Shepard Test Stand

h1. Shepard Test Stand Detailed Design v1.0

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h3. Introduction

h3. Mechanical System

h4. Component Overview

!ShepardMechaniclComponentIdentification.png!

The Shepard Test Stand v1.0 mechanical system (pictured above) is made up of six key components.  They are

# *Test Stand Base* - The *Test Stand Base* (*Base*) is constructed from ripped down 2x10 pine stock, and fits over a 4" x 8" x 16" (nominal) solid concrete block which is available at most hardware stores.  The outer dimensions of the *Base* are 10-7/8" x 21-1/2" x 5-3/16", and its inner dimensions are 7-3/4" x 15-5/8" x 3-1/2".  The key dimensions of the base are the inner dimensions (to allow the base to fit over the concrete block during operation) and an open platform of 20" in length to accommodate the *Test Section Beam*.

# *Back Plate* - The *Back Plate* is constructed from ripped down 2x10 pine stock.  Its function is to provide resistance to the thrust, and a mounting location for the force sensor (on the side facing the motor) and the DAQ electronics (on the side opposite the force sensor).  The dimensions of the *Back Plate* are 7-3/4" x 8-13/16" x 1-1/2".  The key dimensions are the width (to match the top of the *Base*) and the height (which should be no less than 8" to provide enough space to mount the force sensor and the electronics).  Note, there may be one or more holes in the *Back Plate* to feed wires from the sensors to the DAQ board (or other purposes).  In the current version, there is one 3/8" diameter hole drilled through the center of the *Back Plate* approximately 3-7/8" above the *Base* to allow a cord from the *Motor Mount Bracket* to facilitate calibration.  After passing through the *Back Plate* the cord goes over a pulley mounted on the back side of the *Back Plate* so weights can be hung from the cord to simulate thrust applying force to the force sensor.

# *Test Section Beam* - The *Test Section Beam* (*Beam*) is constructed from a 2x4 pine board, and sits vertically on top of the *Base*, along the center line.  It is 20" long (6" longer than the *Rail System*) to provide room for the *Rail System* to retract the *Motor Mount* and *Motor Mount Bracket* away from the *Back Plate* for maintenance.  The key dimension is its length.

# *Rail System* - The *Rail System* restricts the motor under test to motion along the initial thrust vector.  It is made from a "*Liberty* 14 inch Ball Bearing Drawer Slide":http://www.libertyhardware.com/search/detail/?searchType=retail&ID=D80614C-ZP-W&FIN=ZP (PN D80614C-ZP-W, available at "Home Depot":http://www.homedepot.com/buy/liberty-14-in-ball-bearing-full-extension-drawer-slide-d80614c-zp-w.html#.UEAZVNaPWsg).  Note, this was the shortest ball bearing drawer guide available at the time of testing.  If a shorter drawer guide is found, the overall length of the test stand could be reduced.  It is installed along the top of the *Beam* along the *Beam's* center line.

# *Motor Mount* -  The *Motor Mount* is based on an "Estes D and E Engine Mount Kit":http://www.estesrockets.com/rockets/accessories/engine-mounting/303159-d-and-e-engine-mount-kit (PN 303159).  It is assembled according to the instructions for E size motors with four modifications.

## It is assembled without "Centering Rings" (the cardboard rings used to connect the mount to a rocket body)

## 1/4" is removed from the "Engine Block" to leave room for a 3/4" copper plumbing t-connector to be inserted into the aft end of the mount

## A layer of wood glue is spread on the inside of the motor mount at the aft end to seal the surface which will be glued to the t-connector

## A 3/4" copper t-connector is glued into the aft end of the motor mount to redirect the ejection charge

# *Motor Mount Bracket* - The *Motor Mount Bracket* provides a connection between the *Motor Mount* and the *Rail System*.  It is a 1/2" thick plate with a block on the aft end sized to provide the correct contact area with the force sensor.  The current version is constructed from 1/2" sheet of pine plywood (to create the plate) and a pine block cut from a 2x4.  The plate's dimensions are 6-1/4" x 1-23/32" x 1/2" (the 1-23/32" dimension is set to fit the selected force sensor).  The block is 1-1/2" x 1-7/32" x 1-23/32".  The critical dimensions are the overall length of the plate (sufficient to accommodate the block and the *Motor Mount*) and the area presented at the back of the *Motor Mount Bracket* (sized for the force sensor).  The *Motor Mount* is attached to the *Motor Mount Bracket* using 2 plastic zip ties (rated at least 50 lbf), one over the t-connector and the other over the "Engine Retainer Ring" at the front of the *Motor Mount*.  The *Motor Mount Bracket* has a number of holes drilled into it.  Two countersunk holes are used to attach the *Motor Mount Bracket* to the *Rail System*.  Four straight-through holes are used to allow the zip ties to pass through the *Motor Mount Bracket*.  Finally, two grooves are cut in the bottom of the *Motor Mount Bracket* to give the zip ties room between the *Rail System* and the *Motor Mount Bracket*.  Many of these details can be seen in the image below.

!motor_mount_bracket_detail.jpg!  

*Note:*  All of the wooden components are covered in 2 coats of heat resistant spray on primer and 2 coats of heat resistant paint. 

h3. Data AcQuisition (DAQ) System