Mass Driver
Introduction: Mass Driver
What is a Mass driver, "Any device used to propel a ballistic payload".
Mainly associated with electrically derived propulsion but in this case no electricity is required.
Supplies
Wooden Decking board 24cm (L) x 12cm (W) x 2.4cm - Qty 2
Smooth round Steel Rod or tubing ~5.5mm diameter, length 52cm- Qty 5
Hooks 3.81cm long x bore 2mm with 1cm diameter ring - Qty 6
Hooks 4.13cm long x bore 4mm with 1cm diameter ring - Qty 2
Elastic Bands 100cm relaxed length, 5mm diameter - Qty 2
9mm thick plywood for a 56mm diameter disc
5mm diameter ground pegs - Qty 2
Plastic straw, ~6mm internal diameter.
Tools
Drill
5.5mm wood drill
2mm drill bit
3mm drill bit
56mm hole cutter
Taper drill 20mm maximum diameter.
Mallet/Hammer
Small hand size Wooden Block
Pencil/Marker
Ruler
Combination Square
Step 1: Method
The ballistic payload will be a simple rigid plastic straw which has little mass and the driver which uses the potential energy in elastic bands to propel the straw upwards.
Step 2: Design
The design will consist of a self supporting stationary launching tower with a central guiding rail which leads to the exit port.
The payload "hollow straw", will slide up the guiding rail propelled by the tensioned elastic bands.
Prior to launch a metal pin will hold the payload platform under tension.
Pulling the pin at the end of several metres of cord releases the payload platform propelling the payload upward.
At the exit port the payload platform can go no further stopped by the upper platform and the payload continues upwards.
In order to prevent the tower moving during priming and launch it is held in place with ground pegs.
The TinkerCAD design is available here:https://www.tinkercad.com/codeblocks/3NnUoizlCOt
Step 3: Wooden Platforms
The wooden platforms require the bulk of the work making up the base and upper platforms
Cut 2 lengths of decking board each to be 24cm long.
At the midpoint 12cm along by 6cm up mark the centre of the board.
Mark 4cm in at each end and draw a vertical line with the Tri Square.
Extend the centre horizontal line to bisect the two vertical lines drawn
On the vertical line mark in 3cm at each end making a total of 3 marks per line.
Align the two boards in the same plane on top of each other and clamp together in preparation for drilling.
Using a 5.5mm drill bit; drill 5 holes, one at the centre and 4 at the corner marks to a depth of 36mm.
This will make holes all the way through the first board and half way through the second board.
The upper most board will become the upper support platform with ejection port.
The lower board will become the base support.
With a 2mm drill bit; drill a total of 2 holes at the remaining marks along the horizontal mid line previously drawn through both boards.
Into these holes fit the 38.1mm screw eye to which the elastic bands will be looped.
At this pint separate the two boards.
Step 4: Exit Port
Fit the board with the rings previously inserted onto the work surface in preparation for drilling.
Using a taper drill cut a hole with a maximum diameter of 20mm.
This will create a hole that's wider at the point of entry for the projectile than the exit point.
This serves to compensate for some misalignment in the central guide offering guidance to the projectile and smoothing its passage to the exit point. Preventing dead stop issues with the edge of the straw catching on the edge hole if its approximately the same diameter as the straw.
The alignment variation due in part to the central guide only being attached at the base support enabling variation from the vertical. Reduction in this variation can be further enhanced by a shorted rod and/or with greater diameter.
Step 5: Propulsion Platform
This is made by cutting a 56mm diameter circular disc from 9mm thick plywood.
Once cut at the 90 degree intervals 6mm in from the edge mark four points.
With a 2mm drill bit; drill a hole at each of these points through to the other side.
Fit a 38.1mm screw eye in to each of the holes in the circular disc.
Take the previously drilled base support board and fit a rod into the central hole.
Slide the circular disc over the rod and align centrally with the screw points facing down and toward the board. 401