have decided that we will be using stepper motors, we have to decide to which ones we will use. For this we will take into account:

• Power required
• Speed
• Resolution and accuracy
• Price
• Format physical

Power

The power of the stepper motors we use will determine, among other things, what materials we can work with on the CNC and at what speed.

Without getting into too many technicalities, what we need are engines that allow us to work with the materials we plan to work withThe "I'm not too hot" or "I'm not too cold".losing steps".

Selecting engines is not the same, for the same CNCif what we plan to work on are softwoodssuch as balsa wood, which, if we want to work with it, can be used in a variety of ways. aluminiumfor example, or other types of materials, such as hardwoods or plastics.

If we install engines underpoweredwill not have enough strength to make the tool moves through or penetrates into the materialwithout problems such as vibrations, loss of motor steps, overheating, overheating, etc. or, in the worst-case scenario, the blocking of engines or their destruction.

This does not mean that there is a magic, specific point in the engine power at which the engine is no longer suitable for working a material, but rather for working the same material, it will be able to do so, but at lower speed than a more powerful engine..

For example, we can have a small hand-held Dremel that allows us to work on aluminium moving through it to, for example, 15 cm/m (centimetres per minute), whereas a 750 watt milling machine will be able to advance, for example, at 150 cm/m without any problems.

Does this mean that we can work with any material as long as we are going to slowing down further?

No. Absolutely not. 

Lowering the speed means that the tool (drill bit, milling cutter, or whatever we are using) penetrates or moves. more slowly in the material and that creates a big problem: the heat.

We can, to a certain extent, reduce heat by making it the slower the tool advances, the slower the tool rotates.. In other words, by making the motor we use to turn the tool (milling machine, spindle, etc.) rotate more slowly.

The problem is that the milling machines, spindles, etc. have a speed limitsWe can't get away from them, above and below. In addition, the vast majority of engines go losing efficiency (reducing its power) to as its speed drops.

In a CNC, just as important as the power of the engines to move forward is the power they have to hold the position. If the engines are not capable of maintain its position when they are working, exerting quite a lot of pressure, against the material we are working with, we would have problems.

Power is usually measured in Nm (Newtons/meter) or in oz/in (ounces per inch). In my case I opted for 1.9 Nm or 270 oz/in motors.

They are engines with considerable power and so far I have not missed more power on the jobs I have done.

It should be borne in mind that it is not only a question of having the most powerful engine possible, because the choice of a more powerful engine also means having to use a more powerful engine. more powerful drivers, a larger power supply and thicker cabling; which can seriously increase the cost of the project.

Speed

As we have seen, speed is intimately linked to power. It is a two-way street.

Normally, these two parameters are inversely related. A faster engine is usually less powerfulThe relative importance of the

In practice, and in a CNC like this one, the speed of the stepper motors is not going to be a major limitation of the machine and virtually any engine will do of which we can consider "normal"i.e. they do not have special characteristics because they are either too fast or too slow.

It should be noted that stepper motors do not move anything directly, but through a series of belts and sprockets. This allows us to play with the speed to demultiply and make the movements slower, but more powerful.

Resolution and accuracy

In order to obtain precise results with very small movements, it is necessary for the motors to have sufficient resolution and accuracy. This will not be a problem with modern stepper motors, as they usually have steps of 1.8°, which is 200 steps to a complete rotation.

As the engine output is followed by a ratio of reductionThis means that, for each step, or 1.8º of rotation, the movement in very small (a few microns), and we can also change it easily by changing the sprockets for others with a more suitable tooth ratio.

Physical format

The dimensions of the motors to be used in a CNC like this one are standardised and have specific dimensions. Defined as NEMA 17, NEMA 23, and others.

NEMA is the "National Electrical Manufacturers Association" and its standard for motor mounts is commonly used in the industry to ensure that replacement parts fit and are readily available, and that motors from different manufacturers are interchangeable. The NEMA number is related to the diameter of the motor multiplied by 10. So, a NEMA 23 motor is 2.3 inches.

A common misconception is that a larger engine is more powerful, but this is not the case. this is not always the case. There may well be NEMA 17 motors with more power than NEMA 23 motors.

Price

For a CNC like this we will need four engines stepper motors and, although stepper motors are usually not very expensive, they can be an important part of the budget total of the machine.

It should also be borne in mind that not all engines of the machine have to be the sameEach of them can be optimised. For example, in the Y axis this machine has, by design, two motors (one on each side), which means that they share work and, therefore, may be of less power than the X axis, in which there is only one motor dedicated to this movement. 

The price of engines can vary greatly from place to place. It is possible to find the same engine much cheaper or much more expensive depending on where you buy it. The country also has a big influence on the price; The same engine that costs us in China 15 € can cost us in Spain more than 30 €.. Of course, we will have it quickly and with a guarantee (plus we will be giving business to a local business that will probably be able to advise us better).

I bought them in Germany on eBay, but the ones I bought are no longer available. At the moment they are I recommend you to buy them on Amazon, if you want them fast, or on AliExpress if you don't mind waiting some time..

 

Putting it all together

The CNC stepper motors are a very important part.

I recommend that you put good engines with sufficient power, but without going overboard for the machine that it is.

After a lot of searching, I opted for the NEMA 23 of 1.9 Nm and I accepted it completely. They haven't given me a single problem and, so far, they have had enough power, on all axles, for the work I have done (some of it quite aggressive).

These are the engines I recommend you to buy. They are the same ones I bought in Germany and they are available on Amazon with free shipping with Prime.

Please note that you will need four engines, so you will need you must add four units to the basket of the purchase.

Drivers of the CNC motors

Drivers are the electronic elements that receive the low power digital signals of the controller and turn them into the high power analogue signals engines need.

The the right choice of the drivers is very important, both in terms of capacity and functionalities, as well as in terms of their correct operation in conjunction with the particular engines we use.

There are many different possibilities, and many different prices, and in this case I played it safeand that is what I recommend (if you decide to use the same engines as me).

Among the features and functionalities that a driver can have, I would stress:

• Operating voltageIdeally, we should choose drivers that allow us to work at 48VDC.
• Output currentThey have to be able to provide the current needed by the motors (3 Amps on my motors).
• Subdivision range, microsteps or microstepsAllows motors to move in much smaller increments than they are mechanically capable of, increasing their accuracy.

I opted for DM542A drivers.which are capable of supplying an output current of 4.2A (remember that my motors consume 3A and it is advisable to leave a good safety margin) and I got it right. There are drivers very similar and easy to confuse with this one, such as the TB6600, which are a bit cheaper, but I had read on the English language forums too many horror stories about these drivers for me to decide to pay a bit more and play it safe.

The work performed by a CNC is not only very hard, but also very difficult. very long (the CNC can work for several hours at a time)and having electronics you can trust gives you peace of mind.  

If you have previous experience with 3D printers, you may be thinking about using the drivers that are commonly used in 3D printers such as DRV8825 or similar. This is not a good idea. The small drivers used in 3D printers are not capable of delivering the current that the motors of a CNC need (except if the CNC is very small, and very light work is required of it of course).

These are the drivers that I use and that I recommend. They are the same ones I bought in Germany and they are available on Amazon with free shipping with Prime.

Please note that you will need four drivers, one for each engine, so you must add four units to the basket of the purchase.

CNC Controller

At the point of the CNC controller, there are little to say.

The controller consists of exclusively for an Arduino Uno.

The exact wiring will depend on the software we use, so we'll look at that in the next article, along with the software.

We don't even need a connection boardThese are very simple and can be wired directly to the Arduino Uno.

A Good quality Arduino Uno is all we will need.

If you want you can use a connection plate to facilitate connectionsbut it is by no means necessary.

I, as you can see in the pictures, used a small perforated plate to facilitate the small connections.

Feeding

The power supply is essential for everything to work properly.

CNC motors have a relatively high power consumption and must be adequately powered.

Each of the motors I have used can draw a maximum of 3A and there are four motors, so I have opted to put two 36V, 9.7A power supplies

Taking advantage of the fact that there is power to spare, I have connected some 12V LED strips and a few more accessories to these same sources.

The "block" with the Arduino, the drivers and the power supplies has been left (in a quick and dirty assembly, which was provisional but that's how it has been left) like this:

CNC milling machine, spindle or spindle spindle

As I said in the introduction to the construction of this CNCthe milling machine, spindle, or motor is one of the important parts of the CNC.

When I built the CNC I put in a milling machine economic, very similar to the well-known Makita RT0700C (practically a clone), which gave me an excellent result.

Subsequently, I replaced it with a high-frequency motor with inverter..

As I said in the introduction to the construction of this CNCthe milling machine, spindle, or motor is one of the important parts of the CNC.

When I built the CNC I put in an inexpensive milling machine, much like the well-known Makita RT0700C (practically a clone), which gave me an excellent result.

Subsequently, I replaced the milling machine with a high-frequency motor and inverter..

It is a significant outlay (in the order of €300), but in my opinion it is worth it.

The reasons for this change were as follows:

• The milling machine makes a lot of noise. Very uncomfortable to work in a domestic environment (and I have the CNC in the garage of a detached house, I don't even want to imagine what it must be like to have something that makes that noise for hours in a block of neighbours.
• It is possible to regulate the speed by softwareThe programme can then make these speed changes as necessary. In addition, its speed range is wider than that of a milling machine.
• Can work hours on end without flinching or warming up.
• As the cooling of this high-frequency engine is water-cooled does not expel air with which the sawdust does not come outor shavings from the material you are working with, shot all over the garage 🙂
• Allows you to put a huge variety of types and sizes of strawberries.

Conclusion

The electronics of the Root 3 CNC are not complicated, although can easily outdo someone because of the number of options and the difficulty of finding the right combination.

If you find yourself in this situation, I I recommend that you opt for the same components that I have been using. The result has been very good and you can be sure that these are components that work. either jointly and which are balanced.

I will shortly write a new article in this series with the software I used for this project. Subscribe to the Newsletter so you don't miss it.

If you enjoyed the article, I would be very grateful if you could spend a minute to leave a comment below.