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Do-it-yourself FPV racing drone (part 1) - build

Today, the popularity of racing on drones is growing rapidly. Amateur poets grow into serious international competitions, and the number of people involved in this hobby is growing in progression. I myself recently assembled an FPV-quadcopter of the 180th size (the distance in mm between the axes of the motors diagonally) and I hasten to share this experience.




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I described the entire build and configuration process here and here , and below will be a slightly modified version containing more information from my previous articles.

I will leave out the question of entering this hobby and go directly to the quadcopter.

Select quadcopter size



A year ago, quadcopters of the 250th size were the most popular. But now pilots prefer to assemble smaller devices, which is very reasonable: the weight is less, and the power is the same. I chose the 180th size not for some practical reasons, but as a kind of a challenge for the assembly.

In fact, this approach to the selection is not quite correct. It is much more reasonable to choose first the size of the propellers, and already under them - the smallest frame, where the chosen propellers fit. And with this approach, the 180th format is generally rejected. Judge for yourself: the 210th format allows you to put the same 5-inch propellers that the 250th, while the quadric itself turns out easier, and the 4-inch propellers fit into the 160th frame. It turns out that the 180th size is such an intermediate format that is “neither ours nor yours”. It can also be considered weighted 160th. But, nevertheless, I chose him. Perhaps because it is the minimum size that is capable of more or less comfortable with a GoPro or Runcam camera.

Accessories



Let's start with the motors. The “intermediateness” of the 180th size, as well as the richness of their range, make it difficult to choose. On the one hand, you can take what goes on the 160th, on the other - what is set on the 210th or even the 250th. It is necessary to proceed from the propellers and the battery (the number of cans). I see no reason to use the 3S battery, but for the propellers, the general rules are:



In my case, I have a 4 inch propeller size limit, but I have no motor limit. So, the three-blade 4045 bullnose propellers would be the most sensible. They are difficult to balance, but with them control is more responsive and predictable, and the sound is quieter. On the other hand, with two-bladed propellers, the speed of a quadcopter is higher, but I don’t really need it. “Among the people” in the 180s frames the following setup prevails:



In fact, the frame allows you to put the motors from 1306-4000KV to 22XX-2700KV. By the way, I don’t know why, but the 1806-2300KV motors are now in disgrace and are little used.

For my quadric motors, I took - RCX H2205 2633KV . First, I wanted to have a reserve of power (although with my modest piloting skills, it is not clear why). Secondly, my setups have never been super-light, in addition, I also plan to carry an action camera. Specifically RCX motors - a compromise option. They are cheap, but there are a lot of quality complaints. At the time of purchase of components, it was one of the few 2205-2600KV motors on the market. Now (at the time of this writing) the range is much larger and it is better to choose something else.
With the rest of the components acted on the principle of "more challenge":



Flight controller selection



You probably noticed that there is no flight controller in the list. I want to describe his choice in more detail. In inexpensive assembly kits often include a CC3D controller, so now it is probably the cheapest PC. Today there is absolutely no point in buying a CC3D. It is outdated and does not have such necessary things as battery charge control and "beeper". His successor, CC3D Revolution, is a completely different product with rich features, but at a price of over 40 €.
Modern flight controllers have already switched from F1 processors to F3, which made Naze32 PCs of the past generation and significantly reduced its price. Now it is truly a national controller, which has almost everything that the soul wants at a price of 12 €.
Of the new generation of PCs, Seriously Pro Racing F3 is the most popular, and primarily due to the availability of inexpensive clones. The controller itself is not inferior to Naze32, in addition it has a fast F3 processor, a large amount of memory, three UART ports, an integrated inverter for the S.Bus. I chose SPRacingF3 Acro . The remaining modern PCs were not considered because of the price, or some specific features (closed firmware, layout, etc.)
Separately, I note the current trend to combine several boards into one. Most often, PC and OSD or PC and PDB I do not support this idea with a couple of exceptions. I do not want to change the entire flight controller due to a burnt OSD. Moreover, as practice shows, sometimes such an association brings problems .

Wiring diagram



It is clear that all components that need 5V or 12V power supply will receive it from the BECs of the power distribution board. Theoretically, the camera could be powered directly from a 4S battery, since the input voltage allows this, but in no case should you do this. Firstly, all cameras are very susceptible to noise in the circuit from the regulators, which will be reflected in the noise in the picture. Secondly, regulators with active braking (such as my LittleBee), with the activation of this braking, give a very serious impulse to the on-board network that can burn the camera. Moreover, the presence of a pulse is directly dependent on the wear of the battery. New ones do not have it, but old ones do. Here is an informative video on the topic of interference from regulators and how to filter them. So it is better to feed the camera either from BEC, or from a video transmitter.
Also, in order to improve the quality of the picture, it is recommended to send not only the signal wire from the camera to the OSD, but also the “ground”. If you twist these wires in a "pigtail", then the "ground" acts as a shield for the signal wire. True, in this case, I did not.
If we are already talking about the "ground", then they often argue about whether it is necessary to connect the "ground" from the regulators to the PC or just one signal wire. On the usual racing quadcopter definitely need to connect. Its absence can lead to synchronization failures ( confirmation ).
The final wiring scheme turned out simple and concise, but with a couple of nuances:




Assembly



First, a few general assembly tips:



I prefer to start assembly with motors and regulators. Here is a good video on the assembly of a small quadrocopter, from which I adopted the idea of ​​the location of the wires of the motors.

Separately, I want to say about the mounting of the regulators: where and how? They can be mounted on and under the beam. I chose the first option, as it seems to me that in this position the regulator is more protected (these are my conjectures, not confirmed by practice). In addition, when mounted on the beam, the regulator is perfectly cooled by air from the propeller. Now how to fix the regulator. Many ways, the most popular - double-sided tape + one or two screeds. “Cheap and angry,” besides dismantling the difficulties will not deliver. Worse, with such a mount, you can damage the regulator board (if you put a tie on it) or wires (if attached to them). So I decided to mount the regulators with a shrink tube (25mm) and sealed them together with the beams. There is one caveat: the regulator itself must also be in heat shrinkage (mine were sold in it), so as not to come into contact with the carbon ray of the beam, otherwise - short-circuit.



It also makes sense to glue a piece of double-sided scotch on the bottom of each beam at the point of attachment of the motor. First, it will protect the motor bearing from dust. Secondly, if for some reason one of the bolts is unscrewed, it will not fall out during flight and will not be lost.
When assembling the frame did not use a single bolt from the kit, since they are all indecently short. Instead, I got a little longer and with a Phillips screwdriver head (there is such a personal preference).

The camera did not fit the width between the side plates of the frame. Slightly processed the edges of her board with a file (rather, he grunted roughness) and she got up without any problems. But the difficulties did not end there. I really liked the quality of the holder for the camera from Diatone, but the camera with it did not fit into the frame in height (about 8-10mm). At first I prikolhozil holder on the outer (upper) side of the plate through a neoprene damper, but the design turned out to be unreliable. Later came the idea of ​​the most simple and reliable fastening. I took only the clamp from the Diatone`s mount and put it on a piece of rod with M3 thread. To prevent the camera from moving sideways, I fixed the clamp with nylon couplings.



I liked very much that only connectors for regulators had to be soldered from the connectors to the PC. I did not fit the full three-pin connectors in height, I had to go to the trick and use two-pin. For the first five channels (4 for regulators + 1 “for every fireman”) I soldered the connectors to the signal area and the “ground”, for the other three - to the “plus” and “ground” so that the PC itself can be powered and already from it - backlight. Given that the Chinese clones of flight controllers sin by unreliable fixation of the USB connector, I lost it too. Another point characteristic of the clone SPRacingF3, is the connector "tweeter". As in the case of vbat, there is a two-contact connector JST-XH on the upper side of the board, and on the lower side it is duplicated by contact pads. The hitch is that the clone "earth" on the connector is constant and when it is used, the "squeaker" will always be activated. Normal work for the "tweeter" "earth" is derived only on the contact pad. This is easily checked by the tester: the “plus” of the connector is called with the “plus” on the pad, and the “minus” is not called. Therefore, it is necessary to solder the wires for the "pusher" to the underside of the PC.



Three-pin connectors regulators also had to be replaced. It was possible to use four two-pin plugs, but instead, I took two four-pin plugs and inserted all regulators into one “ground”, into the second (observing the order of motor connection) - a signal wire.



The backlit plate is wider than the frame and protrudes at the sides. The only place where the propellers do not bring her down is under the frame. I had to collective farm: I took long bolts, put nylon sleeves with previously made cuts on them (so that the fasteners fastening the backlight could be fixed) and screwed it through the bottom plate into the frame stands. To the resulting legs with ties, he pulled the plate with the LEDs (the holes in the plate fit perfectly) and filled the ties with hot glue. On the back of the plate soldered connectors.
Already after assembly, at the stage of adjustment, it turned out that there was something wrong with the squeaker. Immediately after connecting the battery, it began to monotonously squeak, and if you activate it from the console, then this monotonous squeak superimposed also rhythmic. At first I sinned on a PC, but after measuring the voltage with a multimeter, it became clear exactly where the problem was. In fact, it was possible from the very beginning to connect a conventional LED to the tweeter wires. In the end, I ordered several tweeters at once, listened to them and installed the loudest one.





Often the PDB and the controller are attached to the frame with nylon bolts, but I do not trust their strength. Therefore, I used 20mm metal bolts and nylon couplings. After installing PDB, I soldered the power supply to the regulators (the other wires were soldered in advance) and filled the soldering places with hot melt glue. The main power wire going to the battery was fastened to the frame with a coupler so that it would not be torn out in the event of an accident.



I removed all connectors from the receiver with pliers, except for the required three, and the jumper between the third and fourth channels disappeared directly on the board. As I wrote above, it would be wiser to take the receiver without connectors. I also deployed his antenna and heat-shrink it. On the frame, the receiver fits well between the PBD and the rear rack. With such an arrangement, its indicators are clearly visible and there is access to the bind button.



I fixed the video transmitter with screeds and hot melt adhesive to the upper frame plate so that through the slot there was access to the channel switching button and LED indicators.



For mounting the video transmitter antenna in the frame there is a special hole. But do not connect it directly to the transmitter. It turns out a kind of lever, where the antenna serves as one shoulder, the other with the transmitter itself with all the wires, and the point of attachment of the connector will be the fulcrum at which the load will fall. Thus, in the event of an accident with almost 100% probability, the connector on the transmitter board will break off. Therefore, it is necessary to mount the antenna through some kind of adapter or extension cord.

For MinimOSD, I decided to solder the connectors, not the wires directly. On the forums they write that this board often burns, therefore it is reasonable to immediately prepare for a possible replacement. I took the bar with connectors in two rows, bottom soldered to the contact pads with holes, and on the top brought vIn and vOut. After that, he filled in the soldering places with hot melt glue and packed the entire board in heat shrinkage.



The final touch is a sticker with a phone number. She will give at least a little hope in case of loss of the quadcopter.



The assembly on this came to an end. It turned out compact and at the same time saved access to all the necessary controls. More photos can be viewed here . The quadcopter mass without a battery is 330g, with a battery - 470g. And this is still without an action camera and mounting for it. In the next article I will talk about the firmware and setting up the resulting quadcopter.

Source: https://habr.com/ru/post/395455/


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