In autumn of 2006 Chris Boden began on the next set of upgrades for Project Thumper with the idea of finally replacing the "Broker Enhanced Safety Switch" with something a little more snappy, a triggered spark gap. Other upgrades would include a holding device for the pop cans and other items we may want to experiment with instead of just placing things under the hinged arm and letting the wires come together. Some serious upgrades to the discharge table cabling design were also planned.

The final result came out looking excellent.

After a discussion among the members in the forums the idea of a pneumatically actuated anvil type gap was decided upon. This has the advantage of being rock reliable and doesn't require the added complexity of a seperate high voltage system for a gap trigger. In it's simplest form we just have to smack a pair of really large contacts together. Though, in practice it's a little more complicated than that.

With the combined engineering genius of Sean Taylor, Chris Boden, and Ron The Funky Machinist we were able to take a pile of very expensive metal from Alro and shape it into a functional gap in a weekend. The main component of the gap is a $200 piece of solid copper bar that is 5 inches wide and an inch thick. the contact anvils are made from a 3" diameter pair of solid brass pucks over an inch thick. The structure of the gap is reinforced with large aluminum plates and the entire assembly is mounted to a pair of UHMW insulative plates to shield it from the table.

The entire process of actually building the gap can be summed up in seven words, "Tapping holes in thick copper sucks *hard*."

However, we did produce an incredible piece of functional art.

Here is the finished gap with it's blast containment cover. The cover is made from 1/8" Lexan for the sides with double layers directly in the middle where the blast dispersion happens. This way we can replace them when they get aged/pocked/cracked. the top and ends are made from 1/2" Makrolon ballistics rated plastic.

Here's another shot of the gap completely installed.

Here's the chewy center of happiness. The pneumatic cylinder is double acting and one side is always under pressure. This prevents the danger of the gap drifting too close together and triggering unintentionally. The needle valves on top (the little top-hat things above the air inlet hoses) allow us to fine-tune the speed at which the gap opens or closes.

Here's where the magic happens. The bolt on the side of the left puck is a 1/4"-20 bolt to give you an idea of how massive this is. Upon actuation the Hammer Puck (left) is driven foreword at high speed and slammed next to the Anvil Puck (right) as close as possible without actually letting them touch. The gap between them is *just* barely enough to see light through, only a few thousands of an inch. We cannot let them actually slam together because the discharge energy would instantly weld them together permanantly and that gets expensive in short order.

Here are the valves that Sean put together on this nifty little plate to actuate the gap. One valve is always open, one is always closed. When the fire button is pressed, they reverse states.

The can holder was a little weekend project of Ron's that turned out to be incredibly useful for countless applications other than just can's.

Made from nothing more than some simple stock materials Ron crafted a handy little holder from a pair of custom-bent copper plates, some copper bar stock we had leftover from the gap assembly, and some UHMW with a little scrap piece of Lexan. It was designed to fit the smaller juice cans, but handles standard cans just fine.

The gates of hell.

Here you can see it installed in it's finished setup.

To trigger the gap Chris wired up a giant 4" diameter red mushroom headed emergency stop button to a small box on the end of a 20 foot cable. This is placed on the floor and a random spectator chosen who gets to fire the system. Obviously this is incredibly awesome for the students to have this opportunity.

With the final assembly done and the new wiring installed Thumper looked markedly improved and worked much better. The crowd loved being able to take an active part in the demonstration now by being able to push The Big Red Button Of Science.

The finished Mark-6 Prototype with it's blast shields in place.