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140 lines
6.3 KiB
Markdown
140 lines
6.3 KiB
Markdown
# Omnicopter
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An Omnicopter is a multicopter that can provide thrust in all directions (6 degrees of freedom).
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This allows it to move in any direction without having to tilt, and it can hover at an arbitrary tilt angle.
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All of this is achieved by arranging the motor positions and thrust axis in specific ways:
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This build follows the original design from [Brescianini, Dario, and Raffaello D'Andrea](https://www.youtube.com/watch?v=sIi80LMLJSY).
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## Bill of Materials
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The components needed for this build are:
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- Electronics:
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- Flight controller: [Holybro KakuteH7](../flight_controller/kakuteh7.md)
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- Coupled with 2x [Tekko32 F4 4in1 ESCs](https://holybro.com/products/tekko32-f4-4in1-50a-esc)
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::: info
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You can select your own flight controller of choice, it just needs to support 8 DShot outputs.
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:::
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- GPS: [ZED-F9P](https://gnss.store/zed-f9p-gnss-modules/105-elt0092.html)
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- [GPS helix antenna](https://gnss.store/gnss-rtk-multiband-antennas/28-elt0014.html)
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::: info
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Any other GPS may work as well, however a helix antenna is expected to perform better for inverted flights.
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:::
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- Any RC receiver
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- An external Magnetometer. We used the [RM-3100](https://store-drotek.com/893-professional-grade-magnetometer-rm3100.html).
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- Telemetry link, e.g. [WiFi](../telemetry/telemetry_wifi.md)
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- Propulsion:
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- Motors: 8x [BrotherHobby LPD 2306.5 2000KV/2450KV/2650KV](https://www.getfpv.com/brotherhobby-lpd-2306-5-2000kv-2450kv-2650kv-motor.html)
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- 3D Propellers: 2x [HQProp 3D 5X3.5X3 3-Blade Propeller (Set of 4)](https://www.getfpv.com/hqprop-3d-5x3-5x3-3-blade-propeller-set-of-4.html) or 2x [Gemfan 513D 3-Blade 3D Propeller (Set of 4)](https://www.getfpv.com/gemfan-513d-durable-3-blade-propeller-set-of-4.html)
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- Battery: we used a 6S 3300mAh LiPo. Make sure to check the dimensions so it fits the frame.
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- Battery strap
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- Frame:
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- Carbon square tube R 8mm X 7mm X 1000mm, e.g. [here on shop.swiss-composite.ch](https://shop.swiss-composite.ch/pi.php/Halbfabrikate/Rohre/Vierkant-Rohre/CFK-Vierkantrohr-8x8-7x7mm.html)
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- Carbon Rods R 3mm X 2mm X 1000mm, e.g. [here on shop.swiss-composite.ch](https://shop.swiss-composite.ch/pi.php/Halbfabrikate/Rohre/CFK-Rohre-pultrudiert-pullwinding/Carbon-Microtubes-100cm-x-20-3mm.html)
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- Required lengths:
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- square tube: 8 pieces with length of 248mm
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- rods: 12x328mm, 6x465mm
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- Screws:
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- Motors and standoffs: 40x M3x12mm
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- FC mount: 4x M3x35mm, 4x M3 nuts
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- Standoffs: 4x 40mm
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- [3D model](https://cad.onshape.com/documents/eaff30985f1298dc6ce8ce13/w/2f662e604240c4082682e5e3/e/ad2b2245b73393cf369132f7)
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## Assembly
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### Frame
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- Print the 3D parts
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::: info
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The orientation of the corner pieces matters.
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You will notice if it's wrong when the angles of the rods are not correct.
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:::
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- Cut the rods
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- Test that it all works by connecting the frame pieces together:
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- Place the motors as far out as possible, without the propellers touching the rods.
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### Electronics
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Solder the peripherals to the flight controller. We used the following assignments:
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- ESCs: the 2 ESCs can be connected directly to the two connectors of the KakuteH7.
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To avoid conflicts we removed the power pin (right-most pin) from one of the connectors.
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- Telemetry to UART1
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- GPS to UART4
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- RC to UART6
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Remarks:
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- Make sure the magnetometer is placed away from power.
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We ended up placing it to the bottom of the center-piece with a 4cm padding styrofoam.
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- Put some tape on the barometer (without taping the opening!) to avoid any influence from light.
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- We did not glue the frame.
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It is certainly advisible to do so after initial test flights, but it might work without.
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## Software Configuration
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### ESC
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First, configure the ESCs to 3D mode (bidirectional).
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We had issues with the stock ESC settings in 3D mode: when trying to switch direction, a motor sometimes did not start anymore until the ESC was rebooted.
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So we had to change ESC settings.
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To do so, you can use Betaflight on the flight controller and then use pass-through mode and the BL Heli suite (make sure there is an airframe with 8 motors configured in Betaflight).
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These are the settings:
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In particular:
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- set the Motor Direction to **Bidirectional Soft**
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- increase the Rampup Power to **100%** (this is conservative and might reduce efficiency)
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::: info
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Make sure the motors do not overheat with the changed settings.
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:::
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### PX4
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- Select a generic multicopter airframe
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- Use an [arming switch](../advanced_config/prearm_arm_disarm.md#arming-button-switch), do not use stick arming
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- [Select DShot](../config/actuators.md) as output protocol on all eight outputs
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- Configure the motors according to this:
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We used the following convention: the motors are facing the direction of where the axis points to.
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The spinning direction matches the direction of positive thrust (moving the motor slider up).
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Make sure to use the right props, as there is a CCW and a CW version.
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- Parameters:
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- Change the desaturation logic for better attitude tracking: set [CA_METHOD](../advanced_config/parameter_reference.md#CA_METHOD) to 0.
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- Disable failure detection: set [FD_FAIL_P](../advanced_config/parameter_reference.md#FD_FAIL_P) and [FD_FAIL_R](../advanced_config/parameter_reference.md#FD_FAIL_R) to 0.
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- [This file](https://github.com/PX4/PX4-Autopilot/raw/main/docs/assets/airframes/multicopter/omnicopter/omnicopter.params) contains all the relevant parameters.
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## Video
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<lite-youtube videoid="nsPkQYugfzs" title="PX4 Based Omnicopter Using the New Dynamic Control Allocation in v1.13"/>
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## Simulation
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There is an omnicopter simulation target in Gazebo Classic:
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```sh
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make px4_sitl gazebo-classic_omnicopter
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```
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## Remarks
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Some general remarks:
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- The hover throttle is about 30%.
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- The flight time is around 4-5min. This could probably be improved a bit by using larger propellers.
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