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1. Rope through the springs which is inside a hollow cylinder (to prevent buckling of the spring) holds the springs compressed.
2. Nichrome wire is used to burn through the Dyneema at the point marked in the diagram below which allows the springs to decompress.

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Rack and Pinion:

1. Pins hold down a rod which is passed through the middle of the spring and locks the springs compressed against a bulkhead.
2. The pinion is turned to allow the rack and pin to slide out of the rod and the springs decompress.
3. Pininon is attached to a motor or servo to do so.

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Torque requirements for this type of actuation are really high and can be calculated using the friction that must be overcome to pull the pins out:

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