Batteries, buses, and power rails

RotorLab models the power system the way it is actually wired: one or more batteries feed named buses (power lines), the motors draw from the motor bus, and every auxiliary rail (a BEC or UBEC) names the bus it sits on. Endurance, current limits, and the checks all follow from that wiring, so a companion computer on a 5 V rail or a video transmitter on a 9 V rail costs the right pack the right amount of energy.

This page covers the two console groups that define the system, Batteries and buses and Power rails, and the animated power-distribution diagram that renders the result.

Batteries and buses#

The Batteries and buses group sits directly under the Airframe group in the Builder console. At the top, the Motor bus selector picks the power line that feeds the motors. Below it, each battery is a card with:

• a name field (for example "Flight pack"),
• S (cells in series), mAh (capacity), and g (pack mass),
• chem (liion or lipo), C (continuous C rating), and C burst,
• bus: the bus this pack sits on. Type a name; existing bus names autocomplete.

Press + Add battery to add a pack and the small x on a card to remove it. Buses are defined by the batteries: naming a new bus on a pack creates it, and the motor bus selector and every rail's bus picker offer the buses your batteries define.

Parallel packs on one bus#

Put two or more packs on the same bus and they are treated as parallel: capacity, current limits, and mass add. Use this for a 2P flight pack. A warning appears if packs on one bus have different cell counts.

A dedicated avionics pack on its own bus#

Give a pack its own bus and route some rails to it to model a dedicated avionics or payload battery that runs independently of the flight pack. Each bus gets its own endurance, listed in the Power buses table inside Performance detail (energy in Wh, hover minutes, and utilization of its continuous rating). Two checks watch this arrangement:

• a warning when an accessory bus runs out of energy before the flight pack does, with both times printed,
• a failure when a power rail is assigned to a bus that has no battery.

Power rails#

Onboard electronics are modeled as regulated rails, not a single flat wattage. In the Power rails group, each rail card has:

• a name field,
• V (output voltage), eff (regulator efficiency), and rating A (continuous current rating),
• bus: which bus the regulator's input draws from,
• a list of loads, each a name and a draw in W. Press + load to add one.

Press + Add rail for a new rail. For every rail RotorLab computes the output current, checked against the regulator rating, and the regulator's input draw, which is added to its bus so endurance includes everything onboard. The Auxiliary power rails table in Performance detail shows each rail's output current against its rating and its load and pack-input watts, and the Checks block fails any rail over its regulator rating.

Adding a part from the payload catalog wires its draw onto a matching rail automatically, creating the rail if none exists at that voltage.

The power-distribution diagram#

Every analysis renders an animated Power distribution diagram at the top of the readout and in the downloaded report: batteries on the left flow into their buses, then into the motors and the BEC or UBEC rails, then out to each load. Wire thickness scales with the current it carries and the dashes animate, so you can see at a glance where the power goes and which lead works hardest.

Related#

• The Builder
• Payload catalog
• Physics reference