I'm going to start a series of posts dedicated to electric RC helicopters.
As with model airplanesWith advances in technology and with China manufacturing cheaper and cheaper, RC helicopters have been priced very reasonably. (Or at least, as with airplanes, we no longer get depressed if we crash them).
The bulk of this series is going to be the assembly of a medium-size helicopter (70 cm rotor diameter), which I am going to show step by step. The reasons for this choice are various, and the main one, the price, since the chassis kit shown in the photo is worth only 8 euros.
There is also infinite information about this family, that of the "450" helicopters. We even have its equivalent in the free FMS simulator, as shown in the following photos.
The level of detail of the model for the simulator is high, as seen in this photo of the screen (not capture).
Introduction to Electric RC Helicopters
Model helicopters have to be approached from another point of view than we had with RC planes. If with airplanes we have a lot of margin for error, and we can fly almost everything that the engine can drag, with helicopters there is no possibility of having a good flight if we have not carefully prepared and adjusted everything. Furthermore, a blow to an airplane can generally be repaired, but a blow to a helicopter usually involves the replacement of many, many parts.
RC helicopters combine model aircraft and mechanics.
I am not an expert on the subject, but they have always fascinated me. Therefore, I am going to share my progress and experiences in ikkaro.
Parts of a helicopter
The fundamental parts are:
- The chassis or frame, which is the main body,
- The main rotor, or rotor, which is the set that rotates with the blades or blades.
- The tail, which is the posterior part in the normal direction of travel, where the
- Tail rotor, which is the one located at the back.
Later we will detail and expand all the parts.
Types of Electric RC Helicopters
The market has become very diversified, we have an immense range, and among other reasons is China's custom of copying everything.
I dare not say where the difference is between a toy and a serious model airplane helicopter. I can not differentiate by size, I can not rely on the materials, or almost not on the price, it is quite complex.
We will begin to describe types of helicopters.
In the lowest step, both for price and size are the indoor micro helicopters.
These helicopters are very small, they incorporate a very common solution in these small devices, which is the COAXIAL ROTOR, that is, two rotors on the same axis, rotating in the opposite direction.
We are going to continue the series on electric radio controlled helicopters.
I do not want to turn this series of posts into instructions to assemble the type 400 helicopter. There are many instructions to assemble it on the internet.
What I intend is that taking advantage of the construction we will learn the reason for the assembly and the operation of each piece.
Therefore, this post is going to be a rather theoretical introduction. !! attack!!!!
Why does a helicopter fly?
Simple, right? We all know how a propeller works, if I push air back with the propeller of an airplane, the airplane moves forward.
If I push air down with a propeller, the helicopter moves up.
Can I make a helicopter with a propeller attached to a motor, that has enough power?
Yes. and I would fly, but for a short time, since here we begin to have problems. It would lift off the ground to tip over and crash.
Write down this phrase in your memory.
FLYING A HELICOPTER WITHOUT A STABILIZATION SYSTEM IS LIKE TRYING TO KEEP AN ICE CUBE ON A PLASTIC BALL.
That is, impossible to maintain beyond tenths of a second, as soon as the slightest bit is overturned, we consider it lost.
What is happening, is not a helicopter similar to a mass hanging from a rope, a pear caught by the tail? Shouldn't it be stable, by intuition?
Not so, no. The helicopter in flight, and especially close to the ground, is actually supported by a mass of air compressed by the propellers themselves. That is to say, we return to the example of the cube and the ball, if the helicopter capsizes a little, the "ball" of air underneath it causes it to quickly crash against the ground.
How then does a helicopter get stable?
There are several solutions. The most common, placing the so-called "stabilizer bar" (in English it is called a "flybar").
Go back to see the video that I put at the beginning. Observe what I indicate at the beginning, a metal rod with two weights at the ends. That's the stabilizer bar. '
You can see how the bar always tries to rotate in a horizontal plane, when I tilt the helicopter. (This is based on the same effect that keeps a top stable).
In the following video you can also check it.
You can also see in both videos how there are small rods that communicate the stabilizer bar with the blades. Therefore, taking advantage of the fact that the bar always tends to rotate horizontally, the pitch or angle of attack of the propellers is acted upon, to return the helicopter to its stable position.
Too many concepts at once, yes. In the next post we will see clearly what the variable pitch of the blades means. And we will mount the bar of the 400. Greetings.
Mounting the stabilizer bar
Before proceeding to assemble this first element we have to see the tools and materials that we may need.
The basic list is as follows:
Small Phillips screwdriver.
Allen key or Allen head screwdriver.
Nut fixing liquid.
Pliers for ball joints.
The first two tools are easy to find, and I guess you all know what they are.
Next I show you the ones that I use, it is a set of assorted screwdrivers.
Nut fixing liquid (screw fixing).
A nut fixing liquid is a glue that is applied to the screws before they are inserted, which locks them when it dries and prevents them from loosening with vibrations or efforts.
There is an infinite range on the market. Its main characteristic is the "force" with which it holds the screw.
They exist from the very soft ones, that allow to loosen the screw without effort to the very strong ones.
If we refer to the «Patanegra» helicopter from which they have been copied to make our kit, the TREX400, we can see that for its assembly it recommends two nut fixing liquids, one for the screws and the other for the bearings.
The Kit that we are going to make comes pre-assembled. It means that the most complex parts to assemble are already fixed in the factory, including all the bearings.
Therefore we only have to worry about looking for a fastener.
The fastener that comes in the TREX is one called T43. This is equivalent according to the literature, to Loctite 242. (Loctite is the reference brand, the best, therefore we are not going to buy it).
It is called "anaerobic medium force nut set."
On the page where we bought the Kit, we can find "copies" of that nut for 1 dollar a pot. In the following photo I show you the one that I have used for a long time for everything, which is of medium resistance and that I am going to use for the helicopter, and one called "Strong" purchased on the Helicopter Kit page.
Look, out of curiosity, how the jars are exactly the same, the old one I bought more than 10 years ago in a hardware store. It turns out that very little is spent on each screw.
We could be talking about several posts about lubricating oils, without being an expert on this subject.
But let's get down to business.
What is the possibility that my helicopter will fail due to not choosing the correct oil? Well, practically nil.
Will it last less if I don't add the correct oil? Well, yes, but we do not fight against reliability or durability, now we are only thinking about not crashing it on the first flights.
That is to say, take the fluid lubricating oil that you have more at hand.
I show you in the next photo some, and I tell you which are the most recommended.
The one that is discussed in the forums that works very well for axles is the WD. But the classic 3-in-1 is sure to work the same.
What does not damage the plastic parts is the Vaseline grease, or the silicone grease, which can be ideal for the main crown. But we are not going to have a problem with lithium grease or thick bearing grease either.
I already tell you, before your helicopter has problems due to not choosing the right oil, we will have crashed it 5 times.
Ball joint pliers.
In our helicopter, control rods are used that are finished in ball joints.
To make the adjustments, they must be mounted and disassembled frequently, and for this we need special pliers. I am hesitating between making them or buying them.
In English they are called "Ball link pliers" or pliers for spherical transmissions.
They are worth little 4 or 5 euros. They will be needed later.
Another tool that will be useful is the caliper or caliper. You can try to work with a ruler, but in some steps it will be difficult to measure with it.
Stabilizer bar mounting.
To mount the stabilizer bar we need to loosen the upper screws as indicated in the following photo.
We extract a lateral screw (which is only there to hold the pieces together) and introduce the stabilizer bar rod.
We pass it through the inside of the rotor and do the same on the other side.
With the bar already in place, we proceed to place the counterweights on each side and screw the blades into the ends, to the bottom of the thread.
Both blades must be in the same plane. We can see this by looking at them in profile, as shown in the photo.
The blades have to stay perfectly aligned with the support they cross.
We must also measure with the gauge, and leave the same length of rod on both sides.
Once these points have been verified, we can proceed to smear the headless screws with the nut fixing liquid and leave the bar attached.
We are not going to fix the counterweights at the moment with the nut set.
In the next post we will talk about the theory again. We will see that if stabilizing a helicopter was already painted black, things are even more complicated due to the gyroscopic effect of the rotating blades and the precession forces.
Stability and gyroscopic effect
We are going to make a stop in the, already in itself, slow path that I have traveled with the construction of the helicopter. A stop for theory and physical principles.
I like to create my own content for posts, but this video is so enlightening that we are going to reflect on it.
What are we watching?
A bicycle wheel, which when it is still, hangs on a rope by the end of the axle, but when it is turning, it remains mysteriously upright ???????
It is the best demonstration I have found of the precession forces, which are those involved in the gyroscopic effect.
What explanation does this have?
Well, in the video what happens is that the forces of gravity that pull the wheel down to put the wheel in a horizontal position, cause the wheel to move around the rope, as if it were the axis.
This is the same thing that happens in a spinning top, spinning top or spinning top, depending on what you say.
In a top, the force of gravity tries to overturn it, but as in the bicycle wheel, forces appear perpendicular to it that correct the position and prevent it from tipping over while the top is rotating.
And will you say, what does this have to do with helicopters? !!!!!
Well, it turns out that the blades of a rotating helicopter behave like a bicycle wheel or a spinning top. They are that, a spinning mass.
what does this mean?
Well, to balance a helicopter, the rotor must be controlled, and as we have already seen, a force that tries to tilt the rotor will cause a reaction on a different axis.
This is the driest post of images that I have put in Ikkaro. But I have not found anything, so, although I draw quite badly, here is a sketch, comparing the wheel with a helicopter.
The force of gravity pulls downward and causes the wheel to move counterclockwise with the rope as the axis.
In a helicopter, we will see that to stabilize it, we will apply a force, for example at the indicated point, if what we want is to stabilize it backwards.
In the next post, we will continue with the construction. Regards.
Riding the tail
We are going to proceed with the assembly of the tail of the TRex 450 clone helicopter.
Remember that it is a cheap kit, probably they have not been very careful in its manufacture, therefore, I recommend going over all the screws and adding a bit of nut holders, just in case.
Also tell you that you can follow the instructions in a manual of the original device, just do a google search for "T-REX_450SA_ARF_Manual.pdf", without the quotes.
All that said, I show you what I have done.
The strap is passed through the inside of the tube and we proceed to hold the tail rotor assembly.
First, the screws on the tail are loosened a little, and the tube is inserted through the side that has a hole, which has to fit into the notch that has the plastic inside.
The vertical stabilizer is then attached. The screws are long. In the manual you have an indication of the length of the screws of each part.
The tail rotor blades can also be attached. These screws have a smooth section.
Before doing this, it is advisable to remove the bolts from the hub of the rotor blades and tighten them.
To insert the aluminum tail tube into the body of the helicopter it is necessary to loosen the screws in the area.
Before doing this, you must introduce all these pieces in the aluminum tube. We will always be in time to cancel them if they do not suit us.
We can adjust the tension of the strap, according to the manual, introducing the tube more or less in the body, taking care that there is a notch in which we have to insert the tube. At the same time we must verify the direction of rotation of the tail. Seen from above, when turning the tail in its direction, you must turn the pinion where it engages counter-clockwise. If this is not the case, simply loosen the strap and reattach it turned.
Then we can proceed to mount the horizontal stabilizer and the bracing ties of the tail.
These are formed by two rods of carbon fiber or glass with black resin. Black they are.
I glue them to the supports with epoxy. Notice that I let them dry assembled, so that the orientation of the terminals matches the orientation of the screws that are going to hold them.
Here you can see the tie rods with their screws to the horizontal stabilizer.
We already have the tail mounted. In two or three more posts, we will have the complete helicopter. Then the adjustments will come….
I will be putting you some video of the flights, so that you motivate yourself. Greetings.
Mounting servos and motor
I put a video with the first flight tests.
As the manufacturer says, This is not a toy. Shovels can cause very serious injuries. Only do the tests if you are an adult or accompanied by one. To fly a helicopter of this size you must always be behind a fence.
The intention is to build the device with the cheapest possible parts, therefore I have placed as servos to tilt the collective plate, the cheap servo of 1.5 euros.
In the following photos you can see how they are placed.
It may be necessary to remove the chassis screws to fit them.
These are the two front servos
And this is the posterior sevo.
These are the pieces that are attached to hold the servos.
Next we are going to assemble the motor and gear.
The axis is passed.
The gear is screwed with its rear nut, always with a nut set.
The motor is inserted in its place and fastened with the allen screws.
fit the nut fixers and the self-locking washers.
The motor should be slightly separated from the gears (tenths of a millimeter). It should not be pressing perpendicularly, just be very close.
In the next post we will talk about the gyroscope.
[highlighted] This article was originally written by Belmon for Ikkaro [/ highlighted]