Re: Cutdown device?

Bill Brown

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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