I have now finished all the sub-assemblies of my Cularis, so before sticking the fuselage together, I decided todo a trial balance to check on the COG. Here it is, poised on the wingdimples. The airframe, with installed servos, but not motor, batteryetc. weighs 1.1kg including the two steel balls located in the tailsection.

In the photo below, you can see the Pentax A30 camera mounted down in the cockpit area which I expanded to a width of 60mm by machining out 6mm from each side wall. I then stuck the perspex side panels with thick CA as recommended to increaserigidity. The large nut and bolt weighs a little more than thePico-Pilot NA which have now bought second hand. There is a 3P2500mAH LiPo battery pushed up under the wing root with the stockMultiplex motor, ESC and spinner up front and a Multiplex dual conversion 7 channel Rx.

The real trick that made this all work was moving the elevator and aileron servos to the rear. Because of the 4:1 leverage, some 35gm of servos is now balancing 140gm of camera. It needs some careful work to machine out the interior ofthe tail section to mount the servo, but the result is worth it. I will post more details of my modifications in the Cularis building thread on rcgroups.

Building a UAV for phot mapping - Previous Posts

1. The Goal
2. Camera Selection
   
3. Packing it all in
4. Autopilot
5. Kit Mods
6. Trail Balance
   

First I must thank Jeffrey Johnson who posted a set of images of the Cularis he is building for photo mapping. He has made a really neatmodification by moving the rudder and elevator servos from the stockposition in the cockpit, to tail mounting in the fuselage. Not onlydoes this free up space in the cockpit area, which will make it easierto enlarge to take the camera, but it also moves some 35gm of weightto the rear. This should greatly help in balancing the plane withoutadding too much lead.

I have also now read some 670 posts in the Cularis building thread on the rcgroups forum. There is a wealth of good stuff there, includinga number of modifications to the stock kit to improve performance and ease of use. Specifically, I now plan to do the following.

• Extend the travel of the flaps by reversing the control horns, thus allowing for slower landings
• Reverse the direction of one of the flap servos so that if can be connected to the other flap servo with a simple Y lead.
• Remove some 30% of the hinge material from the ailerons and flaps to reduce the load on the wing servos.
• Cut away the stock mountings for the mating connectors in the wing roots and run the cables through to connect by hand. This seems to be amajor cause of poor reliability as if the wing moves a little inflight, the connectors can cease to make contact, leading to loss ofcontrol in the wing.
• Replace the side canopy latches with a single magnetic mount on the rear bulkhead. This also makes it easier to enlarge the cockpit area totake the camera.
• Move the servos for rudder and elevator to the rear.
• Sand the trailing edges of the rear stabilizers a little to reduce drag.

There is one other modification that I am in two minds about and that is a secondary means of fixing the wings. In the stock kit, the wings areheld in place with plastic catches. These are design to open in theevent of a heavy landing so that the wings break away. If wouldseem, however, that some have opened in flight leading to spectacularcrashes. Jeffrey has a a similar modification to several shown inthe thread that involve using a secondary pin through the wing root.While this will certainly keep the wings solidly in place, I am notsure if it is better or worse in the case of a bad landing.

Building a UAV for phot mapping - Previous Posts

1. The Goal
2. Camera Selection
   
3. Packing it all in
4. Autopilot
5. Kit Mods
   

Ahh!! CRASH and BURN!!

I had planned to use the Pico-Pilot and Pico-GPS for the autopilot in my UAV, but I have now discovered that since Jan 2007, they have been classed as MILITARY technology and are controlled by US Export License regulations. Specifically theregulations cover,

a. “UAVs” having any of the following:

a.1. An autonomous flight control and navigation capability (e.g., an autopilot with an Inertial

Navigation System); or

a.2. Capability of controlled flight out of the direct visual range involving a human operator

(e.g., televisual remote control).

b. Associated systems, equipment and components as follows:

b.1. Equipment specially designed for remotely controlling the “UAVs” controlled by 9A012.a.;

b.2. Guidance or control systems, other than those controlled in Category 7, specially designed for

integration into “UAVs” controlled by 9A012.a.;

b.3. Equipment and components specially designed to convert a manned “aircraft” to a “UAV”

controlled by 9A012.a.

Note: 9A012 does not control model aircraft.

Despite the last sentence, UNAV, who make the Pico Pilot have now told me that none of the applications for export licenses they have made thisyear have yet been granted. Back to the drawing board.

The other common low cost option for an autopilot seems to be based on the FMA Co-Pilot for flight stability with an additional board suchas the RCAP2 plus a GPS receiver for navigation. While a cheaperalternative, I had already discounted this approach because it isbased on thermopile sensors. For my terrain, I cannot get a clear360degree view of the horizon to calibrate the system before launch.In addition, the various different terrain types , forest, grassland,lakes etc. could give problems in flight, irrespective of thetemperature differences that can occur if different parts of a valleyare in sunlight or shade.

During my initial research into autopilots, I also looked at the Paparazzi project. While there is a wealth of open source stuff there, thecurrent Tiny autopilot still uses thermopile sensors for stability,although it does have an on board GPS unit for navigation. An all singing, dancing IMU with gyro's , mangetometers etc. is under development. Althoughall the designs are published, there is still no commercial source ofassembled units or PCB's.

A recent post on this forum (can't find it now), talked about the the UAV development board from Sparkfun. I had a brief look at this, butinitially discounted as they claim that the firmware is a guidelineonly. It is also written in assembly code and I am far to old tostart writing in assembler again. Still I shall have another look atthis over Christmas, as the board does have a proper IMU with 2 gyrosand a 3 axis accelerometer.

Conclusions and Questions

1. I cannot use my prefered autopilot option owing to US export regulations.
   
2. What other, non US manufactured, commercial autopilots are people using?
   
3. Any other suggestions for a home built unit with an IMU rather than thermopiles?
   

1. The Goal
2. Camera Selection
   
3. Packing it all in
4. Autopilot
   

The first image shows the recommended distribution of components for the electric version of the Cularis. (Click for higher resolution). In this configuration, the plane balances at the CGO with 3 weights (supplied in the kit) fixed under the tail plane. The component weight budget is

• Motor/Prop Assemply 225gm
• Multiplex ESC 34gm
• Fight Battery 149gm
• 7Ch Rx 30gm
• Rx Battery 112gm
• Cularis cable set 50gm
• 6 servos 70gm

This gives a total of 670gm. The manufactures claim an all up weight of 1680gm with a wing loading of 30.5g/dm2.

In this image, I have added the Pentax A30 camera and a PicoPilot with PicoGPS. The camera is about 8mm wider than the center opening in the fuselage, so I will have cut back the sides for it to fit. I will also machine out a stepped hole in the base for the extended lens to sit in and see through. If I try to locate the camera further back, then I will have to machine out the two servo openings as well.

The addional weight is

• Pentax A30 with battery and SD Card 150gm
• Pico Pilot and GPS 63gm

However, I think the real problem is not the weight but the COG. A simplified calculation of the moments of the camera, the autopilot and the new position of the Tx about the COG, suggest that I will have to add about 70gm to the tail in order to bring the plane back into balance. So the total additional weight will be in the order of 283gm. This will increase the all up weight to 1963gm with a 16% increase in wing loading to 35.6g/dm2.

Although it may be standard practice, I am not really happy about have separate Fight and RX batteries. There are two things to charge and check before each flight and it just seems more elegant to have a single power source with a switch mode SportsBEC. With some searching, I found a DuraMax UltraPro 3s 3600mA Li-po with a flat form factor. The dimensions are 145mm x 50mm x 16.2mm. With a small amount of machining, this will fit in the space previously occupied by the Rx battery. The weight at 280gmplus a Sports BEC is only 35gm more than the previous batteryconfiguration. The real gain is in the balance, as the new heavierbattery is behind the COG.

By moving the Rx and autopilot back as shown, the balance weight reduces to 25gm, so in all this solution is a little lighter than the previous one and I get more battery power

1. With some careful cutting, I can fit the camera and PicoPilot into the Cularis airframe.
2. What will happen to the performance of the plane with a 16% increase in wing loading?
3. Is it a good idea to use a single battery with a SportsBEC? How about noise on the 5V power for the autopilot and GPS?

1. The Goal
2. Camera Selection
   
3. Packing it all in
   

I have bought a Pentax Optio A30 to use as my aerial camera. It is similar to a number of the latest generation of sub-compact 10Mpixel cameras and has good reviews, especially in terms of its image quality. It weighs about 160gm with battery and SD memory card and at 58mm,has one of the smallest widths I have found – important for fittinginto the Cularis body.

The highest resolution image is quoted as 3648 x 2736 pixels. Based on the handbook, a 4Gbyte SD memory card at the best quality jpeg setting, should give about 1200 images. The camera has a continuous mode where images are taken and downloaded to the SD card as fast as possible as long as the shutteris pressed. One option for using the camera in the UAV, is to set itrunning in continuous mode and then select 1 in n of the imagesproduced to make the photo-composite.

With a fully charged battery, I tested the camera in continuous mode while photographing a clock. The camera managed to capture 1613 images at full resolution in high quality mode in 23 minutes before filling the 4Gbyte SD card. The battery indicator showed about half full at the end of the run.Although the average interval was about 1.2 seconds, there were somegaps between images of up to 8 seconds and in other cases, 2sequential images showed the same time. Both results suggest thatthe timing is not constant, but is a function of the amount of datathat needs to be stored on the card. The review also states that thefile size varies a lot depending upon the image content, so this makematters worse.

I then tried taking photos at timed intervals. I could get down to about a 4 second interval with only an occasional missed image, although this may have been finger trouble. So if I want images taken at regular, known intervals, I will have to use a servo driven IR interface such as the PRISM.

Now to look at flying the camera. There are two limiting scenarios.

1. Fly at 120m (400ft) altitude. The ground area covered with the A30 lens set to wide angle (40mm equivalent in 35mm film terms) would be 108m x 72m. This gives a pixel resolution of about 3cm per pixel or 3 times the target of 12cm per pixel. Assuming a 30% overlap between images in thedirection of flight, then the distance between images is 75m and themaximum speed of the plane taking an image every 4 seconds is19m/sec or about 68kph (about 40mph).
2. Fly at 480m (1600ft) Now the ground area is 432m by 288m which gives the required 12cm resolution. The distance between images to give a 30% overlap would now be 302m

Comments and Questions.

1. Assuming a 20-30min flight, the memory size and battery power for the camera are not limiting factors.
2. For regular images at known times and or positions, the camera will have to be fitted with an IR trigger.
3. What should I aim for as a cruising speed for my Multiplex Cularis as this will impact the number of photos taken during each flight?
4. Is it better to fly lower and use the additional resolution in post processing of the images to end up with corrected 12cm resolution map?

1. The Goal
2. Camera Selection
   
3. Packing it all in

1. The Goal
2. Camera Selection
   
3. Packing it all in