KD7LMO - Cut Down


Payloads Payload Computer Micro Beacon Cut Down Overview Hardware Source Code HF-APRS Video Link Pico Beacon NSRV Beacon APRS Beacon

Cut Down

The cut down mechanism is used to release the balloon from the payload train. This is typically done if the flight is traveling to an undesirable area or faster than predicted. It is also used after the balloon bursts to release the trailing balloon chards that may foul the parachute. The cut down utilizes a piece of Nichrome wire wrapped around the nylon string. To activate the cut down, power is passed through the wire to heat it. The heat melts and severs the nylon cord.

Two versions of the cut down have been designed and built. The first design contains a wireless receiver that activates the cut down. The second, is a hardwired with a pair of Teflon coated wires to the payload computer.

In both designs, a solid steel loop is used to connect the nylon string to the aluminum plate. Two independent outputs are provided for a redundant cut down or to allow for two separate balloons. A 6 volt Lithium camera battery is used to power the controller. The Lithium battery is capable of high current output even at the temperatures as low as -40° C. A 6 amp MOSFET switch is used instead of a relay for reliability. Most components are rated for operation down to -55° C.


Cut Down Top View.	Cut Down Bottom View.

Shown below is the hardwired design that also utilizes the same Nichrome wire. Although this design requires a pair of Teflon wires to the payload computer, it doesn't require a transmitter modules. The wires connecting the cut down to the activation or payload computer should be Teflon coated. Teflon insulation doesn't become brittle at low temperatures like common CAT-5 Ethernet cable or telephone hookup wire.

Cut Down - Hardwired Design.

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