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Hello there,
this topic shall serve as an introduction to an interesting facette of RC submarine activities: FPV (First Pilot’s View) under water.
FPV is meanwhile widely used within the airborne RC community, so why not introducing this fascinating option in our underwater hobby.
For this purpose, a sub needs to be equipped with a forward looking video camera inside a watertight compartment which is transmitting its live video stream to the operator ashore via a high frequency link.
In order to suppress disturbing ambient light, it is convenient for the operator to wear a special goggle, similar to those for virtual reality activities (http://www.fatshark.com/).
This current thread is only describing the basics for this kind of sub operation. In a few weeks, more information, covering real sub deployment with figures of Hardware, etc. will be added.
Concerning a suitable sub model, the Seawolf from TT Robotix (http://ttrobotix.com/product/seawolf) will serve as a workhorse for this project. RC equipment is German standard (40 MHz).
Please bear with the author that only an outline for such an approach is presented here; the experienced sub modeler will know how to interpret these lines.
FPV operation of a sub is offering the possibility of performing extended underwater cruises with an operational range of a few hundred feet. However, in order to obtain these distances, a few modifications of the model and its RC equipment are required.
During “normal” operations close to shore, the radio waves from the transmitter (Tx) are entering the water at quite steep angles; thus permitting sub operation down to some 10 ft to 15 ft in sweet water.
In case one is willing to operate a sub at longer distances (say a few hundred feet), these radio waves will touch the water at the sub’s location at a quite shallow angle. In fact, most of the transmitted energy will be reflected upwards and only a tiny fraction will enter the water towards the sub’s antenna.
In order to overcome this problem, the receiver (Rx) inside the sub will be connected to a small tethered float (e.g. a 2 ft x 2 ft Styrofoam plate) on the water surface by means of a cable with a length of some 40 ft. This float is carrying a specially designed Rx antenna (e.g. a thin brass tube). The following figure is illustrating the basics of this arrangement.
The length of this overwater antenna needs to match specific criteria; depending on the RC frequency in use:
- 75 MHz (US): 3,3 ft (appr. 100 cm) or
- 40 MHz (Europe): 6,2 ft (appr. 188 cm)
These dimensions are corresponding to ΒΌ RC wavelength. Antennas of this type are called “Marconi-antenna”, remembering the Italian inventor of radio communication Guglielmo Marconi (https://en.wikipedia.org/wiki/Guglielmo_Marconi). With these dimensions the impedance (RF resistance) at the bottom of the antennas is 50 Ohm.
A common 50 Ohm coax cable, e.g. the thin RG 174 (only 0,11 inch diameter) is ideally matching to these antennas and will forward the Tx signal to the sub. Only the center part of the coax cable will be connected here. The outer shielding is carefully isolated (watertight). A convenient solution is to use the interior of a plug – mounted at plate on top of the float - that fits into the bottom of the antenna, so that antenna and cable can be disconnected for transportation.
The cable is entering the sub’s hull by means of a watertight throughput and is directly connected to the RC receiver. It is suggested to place this throughput at the sub’s centre of gravity (c. g.), minimizing disturbing drag by the cable.
Now, the housing of the RC receiver needs to be opened and the original long wire antenna will be removed with a soldering iron.
The center part of the coax cable is soldered to the original antenna input and its shielding is soldered to the receiver GND (ground).
It is suggested to use a small SMA connector (https://en.wikipedia.org/wiki/SMA_connector) outside the sub so that the long cable can be removed from the model for transportation. Otherwise one may wrap this cable around the hull.
Having done this, the sub can be controlled over extended distances.
Now the video section: A tiny video camera inside a watertight transparent case is installed inside the sub’s front section. One should use a camera with a wide angle lens (field of view at least 100 degrees) for optimum visual underwater navigation.
This camera is powered by a battery that is also mounted onboard the above mentioned float (see figure above).
It will send its video signal via the same type of 50 Ohm coax cable. In general these cameras have an output impedance of 50 Ohm; again a perfect match.
Since this cable is already connected to the GND pole of the camera, only one additional thin wire needs to be added for the positive pole of the camera supply voltage.
The video coax cable is connected to the video transmitter that is placed alongside the battery on the float.
Watertight throughputs will be used for the camera case.
Overall we now have three cables to work with:
- Coax cable for the downlink of the Tx signal
- Coax cable for the uplink of the video signal
- Single thin wire for the Plus-supply voltage of the camera
It is suggested to combine these three elements by means of short sleeves of shrinking tube or cable ties; appr. every 3 ft. In order avoid disturbance to the sub’s vertical trimming it is suggested to add small floating elements along this cable arrangement so the cable itself is floating with neutral buoyancy.
So far the theory behind underwater FPV.
As said, more details will be reported, once the hardware for this project will have been realized within a few weeks. So, stay tuned.
For the meantime: Critics and suggestions are always welcome !
Cheers
Volker
this topic shall serve as an introduction to an interesting facette of RC submarine activities: FPV (First Pilot’s View) under water.
FPV is meanwhile widely used within the airborne RC community, so why not introducing this fascinating option in our underwater hobby.
For this purpose, a sub needs to be equipped with a forward looking video camera inside a watertight compartment which is transmitting its live video stream to the operator ashore via a high frequency link.
In order to suppress disturbing ambient light, it is convenient for the operator to wear a special goggle, similar to those for virtual reality activities (http://www.fatshark.com/).
This current thread is only describing the basics for this kind of sub operation. In a few weeks, more information, covering real sub deployment with figures of Hardware, etc. will be added.
Concerning a suitable sub model, the Seawolf from TT Robotix (http://ttrobotix.com/product/seawolf) will serve as a workhorse for this project. RC equipment is German standard (40 MHz).
Please bear with the author that only an outline for such an approach is presented here; the experienced sub modeler will know how to interpret these lines.
FPV operation of a sub is offering the possibility of performing extended underwater cruises with an operational range of a few hundred feet. However, in order to obtain these distances, a few modifications of the model and its RC equipment are required.
During “normal” operations close to shore, the radio waves from the transmitter (Tx) are entering the water at quite steep angles; thus permitting sub operation down to some 10 ft to 15 ft in sweet water.
In case one is willing to operate a sub at longer distances (say a few hundred feet), these radio waves will touch the water at the sub’s location at a quite shallow angle. In fact, most of the transmitted energy will be reflected upwards and only a tiny fraction will enter the water towards the sub’s antenna.
In order to overcome this problem, the receiver (Rx) inside the sub will be connected to a small tethered float (e.g. a 2 ft x 2 ft Styrofoam plate) on the water surface by means of a cable with a length of some 40 ft. This float is carrying a specially designed Rx antenna (e.g. a thin brass tube). The following figure is illustrating the basics of this arrangement.
The length of this overwater antenna needs to match specific criteria; depending on the RC frequency in use:
- 75 MHz (US): 3,3 ft (appr. 100 cm) or
- 40 MHz (Europe): 6,2 ft (appr. 188 cm)
These dimensions are corresponding to ΒΌ RC wavelength. Antennas of this type are called “Marconi-antenna”, remembering the Italian inventor of radio communication Guglielmo Marconi (https://en.wikipedia.org/wiki/Guglielmo_Marconi). With these dimensions the impedance (RF resistance) at the bottom of the antennas is 50 Ohm.
A common 50 Ohm coax cable, e.g. the thin RG 174 (only 0,11 inch diameter) is ideally matching to these antennas and will forward the Tx signal to the sub. Only the center part of the coax cable will be connected here. The outer shielding is carefully isolated (watertight). A convenient solution is to use the interior of a plug – mounted at plate on top of the float - that fits into the bottom of the antenna, so that antenna and cable can be disconnected for transportation.
The cable is entering the sub’s hull by means of a watertight throughput and is directly connected to the RC receiver. It is suggested to place this throughput at the sub’s centre of gravity (c. g.), minimizing disturbing drag by the cable.
Now, the housing of the RC receiver needs to be opened and the original long wire antenna will be removed with a soldering iron.
The center part of the coax cable is soldered to the original antenna input and its shielding is soldered to the receiver GND (ground).
It is suggested to use a small SMA connector (https://en.wikipedia.org/wiki/SMA_connector) outside the sub so that the long cable can be removed from the model for transportation. Otherwise one may wrap this cable around the hull.
Having done this, the sub can be controlled over extended distances.
Now the video section: A tiny video camera inside a watertight transparent case is installed inside the sub’s front section. One should use a camera with a wide angle lens (field of view at least 100 degrees) for optimum visual underwater navigation.
This camera is powered by a battery that is also mounted onboard the above mentioned float (see figure above).
It will send its video signal via the same type of 50 Ohm coax cable. In general these cameras have an output impedance of 50 Ohm; again a perfect match.
Since this cable is already connected to the GND pole of the camera, only one additional thin wire needs to be added for the positive pole of the camera supply voltage.
The video coax cable is connected to the video transmitter that is placed alongside the battery on the float.
Watertight throughputs will be used for the camera case.
Overall we now have three cables to work with:
- Coax cable for the downlink of the Tx signal
- Coax cable for the uplink of the video signal
- Single thin wire for the Plus-supply voltage of the camera
It is suggested to combine these three elements by means of short sleeves of shrinking tube or cable ties; appr. every 3 ft. In order avoid disturbance to the sub’s vertical trimming it is suggested to add small floating elements along this cable arrangement so the cable itself is floating with neutral buoyancy.
So far the theory behind underwater FPV.
As said, more details will be reported, once the hardware for this project will have been realized within a few weeks. So, stay tuned.
For the meantime: Critics and suggestions are always welcome !
Cheers
Volker
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