Hi all,

The recently released SF02 laser "altimeter" from http://lightware.co.za/ has sparked a lot of discussion in the forum thread here. I asked if I could get a sample to review, and to use on my gas powered 100cc homemade drone. They said yes, and promptly shipped one to me, so here is my first (ground based) review. I'm not affiliated with the company in any way, and they have not read nor approved (nor disapproved) of this review. If I get anything wrong, I am sure they will clarify in the comments section!

Frankly I was doubtful whether it would work very well at all. The laser it uses is a class 1M, which means it is less powerful than most cheap laser pointers on the market, which are mostly class 2 or above. But I was assured that the secret was in the sensitive receiver optics and electronics, which meant that the power of the laser could be limited to a very low (and safe) level.

Now I use the word "altimeter" in quotation marks, because it's not an altimeter. It's more of an electronic tape measure. Point it anywhere, and it will shoot off a small infra-red laser. The time it takes for the laser light to be received is then calculated into a distance, which can be read using a serial port, USB or analog voltage. So it could be used as an altimeter, an object detector, or more intriguingly, it could be mounted on a servo and be used as a crude 2D laser range finder. It takes 12 readings per second, so that should be good enough on a slow moving servo.

Make no mistake, this is a Time of Flight (TOF) device. It measures the time it takes for the beam to bounce back. So unlike those cheap IR distance measures, it does not depend on an angle measurement, and the distance error should not be any different for close or far objects. Also, as it doesn't use sonar (sound waves) it should work over far longer distances and in many varied conditions and varied surfaces.

Opening the box, I was pleased to see a very professional bit of kit. The PCB is surface mount, and double loaded. (components on both sides). One side has a very large and powerful Actel SmartFusion Arm processor, and the other side has mostly sticky-tape components and some regulators. Pinouts are through a very small 10 way screw terminal header. Not the best option for my vibration prone plane, but I can always solder to the pins directly and run a hard wired cable lead to the connector of my choice. 

You can see in the photo above, that the business end of the PCB which houses the laser diode, and pickup, is sandwitched with the optics assembly. There is a good 10mm of PCB overlapping the optics assembly. The result is a very rugged union which suggests the designer spent some time making sure that the board would stand up to a bit of abuse.

The LightWare software for USB control installed quickly and without fuss. I plugged in the SF02 and hit connect. Immediately the screen filled with a string of measurements. The software also allows simple datalogging recording to a text file, and some other parameters can be changed, but nothing very interesting.

So I started pointing it at things around the room, and the SF02 had no issues at measuring any surface I could find. I thought I could trick it with surfaces that had a 45 degree angle, or a shiny metallic surface, but it didn't have a problem with any of them. So with my plane still being about a week away from its maiden flight, I thought I would strap the SF02 to my car and drive around taking distance measurements. 

The following video shows the SF02 mounted to the side of my car. I think it is a good test of what a copter or fixed wing plane would see as it rushed past varying terrain. Actually, since there are a lot of shiny cars, glass windows, and the chance of direct sunlight, not to mention bushes and trees, I think it could be classified as an extreme test. 

For those that are interested in crunching the data, you can see in the video when I hit "log data" and when I hit "stop logging data". If you are nerdy enough, you can play back the data at the corresponding rate of the video, and you can therefore measure the distance to everything that I pass.

Here is the measurement data  t1.txt.

And here is the video:

It was a nice sunny day today, so perfect weather to see if the sun had any influence on the measurements.

Results: Very good. Where you see a "--" in the data, the sensor did not receive enough photons to trigger a calculation. This occurs often, but not enough to be a problem. There is a longer stretch of bad data as I drive along the beach, where obstacles are more than 40m away. There are two problems that I see: The range of 40m is probably just ok for a copter, but not enough for a plane. Our laws here in Australia allow RC flights up to 400 feet altitude, so I would like to have a sensor that would be able to do that sort of distance. Naturally that may mean a more powerful laser that may then require eye protection, but maybe there is a nice tricky way of souping up the existing laser and optics to stay within the safety limits as well as having about 100m range?

The second problem is that I could not get the SF02 to work well through glass. It would work, but the range and reliability was severely reduced. Being in a gasoline powered plane, I would have liked for it to work through glass so that it would be protected from the elements, oil, gasoline, and dirt. 

All in all, a great bit of kit. I see its use best as an aid in auto-landings and FPV landings, where a precise altitude could be used to flare just before touchdown. I'm also very surprised to see it works very well detecting complex structures such as bushes, leaves, grass... Thanks to Laser Developer for sending me the sample!

I'll have my drone up in the air soon, and hopefully (if it doesn't crash on it's maiden,) I'll have some more data from the air. I'll see if I can write a text to speech program for real time altitude updates, similar to what airliners use as they come in to land! That would be cool. I'm also interested in what tasks others are putting the SF02 to work in. Leave a comment!

See blog 1 here, blog 2 here.

So this is blog number 3 of my home made Ground Control Trailer build, and home made drone build, and as the title suggests, I have re-designed quite a bit of it on the fly.

Firstly, the GCS trailer is completely finished. All insulated, and powered up. And the old 6x9 trailer that it is based on has had a spruce up with new tyres, wheels, bearings, LED lights, safety chain, etc. Inside you can see 5 permanently mounted LCD screens. Four of the screens are connected to a single PC through a 4 way graphics card, and the fifth connected to a laptop. The idea is to use one PC for most functions, including Mission Planner, web based weather radar, and video feed, and for the laptop to serve as a backup if the main PC or data link fails. 

External to the trailer there is a 4 metre steel telescopic antenna mount for an RFD900 radio. The higher the radio, the better the range after all. I'm looking forward to doing some range tests!

Now for the drone build.

I decided that the tailplane in blog 2 was too heavy and the fibreglass that I was using was too thick. So instead of pressing on and trying to fly the plane, I made the reluctant choice to rip it all off and use a thinner glass fibre. Also, the tail plane was still feeling on the heavy side, so I made up a new one with solid flat balsa wood. Much lighter, and less drag than the foam fiberglass tailplane that I scrapped.

Also, one of the biggest changes was a complete re-design of the fuselage. The original plan was to build the fuse out of water jet cut aluminium, bent into a box. I started the solidworks model, but I couldn't get the weight down no matter how hard I tried. So I decided to go for a fuse built with 25mm box section extruded aluminium. The walls of the box section are only 1.2mm thick, so it is light, but very very strong. So strong that after building it, I feel that I have over-done some sections, and I could have gotten away with less material.

Anyways, here it is so far with a foam surround. The top cover will be corflute material strengthened with a few aluminium stringers. The entire fuse has a flat bottom, with rounded wing cross-section, so I hope that it will add to the lift generated by the wings:

Unfortunately some aluminium dust got rubbed into the wings, which makes it look like a bit of an ugly duckling in the next photo. I might paint it, I might not. Never mind, I'm not terribly interested in looks. The aim is to have a long range drone capable of carrying a good amount of electronics. Just to add to the list of changes, I changed the two rods connecting the tail plane to the fuselage. The old 16mm ones seemed to be strong, but after mounting, I felt that they were too flexible, so they had to be changed to, you guessed it, 25mm box section aluminium. It just goes to show, that even with good PC design tools, sometimes a bit of trial and error never goes astray. 

With the added width of the new fuse, the wingspan is now 3.5 metres. That 50cc engine I had planned to use is starting to look a little small for a plane which is starting to tip 25 Kg fully loaded. So my next mod may be to add another engine. One 50cc engine in a pusher config at the back, and one 50cc engine pulling from the front. A two engine set-up would ensure good acceleration and take-off time, and would also help in reliability, as only one engine would be needed to stay airborne. 

Hopefully the next blog will have a vid of the maiden flight. It might be just a few weeks away. Can't wait!

Well it's been a few months since my last blog post, so here is an update and some photos.

The ground control trailer is going well. I have finished putting on the steel cladding, and insulated with 10mm foamboard. In my last blog post, I referred to a generator which I was thinking of including.....I have decided to leave it out of the build, as I have decided to use two car batteries, 100W solar panel, and the tow car's alternator as a last resort to run the 2KW inverter. Should be plenty of power. The generator would be very loud if I incorporated it into the build, though it would allow me to have air conditioning, which would be nice!

 And a vid never goes astray, subscribe for more :-)

 Now the plane is taking shape too. See previous blog for the solidworks drawing. Basically it's an aluminium skeleton made from box section, and hot wire cut foam wings. The wings are 3m tip to tip. and there are two 16mm tubes joining the tail plane to the wings. The fuselage is a work in progress, but it will probably be made from water jet cut 3mm aluminium, then bent into a box.

The wings are cut from "medium density" insulation foam. The local insulation shop had offcuts of a suitable size, which they parted with for $30. Nice!

This is my first build of this size, so I really am not sure if it will be strong enough. Time will tell!

That's a two car garage, so the build is getting bigger and bigger! 

 That's a CRRCPro 50cc two stroke gas engine. It's a low cost Chinese engine. Reliability? Yet to be proven, but I can only find great reviews online, and only one unhappy review from someone that didn't like the BOX it came in?!?!?!

 Landing gear, and motor mount fitted. Servo compartments cut... 

 Now for the fun part (NOT) ... fiberglassing!

I purchased some fiberglass cloth from ebay. It was the remains of some stock used for building wind turbines. So I thought it would be perfect...... Well, this stuff is strong, but it is VERRRRY heavy... The tail plane alone, after the fiberglass treatment, is 4KG! So the entire aeroplane will weigh around 20Kg before I add a payload, electronics and fuel. Too heavy? Again time will tell!

I'd like to introduce myself to the DIY drones community, and show some photos of what I have been building. 

I am building a 50cc gas powered drone, with 3m wingspan. It will be all aluminium and foam and fibreglass, with no wood components.

Above is the solidworks image of the start of the design. I plan on using a hot wire cutter to cut the foam wings, and to have two voids down the center for two aluminium spars to go the length of the wings. Then, I will cover the lot with a single sheet of fibreglass and epoxy to keep out the 2-stroke fuel from the engine, and to strengthen the foam. I am using medium density foam as used by house renderers. Has anyone done anything similar to this before? There are many foam cut planes out there, but it seems nobody makes large ones. I think that the aluminium spars down the length of the wings, and the fibreglass skin will be enough to keep things nice and strong. I'll also add some aluminium tubes to connect the two spars together at the tip of the wings, to stop any torsional forces.

I haven't designed the motor mount and fuselage yet, but I am thinking of a pusher propeller at the rear of the wing, mounted to an aluminium plate which also secures to the wing spars.

The fuselage will have to be quite large, as I would like it to house:

1. Mini ATX motherboard (to run labview video recognition)

2. 10 Ah or more of 11.1V lithium batteries

3. Sony PTZ cam with 25X zoom

4. Ubiquiti Nanostation with directional antenna and associated tracking servos

5. Enough 2-stroke fuel for at least an hour long flight

I picked up this Sony camera on Ebay a while ago. The zoom is amazing on this thing!

As I have just had a baby, my man room has vanished. So I thought it would be a good idea to convert one of my trailers into a small work-room and storage area. And while I was at it, I thought it would be cool to deck it out with a multi-monitor permanent setup for FPV, flight sim, and GCS all in one. Then I could just hitch it to the car and take it to an air field. This would make setting up and tinkering a breeze.

Below is the solidworks model. I picked up a whole heap of Samsung 22" monitors cheap, and I'm running 4 of them off a matrox quad card, and the fifth off a USB to DVI connector.

I know that DIYD basically specialise in trying to get everything onto the one screen, but since I have the luxury of many screens I am looking for suggestions of GCS software which works well with a multi-screen setup.

Otherwise I was thinking one screen would be HappyKillmore's GCS, and the others would be google earth, weather info, live video feed, and command line telemetry respectively.

The box on the bottom left is space for an external petrol generator. I have a Honda generator which I am converting to run 2 x 12V alternators, which will charge 2 x car batteries. I have a 600W inverter to step up the power to 240V. This will act as a sort of UPS if I don't want to run the generator all the time, or if the air field has power, I can then just plug it in to charge.

The whole trailer will be insulated, and I will have an air vent directly over my head to push in fresh air. In Australia, the summer sun gets very hot!! Also, not pictured is an aluminium tube for the antenna stack.

So far, I have purchased:

Camera

50cc engine

Ubiquiti nanostation loco pair

20ah of 11.1V  laptop batteries

Spektrum DX6i

Xtend 900mhz module

All the aluminium

M3-ATX 12V power supply

Epoxy

Fibreglass

High Torque servos

Dome for camera

and a whole heap of other stuff......

Enough of the computer generated stuff.... Now, for the real build. I started building the GCS trailer yesterday. Here are some real life progress photos!

Please leave any suggestions! I haven't ordered the APM2.5 yet. I want to build the trailer and plane and make sure it all flies nicely. By that time, we will be up to APM3, or 4 or 5.... I do have an old ardupilot board that I will connect up to do some preliminary tests for the GCS tho.

Also, if there is anyone in Melbourne VIC Australia that flies with APM, please let me know which field you fly at, and I'd love to come down and have a good chat..... My local field doesn't really have anyone that does any sort of "technical flying" no FPV or anything fancy.