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.

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

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.

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

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.

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.

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.

Press the circular board firmly to leave 4 marks at the cardinal points aligned to the 4 sides of the base support board.

Remove the rod and the circular board.

Grind the screw points on the screw eyes flat, level with the disc

Left with the base support board, drill two 3mm holes at the North and South holes previously made with the board aligned with the longer dimension horizontally.

Fit the two 41.2mm screw eye at these points.

Using a 5.5mm drill bit drill two holes at the locations previously drilled with the 2mm holes.

These holes will allow insertion of the ground pegs to anchor the structure.

Fit all 5 rods into the predrilled holes in the base support board.

First with hand pressure than lightly tapped with a mallet and/or block of wood to level up and secure in place.

Next fit the propulsion disc on the central rod with screw eyes facing down.

Now fit the upper board with screw eyes facing down.

Align the holes with the rods and first with hand pressure push the board onto the rods until they are all in place.

Once aligned tap with the mallet/block of wood to secure and level up.

Look through the exit port and verify the alignment of the central guide.

If the central guide is too close to the edge apply pressure on the opposing side at the entry point to the base support board or remove and if possible lightly bend the bar to bring it back centrally.

Continue until the alignment is central.

Loop one elastic band on each screw eye to secure in place and simply place around a lower screw eye without tying.

Fit the ground pegs into the holes and push down into the ground to secure the structure.

Slide the straw on to the central guide and push down on the propulsion platform and push a nail or robust metal pin with several metres of cord to enable remote extraction with the pin or pins aligned at the cardinal points South or North at the extreme of the stretch.

For extra securely a second pin on the opposite side can be inserted to prevent accidental launch if the main pin with the string is inadvertently pulled.

*******************************************Warnings ****************************************

During the priming and firing process do not lean over the exit port in case of accidental release.

Always wear eye protection.

As an added safeguard fit a cover over the exit port and open prior to launch.

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Prepare for lift off.

Pull back the pin and watch the projectile fly.