Grasshopper 5

15. Oktober 2024

Introduction:

The Grasshopper 5 is a 5-inch FPV frame that allows adjustable angles between the rotor plane and the body, is 3D-printing-friendly, and has excellent compatibility with mainstream FPV drone hardware.

Not all about science, but all about fun!

Grasshopper 5 Design Concept:

I know that designing a drone with an angled rotor plane is not a novel idea. Many similar designs exist, with DJI FPV being one of the most well-known examples. However, none of these designs cater to DIY enthusiasts or are compatible with the current mainstream FPV hardware. Therefore, I wanted to create a frame where the rotor plane could be angled relative to the body and the angle could be flexibly adjusted using 3D-printed parts. This would make it easier for more people to try out this layout and explore its potential benefits.

The design isn't strictly science-based but still exciting to explore.

Features of the Grasshopper 5:

Reduces drag generated by the body, improving flight efficiency.
Adjustable tilt angle (by swapping out two 3D-printed parts) to suit different forward flight speeds.
Compatible with mainstream open-source flight controllers such as Betaflight, Ardupilot, INAV, and more with simple configuration.
Compatible with most mainstream FPV hardware and installation methods.
Optional wings can be added to further increase flight efficiency during forward flight (coming soon).
Integrated and well-placed sensors like the compass, GPS, TOF, and optical flow to minimize interference, achieving high precision in position control.
Supports GPS-based hovering, waypoint flight, autonomous return-to-home, autonomous landing, and optical flow-assisted hovering and position flight.

Application Scenarios for the Grasshopper 5:

Suitable for multirotor drones where forward flight is the primary operating condition.
Requires autonomous positioning capabilities.
Long-range flight.
Carries light payloads that need to face the flight direction.
FPV Freestyle.
Other unexplored uses...

Design Details of the Grasshopper 5:

The Grasshopper 5 doesn't aim for extreme forward flight speed or peak flight efficiency, nor is it designed for academic research or maximum durability. Instead, it seeks to explore new layout possibilities in a market where FPV frames are becoming increasingly homogenous, and it does so by making these designs open-source to encourage creative experimentation.

Technically speaking, on a small 5-inch frame (at low Reynolds numbers), reducing the frontal area might not yield significant results, and at lower forward speeds, the benefits may not outweigh the additional weight of the tilt mechanism. However, the 5-inch frame is an excellent and cost-effective testing platform. Once some designs are validated, they can be easily replicated onto larger frames like 7-inch, 10-inch, or even bigger ones, where the advantages of this design truly shine.

With this background, the Grasshopper 5 is designed to be manufactured entirely through 3D printing or through a combination of 3D printing and carbon fiber. This ensures flexibility for modifications and upgrades while keeping costs low. For simple test flights, the frame can be made entirely via 3D printing. For better performance, the 3D printing and carbon fiber hybrid option is available.

Below are the specific design details:

(1) Camera Mounting:

Mainstream FPV drones typically use aluminum parts combined with TPU printed pieces to mount the camera, which greatly improves sturdiness but doesn’t offer reliable vibration isolation. For DIY drones, achieving consistent vibration control can be challenging, and excessive vibrations make effective vibration damping difficult.

The Grasshopper 5 uses damping balls and a similar damping system as DJI AVATA 2, with the same size damping balls made of rubber for excellent vibration attenuation and better image quality.

(2) Flight Controller and ESC Mounting:

The mounting holes for the flight controller and ESC are 30.5mm x 30.5mm and 20mm x 20mm, compatible with over 90% of FPV flight controllers on the market. The flight controller and ESC are stacked tower-style, following traditional FPV frame installation methods.

(3) Video Transmitter and Antenna Mounting:

The Grasshopper 5 is compatible with both DJI O3 and traditional analog video transmitters, supporting two common installation methods as shown in the image.

(4) Receiver/Telemetry and Antenna Mounting:

Since I’m using Ardupilot firmware, telemetry is essential. Therefore, I used the LR24F-Mini from Micoair, which integrates both receiver and telemetry into one compact unit, ideal for Ardupilot applications.

(5) GPS, Compass, Optical Flow, and TOF Sensors:

The GPS is mounted above the battery using a custom-designed protective case with a groove on top. Through multiple test flights, this position was found to cause the least interference with GPS and compass signals. At the rear, I installed the MTF-01P optical flow & laser ranging sensor (the mount also supports other Micoair sensors such as MTF-01, MTF-02, and MTF-02P). The optical flow assists with positioning when GPS signals are weak, while the laser ranging sensor helps with precise altitude hold near the ground and assists with takeoff and landing. Based on my tests, the effective range is around 10 meters.

(6) Rotor Plane to Body Connection and Angle Adjustment:

The Grasshopper 5 secures the rotor plane to the body using two symmetrically installed 3D-printed parts. By replacing these parts, you can adjust the angle between the rotor plane and the body. I’ve designed three angle options: 20°, 30°, and 45°, which can be swapped depending on the flight needs. You can also design your own custom angles.

Special Flight Controller Setup

The only difference compared to traditional setups is that the IMU on the flight controller is mounted at an angle to the rotor plane. This means you’ll need to set this angle in the flight controller. Assuming the angle between the rotor plane and the body is 45 degrees, here are examples using some common flight controllers:

Ardupilot:

Using my MicoAir 743 flight controller as an example, I installed the flight controller facing backwards for a cleaner wiring setup, as shown in the image. With this orientation, I configured the following parameters (note: in Ardupilot firmware, the compass angle is automatically detected and set during calibration, so manual setup is typically unnecessary):

CUST_ROT_ENABLE: 1

CUST_ROT1_PITCH: -45

CUST_ROT1_YAW: 180

INAV:

With the same installation orientation, you can configure the settings visually in INAV, as shown in the image.

If you're using a compass, you'll also need to set its installation direction. In my example, I'm using the MicoAir M9 GPS. Different GPS modules may have different compass orientations, but the setup logic remains the same.

Betaflight:

For Betaflight, the setup is similar, with visual configuration available as shown in the image.

Verification:

No matter what flight controller you use, be sure to follow this verification step to ensure your setup is correct. Place the aircraft as shown in the image—you can use the “IMU setup and leveling bracket” part, or another method to make sure the rotor plane is parallel to the ground. Then, connect the flight controller to the ground station, and the HUD should appear level or nearly level.

Once confirmed, pick up the aircraft and rotate it in pitch, roll, and yaw, using the rotor plane as the reference. Ensure that the ground station's HUD or aircraft animation matches the actual movement of the aircraft. Once this is done, your setup is fully verified.

3D Printing Considerations:

If you plan to 3D print the entire Grasshopper 5, you’ll need to carefully select your printing materials. I recommend using ABS or PETG, with ABS-CF or PETG-CF being even better. The motor arms, ESCs, and video transmission areas are often exposed to high temperatures, so using these materials will meet basic flight requirements.

Most parts don’t require support, with only a few needing minimal support from the base, which can be easily removed afterward. I typically set infill rates between 50% and 70%.