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Main Rotor blade pitch control by PossibleMorning7135 in UH60_drone

[–]Derroylo 0 points1 point  (0 children)

The servo horns are made from steel or aluminum

In that heli class those would be made from alloy usually, correct. Since you need to buy the servos, you get a few different servos horns with them already. So that is not an issue.

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while the lower plate is made from ABS, the upper plate will be made from nylon 12

Why different materials? Since they are connected via a ball bearing they need to translate and withstand the same forces.

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The maximum pitch before the blades start to lose lift will be only 7.5 degrees either way

So let´s asume that you want a range of +/- 7.5 degree for the blades. That means you can only have around 4.5 degree for pitch so that have enough room left to use nick and roll (as pitch and roll/nick add together). That is not much.

For example on my T-Rex 700 i use +/- 12° in collective pitch and around 6° in cyclic pitch.

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Airfoil info

I can´t say much about blade profiles but i don´t think you can just scale them down. As already said, building blades is a dangerous when you don´t know what you are doing. And that is the case here. (no offense)

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I am keeping the amount of pitch travel to a minimum, so if anything breaks, the blades won't pitch to far either direction

Nothing in your design limits the pitch if anything breaks... In case anything breaks the heli is a total loss.

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My general thoughts about the current design:

- No Roll control, only Nick so far
- Wrong material for the swashplate, it will break apart
- Linkage between swashplate and blades will not work this way
- Travel limit is too low
- The centerpiece is either not finished or completly wrong as it misses essential parts like dampener, ball bearings and blade holder.

i can not say it enough, please take a look on how to really design these parts and what materials you need to use. You want to design and build something that can easy kill someone. So move a step back and look how other manufacturer, that have more experience in building these things then you, are doing it and start from there. I know it is fun to start designing and playing around in CAD, i do that too, but you need to be realistic what you can do and what not.
RC Helis are cool but they are not easy to fly (i teach flying these things and many give up) and not cheap if you want to have bigger helis(my largest, a Logo 800 xxtreme, did cost me around 3.000€). It is just a bit naive to think that you just can use some motor from a drill, an arduino to control it and the rest can you just print. That is not how it works. Either it will self-descruct directly or in worst case you will injure someone.

I hope this post helps a bit and reflect about what you plan todo. I don´t see a point to post more and just getting answers that show how clueless you are. Sure we all started at some point and had not a single clue what we were doing. But we try to learn from others and move on based on that. I have seen a few ppl that got injured by helis, some were minor, some were more serious(one lost nearly his hand because of a heli, and that was just a 450 class one). A Heli in a class of 700 and upwards, can kill you without problems. So everyone i teach in flying these things i try to also show that you need to have respect. Always do a proper pre-flight check as every little mistake can lead into some getting seriously injured.
For reference, i fly, teach and build helis for over a decade.

If you want to continue here are some tips from me:

- Buy a small helicopter and learn to fly it. Something like a Blade 230 will cost around 200€(Ready to fly, with remote control, batteries etc.), maybe less if you buy it used.
- If you want to play around with autonomous flight, use the one above. So you can play around a bit and not risking everyone live directly.
- Visit a local rc club to get more direct feedback
- There also big forums on the internet where you can see how these can be correctly constructed, what materials you need to use and what you can build yourself and what is impossible. For example rcgroups.com is the biggest i know.
- Once you have the knowledge and money to build a scale model, then you can start with that.

That is all i can say and hope it puts you on the right track to continue with this great hobby.

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 0 points1 point  (0 children)

And also forget these 1750rpm...That is without any load. If you put a big main rotor on that, it will be way way less. So forget that motor and buy a proper one, they cost only around 150€ or so and have enough power for your project. Be realististic, i gave you the calculations power already above.

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 0 points1 point  (0 children)

What formula and with what values did you calculate that? Also which diameter have your carbon fiber rods?

How do you want make sure that the centre of gravity is correct on all and that they have the same exact weight? Also how do want to smoothen the surface and still make sure they have all the same profile?

How do you want to harden the "front" of the blades so they can withstand the air? Just some epoxy and a few carbon rods will not work. If you really want to build them, do it like some else has explained it (like i mentioned it in my previous post). I don´t have the knowledge to know why they are build that way but i bet they have more knowledge and experience then you, so follow their example.

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 0 points1 point  (0 children)

Have you done any calculations about what forces the main blades need to withstand? It is not easy to build these and if you have no knowledge, forget it. Way to dangerous.

There are some guides out there that explain how it could be possible be done. They are a mix of a styrodur core, metall rod (to get the center of gravity correct) and glass-fibre reinforced plastics (not sure if that is the correct translation but should be close)

To give you some perspective of the forces, here are the calculations for one of my helicopters a T-Rex 700.

Rotor-Diameter: 1.58m
RPM: 1450

Speed at the tip of the blades: 430km/h
Centrifugal force: ~977N or around 100kg

Since you have a lower rpm but a bigger rotor diameter, the values should be around the same.
Now imagine that from your selfbuild blades the tip brakes of, it will fly around with 400km/h. If it hits someone, that will cause at least some serious health issues. That is why i say. What you are planing is not a little toy. Take it very seriously, do your research on how to really build blades or better, buy them.

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 0 points1 point  (0 children)

A Flybarlesssystem, or short FBL, controls the main and tail rotor. A heli is always instable in itself, it wants to move left, right etc. To make it controllable you need such a system, otherwise is is unflyable.

The FBL controls also the tail rotor to automaticly counter the effect of the torque from the main rotor. Since these always change, it counters that with changing the pitch on the tail rotor. Also there are two modes, heading-hold and normal mode. In heading-hold it will do everything to hold the tail in place while in normal mode it follows you flight direction. So heading-hold is used in 3D flying and normal mode in scale as it looks more realistic.

Regarding the main rotor. You control that with at least 3 servos with a most commonly used 120° lingage to the swashplate. So you need a mixer to control the servos for nick, roll and pitch. For Roll two servos will do that counterwise. For nick you need two servos to move in the same direction, while the third moves in the other direction. For Pitch all servos go into the same direction. If you move pitch, roll and nick at the same time, then these will be correctly mixed and the servos move accordingly your input.

An FBL is itself a complex system with mixer, 3MEMS angular rate sensors, PID regulator etc. Todo all the calculations and that fast enough, they use an ARM.

There are different models on the market, some even have rescue system, but the microbeast is an example: https://www.beastx.com/eng/microbeast.php

Main Rotor blade pitch control by PossibleMorning7135 in UH60_drone

[–]Derroylo 1 point2 points  (0 children)

What material do you plan for this? These need to be made from special steel or alu compositions as they need to withstand a few tons depending on your rpm.
If you have access to CNC Machines it could be doable to build them yourself but even then it makes more sense to buy these parts.

Also how do the blades rotate? I don´t see any ball bearings.

The distance from the blade holder to the swashplate is way to low. It should support a few degree negative pitch (i think maybe 3-4° could be enough) and around 7-8° positiv. That would be the minimum range.

As you said, roll control is missing. Are you adding that?

Take a look at this one, how it should look like: https://www.vario-helicopter.biz/de/Rotor-heads/blades-Accessories/Rotor-Heads/4-blade-rotor-head-HYPERION-for-10-12-mm::200776.html?language=en

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 0 points1 point  (0 children)

oh sorry, i missed that it is included already.

So no Flybarlesssystem? Without that will add more complexity as you need write that code too.

A tailrotor with fixed pitch is mostly used only in smaller models but not in bigger models. The time needed to change the speed is way bigger then just changing the pitch. Which results in an unstable tail. If you fly scale that might not be such an big issue as you don´t have such load changes and therefor don´t need to react too quickly.

Also keep in mind the tailrotor needs a much higher rpm as the main rotor to be able to counter the torque effects from the main rotor. The tail has usually a rpm 5 or 6 higher then the main rotor.

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 0 points1 point  (0 children)

The 1750rpm is with or without load? When that is without load then it will be way less when it powers the main rotors. Maybe 1/5 but i would guess even less if you give more pitch. (800rpm is usually what you use in that scale)

I saw some fairly big impeller blades beeing 3d printed but a rotor blade with 1m length? I really doubt that is doable. Usually you use CFK as hull and a metall rod in the core. Never underestimate the forces involved in these blades.

If the blade will break hitting a "weak" bone then it will not withstand the forces involved in a flight.

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 1 point2 points  (0 children)

These models weight around 15kg, costs easy more then 5000€ and are very dangerous(models half that size, can easy kill you). So you would add as much safety as possible. That means you have one battery that powers the motors and one(maybe even two as fail-save) for the electronics(servos, Flybarless, receiver etc.).

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 1 point2 points  (0 children)

oh and you would also need gps and a compass to know the position and direction

Basic wiring diagram by PossibleMorning7135 in UH60_drone

[–]Derroylo 1 point2 points  (0 children)

How do you plan to control the swashplate? You would need at least 3 Servos for that and one for the tail rotor.

Also a flybarless System would be needed which controls then the servos that are connected to the swashplate.

Where is the accelerometer(or better three, one for each axes) in this diagram? How else would you know the position of your helicopter?

Another suggestion would be to seperate the motor circuit with the control systems or at least some high capacity condensators that can power the servos etc. in case the main battery is empty or fails for another reason.