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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
So many projects, so little time!
Mike / KD2EAT
On 11/24/2020 12:17 PM, Bill Brown via groups.io wrote:
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
From: Michael Hojnowski <kd2eat@...>
Sent: Sat, Nov 21, 2020 7:52 pm
Subject: Re: [GPSL] Cutdown device?
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
Thanks for any info you might share,
On 11/21/2020 10:31 AM, Chief Surfer via groups.io
I invite you to review a cut down I made here