Saturday, June 11, 2022

60" Build Step #36

Many emails ask, 'Master, how do we wire our drones? Teach us, that we might know.'

And indeed we are at a juncture as we need to decide to use a common battery bus or a distributed power arrangement. And do we go for flat packs, or bricks like these?

This is the pilot-eye view of an auspicious arrangement going forward. You will have seen how we modified the airframe to make all four sides match, so what goes for the front-end here (now marked by an arrow as a reminder) goes for remaining motors.

These are six-cell packs that we have most often used in the past for test-flights, and generally just two of them wired in series was enough for trial runs of prototypes with eight U13 motors. With a switch to larger U15s at nearly double the wattage, however, we need to up our game.

A distributed power arrangement where batteries address motors directly and may be co-located can be seen in Lifts 'Hexa' prototype, though one is also used in Dragon's 'Airboard' in Florida, flown by the fragrant Mariah. Notice in the latter case that four pairs of packs like these power eight U15 motors, and for a surprisingly long time.

We could therefore up the voltage and use seven-cell packs of a smaller capacity than the 22,000 mAh types seen here. This would lower the weight of the machine, so that for test purposes a 'virtuous circle' operates wherein lighter batteries have less to do.

Nonetheless I've gone with the stock option for the moment and packs in regular use with the heaviest drones. A benefit of how they fit here is that the perforated grille that allows the propeller to breathe also forms a pegboard for pop-rivets. This means that to switch from six-cell packs to seven-cell the rivets need only be drilled out and the angle-alloy stepped back to accommodate the wider type.

To ensure that holes in the angle-alloy coincide with those in the grille, clamp it in place and go in from the underside ~ which practically means upending it against the garage wall.

I did consider batteries under-seat along with power distribution board and associated wiring, but there were three reasons why not:

(1)    If they caught fire I'd have a very hot bottom.

(2)   I'd like to reserve the under-seat space for avionics.

(3)   They're easily connected from within or without the vehicle.