I have designed gas engines to be used with drones. The problem I have is that the esc cannot control the servo which opens and closes and regulates the fuel into the gas engine. Does anyone know of an autopilot which could control six servos in the same manner it controls the brush less motor. Just remember when the autopilot senses a gyroscopic movement, it needs to open the servo valve accordingly to allow the drone to stabilize. I hope that I am making some sense here
You are correct that an ESC cannot control a servo. However, a typical ESC operates on the same PWM signal that a servo operates on. So the servo would replace the ESC and be controlled by whatever you have to control the ESC.
I've not used any autopilot systems, so I don't know which would work in your situation. Maybe ArduPilot? That's the only one I can think of off the top of my head.
Curious as to why you would want to use gas engines instead of electric motors. Is it just to see if you can do it? That's always been a good enough reason for me to try something different.
Good luck with your project.
I've not used any autopilot systems, so I don't know which would work in your situation. Maybe ArduPilot? That's the only one I can think of off the top of my head.
Curious as to why you would want to use gas engines instead of electric motors. Is it just to see if you can do it? That's always been a good enough reason for me to try something different.
Good luck with your project.
Thanks for your reply. I will investigate the issue of using a servo directly to the pins which drives the ESC and use the same power source to drive them. The reason I want to use gas engines:
1. They are quite robust
2. They dont need propellers
3. The are faster
4. They can reach higher altitudes as they do not need air lift. They use thrust.
5. Much longer flight time
6. Longer battery life as it requires a fraction of the power compared to brush-less motor consumption.
7. The drones can be built quite large.
Thus if like you mentioned, use the PWM signal directly from the controller (which In our case, the pixhawk) But all these autopilots are basically the same.
Using a normal RC radio to throttle the six engines (the throttles are controlled by a servo respectively) works fine. It stabilizes the engines according to the sensor such as the gyroscopes etc.
But now we want to use this drone in an autonomous state using an autopilot.
1. They are quite robust
2. They dont need propellers
3. The are faster
4. They can reach higher altitudes as they do not need air lift. They use thrust.
5. Much longer flight time
6. Longer battery life as it requires a fraction of the power compared to brush-less motor consumption.
7. The drones can be built quite large.
Thus if like you mentioned, use the PWM signal directly from the controller (which In our case, the pixhawk) But all these autopilots are basically the same.
Using a normal RC radio to throttle the six engines (the throttles are controlled by a servo respectively) works fine. It stabilizes the engines according to the sensor such as the gyroscopes etc.
But now we want to use this drone in an autonomous state using an autopilot.
Just out of curiosity, if you are controlling engine speed via a throttle what about wear in the 'carb'?
I am just imagining the thousands of minute tweaks that would be necessary in a normal carb and the wear that would take place in butterfly shaft bearings or slides or needles or jets. Of course I may be completely up the left with how such engines are fueled nowadays.
I am just imagining the thousands of minute tweaks that would be necessary in a normal carb and the wear that would take place in butterfly shaft bearings or slides or needles or jets. Of course I may be completely up the left with how such engines are fueled nowadays.
harleydude
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I would think controlling fuel flow would have too much latency. The IMU would probably go nuts trying to compensate. Instead, I would control prop pitch. Especially if you're using 6 engines. I know it induces more mechanical complexity into the design, but it would all but eliminate latency. And then you could use a single servo NOT on an ESC to control fuel flow to all 6 engines at once. Either through a manifold system or 6 linkages off a single servo. In the case of the latter you could sync the engines' fuel flow by adjusting the individual linkage lengths. Just food for thought.
D
harleydude
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From Wikipedia, the free encyclopedia
A cold gas thruster (or a cold gas propulsion system) is a type of rocket engine which uses the expansion of a (typically inert) pressurized gas to generate thrust. As opposed to traditional rocket engines, a cold gas thruster does not house any combustion and therefore has lower thrust and efficiency compared to conventional monopropellant and bipropellant rocket engines. Cold gas thrusters have been referred to as the "simplest manifestation of a rocket engine" because their design consists only of a fuel tank, a regulating valve, a propelling nozzle, and the little required plumbing. They are the cheapest, simplest, and most reliable propulsion systems available for orbital maintenance, maneuvering and attitude control.[
harleydude
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Well, I guess I learned something new today.
"Lower thrust and efficiency" caught my eye. So what kind of pressure are we talking in what size tank that weighs how much for how long of a flight? In the industry, we call that a run-on sentence....<;^)
D
The question of latency does not exist as the expansion occurs is in microseconds. Feed rate of the fuel into the expansion gas chambers is controlled by the servos.
Servos function: 20RPM for startup. Full thrust = 200rpm Hover is around 80RPM.
It is obvious that it would be absolutely impossible drive the screw feeders with brushless motors and ESC's. They usually spin around 40,000RPM. Thus as was suggested, the following diagram illustrates the workings and the use of direct continuous servos.
The question of latency does not exist as the expansion occurs is in microseconds. Feed rate of the fuel into the expansion gas chambers is controlled by the servos. Weight is minimal. Our system uses 1litre. Being in a liquid state does not require too much pressure. At least 100 times expansion speed that of freon in fridge evaporators
Servos function: 20RPM for startup. Full thrust = 200rpm Hover is around 80RPM.
It is obvious that it would be absolutely impossible drive the screw feeders with brushless motors and ESC's. They usually spin around 40,000RPM. Thus as was suggested, the following diagram illustrates the workings and the use of direct continuous servos.
harleydude
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So the answer to my question, "So what kind of pressure are we talking?" is...
And the answer to my question of, "...in what size tank...??" is....
And the answer to my question of, "...that weighs how much....??" is....
And the answer to my question of, "...for how long of a flight?" is...
I'm glad we had this chat. Very strange and eclectic.
There's "avoiding the question," and then there's this....LOL....
Good luck.
D
And the answer to my question of, "...in what size tank...??" is....
And the answer to my question of, "...that weighs how much....??" is....
And the answer to my question of, "...for how long of a flight?" is...
I'm glad we had this chat. Very strange and eclectic.
There's "avoiding the question," and then there's this....LOL....
Good luck.
D
Answers were given according to previous post about latency etc. Regarding weight, pressure and size, I do not regard that as important. There are numerous cold fuels out there and their specific gravity varies. Tanks are usually pvc and lightweight. A liter tank is around 190g. Pressure is not a question as it rarely exceeds 2 bar. Flight time varies according to jet engine size and overall weight. Ours weigh complete with 1 litre fuel and all components, 3.2 kg. Each engine has a thrust of 1.1kg full throttle and 510g at hover. Flight time 38min -50min I hope this answers your question.
It does confirm this is just a troll post unless you either have no idea of what you're talking about or the laws of thermodynamics somehow don't apply to you.
Unfortunately, we use propriety fuel. It is manufactured by our subsidiary here in South Africa. You will have to design your own jet engine in order to use it. Do your homework and try and manufacture your own fuel and jet engine. Ours is in prototype stage currently and so far so good. It works and has nothing to do with the concept of thermodynamics. It is unethical to expect some company to share their trade secrets and use "troll" etc as a means of cheap extortion
Also, my purpose for this post was simply to get some help in connecting 6 servos to a pixhawk (which thankfully was received from another forum). I have shared this post as a pdf schematic of a pixhawk connected to 6 servos, which was not necessary at all, just in good faith for those who are intrigued with the mechanics of simple jet power engines. The dynamics of our jet engine was not intended as a primary discussion. So how does it become a "troll post"?
