How to build an FPV Glider from scratch: 2014

Dec 21, 2014

Estimations, iterations and final choice of components

These are some scanned sheets from the process of decisions making and the iteration process:

Example of similar components approach. Payload estimation.

Rules determining the class of components

Weight estimation

On one hand, there is the empty weight, the weight of the structure without its components. This empty weight is not the same as defined for manned aircraft, where it takes into account all the electronic components and all the other necessary things to fly except the fuel, crew and passengers.

This weight will be defined by the mass of the fuselage, wings, horizontal and vertical stabilizers and the landing gear. The mass is defined by the volume of the aircraft and the density of the material chosen.

Similar models without camera, gimbal, smaller battery and motor and made of foam weight from 1500 to 2500 kg. It is expected that just changing to carbon fiber increases the weight significantly (carbon fiber density = 1.55 g/cm³, EPO density = 0.8 g/cm³).

The payload definition for this unmanned aircraft is the group of electronic components.

First estimation range (specs, weights, dimensions and prices)

First estimation:
• Battery (Zippy Compact 5800mAh 3s 60C) – 500 to 600g (max. 900g) – 158x45x32 – 37€
• ESC (Turnigy K-Force 40A) – 38g – 59x27x12 – 25€
• Motor (RC Tiger 2820 830kV) – 132g (130 to 240g) – 35x42 – 57€
• Propeller (10x6in) – 254mm – 2€
• Camera (Walkera iLook+ FullHD 170fov WiFi) – 125g – 82x44x41 – 150€
• Servos – 4x9g = 36g or 4x17.4g = 70g – 10 or 50€
• Gimbal (2 axis ACK GoPro and Action Cam, controllers + motors AXN) – 209g – 110€

Payload: from 1040g to 1192g (max. 1622g)

Let’s say, with the similar planes, the empty weight is 2000g, minus the motor, ESC, battery and servos (~474g) is 1500g approximately, plus the carbon fiber weight, climbs to 2500-3000. If the previous components are added it reaches a take-off weight of 3500 to 4300g (max. 4600g).

If the volume of the plane is mostly made out of foam, the weight of the structure shouldn’t be over 2000 g.
Taking different components, the payload might be over 1000 g. So the final weight would be almost 3000 g.

Weights scheme

Now the website ecalc.ch is the next tool to find which components combined together will make the plane fly wihout performance issues.
After several iterations and finding the correct data of the components that are manufactured and can be bought online nowadays, these are two suitable options:

The third option is better because of its shorter propeller and lighter motor

The performance is good enough, there are no issues with the thrust to weight ratio and the motor cooling is optimal.

Final choice

This final selection has a perfect compatibility between its components. All the power system is from the manufacturer Turnigy, which is one of the leading companies in the RC world. The servos are not from this trademark but it doesn’t state a problem (although they can be chosen with the same specs labelled Turnigy too), and Hextronic has very good reviews too for servomotors.
The high capacity battery gives a flight time of 20 minutes, which can be extended if good use of gliding is carried out.
The Electronic Speed Controller has a Battery Eliminator Circuit installed so the same battery can power the receiver and servos.
Gyroscopes PCB has the same connections as all standard receiver cables. It is just a bridge between the receiver and the servos.
The only missing data is the structure price. If it’s foam it will be cheap but if carbon fiber is added the price might increase a bit more than expected.
The rest of the manufacturing cost for the mission is completed by the systems on the ground, whose weight is not taken into consideration.

The final flying model is expected to cost less than 1000 €, all included. A study of the sale price for a mass production plane will be made further on.

Extra scans

Random notes in Spanish

Modified first draft. Completed and uncompleted tasks in post-it schedule.

Drafts for camera, landing gear and tail configuration

Video through mobile phone network

“Upgrading the flight range”

To broadcast video, the most known connection is WiFi, but its range is very low.
A very good alternative is to broadcast through the 4G/LTE or 3G cell phone band, which uses the antennas from several telecommunications companies all around the world.
With this in mind, the plane could fly as far as the battery lets him, maybe from coast to coast of Spain.
A SIM card system must be implemented with the transmitter of the video, the signal exiting the camera, and it needs a mobile data plan with a company operating in the country where it is going to fly.
With a simple approach between mobile network providers, the cost of broadcasting Full HD during an hour via satellite to the ground is equal to: 15€.

There is someone who has already implemented this idea into a camera, as it was shown before, in the camera option number 1. The disadvantage is that the whole system (app included) costs 400 €.

Dec 9, 2014

Materials

Carbon fiber vs fiberglass:

Carbon fiber is often used to make RC structures. The dynamic soaring gliders are typically built exclusively from carbon fiber.
On really light weight structures, light weight carbons are very, very, very expensive. Some can be $200 per yard while an equal volume of fiberglass is $5 a yard.
If stiffness is an objective of the structure then carbon is almost always used. This is why it is added to glass structures. It can be added to just certain areas (spars, fuse sides) to create the required stiffness. Having it everywhere isn't always necessary or beneficial.
Carbon fiber also blocks radio signals while Kevlar and fiberglass do not. In the modern age were 2.4 receivers have short antennas getting them outside the carbon fiber in varying orientations becomes difficult.
Carbon structures can be lighter for the same strength, but due to material availability it's not always a reality.

Weight: Carbon fiber is lighter than fiberglass, it’s 70% lighter than steel, 40% lighter than Aluminum.

Strength vs Rigidity: Carbon fiber and fiberglass are both very strong, but Carbon fiber is more rigid. Carbon fiber is about 3 times stiffer than steel and aluminum for a given weight.

In applications where a small amount of flexibility is allowed, we should use carbon fiber. Fiberglass is better suited to extreme flex patterns, while carbon fiber has a relatively small flex window.

Toughness: The shape of Carbon fiber doesn’t deteriorating slowly over time. That means the shape of carbon fiber doesn’t change when consistent and constant force is applied.
Fiberglass however being more flexible, it means that glass-fiber typically has a higher ultimate breaking point than a similarly shaped carbon fiber product, therefore having higher strength-to-weight ratio. In general it is a “tougher” material but the incredible rigidity of carbon makes it less capable of enduring certain abuses than fiberglass.

Characteristics: As opposed to most other materials, carbon fiber has a negative coefficient of thermal expansion which means they don’t expand or shrink as much as fiberglass when the temperature changes. This is a desirable quality for applications that have to operate in a wide range of temperatures.

Fiberglass composites are insulators, which means they do not respond to an electric field and resist the flow of electric charge. Fiberglass composites are very radiolucent, which means they allow radiation to pass through it freely. This makes fiberglass rods a useful material for antennas.

Price: Fiberglass is much cost effective. Long strands of carbon fibers are very difficult and expensive to manufacture, while fiberglass processes much easier. As a result, fiberglass is considerably less expensive than carbon fiber. Fiberglass composites are less expensive than carbon composites in most cases.

If stiffness isn't a driving factor then fiberglass is often very suitable. Fiberglass is easier, faster, and cheaper to use. Kevlar is very timely to cut compared to carbon and glass.

When it comes to toughness, glass can perform better than carbon due to its higher strain properties and be easier to repair.

Foams:

EPO (Elapor is Multiplex's trademark foam) is a very durable foam, easily glued back together with medium CA (Cyanoacrylate, same as Loctite Super Glue 3) and kicker (accelerator, triggers quick polymerization of glue).

EPP is Expanded Polypropylene, and is highly durable, and flexes a lot, so generally, people use carbon flat spars or tubes with it to stiffen it. It is also glued back together with medium CA and kicker. Planes made of it generally bounce off of anything they hit.

EPS is Expanded Polystyrene if I remember right. It's basically Styrofoam/Styropor, which is commonly used in cheaper planes, and jets because it can be molded.

Depron is basically flooring insulation that was banned in the US for sale. It's a very popular material that is mostly used with 3D aircraft, because it yields very light wing loadings which allow the planes to basically float around. It's also used for sport jets, or unique aircraft because it's pretty easy to build with.

EPO and EPP are more durable than EPS and Depron.

Some examples:

Elapor

MultiPlex Easy Star

MultiPlex Easy Glider

Magister, MiniMag, Space Scooter, Twin Star II, just about everything from Multiplex

This type of foam is characterized by rather large 'cells'. It also has a slightly 'greasy' feel to it.

EPS Expanded PolyStyrene

GWS E-Starter

GWS Formosa I

GWS Pico Tiger Moth

GWS Tiger Moth 400

GWS DeHavilland Beaver

GWS PT-17 Stearman

Fine-beaded cells; EPS foam is very prone to hanger rash but is supposedly quite good at absorbing bad landings. More major crashes usually require collecting all the pieces in a plastic bag, but it's usually possible to just reassemble the jigsaw of pieces with glue. Sometimes referred to as 'beer cooler' foam.

Regular Styrofoam

Mountain Models MagPie

Mountain Models MagPie AP (Aerial Photography)

This is the unexpanded PolyStyrene. Very crumbly, with no defined 'cell' structure. This type of styrofoam must be protected from literally crumbling into thousands of tiny chunks of styrofoam by wrapping with tape. Once wrapped it becomes a very strong, durable and light material.

EPO - Expanded PolyOlefin

GWS AT-6 Texan

GWS F-15

GWS FW-190

GWS P-40

This is 'supposedly' identical to the Elapor foam of which the MultiPlex Easy Star is made. GWS is starting to make their newest planes of this material. Large beaded cells, and with the same 'greasy' feel to it.

EPP - Expanded PolyPropylene

AeroHog AeroAce

EPP foam doesn't dent or break. It has a 'spongy' quality to it, so on impact it compresses and pops back to shape.

Z-Foam

HobbyZone Super Cub

ParkZone F-27C

ParkZone T-28 Trojan

Similar in appearance and large cell size to Elapor and EPO, but without the 'greasy' feel to it. It's not quite as elastic as Elapor and EPO; in other words, a bit more brittle.

References:

http://www.rcgroups.com/forums/showthread.php?t=1631821
http://blog.oscarliang.net/carbon-vs-fibreglass/
http://www.rcgroups.com/forums/showthread.php?t=986842

Conclusion

With all the collected data, the carbon fiber choice seems the most plausible option because of its strength and lightweight, at least for the plane’s main structure (spars, some ribs in the wings and fuselage and a lengthwise beam). Otherwise it increases too much the final weight, almost doubling it if we compare volumes of similar planes and change the density from foam to carbon fiber.

The shape of the fuselage can be made out of foam, with carbon fiber or fiberglass reinforcements in the areas with most risk of impact/crash.

Dec 4, 2014

List of components needed (with weight, size and price)

There is a wide range for choosing the necessary plane components, there are a lot of specialized websites and lots of manufacturers and varieties.

Hobbyking.com has a huge database of all these components and more, so it’s the chosen one to take the information from. For cameras and extras, Nitroplanes.com is another useful website.

The plane will need:

Servos (2 x Aileron, 1 x Elevator, 1 x Rudder):

14.4g, 25x19.6x8
2.51€

www.hobbyking.com/hobbyking/store/__3715__Hobby_King_S0361_3_6g_45kg_12sec_Micro_Servo.html

9 g, Size : 21x12x22 mm
2.1€

www.hobbyking.com/hobbyking/store/__662__HXT900_9g_1_6kg_12sec_Micro_Servo.html

17.4g, Size: 26x13x26
13.03€

www.hobbyking.com/hobbyking/store/__8760__Turnigy_380MAX_Micro_Servo_Metal_Gear_4_1kg_16sec_17_4g.html

51g, 44x40x20
5.15€

www.hobbyking.com/hobbyking/store/__16266__HK15288A_Analog_BB_MG_Servo_51g_9kg_0_20s.html

· 1 x Electronic speed controller (ESC)

32 g, Size: 54 x 26 x 11mm

www.hobbyking.com/hobbyking/store/__15205__Hobby_King_30A_ESC_3A_UBEC.html

25g, size: 50x26x12
10.1€

http://www.hobbyking.com/hobbyking/store/__11617__Turnigy_AE_30A_Brushless_ESC.html

25g, Size 45x24x11
10.26€

http://www.hobbyking.com/hobbyking/store/__2164__TURNIGY_Plush_30amp_Speed_Controller.html

33g, 55x28x13
17,15€

http://www.hobbyking.com/hobbyking/store/__2165__TURNIGY_Plush_40amp_Speed_Controller.html

35g, size: 60x28x10
15.52€

http://www.hobbyking.com/hobbyking/store/__39566__Corona_40A_Brushless_Speed_Controller_2_6s_3A_UBEC.html

54g, size 45.5x33x23
17.8€

http://www.hobbyking.com/hobbyking/store/__16364__Turnigy_dlux_40A_SBEC_Brushless_Speed_Controller_w_Data_Logging.html

38g, size: 59x27x12
24,65€

http://www.hobbyking.com/hobbyking/store/__8922__TURNIGY_K_Force_40A_Brushless_ESC.html

61g, size: 70x32x17mm
14.24€

http://www.hobbyking.com/hobbyking/store/__16892__Hobby_King_60A_ESC_4A_UBEC.html

· Battery (choose one of the best, crucial component):

- NiMh, Nickel Metal hybrid: less powerful, less expensive.

- NiCad, Nickel Cadmium: less power, more battery life, heavier.

- LiPo, Lithium Polymer: both light weight and long lasting, more expensive.

Things to know about batteries:

2000mAh is the capacity and the most important figure.
Fully charged: 4.2 V (in each cell). Discharged: 3.0 V (in each cell).
A battery with a discharge rating of 10C would mean you could theoretically & safely discharge it at a rate 10 times more than the capacity of the pack (15C pack = 15 times more or 1C discharges the battery in 1/1 hours or 1 hour and 2C discharges the battery in ½ hour). A 2000mAh cell discharged at 6 amps is being discharged at 3C (2000mA x 3).

If you have 2 2000mAh cells and you wire them in parallel then the result is the same as 1 4000mAh cell (it has the same C rating as the original 2000mAh cells did). Thus if the 2000mAh cells could discharge at a maximum of 5C, or 10 amps then the new 4000mAh cell can also discharge at 5C or (4000mA x 5) 20 amps. This method of battery pack building allows us to use LiPo batteries at higher currents than single cells could produce.
If you get a pack with a C discharge rating at least double of the maximum you intend to pull out of it; with proper care, there's no reason you shouldn't be able to get at least 400 charge and discharge cycles out of it with average degradation.

The XSXP method: for example a 3S4P pack of 2100mAh cells has a total of 12 cells inside. It will have the voltage of any other 3S pack since the number of cells in series determines the voltage. It will have the current handling of 4 times the maximum C rating of the 12 individual cells. So say our 3S4P pack had a maximum discharge of 6C. That means that it has a nominal voltage of 10.8 volts (3x3.6) and a maximum discharge rate of 50.4 amps (2100mAh x 6Cx4P).

Important to use a programmable ESC since the correct voltage cutoff is critical to the life of the batteries. Use the ESC's programming mode to set the LVC to 3.0 volts per cell with a hard cutoff, or 3.3 volts per cell with a soft cutoff. If the ESC has an automatic lithium mode. Use it, it will correctly sense the number of cells and set the auto cutoff appropriately.

Performance graphs from manufacturer. Looking at how low the voltage of the cell drops at various amperages will give you a metric to compare that battery to similar size/weight batteries.

(http://diydrones.com/profiles/blogs/complete-guide-on-lipo-batteries)
(http://www.rchelicopterfun.com/rc-lipo-batteries.html)

electronics.stackexchange.com/questions/64056/calculating-useable-amps

User “henkvdw” at fpvlab.com/forums/showthread.php?6348-3S-or-4S-lipo explains:

A 3S pack delivers nominally 11.1V. A 4S pack delivers nominally 14.8V.

The ESC controls how many volts the motor sees. For low RPM, the motor sees low Volts. This is where kV (Voltage constant) comes in:

kV = 900 RPM/Volt, like in your motor, means that motor will spin 900 RPM for every Volt supplied to it in the unloaded case (no prop). When loaded with a prop the RPM comes down. If the ESC supplies 1 Volt, the motor spin 900 RPM. If the ESC supplies 10V, the motor spins 9000 RPM etc. How many Volt the ESC supplies, is controlled by your throttle stick.

So with a 3S pack you probably get 11.1V at full throttle and maybe 6.5V at half throttle although this is not always very linear. With a 4S pack you will reach the 11.1V mark maybe at ~3/4 throttle. So essentially then up to the ~3/4 throttle mark, it is to the motor as though you are running a 3S pack.

The extra heat will come when you exceed the 11.1V. Now the motor will try spinning the same prop faster and draw more current at higher volts meaning more watts and heat.

At full throttle the motor will see the full 14.8V and even though the current drawn may be lower the input watts will be higher since p=vi (Input Watts = Voltage x Current).

So not to exceed the input watts drawn on a 3S say at 20Amps = 11.1x20=222W you should not exceed 222W/14.8V = 15A on 4S. With the same prop this would not be the case. You will have to prop down to get to that Amp draw of 15A on 4S. You may already be over propped for 3S if the motors get to hot.

161 g, Dimensions: 115x35x21mm
12.24€

www.hobbyking.com/hobbyking/store/__11908__Turnigy_nano_tech_1800mah_3S_25_50C_Lipo_Pack.html

188g, size: 105x33x24mm
8.48€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8934

204g, size: 104x27x35
13.59€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10279

270g, size: 133x44x21mm
25,59€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11949

351g, size: 145x50x21mm
21.24€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9957

408g, size: 144x51x27mm
24.1€

https://www.hobbyking.com/hobbyking/store/__8587__ZIPPY_Flightmax_5000mAh_3S1P_30C.html

536g, size: 148x49x33mm
26.39€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9177

482g, size: 149x49x30mm
33.43€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10286

569g, size: 162x46x40mm
35.87€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=21381

448g, size: 158x45x32mm
36.60€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=63428

908g, size: 167x49x55mm
64.49€

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11941

Motor, brushless outrunner type (best power-to-weight ratio, more torque, simpler):

Depends on the weight of the plane. It determines the propeller size

About using a blades pusher propeller or an electric ducted fan (EDF) let’s make a comparison of different parameters that set the overall performance.
As user “KenP“ detailed at www.rcgroups.com/forums/showthread.php?t=351759:

1) Flight times
Pusher will get better flight times for a given battery since you can run a more efficient propeller than you can in a EDF.

2) Speed
All depends on how much you want to spend but you can spend less on a pusher to get a given speed then you can with an EDF. Making an 80+ pusher is easy but to get an EDF to do those speeds you start looking at big bucks. Most pylon planes are props for a reason.

3) Maneuverability
I would say this is a wash, maneuverability all depends on the airframe. Unless that is you make vectored thrust then the EDF wins.

4) Pushers to get a given speed, flight times are a LOT less expensive, I would say on the order of half of a EDF. For example to make a GWS EDF fly good you need two brushless motors in the EDF units, but make the pods hold two brushed speed 300 motors with pusher props and you get good performance. Big difference in cost there.

5) Construction difficulty
With pusher setups you do not have to worry about the ducting being smooth having intakes that are big enough etc. You just need enough space behind the plane to swing the prop you want.

6) Number of blades
All depends on what you want the plane to do. Do you want speed or vertical thrust? I like to have a speed in the 70+ range with almost a 1:1 thrust I don't get unlimited vertical but in the size of planes I like they get small really quick, so unlimited vertical is not needed.

51 g, Dimension: 32mm x 26mm, 48mm (with shaft)

13.42€

www.hobbyking.com/hobbyking/store/__8502__Turnigy_2632_Brushless_Motor_1000kv.html

http://www.nitroplanes.com/02p-motor-371-as2820-kv920.html

http://www.hobbyking.com/hobbyking/store/__19621__NTM_Prop_Drive_Series_42_48_650KV_1295W.html

http://www.hobbyking.com/hobbyking/store/__14847__NTM_Prop_Drive_Series_35_36A_910Kv_350W.html

http://www.hobbyking.com/hobbyking/store/__55418__NTM_Prop_Drive_Series_35_36A_800Kv_722w.html

132g, Φ35×42mm
56.9€

http://www.rctigermotor.com/html/2013/Professional_0912/47.html

Combo motor + ESC
12.76€

http://www.hobbyking.com/hobbyking/store/__40269__HobbyKing_Donkey_ST3511_810kv_Brushless_Power_System_Combo.html

Propeller (must be foldable for unpowered flight)

15 cm. Size 203.2x152.4mm

2 €

www.nitroplanes.com/95a289-09-propeller.html

And too many more to put here.

Transmitter (two sticks operated by pilot)

24€

www.hobbyking.com/hobbyking/store/__16239__HobbyKing_HK6S_2_4Ghz_FHSS_6Ch_Tx_Rx_Mode_2_.html
2.4 GHz
6 channel

· Receiver (mounted on the plane): depends on the transmitter. Connected to servos.

· Telemetry system?

Mission specific devices:

FPV camera

Available video resolutions

http://static.dscuento.com/images/wp-content/uploads/2014/07/17/1405605444766/800px-common_video_resolutions_2svg.png

Camera option 1 (1080p 4G connection, unlimited range):

165g, 83.9x56.4x56 mm

400€

www.skydrone.aero/fpv/features-fpv

Camera option 2 (1080p (Full HD) WiFi):

640 g approx. Size 62x42x7mm

90 €

www.nitroplanes.com/70p-302-s2-wifi-sport-pro-cam-silver.html
Video resolution: Full HD recording, 1080P 30fps; 720P60fps
WiFi function (2.4 GHz or 5 GHz?)
120 degree
Support up to 32 GB Micro SD Card
90 min battery life

+ antenna + mission planner
http://diydrones.com/profiles/blogs/how-to-build-an-fpv-antenna-tracker-for-use-with-mission-planner

Camera option 3 (1080p (Full HD) with own 5.8GHz transmitter) :

Size 82*44*41

iLook+ (1080p): 150 €

iLook (720p): 100 €

http://www.walkera.com/en/showgoods.php?id=2611
130 degree
Support to 64 GB
1 km range

Camera option 4 (720p (HDTV) WiFi, small)

60€

www.nitroplanes.com/78p-301-wifi-ip-cam-black.html

Camera option 5 (1080p (FullHD), small):

57 €

37 g, size 64*38*16mm

www.nitroplanes.com/78p-405-1080p-mini-cam.html
140 degree
Support up to 32 GB

Camera option 6 (576p (PAL) with Pant/Tilt system, NTSC would be 640x480 px (480i)):
18 g, Size: 38*38mm
13.59€

www.hobbyking.com/hobbyking/store/__11977__1_3_inch_SONY_CCD_Video_Camera_PAL_.html

10 g + 10 g servos, Dimensions: 42x40mm

www.hobbyking.com/hobbyking/store/__12875__FPV_Fiberglass_Pan_Tilt_Camera_Mount_L_Size_.html

Camera option 7. Mobius Cam (Full HD):

39g, 35x61x18.3mm

http://www.hobbyking.com/hobbyking/store/__54706__Mobius_Wide_Angle_B_Lens_ActionCam_a_1080p_HD_Video_Camera_Set_With_Live_Video_Out.html

Camera option 8. HD Wing Camera (HD):

29.4g, 74x28x15mm

http://www.hobbyking.com/hobbyking/store/__17200__HD_Wing_Camera_1280x720p_30fps_5MP_CMOS.html

Camera option 9. HD Mini Cam with integrated WiFi:

http://www.hobbyking.com/hobbyking/store/__56990__Boscam_TR1_FPV_All_In_One_Camera_and_5_8_GHz_Transmitter_with_HD_Video_recorder.html

Innovative idea, use 2 cameras separated by the eyes distance, to broadcast one image to each eye in the goggles, so the pilot sees in 3D when flying between:

Looking around the web there are some projects with the same idea, already implemented and with limited sales from 300 to 800 USD.