Homebuilt Helo #51

It all began with a spare chair knocking around the workshop and as we contemplate a way forward one option with the three-quarter scaler is to build entirely from scrap as we've done to date and to use it solely for a promo pic for the website.

What it principally functions as is a means of figuring out how it all hangs together and whether it looks viable to scale up. Nonetheless we cannot risk trying to fly an overly flexible drone and failing, because that costs money and time and effort.

Better I think to bite the bullet once back from the studio with the current build, and commence a full-scale version with more exotic materials that provide the required rigidity.

If nothing else I'll be left with a very high-tech chair to sit on, and between you and me I think it's the most imaginative part of the whole exercise. I've posted papers to the digital commons and actually the bulk of commercial interest judging from the data is actually in the stand-up version of the suspended space-frame.

Again tho' we shall persevere with seated versions because, to paraphrase JFK I do it not because it is hard, but because it is easy.

Note from the pic that the 15-inch footprint used for the child-sized flyer has only to be enlarged to around 18- or 20-inches in order that I can sit in it myself.

Prior to that decision we shall need to see what size of space-frame I can squeeze into, as we're flying on the edge here. As ever there are precedents... Nigel Mansell's F1 cockpit was so tight a fit that he'd to cut the toes off his footwear in order to race.

Homebuilt Helo #50

Here's an overview of how we're fitting that bracket on the cantilever so as to mount the motors... note the overhang at the far end which will allow the outermost motor to be mounted inverted.

I've also managed to locate 20mm conduit clips with which to secure and we'll double down on them with a rivet fired into either side.

The world of furniture and buildings (what the French call movables and immovables) is essentially a square one and eminently suit the square sections we used to build the suspended space-frame. When it comes to the machinery of life, however, tubular sections of a round profile generally dominate and for good reasons.

In Europe they focus at this scale on 20mm and 22mm fittings designed for electrical and plumbing installations respectively. Carbon fibre tubing, which we'll use when the time is right, is happily provided at 20mm gauge too.

Am still agonising over whether the drone itself should be complete and independent of the passenger frame if only for transportation purposes, but I shall persevere with the current solution where the space-frame includes the flight controller and the four cantilevers are removable.

If nothing else this provides for separate transportation of the space-frame and the cantilevers prior to final assembly... which is not unlike the way the the wings of the giant Airbus 380 arrive in Toulouse from the UK under separate cover, to be married permanently to the fuselage.

Homebuilt Helo #49

While we wait for those M3 bolts to arrive, let us consider another aspect of the proof of concept craft relating to battery stowage. Currently we've a pack addressing each of the motors, although we are likely to revert to past practise and use a single pack via a PDB or Power Distribution Board.

The reason for so doing is that I'd like to stow the substantial battery mass behind the head of the occupant on a perforated sheet upon which both this and a head-rest can be mounted.

A further reason is that there is a limited amount of room up top and from operational points of view a pack that can be swapped out conveniently from the rear works best.

The principal benefit of hanging battery packs here however is that it re-balances the vehicle given that the lower limbs of the occupant overhang the outline of its frame.

Building prototypes does take you down rabbit-holes and wondering what our lower limbs weigh is one such. There's a secure unit down the road here and one option was to have interviewed any number of chain-saw murderers to see if they could cast any light on the subject?

Alternatively you can scour the net at cost of being suspected of planning for body-part disposal yourself... though I've taken that bullet for you.

Using the table above we're looking at around 7.5% of body mass for the lower leg and foot (plural) and some 8.5% for a pair of thighs. I'm taking some of that seeing as how they overhang the edge of the seat, and so let's call it 12% all in. Give me a break here, because you're wearing a pair of boots unless you're levitating for enlightenment?

Apparently mens' perceived ideal weight in the UK is 77kg, which is me with clothes on... and no surprise that I'm perfect in that way too. That means we can hang 10kg of battery out back there on a full-scale prototype, which is a very respectable payload. In fact it is just about four of the largest six-cell LiPo battery-packs each providing for 22,000 milliamp hours.

A target application for a machine of this type is shuttling you upwards for a birds-eye view of the world ~ for which tourists will always part with money ~ or else launching parachutists or powder-skiers by a more cost-effective means. For most such uses a means of swapping out battery-packs quickly and efficiently would be required.

Homebuilt Helo #48

With the brackets cut out, apply the printouts from the motor specs ready for drilling the four holes necessary for connecting them.

Though these are for 3mm bolts I may well use a 4mm drill-bit firstly because it gives a little leeway for mounting the motors and secondly because I use the same bit for the pop-rivets and can't be bothered swapping it out.

We'll go for M3 Pan Pozi 8mm bolts at a cost of one penny apiece, I think.

Take a break now and make yourself a melted tuna-cheese toastie.

Homebuilt Helo #47

Here's how the motors will be mounted on the dog-bone mounting bracket. Practically this forms a demountable bogey that can be swapped out for rapid turnarounds in the event of breakage or failure.

In my experience drone-builders don't really get designing for personal air vehicles and not least because they've not flown their ass in a variety of machines as I've done over the course of some fifteen thousand hours.

One consideration for instance that rates this arrangement over co-axial propellers is that the brackets will be fitted with that left-most side nearest the airframe in order that the associated propeller is pitched clear of the occupant.

In a risk assessment scenario I've conducted, two people go flying in these suspended chairs in the Grand Canyon and one points to an interesting feature up above, loses a hand and bleeds out.

We need to eliminate each risk step-by-step while acknowledging flying is inherently risky. The reason people duck when boarding helicopters is that those not doing so do occasionally get their heads chopped off. Or die walking into tail-rotors or propellers on aeroplanes, or sucked into jet-engines.

That's why most of this type of work takes place beyond the shores of the UK, where what most needs saving from peril is the index-linked pensions of those overseeing its evolution. I should have gone to the US years ago, but it's too late now...

Because there are no rules for building electrified personal air vehicles and the reason we're working with parts off the shelf is that this is what happens at the birth of each technology.

I've seen the original steam locomotives with parts sealed with the leather and grease from cattle, and cars built from horse-drawn carriages. My old man was a telephone engineer for forty years and when I saw the first electrical computers being operated at Bletchley Park ~ where Enigma was cracked ~ I recognised the parts straightway.

From the analogue telephone exchanges I wandered as a child. 

Homebuilt Helo #46

I've gone ahead and continued with those tins of tuna in place of the motors as they are a close enough fit. Width-wise I've used a simple ruler as a masking template as again, it's good enough for government work.

If you think I'm kidding, a report into a nuclear submarine incident in the UK last week revealed that rather than using a new bolt in a component, the engineer used super glue to reattach a head that had sheared off.

If Putin's reading this, incidentally, I'd be heading for those shelters around about now.

Needless to say ~ okay, we need to say it ~ once you've cut one dog-bone out you can use that as a template for the remaining three.

Alternatively you may wish to use carbon-fibre sheet and a CNC or laser cutter... tho' that's not us, is it?

Homebuilt Helo #45

Why though are we using a pair of clockwise-rotating propellers, as here? Well from this photo it is clear that the overlapping areas of each disk will in fact rotate in the opposite direction.

This is important because overlapping propellers are not at all efficient, and altogether less so if the first swirls the efflux in the same direction as the next. An exception to this is the jet-engine, where the stages do all rotate the same way upon the same axis but are able to accommodate this with flow-straighteners in the interstitial stages.

Don't ask, basically.

Using the laser-guided set-squares I have here, however, it is clear to see that a ten-inch space (254mm) is a suitable separation distance for each pair of U7 motors.

Homebuilt Helo #44

The good news (and was there ever any bad about this?) is that relatively inexpensive carbon-fibre tubes at (!) 22mm are out there in the universe...

https://www.ecfibreglasssupplies.co.uk/carbon-fibre-tube-22mm-19mm

... and we'll likely need them before we fly as the sixteenth-inch alloy tubing that we saw yesterday will I fear not be as rigid as we need in order to preclude vibration.

Bear in mind too that I'll be leaving them in native black (though carbon-fibre comes in red now too) and thus I don't need anyone wanting their money back if the product doesn't match the picture... frankly nowadays, when does it ever?

Let's move on however to today's sermon in an effort to keep up the momentum. By way of recap we're looking at using our proprietary offset co-rotating propellers and not the conventional (X-8) co-axial arrangement because:

(a)    It's expected to be more efficient, and

(b)    We don't need complex motor-mounts.

Accordingly for today's exercise we shall be trialling what I shall call 'dog-bone' motor-mounts. This is one for the whole family to enjoy as it can be done indoors on a table-top like a giant game of Cluedo.

The ingredients include matching propellers, a pen, a sheet of plywood, U7 templates, tins of tuna and (if you can get hold of one) a Nigella Lawson.

The tins of tuna are subbing for motors at this stage because:

(a)    In the event of dropping one there are no more tears, and

(b)    They make a perfect melted tuna-cheese sub afterwards.

Homebuilt Helo #43

I'll call these cantilevers 'lances', because it's my party and I get to choose.

And you'll mail me of course, with"Master, how long shall we make our cantilevers?".

Foolish generation, can you not see fifteen inches is sufficient to clear the airframe, and twenty-two for the top-most propeller?

Go forth therefore, and make your cantilevers thirty-seven inches.

Homebuilt Helo #42

After a good deal of heart-searching and visits to my priest and psychoanalyst I have decided to mount the cantilevers around the sides of our airframe, so that the whole design effectively features snap-on modules.

To do so I've mounted conduit-clips where the rivets penetrate the tube-connectors and the frame is thickest. If you don't think this meets aerospace standards, trying getting these off with bare hands: it features in Britain's Strongest Man as I write.

The clips fit 22mm electrical conduit and we'll be mounting 20mm alloy tubing, simply because it's all we have left in terms of the leftovers of which our proof of concept is being constructed.

As you will see though, much in life is fudge-able besides your CV.

Homebuilt Helo #41

As a part of that 'base camp' review I decide to ditch the fascias round the uppermost part of the booth. We lose the logo, but this can be transferred to a dome up top that will cover the avionics like a hood.

At the same time there was always the choice as to whether to build the drone apart from the accommodation, but at this stage and possibly into the future the latter may form the basis of the co-rotating octocopter from which the passenger is suspended.

I've taken a side of the original four-pronged drone to use as a means of capping the space-frame, and at the same time transferred the expanded foam sheet to pack out the roof-space.

Principally this aims at damping vibrations from being passed to the flight controller and being interpreted as instant trajectories of the airframe instead of the transient fluctuations they are.

As the NTSB found after Boeing's own personal air vehicle prototype fell from the sky:

The June 4 crash of Boeing's urban air mobility prototype occurred after resonant aircraft vibrations incorrectly activated the vehicle's ground mode, commanding the motors to shut down.

After the incident the manufacturer abandoned development as I recall, and we don't want to give up that easily do we?

Homebuilt Helo #40

It's worth at every stage of prototyping stepping back to review progress and consider if at all it would be worth proceeding... a consideration from within base camp. James Dyson is the UK's most successful contemporary industrialist and in the time he took developing his vacuum cleaner, his son developed from toddler to seventeen year old.

It pays also to identify a marketing niche, and I think this has to be along a DIY route. The kit-built helicopter market has a spotted history, which is unsurprising given the fact that the conventional helicopter is relatively complex, and has to be got right. It is also probably true that like most kit aeroplanes, kit helicopters are rarely completed if only because they are pre-deceased by their owners.

On the other hand the world's most successful helicopter is probably the R22, which was sold ex-factory from the get-go and an examination of its pricing (according to its wiki page) is worthwhile. Pitched at around $18,000 by Frank Robinson at the outset it would eventually retail for nearly double in 1979, and still does so today at $375,000. In other words it sold for around double what he thought it would and continues to do so even nowadays, albeit it at a cost around twenty times beyond expectation.

It does suggest that eVTOLs designed admittedly for a single operator in place of two may in the long term present a viable business opportunity, but most likely in ARTF or 'almost ready to fly' format. This is a halfway house that broadly satisfies regulators as well as insurers and owners, in that it represents a proven product that unlike the run of kits is likely to see daylight.

It will likely to become easier with the passage of time to build airframes like the one in the picture: in the way that personal computing devices started out as a kit of parts that had to be assembled by its owner unlike shiny smartphones that appear from out of a box. And in the long run people will simply build and fly them for fun if the price point is right, in the way that both cars and aircraft developed from their beginnings.

Most electrical scooters in the world (like cars) are operated illegally, in the way most people watch soccer matches on TV illegally. The focus of product development is not so much to outlaw what people would like to do in their own back yard so much as to make sure they don't kill themselves doing it.

We've still retrospective adjustments to make to our people-carrying drone in coming days, so hang on in there.

Homebuilt Helo #39

Frankly I'm going to take a break now until the world provides the 3 x 30mm bolts that I feel it owes me...

Homebuilt Helo #38

And now I know why these were 3D-printed by the poor bastard who had to fit these motors to the last prototype, for they raise the spindle clear of the airframe.

Another of the joys of working with the U7 motor is that it uses shitty little 3mm bolts to fix it in place, for which ideally I need bolts of 30mm length that UK DIY depots do not generally stock.

There will therefore be an interlude whilst I reduce sixteen 40mm bolts from the local hardware store to a 30mm shank using an angle-grinder.

An exercise that will convince you ~ if nothing else does ~ of the futility of life.

Homebuilt Helo #37

Here's the base of the U7 motor, from where we can see that the spindle to which the rotor is attached (the cylinder or 'out-runner' at left which does the turning) extends beyond the fixed base... guaranteeing that as you tighten the motor in place, it acts as a brake preventing the motor from operating.

Larger motors from the same company do not include this feature, and I guess at the quarterly sales meets that there's a bonus for shifting the stock on the unsuspecting.

A suitable rename of the U7 as a part of this effort might perhaps be the FU7.

Why am I doing this?

Homebuilt Helo #36

I devote the next three posts to T-motor's U7 V2 that I'm using here, and which can best be described as 'useless'.

Blow the pic up and you'll see how the bolt-holes perfectly align with that black wire which powers the motor, to the extent that you short-circuit it should those bolts go just a little too far. Had they pitched holes at 35mm instead of 30mm you'd be home clear, but where's the fun in that?

This incidentally is the improved 'V2' version of the motor... those with the V1 version are advised to slit their wrists at this stage.

Homebuilt Helo #35

Here's a bird's eye view, or at least to the extent any bird would want to be garaged.

The ends of each undercarriage leg include a length of threaded rod glued in place so as to support a threaded door-knob.

This means that should there be any movement during touchdown, the undercarriage has less chance of snagging the surface.

Homebuilt Helo #34

Here's a simple undercarriage that I've used previously and follows TELEDRONE rules to the extent that this form a removable module along with the accommodation and the quad itself, principally for ease of transport.

Conduit clips are used to retain a quarter-inch GRP tube and I recommend riveting the clips with the tube in place so that it fits snugly whilst still being removable.

Homebuilt Helo #33

This is a job you can do indoors on a rainy day. I've printed the spec for the motor that includes a technical drawing of the threaded holes on its base that are used to attach it. They require M3 bolts spaced around a 30mm diameter circle and for our purposes we need use only two (an advantage of square tubing being that motors sit flush on the arms and require no adapter).

Due holes in the re-used arms I've had to set the templates a half-inch nearer to the centre-body of the drone than I would have liked, but it is what it is. I've also used templates to locate motors on the underside of the arms at each end, and all will be centre-punched as a guide to drilling 3mm holes.

A further advantage of drilling through the depth of each arm is that the motors can be attached with bolts of a reasonable length, which is a whole lot easier to manage.

Separating the motors along the length of the arm in this way provides for easy access to fit motors from above or below: a reason I prefer the arrangement to co-axial ones that require special fixtures.