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.

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...

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!

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...

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!

Joost doon't 'ave the poower!

I made the adapter cable with the Deans connectors (cut off the end of the umbilical) and 4mm bullets fitted to mate with the Li-Po. I didn't know how charged the battery was, but I had to try it...

With just the battery (no extra weights) I powered up and "hovered" for a minute or so; all 3 EDFs running and plenty of power. I then added the 2 blocks of metal again. These are just bits I've been using to help in the construction so far, as weights or a square-edge. So powering again, it got off the ground but was obviously loaded. Second attempt and it just got off the ground and I hit max on the controller. I backed off, then tried again - now barely lifting. I took off the heavier block and re-tried - only slightly better. The battery must be dead! As I said; I don't know what the state of charge was beforehand and the charger hasn't arrived yet...

Disheartened by the sub-60 second runtime, I was thinking the battery couldn't have been charged. I wasn't expecting much, maybe 2 or 3 minutes. I also thought I should check and quantify the "other stuff", so went off to weigh the 2 blocks. They were a lot heavier than I thought: the larger block of aluminium was 335g and the smaller stainless steel block was 414g! For comparison, the battery is 408g (listed as 412g). That made me feel a little better; I'd added a lot more than necessary, an additional 759g (1.65lb for those working in old money). So fingers-crossed; if I can keep the weight of all that "other stuff" down and with a fully charged battery, it might just work... for a couple of minutes.

Clarification

I thought I should clarify that although I'm using some RC gear, I'm not using RC in the traditional sense. I have no transmitter or receiver as a couple of MCUs will be doing the work, these will have a radio link to a base station of some kind where the operator can monitor and guide the aircraft. Any operator inputs will feed in to the control loop as error offsets rather than direct control of servos. At least, that's the plan...

Gear mounts and tail test fit

I've got the L/G mounts sorted and hacked up the lower tail fins. I still have the L/G arms to fabricate and it's starting to get heavy! I'm not going to add any control surfaces to the tail yet (if at all), or actuate the L/G, as I'd like to have a stab at some kind of controlled flight as soon as possible. I do think I'll need control vanes on the rear EDF though.

Rework and headaches

I've reworked the nacelle steerer setup because I wasn't happy with the gears, and it wasn't working as I'd planned. The servos used here are old cheapo ones but one is modifed to work in reverse. I can't remember how I did this (I'll post it when I remember) but it was convenient as the same signal can applied to both servos to make the nacelles turn the same way.

The first front leg is fixed in place and a rear one is getting there. I abandoned the vertical offset angle just for simplicity, as I'd like to move on to the flight systems.

Next: finish L/G and start on tail.

L/G - doing things the hard way

Because I want a cargo ramp on the bottom, to allow for a small rover, the ground clearance has to be quite high. I also want the L/G to be sprung to absorb the impact of touchdown, and they'll have to fit at in a tight spot at an odd angle (both vertically and horizontally).

I've spent hours trying to figure out how I want these to mount.

I used the drawing (see previous post) as a template for the parts.

The mock-up of the mech works as expected (shown below, without the "leg" part attached).

They'll be painted eventually.

I had to make a small mod to stop the coil spring clashing with the lower arm.

I think I'll have to make it a bit shorter too.

Landing gear design

I've been working on the design for the landing gear. I had a specific style in mind and it will have to provide enough ground clearance for the payload ramp, some sprung shock absorbtion and work with the odd body angles in the planned loaction. I'll make some parts to check that the concept works and won't conflict with anything before making all of them. I also need to check for conflicts with the nacelle steerer servos.

Scribbles for my mind

To help me get things straight in my mind, I sketch with that old fashioned pen and paper stuff! I have to get a feel for whether I could make it without huge complications or expense.

I thought about props and motors for lift but I wasn't quite happy with the look that they would give. I really wanted something like a ducted fan, so I Googled. I found EDFs (electric ducted fans) that hadn't really been around (common or affordable at least) when I was last crashing RC aircraft. I found the largest size, common enough not to be "specialist", was about 90mm diameter and could provide well over 1Kg of thrust. Not bad.

In order to see what was out there and how things had changed, I searched YouTube. I found Dave Powers and Co (of rcpowers.com) doing some really useful guides and general videos proving that RC planes don't have to be perfect precision machines in order to fly. Dave regularly uses tape, glue and junk to get his aircraft back in the sky. He earns the first linky-link in the sidebar ;-). Check out his videos.