60" Build Step #29

Cash-flow is king when you're building your own flying machine, and I am mocking up the motors for the 'look and feel' of the final product and for ideas on how to mount the real thing, as and when. You can do no better for this than floral foam, and here I have separated one of the polyurethane foam inserts from its plastic well, which can be upended and glued to the top of an intact unit to produce a double-sided cylinder of broadly the same dimensions as the T-motor U15 units set eventually to take their place. This costs around £4 instead of the £600 that would be needed for the original. If you want to try this yourself, use rubber solution glue because the solvent in most glues will simply dissolve PU foam: though rarely an issue for flower arrangements.

60" Build Step #28

One of the design criteria is that the vehicle can be pitched on its side for storage and transport. Nonetheless the motors will be mounted centrally on the perimeter sides of the airframe so that they overhang by a couple of inches. In order that the airframe is not resting on one or other of the motors when manoeuvred in this way, I am going to have to reorientate the four uppermost 'prongs' from a vertical orientation to extend fore and aft. On one hand this overhang will protect the motors in this case, though it will also provide a carrying handle at each corner with which four people can between them carry the airframe prior to launch... picture to follow as and when.

60" Build Step #27

A few mods as we go along here, principal among them the replacement of the skids ~ which are inessential in a vehicle of this kind ~ with removable feet that I like to call lunar landers. At the same time I have taken the opportunity to extend the legs to one foot in height, and at the same time I have flipped the platform to mount its grilles up top.

The seat has been replaced with one that can incorporate a lap-strap, in the form of a stackable chair whose legs are removed and which is snapped into place with conduit brackets.  A number of the alloy lengths from the previous post have been shortened so that the podium supporting the seat is 12" high instead of 18", this being because it looked rather better but also because it pitches my feet at the airframe perimeter; in the fulness of time I'd like rudder pedals mounted here.

60" Build Step #26

This step, resuming construction, is a modification to the seating arrangement so as to enhance both its comfort and security. We start with twelve 16" (405mm) lengths of the 1/16th alloy section that we have used throughout. These are sold by my supplier in lengths of five metres ~ around 197 inches ~ so that all dozen parts can be off-cut with a minimum of waste as ever.

60" Build Step #25

This is what I mean. Here a typical pairing of 22.20 volt six-cell LiPo battery-packs are set in the forward left corner of the air vehicle, with the cables set to address an ESC positioned nearest the motor to be fixed centrally upon the perimeter tubing seen top of the photo. Wrapped round the packs is velcro fastening tape to size the battery tray  formed of two off-cut lengths of angle-alloy.

The brackets are marked to show how they line up with a row of perforations, so that a couple of holes can be drilled to house the pairs of pop-rivets that secure them too the safety grille. Afterward two short lengths of velcro tape are riveted to one of those brackets, beside the perimeter tubing itself. You may wish to drill and fasten the latter length of tape PRIOR to fitment of the corresponding bracket opposite, so as to make room for the hand-drill.

As with most operations during this build, repeat a further three times. Battery-packs are located in these positions principally because it's much easier to support their weight when they are placed on the top-side of the airframe than suspended beneath. They are also set at a distance from the pilot-operator, so that the risks associated in (a) connecting the batteries whilst clear of each propeller's arc and (b) fire during their operation is reduced to a minimum.

It also distributes mass evenly around the airframe, albeit at the expense of reducing the manoeuvrability by the same degree due to dispersing it furthest from the C of G: as ever then it's a case of 'Keep it simple, stupid'.

60" Build Step #24

Slight re-jig on the battery placement to accord with the likely wiring layout. Packs will be joined in series with the built-in connectors, and in turn the remaining positive and negative will supply the ESC (electronic speed controller), which in turn connects the motors in the same way.

The ESCs have each to be connected however to the centrally-located flight controller, and this will be via the four arms extending from that section. The end of each arm thus forms a T-junction where 50v wiring from the battery and the 5v from the avionics bay are joined together.

The planned location for the battery-packs have therefore been moved to that corner nearest the associated arm. Accordingly looking at the diagram the pack at top left is designated #1, and then through #4 going clockwise. The associated motor to the right of the first pack is also designated #1 and turns clockwise direction, as is conventional with a quadcopter; the remaining sequence runs anti-clockwise (#2), clockwise (#3) and anti-clockwise (#4).

Avionics continue to occupy the underside of the centre-section, allowing for the fact that a passenger stood upright might be as accommodated as well as a seated might.

60" Build Step #23

We're at the point where we have to decide where to dispose of the battery-packs and we shall put them here basically because we can. It unloads the centre-section, which is already carrying the weight of the passenger; it also allows for a safe approach from each corner in order to connect each power supply while remaining clear of propeller; and it avoids the need for a central bus or distribution board with the messy soldering which that would require.

The batteries in the diagram show the dimensions of a typical pair of seven-cell packs of around 22000 mAh wired in series to produce around 50 volts, together weighing in the order of six kilos (thirteen pounds) per pair.