Mr Parker - I thank you...

I got a good telling-off today, by Mr Parker. He said I'm spending all my time planning my revision timetable and not actually revising (working on the L/G - he wants to see it fly). I should just use a couple of bent wire coat hangers and be done with it.

So, I got home tonight, determined to get a chunk of work done on the legs. I want to get some gear in place for the thing to sit on, so it's doesn't rock and skate around (in theory at least). But you are right, Mr P, so I worked like a crazy man...

I got the rear vertical pieces cut out, sanded, drilled and tapped, then drilled the Alu knees of the rear pair. In a flash of genius I solved the anchor and adjustment problem for the tensioners, so they now operate correctly. I've ditched the LEDs too (for now).

I can lock-out the gear (manually locked in deployed position) and move on...

Everything will need dressing up a bit.

Time to work towards a controlled lift-off and touch-down cycle.

Fiddly legs

I've finished the front pair of landing legs, at least the component parts. I still need to find a neat way to secure the operating linkage, and operation isn't very smooth either. It's really fiddly!

I've been messing with adding lighting to the legs, but I'm not convinced about the effect (lighting not shown in photo).

The leg on the left has the tensioner, LED and wiring in place. Additional wiring will be needed if I add a Weigh-On-Leg sensor.

Ardunio or PIC - Action Priority Matrix

I remembered this:

I don't want the tool to be a major project, unless it needs to be. Arduino's looking good!

Arduino or PIC?

A dilemma: what should I use? Should I buy into the ready-made hardware, tons of examples and accessories of the Arduino or do I stick with the more powerful/flexible PIC, which I've used before, which has a rich selection of peripherals and can make a smaller, neater end solution, but needs a lot more effort to get going?

The trouble is it's been a while since I did any serious PIC work and I'm attracted to the quick and easy Arduino. But I'm also not sure the Arduino will be up to scratch, with respect to I/O, peripherals and physical size (I could get a Nano?) and I'd have to learn a new platform.

So if I go for an Arduino, will I have to re-do everything in a PIC solution later? Should I go straight for a PIC solution, but with the extra time and effort?

I don't know. The Arduino does look like a quick solution...

Arduino website
Microchip PIC website

How many times?

I've fabbed two vertical pieces for the front L/G pair from 6mm polycarbonate and in the process; realised that I could have done it better, sooner, given more thought. But it'll do. Hindsight is a wonderful thing!

Rear pair will be slightly shorter.

I gave one a light coat of paint so it would show up in the photos and give me an idea of what it might look like when done.

I had a small can of "Pewter".

Just resting in place.

I'll add some detail later.

Comparison. I'll have to stop re-designing the gear soon!

Like the caption says, I want to finalise the gear design so I can move on (I've said that before too). I've been thinking about the next step; how to get the desired results without unnecessary work, but that's another post...

New site; UAVpilot.org gives me a mention!

I had an email from Thomas of UAVpilot.org;

Just wanted to say, I stumbled across your site earlier tonight and was really impressed with your do-it-yourself UAV project!

I've recently made a website, it's about...two days old now...but I hope you don't mind my doing a very small article on your project and providing a link, for anyone who might stumble upon me.

So I'm returning the favour with a link in the sidebar, looks like it could be a good resource... go take a look: UAVpilot.org

Landing gear almost done

All four retracts now have arms and swinging brackets that the vertical "foot" mounts to, complete with pivots and end stops. I think I might ditch the slider mechanism after all; save the added complexity for little gain. The polycarbonate arms provide a little spring anyway and I'm hoping to get soft controlled landings. Fixed vertical sections (the "feet" or "shins"?) are next, then the servos/mechs.

Keeping at it

No Worldcup for me, but I did spend a couple of hours tinkering in the garage. I discovered a minor issue with the gear retracts, but think I've got around it. I've worked on the second leg and cut some parts for the rear pair.

I've also been looking at PIC24Fs and will probably look at getting a couple of samples from Microchip. I'm also going to see if it's possible to home etch a PCB for a 100 pin TQFP with a 0.4mm pitch. I'm a bit rusty with PCB layout and C, but I'm sure it'll come back to me.

Longer legs and a blue ball

I've re-made the main arm of the L/G, making it longer and better positioned when stowed. I'm also half way through assembling the second leg (rear pair will probably have to be a different size). I'm having second thoughts about the sprung slider mech too; it adds complexity, weight and it won't even work too well because of the angle. Should I scrap it and go for a fixed lower leg? Would anyone notice? Would anybody care?

Notice the ball in the nose? That'll be the location of the pan/tilt camera and LED "searchlight".

Different angle of the longer leg, deployed.

The stowed position is much better and the wider footprint will improve stability.

Also, I was originally going to have the cargo ramp on the bottom, opening forward, but the L/G isn't going to give much room so I'll have to go for the traditional rear ramp under the tail.

One leg done, three to go!

I've fixed the slider to the pivot arm...

...and fixed the shaped vertical "foot"(?) to the slider mech, then temporarily fitted it into the airframe to test the fit. While I was at it, I clamped a servo in place and connected a pushrod to the retract control linkage, then plugged in the servo controller for a demo (see video, below).

Prototype L/G slider

The slider mech I mentioned in the last post, has to be lightweight and compact. I had come up with a possible solution, but it would've been a bit clunky. The alternative came from a sacrificial plastic vernier caliper that I got free, many moons ago, with some tech magazine. It's very light, free moving and ready made (kind of).

I'm interested in the centre sliding pieces. The cross-section shows the interlocking profiles that would be difficult to replicate by hand.

I hacked a mock-up and glued it to the gear arm, as proof of concept. There's a small spring fitted behind the slide that took around 1.5 kg quite nicely (there will be four of them). My concern is it may be too long to fit snuggly in the fuselage. Video below shows the proof of concept. Now I need to make it more robust.

Obviously, this will all be painted and disguised!

Landing gear prototype - video

Finally, a L/G design that might work!

I got some time to work on the landing gear and came up with a design that gives the desired look and motion, while still being lightweight. I bodged together a prototype that kind-of works. Photos below.

Showing gear in stowed position.

Showing gear in deployed position.

I'm hoping that on the real thing; I can have the vertical piece on a sprung slider, to give added effect and possibly some shock absorption upon touch-down. This really needs a video...

It'll happen when it happens...

My local hobby shop (Power Hobbies) called to say the plastic sheets I'd ordered last week, had come in. I now have 10 sheets of 0.25mm, 10 of 0.5mm and one of the thicker 2mm (all approx. A4 size), so I can go ahead and create the fuselage, in theory.

Damn meerkats have hogged my time recently, on top of my studies, but I'm determined to break this gear issue and make some progress. A friend said they've given up worrying over progress of their projects but I can't help beating myself up over how long it takes me to get anything done.

I had a little time!

A couple of weeks ago I managed to get some time (at a SHDC meet) to hack together some bit-banging code on a PIC to control a RC servo. This crude code, in theory, will allow me to control the servos for the landing gear, nacelle steering and of course the EDF thrust.

I had a little time over Christmas to discover my planned landing gear redesign was halted by my inability to mill a tidy slot in some aluminium channel with my tiny little lathe/mill combo. I need to come up with a simpler mechanism, get the gear done and put some kind of external skin on the airframe, then I can get to the control system!