Ballista for the Renaissance Fair

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Had a chance to talk with Davis during the Comic Con about the rules for the seige weapon face off for the Renaissance Fair next month.

Rules are fairly straight forward for this build:

  1. Period correct look is preferred (but not required)
  2. Firing range to be approximately 100ft and projectiles should not cause harm to spectators beyond that range
  3. Ammo to be wet 2in polyfill balls
  4. Optional ammo of a rubber chicken may be used for bonus points
  5. Targets will be 5 human sized paper targets
  6. There must be a method to lock the ammo in a ready to fire position
  7. No part of the human body can be in or near the machine while firing
  8. Bonus points for having fun or having the loudest crowd

To be frank, figuring out how to build and test this thing in a month has had me a bit anxious, but after seeing someone else’s build, it seems less intimidating, but it definitely looks like something that we will need practice aiming.

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We would have to get jumping on it next week pretty hard n heavy. Since we’re going to have to fire non-traditional ammunition we might want to look into the molotov launchers people have made and try to incorporate it in.

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I have ten 11.8in rubber chickens on the way. I’ll bring them to the space on Monday.

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Can we PLEASE do Screaming Goat Ammunition?!?

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Should have watched the video first before sending it to the event organizers…

Their response:

LOL! Ammo that screams! I love it! And it’s AN ABSOLUTE NO WAY. Hard surfaces on the ammo is a no-no - if we were shooting out in a field with no-one around, I’d be all for it.

So for testing and promotional videos sure.

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We could probably make screaming ammo thats soft. Some of the screaming chicken squeekers on a stabilized ball should make i pleasant screaming to target.

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Actually I’m glad this came up because I was thinking of making them little ping pong ball helmets…

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… could someone 3d print some hamsters for the ping-pong helmets… and maybe a rocket sled for the hamsters…

For science.

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If Screaming Goat Ammunition was shot in a field and no one was around, does it even make a sound?

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okay…

so we will need to pass a safety inspection on the March 26th to make sure the event organizers feel safe with our machine being on site, and also to do some promotional shots (pun intended)…

Who would be free Friday afternoon (3/18) to start making parts for this beast? I’ll hopefully be posting dimension’ed plans in the next couple of days.

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You could test it at the open house

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Call it an unveiling and ask the ten fest coordinator to come in period dress it’s good pr for both of us

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I can chip in on Friday after 7p*, but I’m free all day this Saturday if we got a workable plan.

(*contingent on DnD group)

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As a goat that screams all. the. damn. time., Ivy does not approve.

ivy
ivy1900Ă—2248 1.07 MB

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I left the package of rubber chickens with Judith the robotic arm in the electronics lab.

Now get ta chickenflingin’

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I’ll head over after work on Friday! Hopefully see ya around 6

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Do we have a general blueprint we’re going off of or is the plan:

  1. Meet
  2. Get material
  3. ???
  4. Profit
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I’m working on the blueprint and dropping some long forgotten magical math equations to size the ballista into something intimidating, while minimizing the chances for exploding or somehow catching on fire.

The majority of the making will probably happen in the woodshop.

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  1. Flinging chickens

That would be a good name for a punk band.

opening for magnetic flux… its FLINGING CHICKENS!!!

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found a site that showed the basics behind coming up with dimensions for the ballista…

I’m trying to figure out a good value for the spring constant k that will ensure that we hit the distance with the least amount of force possible…

I’m using metric units to rough out the design, but I think we will be able to build this without putting a ridiculous amount of potential energy into the machine… maybe somewhere around 75 ft lbs (about 100 Nm) to hit our target based on the following:

width of the bow is approx 1.5m (a little under 5ft wide)
mass of the 3in polyfill ball is approx 100g (about 3 oz or the mass of an apple)
acceleration due to gravity is approx 9.81 m/s2
launch height of ball is 1m (a little over 3ft)
distance to target is 36.5m (120ft)

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