The Ballista

I have decided to put the Phoenix project on hold for the rest of the summer as there are more pressing concerns right now re: house building for my daughter.   Many thanks to those folks who have taken an interest in this project, and I’ll be back at it probably sometime in November.   Email dead for the duration.  Cheers,  Nick.

Two degree, counter-posed wedges, seem like a good starting point for our first attempt at an adaption of Mr. Philon’s souped-up torsion machine.

Those extra long wedges will be trimmed to length after the fine tuning is completed.   For experimental purposes the washers will also be capable of fine rotational adjustments.  There are 16 holes in the washers, each 22.5 degrees apart.   There is a 3 hole pattern in the vernier plate*,  with each hole set 15 degrees apart, so that the washers that control spring rotation can be locked down every 7 1/2 degrees.   The second set of three holes is so that there can be two locking pins for each station.   Next will be the radiused pusher bar that sits on top of the wedges.  And then on to springs and limbs.

*Counter plate, or counter washer, if you will.  I prefer “Vernier plate” as the Ampurias finds, whose geometry we are mimicking here, seem to contain the first deliberate use of a logarithmic scale similar to a modern day Vernier.

The notches and locking holes on Phoenix’s washers are complete.

Quite the labyrinth of mechanical possibility ain’t it?

Except for the locking holes and notches for the crossbars, the washers are about finished.

Why “modiolus of doom”?  Because right now I need some kind of hairy provocation to keep this project alive.

Time has a way of elongating, right before it runs out.  You think you have all the time in the world to finish something, and then …. Blam!… you’re done.  The meter runs out.  Which leaves the Catapult Gods smirking at you for the rest of eternity.   Damn their temporal omnipotence anyway!

Also, my laptop is getting hinky.  Email is down.  Correspondence not possible until I get it fixed.

…If I get it fixed.  A hermit-like submergence seems somehow linked to my ability to self-motivate.  Go figure.

I tried to utilize the web to figure the optimum size ratio for an ancient Roman torsion spring, (e.g. it’s length vs. it’s diameter).   The varying opinions quickly got me disoriented.  It was all a bit of a muddle.

So I’ve decided to use a “cut the chatter” kind of strategy and act from what I know already.  Because Firefly’s springs have proven themselves highly successful over the years, especially with the short limb rotations we are currently exploring, I will use that same spring ratio on Phoenix.  That is:  6.6 times as long as they are wide in diameter.  6.6 to 1, if you will.

Firefly has not had her springs adjusted in the last 4 years and has always shot a very consistent 316 fps, plus or minus 10 fps.  Her power is enough to shoot a 520 gram bolt 800 yards.  I believe that if there are gains to be made in performance they will be found somewhere other than the spring ratio.  “The spring ratio is not to be monkeyed with!”,  says my executive function.  A voice that demands obedience from the other functions that keep this project puttering along.

Developing Firefly’s torsion springs was not an easy process.  When gains are hard-won, one tends to be less flippant in considering potential “improvements”.  Counting one’s blessings can make a lot of sense.

Here is a preview of one of Phoenix’s washers, shown in cross section.

The new washers will be 2  3/4″ inches long.  This will make Phoenix’s springs about 16 1/2 ” long, and with their 2 1/2″ diameter, they will be 6.6 times longer than they are wide.

And so, in a gesture of mathematically precise conservatism, Phoenix’s spring ratio will be exactly the same as her older sibling, because, well … why not?  That’s how pleased I am with the performance generated by Firefly’s spring ratio.  No changes needed for Phoenix in this area.

‘Nuff said.