SkyGuard Cutdown
This documentation covers part number 10-0000201
Overview
The SkyGuard Cut Down was developed over years of experience supporting ballooning operations for the research community. Designed with simplicity and reliability in mind, this device offers 16 preset time and pressure triggers to suit a variety of mission profiles. Once the system detects a balloon launch, the timer activates, and the pressure trigger monitors an absolute pressure threshold for optimal cut-down timing.
Unlike traditional hotwire systems, SkyGuard’s innovative mechanical release eliminates the risk of fire and simplifies rigging. Arming and resetting the device is quick and safe, taking only seconds. Housed in a durable 3D-printed enclosure with clear acrylic front and back panels, it allows easy visibility of status LEDs at a glance. All you need to get started is a 9-volt battery!
SkyGuard is simple to use yet highly customizable. The firmware is fully open source, letting you modify settings if the built-in presets don't meet your specific needs. Plus, the front panel features engraved instructions, so there’s no need to fumble with your phone in the field—everything you need is right at your fingertips.
Swiveling rigging points at the top and bottom reduce the risk of line fouling. DIP switch settings are quick to adjust with a pen or toothpick, even in the field. Built-in reverse polarity protection safeguards the device, while a supercapacitor ensures the microcontroller stays powered during servo operation. The SkyGuard Cut Down is rugged, reusable, and field-ready. A consumables kit is also available, so you can reuse the system time and time again with ease. Whether you’re launching high-altitude balloons or conducting atmospheric research, SkyGuard is the trusted solution for safe, reliable, and efficient payload recovery.
Front Panel
The front panel of the instrument has two LED indicators on it and two banks of dip switches.
- Heartbeat - Green LED indicating the device is active.
- Timer Armed - Yellow LED indicating that the flight timer has been armed and is running.
- Time DIP Switches - 4 switches to set the time before the balloon is released.
- Pressure DIP Switches - 4 switches to set the absolute pressure at which the balloon is released.
What's in the Box
Upon receipt of your unit, unpack the contents of the box and inspect all parts for any damage incurred during shipping. Immediately report any missing parts or damage to Leeman Geophysical for replacement. Note that there are many optional accessories available, see the accessories section of the manual for details and usage notes.
- SkyGuard Cutdown Assembly
- Flight Consumables Kit
Specifications
| Parameter | Min | Typ | Max | Unit |
| Physical | ||||
| Weight | - | XX | - | g |
| Width | - | 76 | - | mm |
| Length | - | 55 | - | mm |
| Height | - | 125 | - | mm |
System Components
SkyGuard Cutdown
The cut down unit features a 3D-printed enclosure housing an installed servo, release pin, bottom swivel, and a fully populated circuit board. The front and back acrylic panels protect the electronics from the elements, secured with elastic bands for quick and easy assembly or disassembly.
Parachute Retaining Ring
This is the topmost release ring in the system. When the release pin activates, the parachute retaining ring is freed, allowing the balloon retaining ring to release as well. This process ensures the rigging line drops cleanly, allowing the cut down to fall below the parachute and avoid interfering with its deployment.
Balloon Retaining Ring
The balloon retaining ring supports the load of the balloon, transferring it through the cut down unit to the payload. This ring serves as the primary attachment point for the balloon and facilitates the lifting of the parachute retaining ring when the release mechanism is triggered.
Moisture Plug
The moisture plug fits securely into the top of the parachute retaining ring, sealing the release mechanism against moisture. This protective measure helps prevent icing or fouling, ensuring reliable operation in various weather conditions.
Configuration
Timed Cutdown
If a time threshold is set, the system starts a countdown timer once it’s armed. The release is triggered when the preset elapsed time is reached. By default, the timer activates only after the system detects a pressure drop of 20 hPa below the starting pressure recorded at power-on—equivalent to approximately 550 feet above the initial altitude. This ensures the cutdown can be powered on during pre-launch preparations without starting the timer prematurely. Once the system is armed and in flight, the yellow "Timer Armed" LED on the circuit board will illuminate to confirm activation.
The cutdown time is set by the DIP switches labeled "Time" right below to servo. The times from arming to release are set as shown in the following table.
| Switch 1 | Switch 2 | Switch 3 | Switch 4 | Time (minutes) |
|---|---|---|---|---|
| OFF | OFF | OFF | OFF | Timer Disabled |
| ON | OFF | OFF | OFF | 1 |
| OFF | ON | OFF | OFF | 2 |
| ON | ON | OFF | OFF | 5 |
| OFF | OFF | ON | OFF | 10 |
| ON | OFF | ON | OFF | 20 |
| OFF | ON | ON | OFF | 30 |
| ON | ON | ON | OFF | 40 |
| OFF | OFF | OFF | ON | 50 |
| ON | OFF | OFF | ON | 60 |
| OFF | ON | OFF | ON | 70 |
| ON | ON | OFF | ON | 80 |
| OFF | OFF | ON | ON | 90 |
| ON | OFF | ON | ON | 100 |
| OFF | ON | ON | ON | 110 |
| ON | ON | ON | ON | 120 |
Pressure Cutdown
Pressure cutdown is performed based on the absolute pressure at the instrument. Once the pressure is below the set point which has been selected with the 4 DIP switches labeled "Pressure" the release will be actuated. Since there is no way to know altitude information to determine sea level pressure the absolute pressure is used always.
| Switch 1 | Switch 2 | Switch 3 | Switch 4 | Pressure (hPa) |
|---|---|---|---|---|
| OFF | OFF | OFF | OFF | Pressure Disabled |
| ON | OFF | OFF | OFF | 10 |
| OFF | ON | OFF | OFF | 100 |
| ON | ON | OFF | OFF | 150 |
| OFF | OFF | ON | OFF | 200 |
| ON | OFF | ON | OFF | 250 |
| OFF | ON | ON | OFF | 300 |
| ON | ON | ON | OFF | 350 |
| OFF | OFF | OFF | ON | 400 |
| ON | OFF | OFF | ON | 450 |
| OFF | ON | OFF | ON | 500 |
| ON | ON | OFF | ON | 600 |
| OFF | OFF | ON | ON | 700 |
| ON | OFF | ON | ON | 800 |
| OFF | ON | ON | ON | 900 |
| ON | ON | ON | ON | 1000 |
Operation
- Remove the elastic bands and front/back panels from the housing.
- Using a small pointed object like a toothpick or pen, set the desired time and/or pressure on the DIP switches following the tables in the configuration section. Note that both time and pressure conditions may be set, and whichever is reached first will trigger a release.
- Connect the device to the balloon train following the recommendations in the rigging section of the manual or your SOPs.
- Install a 9V battery onto the battery clip. For best performance in the cold flight environment, we recommend a high-performance lithium 9V. The green and yellow LEDs on the front will alternate to indicate the system is initializing. The servo will also move approximately 20 degrees then back to the home position.
- Reinstall the front and back covers with the elastic bands.
- The cutdown is ready for flight as long as the green LED is flashing.
Rigging
While rigging of your cutdown likely depends on your exact balloon train design, this is the recommended starting point for the development of your procedure.
The basic principle of operation is that the balloon when released also pulls of the line retaining the top of the parachute. This allows the balloon to go free and the cutdown to fall below the parachute to gently fall along with the payload.
- Tie the balloon retaining line to the balloon retaining ring and place it over the release pin. Making a large loop between sides provides the most even lift, but this is not overly important.
- Tie the parachute top line to the parachute retaining ring and install it onto the release pin by pressing the blue button inside the cutdown.
- Tie off the bottom payload line to the payload swivel on the bottom of the cutdown.
Serial Connection
There is a header on the PCB for serial connection at 9600 Baud. With the stock firmware, system status information is printed to the serial terminal as a table as shown below:
To connect to the serial output, connect a 3V3 logic cable to the PCBs ground, transmit, and receive pins as shown below:
If you are unfamiliar with serial terminal operations, be sure to check out our guide in Application Note 0005: Establishing Serial Communication with Instruments Using a Terminal Program.
Customizing the Firmware
The firmware for the cutdown in open-source and available on the GitHub repository. It is stated in the license, but emphasized that the software is provided as-is and to be used/modified at your own risk! We have installed the Arduino bootloader on the cutdown and have it set up as a 3.3V 8MHz Pro-Mini. We recommend using VSCode with the PlatformIO extension to edit and upload the firmware. You will need a 3V3 USB cable to accomplish the programming or to read out serial outputs.
Upload Procedure
- Connect the serial cable as described in the Serial Connection section.
- Using a jumper, connect the Reset pin to ground to hold the processor in reset.
- Open PlatformIO in VSCode and click the "Upload" button (arrow) at the bottom of the screen.
- Remove the jumper from the reset pin when you see "Uploading" appear in the terminal.
Enclosure and Hardware
The SkyGuard Cutdown enclosure is designed using Autodesk Fusion 360, and the design files are freely available in the mechanical GitHub repository for those who wish to explore or modify the mechanical components. The repository includes the Autodesk Fusion 360 project file as well as 3D-printable STL files, allowing users to fabricate their own parts if needed. The circuit board and servo are securely mounted within the enclosure using plastic self-threading high-low screws.
Key components, such as the machined swivel and release rings, are available as replacement parts. To purchase replacements, please contact our support team or purchase the commonly used parts on our website.
The bottom swivel may need to be removed when replacing the enclosure. To remove the swivel, use an external snap ring tool to detach the snap ring securing it. It is strongly recommended to first remove the circuit board to prevent clearance issues that could potentially damage its components during the process.
Accessories
If you will be recovering your SkyGuard for multiple uses, we have accessories that you may be interested in keeping on-hand.
Flight Consumables Kit
10-0000202
Extra hardware to replace that used during a flight. Includes a top and bottom
release ring and water plug.
SkyGuard Cutdown Housing
10-XXXXXXX
After a number of flights your housing may get damaged from landing on hard
surfaces. This kit includes an empty housing and front/back panels with elastic
bands to let you renew your cutdown for many more flights.
3V3 Serial Cable
10-XXXXXXX
Program new firmware to the cutdown or just monitor the serial output for testing.
Revision History
| Date | Changes |
| November 2024 | Initial Release |