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Thursday, April 2, 2015

Drone Recovery Parachute

Failure is a concern that is always present in the operation of a drone. Given the continued increase in acquisition and use of these devices by the general public, safety is of paramount importance. Even the smaller devices of about 2 kg of total weight, in case of total failure at altitude, will fall like a brick and cause damage to whatever is below.

Most configurations such as quadcopters, don't offer any intrinsic redundancy (in spite of having 4 motors). The failure of a single motor will prevent the quadcopter of maintaining level and yaw-locked flight. Some enhanced control algorithms are being developed to provide level and controlled descent in case of single motor failure. Naturally, yaw control is lost, but the on-board inertial sensors and magnetometer are capable of keeping track of the orientation, therefore knowing how to distribute throttle by the surviving motors.

My current goal is to make, and go through the challenges of creating a parachute device that can be deployed in the quadcopter in case of loss of power or freefall.

Right now, I have the physical parachute, that I have built a few months ago, but never had the chance of testing.



As such the first test that I have defined is to carry the parachute on the underbelly of the quadcopter, and hold it through a release mechanism. Even though is well below the expected payload, I have added a cilinder filled with AA batteries, in order to fulfill 250 grams of weight:


The release mechanism is basically a 9 gram servo attached to a plate having a slit through which the edge of rubberband that holds the parachute, is held. A link bar connected to the servo holds the edge of the rubber band. Once the servo is moved, the link bar is moved outside of the slit, and the rubberband is free, therefore releasing the parachute:



The first test can be found here:


The release mechanism worked flawlessly in the two tests that were performed. In the first test the parachute didn't open at all, but also the limited altitude of 8 meters at which the quadcopter was hovering did not allow the necessary airspeed to build up.

In the second test the parachute was dropped higher, and there are already signs of the parachute starting to open.




Finally some canopy inflation tests :)



References:

ExperimentalAirlines - https://www.youtube.com/channel/UClkL_Hmktyh9R_FzwSPjXmA

Monday, March 30, 2015

More UV light photography

It is interesting to discover in everyday objects, the specific fluorescence of each one. The particular wavelength (i.e. color) of visible light which is irradiated depends on the characteristics of the substance illuminated by the ultraviolet light. As such a very interesting combination of colors can occur, depending on the varieties of materials the object has. The following dolls is an example:


Authenticity of money is also based on the markings using special pressing techniques that emit light (fluoresce) upon being irradiated by certains wavelengths of UV light. In the case of the Euro bills, the 400 nm UV doesn't seem to give away much from their characteristics:


The tulle material is quite fluorescent:


Sunday, March 29, 2015

UV Photography

Exploring light wavelengths beyond what our eyes can see constitutes an interesting domain, because in a scientific perspective it can reveal characteristics of the imaged objects, that our eyes and/or visible light based cameras cannot see.

For example UV photography can reveal the story of our skin. Solar UV burns leave scars that are practically invisible to the naked eye, but through long wave ultraviolet these are clearly distinguishable from untouched skin (for example see http://www.huffingtonpost.com/2012/06/22/cara-phillips-ultraviolet-beauties_n_1606131.html)

While not having specialized gear for UV photography I decided to give it a try with a UV power LED that I had laying around:



Given that the LED puts out a not entirely eye safe ammount of UV light (275 mW - see http://www.led1.de/shop/lng/en/prolight-power-led-uv-ultra-violet-275mw-13-watt.html), I have not neglected the shades:


These are regular sunglasses, which normally do a good job at attenuating UV light. Empirically I could verify the shade produced on a UV fluorescent material, providing good evidence that UV light would be blocked by these:


While I did not have the necessary filters to block visible light and let just the UV light pass, nevertheless I managed to achieve interesting photos with the characteristic contrast on the surface level details of the skin (UV light does not penetrate the skin like visible light does). There is always stray visible light from multiples sources of fluorescence, that help soften the image, effectively countering the high contrast result that we are interested in:










Saturday, March 28, 2015

Custom Camera for Image Stacking

On the expectation of obtaining different and better astronomical images I have taken the oportunity to build custom gear for that purpose. The camera itself is an analog Sony CCD HAD 700 TVL based on the Effio chipset. I had it in my quadcopter, and decided to transplant it to this application. It has excelent low light sensitivity (indeed it outperforms the human eye in that respect!), being an interesting candidate for astrophotography.

My task was to adapt an aluminium enclosure to contain the camera sensor and the control keypad:


A special nut to attach the body to a tripod was also added.

Thanks to its C-Mount adapter (common in surveillance CCTV cameras) I can use any lens in the market using this mount type, and with the proper adapter, any kind of lens (e.g. Nikon F-Mount, Canon EF-Mount, T-Mount, etc). For example this F1.2 6mm lens was bundled with the camera, and uses the same C-Mount:


On an SLR. a F1.2 lens is typically on the expensive side. In this small format, these lenses normally don't get past the two figures.

In my setup I have used a T-Mount to C-Mount adaptor in order to fit my Samyang F6.3 500 mm catadioptric lens into this camera:


The sensor has good IR sensitivity in night mode. If I wanted to go further in dropping all of the IR filtering I would probably have to remove the coating on the sensor window, operation which would probably ruin it.


The keypad allows the in-camera OSD to be invoked, and the several settings to be changed: