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Steel initiator chamber is ready for testing!
I have also started to prepare the left wing of the RC plane for sound cannon installation. A buddy of mine suggested that the main tube should be split into parts so it would be easier to install, and I see he has a point, because due to the bending of the tube, it would be impossible to install without major wing surgery, which I need to avoid. I don't wanna leave the wing weaker than before cannon install. I have some silicone tubing that I can use for the joint/joints.
Silver soldering the parts together went OK, but I can see I need a bit more practice before it reaches my standards, but this will be fine for testing.
Cool project and strait forward solutions..thanks for sharing this stuff.
jean, thanks! I enjoy sharing this, and I also use this thread as documentation for my own use.
I tested the new initiator chamber a few days ago, but with 10cm extra main tube, that did not work out very well, and the 3D printed mixer keeps melting.
So I made a mixer from aluminium with a new brass nozzle (M6 brass rod, 0.3mm hole), and attached it to the mixer tube with a 3D printed coupling, this is temporary as I have plans on either use a piece of silicone tubing for connecting the two parts, or make external threads in the aluminium mixer and make a steel adapter with internal threads which can then be silver soldered to the mixer tube.
I also took out the extra 10cm of main tube and went testing tonight in the dark.
What a great experience!
It worked so well! And for so long too! The only part that gave up was the 3D printed barrel, this is the next part I need to make from steel and I know exactly how I want to do it.
The darkness makes it possible to see the blue flames coming out of both the intake and barrel which is really cool. The sound level was amazing and the obtainable rate of fire is good, the last testing was made at 330 shots per minute still with good consistent sound, I think this is a record! It's going to sound really cool with 2 cannons shooting at this speed
Pictures of current setup:
Steel cannon barrel is ready.
I tried to use the tubing from the weed burner, but its OD was 1mm too small to fit tightly inside the main tubing, so I tried to expand the end of the tube, but didn't have much success. So I went to the local plumbing store and got a piece of 3/8" steel pipe, this had the perfect OD for fitting in the main tube but needed boring to get to an ID of 13mm along with a little work on the lathe to get the OD down on the barrel itself. Final weight of the barrel piece was 11.7g.
I managed to make a pretty nice barrel with ID 13mm, OD 14mm and length 60mm. The thicker end fits tightly into the main tube so it was easy to silver solder it in place.
I'm very pleased with the result
I tested the new steel barrel today, and it works flawless even though it is 50% longer than the red 3D printed plastic one I have been using up until now.
On the video I'm shooting at 318 shots per minute. I'm far enough away for not wearing ear protection, but the sound is still too loud for my phone camera mic. How can I record this with better sound, any suggestions?
That's a pretty good result, right there. Nice.
I haven't got any better sound recording of the cannon, I need some better recording equipment than a smartphone.
But I do have some update though. I have long been thinking of the best way to attach the aluminium air/gas mixer to the corrugated mixer tube, and had a few ideas but now I tried one out. The test mixer is turned down from 15mm to 12mm. A M12x1.0 external thread is made on the mixer end, and a normal M10 nut was made into a steel adapter with tapped M12x1.0 internal thread. The adapter is silver soldered to the corrugated mixer tube. This seems to work just perfectly, it takes up almost no space, is lightweight and can easily be disassembled during mounting. The mixer is just a test, the final mixer will be optimized in size/weight when I know the final dimensions.
Seems to be weather for a test run tomorrow
Re: Noise cannon for RC planes
Another thing I have been tinkering with, is a propane pressure sensor. The sound cannon is sensitive to a change in propane pressure which means that I need the full pressure of 9bar/130psi every time I shoot it, otherwise the sound will suffer due to the fast shooting. Since I'm using a very small propane canister, it's temperature (and pressure) will drop significantly when consuming propane. So I have wrapped the propane canister with kapton tape, which is electrical insulating but transfers heat pretty well, and then wrapped some 0.5mm untreated black iron wire around it, acting as a heating device. Power for heating will come from a small 1000mAh 4 cell LiPo battery.
The sensor will then monitor the propane canister pressure, and when pressure drops due to consumption or cold weather, it will turn on the heater until pressure is restored. I will also add a temperature sensor to limit the max temperature on the propane canister.
I'm also thinking of remote readout of the propane pressure, this way I can monitor max pressure on hot summer days and also see if the pressure drops rapidly indicating an empty canister. Maybe I will even make a two-way WiFi communication between sound cannon and smartphone, this way I could adjust rate of fire remotely and change settings on the propane heater e.g. on winter days I might settle for a lower rate of fire which decreases the demand on propane pressure and lowers heater battery load by allowing a lower pressure and temperature on the propane canister.
Anyway, the only affordable sensor I could find that can measure at least 10bar/145psi, is a G1/4" inch 5V 0-1.2 MPa Pressure Transducer from ebay. This is a very big and heavy sensor with steel housing, so I took apart the sensor housing and made a new small and lightweight aluminium housing for the sensor element. I also added a hose input nipple of the correct size. The internal/external threads were the big challenges as they are a custom size, and this was my first attempt at making internal threads on my lathe without a thread tap. It turned out perfectly at 22mm diameter, 19mm length without nipple, weighing only 17g!
I went testing today just before dark. I brought my camera to see if that could capture the sound any better than my smartphone. It's not quite there yet but I'm getting closer. I think a big part was to the added distance between recording device and sound cannon.
I also know what the next step is - to get the propane canister heater working. The canister will drop in temperature very quickly partly due to the cold weather but mostly because of the propane consumption. The firing rate suffers from this, and since I need to consume some propane for tweaking the valve for best sound, the canister is already down on pressure when I'm ready for testing.
I'm convinced I can break my own record with a nice warm propane canister
Amazing! I love logging on here to see new posts on this project haha - made me log in to leave this comment! Regarding frequency - any way you could possibly have two guns using one propane cylinder to save on weight - then fire them out of sync slightly using a micro controller to control the firing - which would work perfectly for all your other micro controller intended additions (pressure monitoring, wireless communication). Also regarding WiFi - there are SO many cool WiFi enabled controllers, but you will use a good bit of power to run them - this won't be a big deal if you aren't intending long flights (i.e. more then 30 minutes) - but if you are, you could look into other wireless protocols such as ZigBee (XBee devices from Digi) or 900 mhz options too.
For WiFi + micro controller + long enough distance to make it worth your while, you may want to consider something that is 'maker friendly' like the Adafruit feather series - which features a powerful yet power efficient micro controller, wifi with a u.FL antenna connection (probably very useful in your case we're you'll want a higher gain antenna) and other sensor ready circuitry like 10 pins for analog inputs (i.e. pressure sensor). It's all wrapped up in a good board with lithium battery input and a charging circuit for said lithium battery (i.e. solar panels on wings could recharge it!). And finally - you can program it using the standard Arduino studio - which makes adding new code, new sensors, and new logic effortless because you have a huge community of contributors out there just like SpudFiles haha. I work with these kind of boards every day at my job so this is probably one of my favorites where ease-of-access is considered!
mobile chernobyl, thanks for the nice comment! I like to share but I like it even better when I get some kind of feedback on all my hard work
I will mount one sound cannon in each wing on my plane, and I believe they can share the same propane canister and ON/OFF valve. The test controller I have built, actually have 2 outputs for the high voltage spark modules, and they are activated in turn, with the exact same amount of time between them, so it will eventually sound as a single cannon shooting very fast - if I can get each cannon to sound the same, but if all dimensions are the same, they should also sound the same.
For WiFi I think I'm going for the ESP8266 with an antenna connector (ESP07) and a 3dB gain antenna. I already have these at hand, and the ESP is a nice compact module with microcontroller included and everything. I'm using the ESP8266 core for Arduino along with Arduino IDE, which is very nice to work with. The ESP will use 170mA max when transmitting which isn't much compared to other stuff on the plane. I have the 1000mAh 4S LiPo battery for the heater which I could tap all power from for the heater (full 4S LiPo voltage), the HV modules (7-8V), the spark controller MCU (3.3V) and the WiFi module (3.3V). I can make some small DC-DC converter circuits for lowering the 4S LiPo voltage for the HV modules and 3.3V stuff, keeping all power for the sound cannon related stuff to one designated battery.
Since the ESP has a powerful MCU, I have been considering to use this for everything, but the valve servo requires a good timed servo signal and the timing of the HV modules can't be too much off, otherwise it could be noticeable. There is also the pincount, the ESP does not have too many pins. I need at least these:
- Digital input from RC receiver.
- Digital servo output to valve servo.
- Analog input from pressure sensor.
- Analog or SPI digital input from propane canister temperature sensor.
- HV modules output (2).
- Analog input for battery voltage monitoring to avoid damage to LiPo battery.
- More HV modules digital output for even more cannons on my bigger plane (6 in total).
- Maybe replacing the valve servo with a stepper motor.
The ESP does not have enough analog I/O for this, so I'll have to use a PIC on the side which I think gets to control everything and then the ESP can read data in by SPI or whatever.
I was going to mention the ESP8266 - wasn't sure on your level of comfort with dealing with them as they can require FTDI programming setups and whatnot - which can be a pain if your not used to the pinout. Look at the ESP32 as well - much more powerful then the 8266, has bluetooth and better wifi stack I believe. Many maker friendly dev boards with the ESP32 already if you want to dev on one of them then transfer to a bare ESP32 unit.
The esp32 has better GPIO in general too such as 12bit ADC vs 10bit, better serial line support, better PWM and has a DAC output.
So many fun options out there, and with the community behind the 8266 you can't go wrong!
ESP32 is not really mature yet, price is still high, maybe due to high demand and out of stock situations. Also the Arduino core for ESP32 is not ready yet, so it will definitely be the ESP8266 at this point in time.
I just got hold of another ESP07 yesterday, I'm planning to see how far 2 of these non-FCC compliant devices can connect to each other using both the chip antenna and my 3dBi antennas.
I have telemetry on my RC system, and I have been thinking of making some additional telemetry for my smartphone using the ESP, but I remembered that it is not allowed to bring your smartphone to the pilot field of my RC site, due to the (though rare) possibility of signal disturbances. It can easily be thousands of dollars flying around in just one plane, so we don't want to crash any plane due to facebook updates or whatever
So, maybe I should employ this in my plane too, no ESP WiFi enabled during flight, only local data logging, WiFi only enabled when on the ground. So if I want real time telemetry during flight, it would be better to find an unused input on the RC telemetry system and interface to that
I couldn't help myself, so I built a new open/close valve based on the same principle as the last one, but this time stripped for un-necessary weight from the aluminium, and with a shorter home-wound return spring. A new attachment for the RC servo is also underway.
During development of the valve, I made a mistake on one of the housings, so I cut it open to show the inner workings, and I got a short video out of it
Propane open/close valve V2 is now done!
I shaved 47% off the weight (not counting the servo) and also got it more compact for easy installation in the RC plane. It's now down to 52g where the RC servo is half of the weight. The valve itself was 30g, now 15g. The servo seems reliable and strong, so I don't want to replace that for saving additional weight.
New nitrile O-rings were used for a tighter seal all around in the valve. New design 3D printed mounting arrangement was developed - it didn't take THAT many revisions
The valve is mounted lower compared to the servo. The overkill steel wire was replaced with nylon cord. Servo mounting screws got a tube for hiding the sharp point of the screw (could rub on servo wires).
I'm not sure how I want to mount it in the plane yet. I'm thinking double sided tape on the side of the servo and a wire strap around for safety. There is no clearance for the wire strap now, but I can print a new holder if that is the method of attachment I choose.
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