ASIT Meeting Notes

CoDR Design:

Separation Mechanism:

This can be done using springs or a piston. The pros and cons for each are listed below:

The mechanism's working is described for a spring system:

1. The initial design consisted of a mechanical attachment of the two stages prior to separation using shear pins that attach to the sustainer nozzle casing.
2. Springs push against the staging cone which pushes against the inside of the sustainer nozzle.
3. The staging cone is still connected to the booster using a shock cord.

The phases of separation are shown in the diagram below along with an explanation of what each part is:

Phase 1:

Phase 2:

Phase 3:

The spring constant required can be calculated by a simple energy balance assuming the springs decompress instantaneously:

Where x = compressed spring length, d = distance sustainer travels after separation.

x here is a design parameter and depends on the possible dimension given the staging cone's dimensions whereas d is the required separation distance.

The force that breaks the shear pins must also be factored into these equations.

Choosing x = 10 cm and d = 20 cm and having 4 shear pins:

For 1 spring:   K = 38290 N/m

For 2 springs: K = 19145 N/m

For 3 springs: K = 12763 N/m

For 4 springs: K = 9572.5 N/m

If the shear pins can be cut using a blade or are not used:

For 1 spring:   K = 9810 N/m

For 2 springs: K = 4905 N/m

For 3 springs: K = 3270 N/m

For 4 springs: K = 2452.5 N/m

Actuators:

There are 4 main actuation methods while using a spring system:

• Dyneema and Nichrome
• Rack and Pinion
• Solenoid
• Rotating Plate

Dyneema and Nichrome:

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.

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.

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:

Assuming a radius of the pinion to be 0.04 m and using the spring force for K = 2452.5 N/m and x = 10 cm, a torque of 6.3 Nm is required which is large.

Solenoid:

This is similar to the Rack and Pinion except for the fact that the springs are locked and compressed using a pin that can be actuated by a solenoid.

Rotating Plate:

This is similar to the Rack and Pinion except for all the pins beings attached to one plate that rotates.

Pros/Cons: Spring Release Mechanisms

Spring + Guide:

1. After the CoDR, it was decided that a physical connection must not be present between both stages.
2. The guide will stop the sustainer from rotating unnecessarily and removes the need for shear pins to connect both stages which reduces spring constant requirements.
3. A tight tolerance with low friction is required.

Final Design - V1:

• Use Nichrome in tension instead of Dyneema.
• Only a single piece of Nichrome is used to hold the springs in compression. From initial calculations, 2 mm gauge Nichrome was enough due to the high tensile strength of Nichrome.
• Nichrome can be wrapped around the bushing at the top of the interior of the staging cone below the screw for attaching the shock cord.
• Spring (5in length, 1.225 in outside diameter): https://www.grainger.com/product/SPEC-Compression-Spring-Heavy-Duty-54NR98
• Tensile testing for Nichrome.

TO DO:

• Meet with Zachary Cordero - Will he let us print this? technical expertise with what problems might arise? Does he have the Aluminium alloy for us to use to print? Surface Roughness? Ask if oxide layer forms
• If 3D printing is not an option, speak to Todd about machining the cone.
• Make sure to include fillets in CAD if so because Mill and lathe manufacturing will create a fillet.