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Power

Current power budgetting budgeting is in Power Distribution Architecture

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Airside Hardware Layout

Where everything airside is going to go

Compute

The Holybro PX_ system should be placed as close to the center of rotation of the drone as possible, offset in ONE axis only to allow for the installation of the VectorNav VN-300 module. There is an arrow on the top of the Pixhawk, which should point toward direction of forward flight. Keep in mind that wires need to be accessible from the “back” of the pixhawk (I/O & FMU Output banks), as well as from the side for USB debugging as well as retrieval of the SD Card.

There is no strict need to electrically isolate the system (the baseboard & cube are already protected), but it could be helpful to mount the system on vibration damped material (yellow sticky tack is good for this purpose).

Batteries & Power Distribution

Transmitters

Cameras & Related Peripherals

GPS Sensors

Peripheral Sensors

Optical flow sensors & rangefinders or lidars should be mounted at the bottom of the drone, in a sensor cluster without obstructions (clear or otherwise) in the fov of the devices.

It is mandatory to have at least 1 hereflow and 1 tfminis lidar module, the rest of the sensors are optional.

Airside Electrical Layout

Harnessing, wiring diagrams, etc.

General Wiring Guidelines

Power Architecture

The drone will run a 12S power system. The drone will be able to run on either 4 batteries or 6 both configurations at 12S. The power from the batteries will pass through a custom High Current Power Module board which will supply a clean 12V and 5V rail. The remaining battery current will pass through the PDB board which will supply directly battery voltage to the ESCs and motors. This PDB will also have a 5V and 12V rail.

Wiring

Connector Standardization

MT30s will be used as a quick connect in the 3-phase wires from the ESC at the entrance to the drone arms. This will allow the drone arms to easily be unplugged from the ESC and taken off. They are rated for 15A nominal and 30A peak which is more than the 14.05A drawn by the motor at 80% throttle.

Bullet connectors will be used for 3-phase connections at the motor to allow the polarity change or disconnecting of the motor to be fast and easy. 3.5mm bullet connectors will be able to handle the current load and are the same size used in last years competitionthe airside components will be mechanically placed in the airframe.

General System Level Electrical Placement & Routing Guidelines/Information:

• The frame should not be electrically connected (aka should be at floating potential)

  • Complies with: UL1740

  • This can be checked with a DMM (when the system is not powered)

  • This means that if a PCB we are using has electrically connected mounting holes we need to take proper steps to achieve isolation

    • Sometimes PCB mounting holes are electrically connected to a GND plane for thermal reasons so we should also approach thermals with caution on sensitive electronics

• Conformal Coating can be used within reason

  • The pro of conformal coating is waterproofing and makes it harder to accidentally should with a screw driver

  • The con of conformal coating is it prevents heat from leaving a PCBA

    • So anything that is conformal coated should receive a thin layer at most

  • Another con is that it can be annoying to remove in the case of reworking a PCBA

  • For example it would be fine to conformal coat a flight controller that runs cool

  • However, for example an RF transmitter we would want to approach with more caution

    • We could place a large heatsink on the primary chip(s) using thermal paste

    • Then we could consider conformal coating the other portions of the board

• Cables, especially longer cables, should be within sheaths when reasonable

  • This offers protection against abrasion during natural flight vibrations

  • Exception to this rule is shorter cables that are placed further from anything that could be abrasive, specifically cables purely within the avionic compartment of our aircraft

• Avoid loops in cable runs if possible

• Varying conductor types should be separated when reasonable

  • Generally we consider four different types of cables: Digital, Analog, Power, & Coax/Rf

    • Digital: Characterized by signals with fast edges

      • Definition of a fast edge in this context and some examples to be added by an EE

      • Generally transcieving in 0 and 1 states asynchronously or synchronously

      • I.E. a GPS module’s cable connection to our flight controller is digital

      • An IMU is an example of a particular digital device that is sensitive to external noise.

    • Analog: Characterized by signals with slow edges

      • Definition of a slow edge in this context and some examples to be added by an EE

      • Generally transcieving data in varying voltage states

        • Though some protocols we consider analog will also transmit some digital data as well

      • I.E. a hobby fpv analog video camera has an analog data output

      • An analog video feed out of an analog camera is an example of a particular digital device that is sensitive to external noise.

    • Power: Characterized by constant voltage varying current designed for power transmission

      • Generally the voltage is constant though higher frequency noise may be present

      • These conductors can have significant current pulses

      • I.E. a connection from a battery to an ESC

    • Coax/Rf: Characterized by oscillating signals across the spectrum (~20kHz to ~300Ghz) intended for wireless transmissions and notably contained within a coaxial cable

      • A coaxial cable, specifically for our applications utilizing an SMA or RP-SMA connector, is generally used to guide sensitive RF signals between transceivers & antennas.

        • It is also worth noting antenna placement is critical, this is noted below in more detail

        • SMA & RP-SMA connector info should be found in the corresponding connectors arch doc section.

      • Because coaxial cables offer strong noise immunity the routing constraints of these cables are looser than others

        • Coax cables are very good at eliminating outside noise

      • For further information see: Coaxial cable

  • Each of these type of conductors should be physically grouped together, however, each type should be separated

    • I.E. All power stuff near each other, all digital near each other, but power separated from digital

    • This grouping and separation is physical distance, though of course there are other factors

    • Within PCBAs these groups may be mixed, this is fine, we will assume the PCB designer has taken the proper care to avoid issues as necessary

• RF Transceiver Care

  • An RF transmitter should not be turned on (given input power) without a proper antenna connected as this can permanently damage the transmitter

    • Possible violations of this policy should be reported in Discord and transmitters should be labelled as damage (notably degraded performance) may not be immediately evident. We don’t want to blame each other, stuff happens, we just want to note it for the future! If you do not feel comfortable stating this publicly feel free to DM a lead you’re comfortable speaking to who can relay the message without naming names.

    • An RF dummy load should be connected instead of an antenna if we would like to power on.

  • Transmitters generally get warm

    • They require a lot of power and therefore require some cooling

    • They are sometimes designed to be mounted outside an airframe for ambient cooling of wind passing the frame. As we may not be doing this we need to approach this with caution.

    • Notes regarding conformal coating are above.

  • The lower the frequency the longer the distance we can get for the same output power generally

  • The higher the frequency means more bandwidth generally

• Antenna mounting

  • GPS sensors in particular are to our 900 MHz and 1.3 GHz transceivers and should be mounted away from antennas operating at these frequency ranges

    • GPS frequencies are fixed frequencies are1100MHz and 1500MHz

    • Our transceivers will hop around frequencies around their range looking for available channels so they are capable of hopping close to GPS frequencies and causing issues

    • For context it’s worth noting a 900MHz and 1.3GHz transceiver are capable of stepping on each others frequencies as well

    • For further reference see Guide: 1.2GHz -1.3GHz FPV Video System - Oscar Liang & GNSS Frequencies and Signals

  • Radio waves do not like to change medium

    • Specifically they do not like to pass through materials of varying dielectric constant

      • Passing waves through some varying materials may be fine, but be careful!

      • At the frequencies WARG operates at (6 GHz and below) foam will not have a considerable impact on signal integrity

      • Rain will have a measurable impact on signal integrity

    • This means mounting antennas outside of cases/airframes and providing LOS when reasonable

  • Antenna polarity should be deliberate

    • Antennas that use diversity should be mounted not in the same plane

      • Antenna diversity

      • There are different types of diversity

        • The VN-300 employs “Spatial Diversity”

        • The RFD9000 employs “Polarization Diversity”

      • Antenna diversity is not the same as true diversity

        • See r/exELI5:Difference between true diversity and antenna diversity

    • Antenna polarity matching follows the below graphic

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• (Antenna Mounting Continued)

  • Ground antenna should be mounted with as much distance away from the ground as possible

    • This is to reduce ground reflection and has a considerable effect on reliability of an RF link

  • Antenna spacing should be minded

    • Any device with diversity (multiple antenna inputs) should have it’s antennas mounted with some spacing between them. Always follow manufacturer guidance here.

      • IE our VN-300 has specific manufacturer recommendations regarding recommended spacings and clearances

    • Different devices should have their antennas spaced out

      • See notes about frequencies and channels above.

• Some notes about lightning

  • This entire section can be ignored for WARG purposes on nice days and the odds of a lightning strike are relatively low so don’t worry too much about these guidelines

  • As long as the current from a lightning strike is allowed to pass through your structure relatively unimpeded it will not harm the system

    • Notably isolating important electronics from the structure is important for this, see above.

    • To ensure this is possible having a somewhat conductive frame helps

      • This is not possible for composite frames and thus more complex techniques can be employed

  • Lightning likes to, if possible, enter and exit through sharp points

    • Ensuring that the sharpest points on a region of the system are all not electrical elements (notably antennas) will ensure lightning passes where we want it to!

    • A side safety note is that people are also relatively sharp points sticking out of the ground, however, unlike structures, you aren’t replaceable.

      • Be sure in lightning prone weather that people are not the path of lowest impedance for a lightning strike! This can be done easily by ensuring taller, pointier, grounded structures are nearby humans.

  • For ground equipment (towers and stations) grounding rods can be used

    • Notably this may not be possible for ecological reasons as well as if our ground station is on pavement

    • Grounding rods should connect into the earth (with a pointed end) electrically to the sharpest point at the peak of the structure

      • Ideally, as mentioned above, the entire structure is conductive which makes this easier to achieve.

Compute

The Holybro PX_ system should be placed as close to the center of rotation of the drone as possible, offset in ONE axis only to allow for the installation of the VectorNav VN-300 module. There is an arrow on the top of the Pixhawk, which should point toward direction of forward flight. Keep in mind that wires need to be accessible from the “back” of the pixhawk (I/O & FMU Output banks), as well as from the side for USB debugging as well as retrieval of the SD Card.

There is no strict need to electrically isolate the system (the baseboard & cube are already protected), but it could be helpful to mount the system on vibration damped material (yellow sticky tack is good for this purpose).

Batteries & Power Distribution

Transmitters

Cameras & Related Peripherals

GPS Sensors

Peripheral Sensors

Optical flow sensors & rangefinders or lidars should be mounted at the bottom of the drone, in a sensor cluster without obstructions (clear or otherwise) in the fov of the devices.

It is mandatory to have at least 1 hereflow and 1 tfminis lidar module, the rest of the sensors are optional.

Airside Electrical Layout

Harnessing, wiring diagrams, etc.

General Wiring Guidelines

Power Architecture

The drone will run a 12S power system. The drone will be able to run on either 4 batteries or 6 both configurations at 12S. The power from the batteries will pass through a custom High Current Power Module board which will supply a clean 12V and 5V rail. The remaining battery current will pass through the PDB board which will supply directly battery voltage to the ESCs and motors. This PDB will also have a 5V and 12V rail.

Wiring

All of the wires for the sensors will be pre-run through the frame in dedicated channels if required, with connectors left exposed near the sensor compartments and the avionics compartment. This means that any time a sensor needs to be replaced, we do not need to re-wire the entire sensor. This also means that when we need to re-wire the flight computers, we can use the cables that are already connected to the interface connectors an simply plug in a few large connector banks to our dev interfaces. Running more cables through the channels should be supported, but all necessary cables should hopefully be routed during assembly (or when it is easiest).

Connector Standardization

MT30s will be used as a quick connect in the 3-phase wires from the ESC at the entrance to the drone arms. This will allow the drone arms to easily be unplugged from the ESC and taken off. They are rated for 15A nominal and 30A peak which is more than the 14.05A drawn by the motor at 80% throttle.

Bullet connectors will be used for 3-phase connections at the motor to allow the polarity change or disconnecting of the motor to be fast and easy. 3.5mm bullet connectors will be able to handle the current load and are the same size used in last years competition.

More General Connector Standards

This section is mostly from 2023 System Architecture so the above standards take precedence.

• Gender Decoding

  • Gender convention WARG will use is the gender defined by the manufacturer for every connector

  • When the manufacturer does not specify the gender is defined by the metal conductors in all cases. Plastic housing should be ignored when deciphering gender if not specified by manufacturer.

• XT series connectors are convenient, common in the hobby world, fairly reliable, and relatively cheap and will therefore be employed for all WARG DC power connections whenever possible.

  • COTS PCBAs after require solder pad connections which we will accommodate, but breakout to our prioritized connectors whenever possible.

• XT60 connectors will be prioritized for any sub 150 A pulsed DC connection

  • For ESCs and anything smaller this should be prioritized

  • XT60-F is on batteries and so the XT60-F should be used on any voltage source and XT60-M should be used on any load. This gender convention is also used in the COTS world and keeps things simple.

    • Manufacturer PN Gender: “-F” is female & “-M” is male

  • Custom hardware will use XT60PW series connectors and follow the above gender convention.

• XT30s will be avoided when possible for simplicity

  • While XT30s are smaller and meet our current requirements for lots of low voltage loads in order to minimize the amount of connectors we need to stock and use XT30s will not be prioritized when an XT60 can be used.

  • COTS loads and sources with XT30s will be adapted to XT60 through harnessing

  • This may change though requires some discussion

• XT90 connectors will be used for any greater than 150 A pulsed DC connections

  • COTS higher current 6S and above batteries often ship with these XT90s and so we will accommodate such a design decision as they are rated for the higher current.

  • Anti-spark XT90s should be used whenever possible to limit sparks from in-rush condition though this may not always be possible.

  • XT90 battery input splitting into ESC and converter connections should be done on a properly specified PCB with XT connections done in harnessing.

• AC Mains is not used on any WARG aircraft and therefore a connector will not be specified

  • No voltage sources exceeding 55 V during nominal continuous operation are to be present on aircraft due to a lack of necessity and safety concerns

• ESC BLDC Motor Controller Phase connectors will be specified in the future and require more decisions in the future.

  • 3.5mm banana connections is a solid option from the hobby world, but they can be a pain. Other size banana connections may be used as well on smaller aircraft as we come up with more specific decisions.

    • Gender Convention: Female on ESCs, Male on motors

  • Anderson Power pole series connectors are promising and have significant use in FRC, but will require validation before we fully adopt them in place of the ol' banana connectors

    • Gender is not present on these but ideally three different colors are used.

• PWM Signal Connections

  • Should be done with with standard twisted PWM cables. Ideally locking stuff so it doesn’t pull out easily.

  • Simplest solution is often the best so sticking with these seems ideal.

  • Gender convention: Male pins on the signal generator and female sockets on the signal receivers.

  • We will use mechanical locking on the headers, copying how it is done in Vex to lock the PWM connectors into the board they connect to.

    • Where this is not viable we will defer to hot glue

• Other low voltage signal connections

  • Debug versions should be done on standard 100mil pitch headers and jumpers

  • Flight versions should copy Pixhawk connectors whenever possible

    • This is for UART/I2C/SPI/ etc

    • Pixhawk Connector Standard

  • Specific components will follow manufacturer recommended connectors if we for sure want to support it

    • i.e. the VectorNav VN-300 has it’s own connector we should just use since we are going to use this component on our system for sure!

  • If all the above do not offer adequate specification for a low voltage signal connector we will defer to automotive and marine standards and document here

LED’s

LEDs are required for realism and legal compliance for flying at night. How LEDs should be handled will need to be defined.

Custom Hardware Mounting Hole Dimension Specification

This standard is copied from 2023 System Architecture and should be upheld. For general custom EE flight PCBAs on ground station and aircraft we will follow this mechanical mounting hole specification:

M3 - Any PCBA with area exceeding 2500 mm^2

3.400mm hole diameter (0.1mm tolerance)

6.000mm annular ring diameter

M2 - Any PCBA with area exceeding 750mm^2 and less than 2500mm^2

2.400mm hole diameter (0.1mm tolerance)

4.200mm annular ring diameter

No Mounting Holes - Any PCBA with area less than 750mm^2

No mounting holes will be present on board of this size.

All Mounting Holes will follow:

Electrically not connected to the PCBA

Eight vias (plated drills) placed evenly in the annular ring (in whichever drill size is used on the board (so effectively left to EE in charge to decide on via size)) for mechanical stiffness.

Electrical components and electrically connected pads should be at least 1mm away from the annular ring to avoid damaging the PCBA when mechanically bolting the board.

Custom Hardware Mounting Hole Pattern Specification

We should define the standard mounting hole pattern we want to use for a few different applications. It was mentioned 30x30mm is common in cots so we should follow that when possible. This standard is essentially how far apart the holes should be from each other generally for a few applications and the reasoning.

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Groundside Architecture

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• How to use RFD900X: https://uwarg-docs.atlassian.net/l/cp/LPn8hwCv

• https://uwarg-docs.atlassian.net/wiki/spaces/ARCHS22/pages/2123431971/2023+System+Architecture#Power:

• VN-300 Rugged pinout: 2023-03-26 - VN-300 Rugged Harness

• ZeroPilot Software ZeroPilot 3.0 Architecture

• [UART]  UART

• [Competition Design Outline] Competition Design Outline

• [Competition Requirements] Competition Requirements

• [CV Search] Search for Landing Pad

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