Saturday, June 19, 2021

All Square?

I delay fitting speed-controllers (ESCs) at this stage to make the airframe easier to work on. Besides, it's important that we set up another look-and-feel session with the test-pilot (who insists on Recaro when it comes to his seating arrangements).

Blade clearance is clearly tight, but then the seat will be elevated and the propellers shrouded to an extent later on to compensate. Worth knowing too that the airframe is slightly under-sized even at half-scale, a result of having been constructed by leftover parts in the workshop.

As a result the perimeter lengths that run around the square which defines the frame run to only .85 metre instead of 1.00 metre, meaning that the propeller axes would be pitched around three-inches further from the centre-section in both directions.

By way of a 'development program' this iteration will likely be programmed for flight in parallel with a rebuild at metre-size, meaning in turn that the electrical equipment can be transferred across with no change in operability.

That said, working now on this vanilla-flavoured quadcopter instead of the octocopter, there's four of everything left over... and enough to build prototype serial number #2.

Mounting Tension

When I first fitted these motors, the question would be quite how? Like most motors for drones, these are 'outrunners' with a canister that itself rotates in place of a rotor. 

Accordingly they include a static base with an array of bolt-holes, which in turn means that there has to be access from beneath for a screwdriver. Some motors include an adapter which pitches the motor-mounts beyond the diameter of the canister, where they can be accessed from either above or below.

As to being set the task originally, I used a simple transfer technique and painted the underside of the motor before applying it to a paper template ~ the way that as kids we made potato prints.

Manufacturers like Boeing need neither potatoes nor poster paint to attach engines, but what they have instead is CAD/CAM. In the absence of this I suggest you get into a word-processing program and draft a template to print off and apply to the brackets at each corner of the airframe. 

Mark with a centre-punch and break for tea prior to drilling, which needs be accurate.

Zen and the Art of Motor Maintenance

The Way of Drone is hard, a life of rigid austerity devoted ultimately to self-levitation.

Looking at my work to date, I realise I have seen something similar in a previous life as an airline captain, during a visit to a shrine in Tokyo in fact.

Accordingly I arrange a pause in proceedings while a Shinto priest recites incantations over the airframe amongst clouds of incense, so as to speed it on its course with every blessing.

As a part of the effort, I compose my own haiku for the occasion:

O drone
Climb Mount Fuji
But slowly, slowly!

(Adapted from the work of Kobayashi Issa, 1763-1828)

All of which stemmed from a moment of supreme enlightenment when I entered a trance-like state in pursuit of the best possible way of fixing the motors.

For in replacing the three-way tube connectors with four-way, I attained nirvana.

Friday, June 18, 2021

California Dream... on.

My mystery shopper in ~ well I can say it now ~ in San Diego has decided to run with his own design, albeit assisted by his local fabricator. As neither of them confess to knowing a thing about drones, the past several days I've devoted much time pointing them In the right direction...  a case of the blind leading the blind if ever there was one.

This was what they had proposed with a view to a machine steerable by weight-shift alone, and the crux of my arguments have been

(a)     don't be fooled by YouTube videos, as few people show the many crashes prior,

(b)    weight-shift machines have generally pitched the mass of motors at the base,

(c)    use more motors rather than fewer,

(d)    and ideally avoid the losses associated with contra-rotating props.

Crucially I suggested that the prototype as envisioned would almost certainly topple over on Day One, taking out several hundred dollars worth of carbon-fibre propeller with it in a best-case scenario.

I'd have gone out there to assist except for the fact travel between the UK and US is embargoed by the UK government's overly-cautious approach to the Covid pandemic.

My efforts over past weeks have thus been among its casualties, albeit one that few of us will mourn beside myself.

I don't regret extending hands of help across the virtual ocean, though it has been a monumental ~ some would say simply mental ~ distraction.

Coincidentally news came through that my pre-existing effort had been granted design registration in the UK, something I use as a matter of record as much as anything:

... although to my chagrin (and doubtless influenced by Monty the mannekin) they've classed it under 'Toys and Games' in order to rub salt into my gaping wounds.

I do feel though like someone who's had a wild fling, and returned to Earth suitably chastened.

And the prototype to which I return ~ unable in the circumstances to celebrate our design registration certificate together ~ still awaits me in the corner of the workshop.

"You bastard!" It shouts, "Off to fucking Pasadena with your fancy octocopter were you? Thought the California girls would melt your popsicle, did you?"

"San Diego, dear..."

"Don't San Diego me, you loser, and don't even think of touching me with that electric screw-driver!"


Wednesday, June 16, 2021

WDA Weigh-In

Proud of this one as it's made of used material throughout, including the three-way tube connectors retrieved from the wheelie-bin and set upon with an angle-grinder. Had angle-grinders been available in Arthurian times, would he still have been king?

It's looking like a credible flyer already, and Monty can't contain his excitement at the WDA (World Drone Association) weigh-in. He's looking like a mini Tyson Fury, another machine made here in Lancashire.

Without the benefit of the speed controllers and wiring loom, we're checking in at 19.8 kilos or 44 pounds. It includes batteries, motors and Monty himself (who accounts for around 20% of the all-up weight).

Initial reactions? Well I've given it the sprung dance-floor treatment and whilst it can support my own weight in 18-gauge tubing (except the skids, which are 1/16th inch) I would prefer it to be a little stiffer. That would be addressed by the anticipated gauge of alloy section, along with the steel-cored tube connectors. These would add weight, but likely mean that the four external steel braces could have been omitted.

The blade-clearance is a little tight, but that will be addressed by my secret-squirrel technique for mounting the motors. Meanwhile there may be an argument for lowering the mannekin's centre of gravity further.

This could be achieved either by providing for a foot-well in the centre-section at the cost of integrity or by tilting him backwards deck-chair-style at the cost of complexity.

FAQ Terence tweets from Tiverton to say, "Fucking rivets? You're a loser who wouldn't know one end of a welding-torch from another!"

ANS Terence mate, if it was good enough for the Titanic then it's good enough for me.

Tuesday, June 15, 2021

Put Out the Moon and Dismantle the Drone

Of the aspects of all this that kept me awake at night, undoubtably the motor-mounts and undercarriage have most often had me weeping gently into my pillow. At 04:00 today however I figure out a solution for the mounts, and as I've already solved the skids the design of the basic airframe is something of a done deal.

With this in view I dismantle the mock-up intending to re-use the parts, together with odds and sods knocking around the workshop, in a half-scale working model. Or not quite, as they're all close enough to the required size without being exact, but I'm not going to destroy the planet for an inch here and there.

I start then with a rebuild of the centre-section, although upped from the 12" square used in the mock-up to the 15" here that I had kicking around. The cantilevers you see here are those lengths that formed the sides of the mock-up's airframe, and these I have left at 24" as I couldn't be bothered getting the jig-saw out. Me at Airbus: "Office please Hilton and explain why one wing is longer than the other?"

I've also repurposed the 18-gauge aluminium tubing for this, though 1/16th would have been my tipple of choice.

Here's a tip though: to line this up in the absence of what professionals call a jig, take two of your cantilever arms and bolt then parallel as shown, using the remaining pair (as indicated by the mystery gloves) as a simple prop. Then BEFORE you rivet the two remaining arms in place, drill the 6mm holes required in order to bolt the abutments together in a material embrace.

All of this works, and only too well. Am unable to re-use the three-way plastic tube connectors used in the mock-up, because they're now stuck faster than Excalibur. Always use silicone instead of mastic, children, if you're going to dismantle the drone. Meanwhile below, in today's double-picture feature, we can see how the assembly is flipped over in order to mark up parts for drilling:

Monday, June 14, 2021

Happy Mondays

Let's do it ~ build the world's lightest and most versatile people-carrying quadcopter.

I've started by envisioning the half-scale proof-of-concept that will haul Monty's ass around the sky. And having started to sketch it out on A4, I quickly abandoned doing so for Apple's Pages. This includes many features of what used to be called 'desktop publishing' back in the day and here its most useful feature is the ability to dimension the parts fairly quickly.

Pages accepts inches as an overwrite for centimetres and thus we can go for an A4 portrait format at the outset, and I have gone for a 1:10 scale diagram of the proof-of-concept (POC), which itself is base upon a 32" outline... and indeed 32" propellers.

Suppliers like T-motor work in metric until talking about propellers, when in deference to the US ~ who invented flying ~ they switch to inches instead. And for the POC I am using what I have in the workshop in the form of 32" propellers fitted to T-motor U13s. 

And the nice thing about the design is that the perimeter lengths match the same diameter of 32" because the three-way connectors that join them together add a further inch to either side (so that the OUTSIDE dimension of the square is 34"). 

As the motors will be pitched centrally on the inch-wide connectors their axes are pitched 33" apart, allowing for blade clearance. So we'll order 4 x 32" x 1/16" lengths of alloy in order to define the 'square-frame' that supports the power-plants.

I guessed at the size of the centre-section and at 16" square it seems to fit the job. Accordingly, with the inside dimensions of the square-frame set at 32" there is eight inches of clearance all around the centre-section. Nonetheless we must subtract the one-inch width of each of the abutting cantilevers, which takes us down to 23".

Beyond that there are threaded inserts in either end of the cantilevers in order to fix the abutment and connect the flight-deck to the square-frame. From our mock-up we saw that a couple of connectors run to around 3/8th inch, so we have the following to order from our tube stockist:

    (a)    4 off at 32" x 1/16" perimeter lengths (total 128")

    (b)    4 off at 22⅝" x 1/16" cantilevers (circa 96")

This adds up to 224" or 5.67 metres in the UK, good if you can find stock lengths of six metres, but bad if like my supplier they only do five. Nonetheless I've enough left-overs to make a start. 

However a quick look at retail sites in the US like:

... reveals that 288" is a stock length, so you've enough left over for four legs too!

How long are the legs going to be? Well I haven't decided yet and I shall deal with it at the same time as the landing skids, which can be tailored to operational circs. There's a precedent for this, as an image search on 'Hughes 500' shows longer and shorter legs over the course of history.

FAQ Dave from Oklahoma asks, "Should I be nervous seeing that the centre-section appears to be overlapped by the prop-disks?"

ANS When will this generation listen? The motors pitch the props higher, and their efflux funnels considerably, reducing any losses. The mannekin will be set above the line of the disks anyhow, as we saw recently in the scriptures:

"And Colin raised them in their hour of need, above the line of their rotor-disks."