Re: Cutdown device?

Michael Hojnowski


Ya, I plan a similar setup.  I want to make a tiny 3D printed box that the balloon line passes through between parachute and balloon.  The box will route the string just like Joe's setup.  It will have a small ESP32 board with bluetooth which can fire the nichrome.  The main payload will have an ESP32 bluetooth/LoRa  flight computer that can decide when to initiate cutdown.  I can either stick an accelerometer in there or use altitude or whatever.  I may put a second cutdown box between the chute and payload box so that if I get stuck in a tree, I have the option of abandoning the chute and cutting away.

I've fallen in love with the ESP32 boards.  They're SUPER cheap ($5 for the cutdown board I plan to use) and have a ton of functionality, and they're just as easy to program as arduino.  I'll probably be switching over to them for most of my applications.

So many projects, so little time!
Mike / KD2EAT

On 11/24/2020 12:17 PM, Bill Brown via wrote:
Hi Mike,

  I designed a cutdown many years ago that had a CR123 battery.  I supported the flight train through some ring lugs to keep it from moving (knotted the line where it went through the ring lugs.  I used a MOSFET to actuate the nichrome wire...a few inches coiled tightly around the flight line.  It flew above the parachute and had a small 434 MHz RF receiver which was activated by turning on the 434 MHz transmitter in the main payoad with a coded serial string.  The cutdown box weighed about 3 ounces and just spun around the parachute after cutting down the balloon.

- Bill WB8ELK

-----Original Message-----
From: Michael Hojnowski <kd2eat@...>
Sent: Sat, Nov 21, 2020 7:52 pm
Subject: Re: [GPSL] Cutdown device?

Hey Joe,

I'm planning to make a quite similar setup myself.  Do you happen to know the current draw you get when that nichrome is engaged?   I'm trying to see if I can fire it with a FET and maybe run both the microcontroller I'll be using AND the nichrome from the same power source to save weight/volume on the cutdown device.  Knowing the current draw would help me understand whether I can ride out the "brown-out" when the voltage gets pulled down, or whether I might have to supplement with some caps/diodes or something to protect it.

Thanks for any info you might share,

On 11/21/2020 10:31 AM, Chief Surfer via wrote:
Hello Larry!

I invite you to review a cut down I made here.


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