Brief

At WARG, most of our drones are broken down into independent subsystems, which often incorporate multiple sub-teams. This page is broken down into these subsystems, with a brief description of the constituent components of the system, and how to configure them. For the functionality and alternatives, please consult the respective Sensors, RF Devices, or Propulsion documentation pages.

Please use this document as a guide and reference point for creating your pre-flight checklists! Do not use it as your pre-flight checklist.

Propulsion System

<< The propulsion system relates to all mechanical and electrical hardware that contributes to generating lift to fly the drone >>

All quadcopter propulsion systems constitute of a few basic parts, but what you see on Houston may not always directly translate to what you see on our next drones! Keep that in mind as you go through this document….

Power Supply

Houston’s batteries are type 3s 4000mah! The full product name is:

Turnigy nano-tech 4000mah 3S 35~70C Lipo Pack w/XT-60

They have soft velcro on the backside, and may be dated YYYYMM##, where YYYY represents the year, MM represents the month, and ## represents the number of the battery within the batch.

Battery Monitoring

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Battery Monitoring on most warg airframes are taken care of using Holybro PM02 Power Modules. On Houston, we are using an analog power module saved from Icarus, which means that it has a few curious points to note:

• It has XT90 connectors, to which we have attached xt60 adapters (since houston is all xt60).

• It must have the correct calibration in software, and this could be affected by adverse weather.

• The current monitoring is no longer accurate.

Please follow Ardupilot documentation, for configuring the power module:

• BATT_VOLT_MULT 18.812

• BATT_AMP_PERVLT 36.364

• BATT_MONITOR 4

It is also recommended to set the failsafe operation for low battery voltage. See Battery Failsafe — Copter documentation (ardupilot.org) for more technical information. This is currently conservatively set to “Land” when batteries reach 3.5V, which allows maximum flight time provided that Houston is within LOS. It is possible to change this to “RTL” at any different voltage using the following parameters:

• BATT_LOW_VOLT If TOTAL voltage is less than this value for 10 seconds, failsafe is engaged.

  • Houston is 3s! so multiply per-cell voltage by 3. 10.5v is the default.

• BATT_FS_LOW_ACT The action taken when failsafe

  • 1 - Land. Pair this with a lower voltage for more total flight time.

  • 2 - RTL. Pair this with a higher voltage for safer operation and less risk of losing a drone.

  • 3 - SmartRTL or RTL. Same as (2) but uses SMARTRTL if possible. Not necessary for us

  • 4 - SmarttRTL or Land. Same as (3) but uses Land instead of RTL

  • 5 - Terminate. Disarms the drone. Not recommended unless bench testing or otherwise.

Power Distribution

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Power comes in, power comes out. On Houston, this is handled as part of the frame! Note the XT60 connectors coming off of the bottom plate towards the ESC’s.

Note the 5th power lead coming out from the side of the pcb! This is typically where you would plug in your power supply, but all positive and ground terminals are connected to each other. Any additional wiring must be the same gauge or thicker.

Testing & Checking

Before you plug anything into your PDB, you should check for continuity on all voltage and ground rails! Do this using a multimeter, and make sure that all positive rails are connected, and likewise for the negative rails. Make sure that the positive rails are on the XT-60 are on the flat part of the connector.

Electronic Speed Controllers (ESC)

Houston currently uses unmarked “opto” ESC’s. These are leftovers from WARG “spare” and “parts” drones, and only accept a PWM signal. Newer revisions of Houston should use opto dshot ESC’s.

These ESC’s are currently soldered directly to the motors, but in the future will use 3.5mm bullet connectors. Motors typically use 16 AWG wire.

In order to calibrate your ESC’s, you may use the in-built ESC Calibration tool within mission planner.

Motors + Propellers

Motor selection is always tricky, but keep in mind the basic principles of motor selection regarding stator volume (diameter vs height), and kv rating! Motor selection is also tied in very closely to propeller selection, so we include this together.

Currently, houston uses 2217 950kV motors. The full name of the motors is

Cobra CM-2217/20 Multirotor Motor, Kv=950

These are, slightly, slightly, underspec for 3s, but are fine for our use and are also carryover from spare and parts. You can find the datasheet for the motors on the cobra motors website:

innov8tivedesigns.com/images/specs/Cobra-CM-2217-20-Specs.htm

Please keep in mind that Houston’s frame only accepts 16x19mm motors.

< Technical drawing here (if possible) >

Tuning for motor/prop combinations

All motor+propeller combinations react slightly differently, so when changing configurations, it is recommended to switch back to defaults, by using the “initial parameters” tab and re-updating the tune.

Houston will only have enough battery to run autotune in (one) axis at a time, set autotune_axes appropriately. Please make sure that you follow AutoTune — Copter documentation (ardupilot.org), and make sure that you follow the tune. See Software Configuration for more infoflight mode changes here exactly:

1. Takeoff in loiter

2. Switch to flight mode autotune when at a safe distance

3. When autotune is complete, switch back to flight mode loiter

4. You are currently still in the old tune. Fly to a safe location where you can easily visually confirm the function of the drone.

5. Switch into flight mode autotune. This applies the new tune. Apply some impulses in the tuned axes and make any notes of instability.

6. Land and disarm without changing flight modes. Exiting to any other flight mode will erase your tunes. Exiting to any flight mode and returning to autotune will also erase your tunes.

Flight Dynamics System

Flight Computers

Houston currently uses a pixhawk 5x which has been fully configured, but can accept any regular flight controller. Make sure the orientation matches with Red to left and White to right.

PWM ESC’s can be plugged into any port, but DShot ESC’s must be plugged into FMU or MAIN out. Using “IO” or “AUX” will not work. See software configuration for more information.

Communication Links

There are 2 RF links on houston, one for RC control, and one for telemetry. Both of these currently exist on different frequencies, but can easily be changed should you desire. Remember to configure the software properly when you do so.

Both airside antennas use U.FL connectors (someone please correct me if wrong).

Control Link

The current control link is a 915 frequency TBS Crossfire system. The full name of the airside receiver is:

TBS Crossfire Nano RX

This receiver is mounted on the back-left arm, with the dipole antenna mounted vertically on the aluminum leg. This is done so that there is optimal signal in any orientation (review your antenna radiation patterns kids!). Be careful not to damage this antenna when working on the drone.

Binding is done by entering the “TBS Agent Lite” lua script, choosing your TX module, and then pressing “bind” while pressing the bind button on the receiver. See the TBS-Crossfire-Manual

Telemetry Link

The current telemetry link is a 2.4 GHz ELRS link, configured to do bidirectional serial passthrough, connected to TLM1 port. The receiver is a standard serial receiver, soldered directly to a 7-pin connector.

See our ELRS workshops for more information on how to do this! Operation is quite simple and ever-changing as ELRS devs push out more updates. (in fact, the method we used on Houston in May 2023 is already out of date as of August 2023!)

Sensors

Houston is quite simple, so there’s really only 1 mandatory sensor, which is a GPS! This is critical for position-hold flight modes. It is mounted on top of the drone, and plugs directly into the GPS1 port.

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Optional Sensors

for optional sensors, please see the sensors information page for the other possible sensors. Most of these can be configured on houston should the need arise.

Calibration

Compass Calibration

Please perform this ONCE per flying field. There are two compasses onboard Houston, one in the NEO M9N GPS, and one internal on the pixhawk. Both should agree with each other. Spin houston in all axis, slowly, as well as on as many off-axis orientations that you can make. The goal is to have houston “point” towards every point in a sphere at least once, slowly (so that ardupilot can map it all out).

I encourage using the battery and telemetry link to run compass calibration, as this puts the same amount of noise into the system as would be present during flight, but it can be done tethered (it is just annoying).

Level Calibration

This is a quick way to “trim” out level flight if the flight controller is not level. Not recommended for houston sized aircraft since an accelerometer calibration is just as easy.

Accelerometer Calibration

This is the better way to recalibrate accelerometers. Doing this over telemetry vs with a cable has no difference on the final calibration.

Payload

The “payload” refers to anything which sits in the third tray of Houston. Currently this is the 200$ camera, an FPV camera, and the Jetson.

Layout of the Third Tray

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CV Camera Mount

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Using 4 M2 screws and 4 hex nuts the CV Camera Mount can be attached to the third tray. Place the CV Camera in the CV Camera Mount and line it up with the holes on the third tray with the CV Camera facing down. As you can see from the third tray layout, one side of the square that is cut for the CV Camera is extended more. This cut is to account for the cord that attaches to the port on the CV Camera. Make sure the port is on the side of the extended cut so it can be accessible from the top of the third tray. You can now start inserting the screws in the holes and using the bolts to tighten them.

FPV Camera Mount

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Using 4 M3 screws, 2 M2 screws, and 4 hex nuts the FPV Camera Mount can be attached to the third tray. Start by lining up the FPV Camera mount to the holes on the third tray with the mount facing downward. Insert the M3 Screws and tighten them with the bolts. The FPV Camera should have holes on the side of it. Line these holes up with the two holes on the side of the FPV Camera mount. Using the two M2 Screws, start screwing them into these holes. Instead of screwing them tight, leave them a little loose to allow the FPV Camera to move back and forth. The port for the FPV Camera can be accessed through the hole on the top of the third tray.

Jetson