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Zheng3 Penny Ballista

by zheng3, published

Zheng3 Penny Ballista by zheng3 May 22, 2012

Description

This nefarious device can easily launch a U.S. penny across a room when printed at 1:1 scale.

It's the first upgrade many Seej players seek when they need a little more oomph than the Zheng3 Penny Catapult can provide.

Seej is an open-source tabletop wargame based around 3D printing. Rules for Seej are at [http://s33j.net](http://www.s33j.net)

Do you need this in your arsenal? Yes. Yes you do.

Penny not included!

***
The Zheng3 Penny Catapult is available as a pay-what-you-like download at [The Bazaar](http://bazaar.zheng3.com). Stoke the fires of The Forge by supporting Open Source design!

Recent Comments

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Just printed this and I think you should make it so the penny carriage stays on track, other than that, it's pretty damn cool!
Thanks for sharing!
Thanks, those are excellent ideas. I'll take them into account for the next iteration.
This is a great idea, but few improvements will go a long way towards the easy construction and firing of this device. Please take these points as constructive criticism, since I admire your work and the fact you're sharing it with us.1. Enable the nock to go into the tunnel without leaving it. I don't have the proper technical names, so I'm sorry if it's unclear, but the fact that the nock can just leave the tunnel at any timepoint is really annoying, and also detracts from the accuracy.2. Create hooks or other similar add-ons on the nock, to tie the bands there. Tying them around the nock itself is particularly bothersome and prone to mishaps.I would do the alterations myself, but as I have no skill with 3D designing, all that's left for me to do is give advice to others :)Again, thank you for sharing your work!

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License

Zheng3 Penny Ballista by zheng3 is licensed under the Creative Commons - Attribution license.

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Instructions

zheng3.com/?p=361
Construction is really simple! Needlenose pliers are recommended, but not strictly necessary.
You'll need two elastic bands to complete this ballista. Tie a single band through the bore on one of the two D-shaped locking keys. Repeat the process with the other locking key.
Feed the end of one band through the rectangular bore on the ballista's left post. Insert the tenons of the locking key into the square mortises on the post to lock the band in place. You'll be tempted to repeat the process with the other side, but don't give in. It will save you precious minutes of frustration.
Unlike the Zheng3 Penny Catapult, these locking keys should be a snug fit. If some settling of the plastic during printing has made the mortises too small, trim the tenons a bit with your blade of choice.
Center the nock on the knot that connects the two rubber bands. Make sure that the penny's cradle is facing forward.
Feed the end of the band that's been locked down through the rectangular bore on the nock. Tie the free end of the band to the second band. Now feed the free end of the second band through the outside of the rectangular bore on the right post and loop it through the second locking key.
The nock has a wee nub on its underside. Slide this nub into the ballista's firing groove; it will improve accuracy.
Load a penny into the nock, pull it back, and fire away. Be safe!
Seej is a tabletop wargame based around 3D printing. Check out s33j.net for rules and more information.
Or just jump right in and download the Seej Starter Set: thingiverse.com/thing:24013
You can also search Thingiverse for Things with the seej tag.

Be sure to check Zheng3.com for updates. If twitter's more your thing than follow Zheng3 at twitter.com/Zheng3_Jim
Flagrant stagecraft alert: There's a piece of hookup wire holding the nock in firing position for dramatic flair.
Thing-O-Matic users may want to check out the Zheng3 Short Stock Penny Ballista, which will fit on a 120x120mm build platform: thingiverse.com/thing:23545/
EDIT 6/1/12: There's a new STL that fixes some flipped normals and weird N-gons on the locking keys. If you're having problems printing the previous version, try the clean model. ReplicatorG is pretty forgiving, but other slicing software may be less so. Good luck. We're all counting on you.
Just printed this and I think you should make it so the penny carriage stays on track, other than that, it's pretty damn cool!
Thanks for sharing!
This is a great idea, but few improvements will go a long way towards the easy construction and firing of this device. Please take these points as constructive criticism, since I admire your work and the fact you're sharing it with us.1. Enable the nock to go into the tunnel without leaving it. I don't have the proper technical names, so I'm sorry if it's unclear, but the fact that the nock can just leave the tunnel at any timepoint is really annoying, and also detracts from the accuracy.2. Create hooks or other similar add-ons on the nock, to tie the bands there. Tying them around the nock itself is particularly bothersome and prone to mishaps.I would do the alterations myself, but as I have no skill with 3D designing, all that's left for me to do is give advice to others :)Again, thank you for sharing your work!
Thanks, those are excellent ideas. I'll take them into account for the next iteration.
36Soon to be leaving thingiverse because of Makerbot's behavior towards open source.Details: fabbaloo.com/blog/2014/5/25/has-makerbot-crossed-the-line-for-some-yes
how far does this shoot?
Thanks for this ballista I just printed it. Tommorow I will get the rubber bands and we´ll see if it works
I printed the ballista and it looks great. The problem I am having now is that I cannot figure out how to attach the rubber bands. I have them both connected to the half-round pieces but I can't figure out how to connect the two rubber bands without offsetting the penny holder. It says to center the holder on the knot but that doesn't seem to work out. Am I really supposed to tie the two rubber bands together? Wouldn't some type of hook have worked?
Can you upload just the parts as files? When I printed, only the crossbow came out correctly.
Looks like you designed this for US elastic bands. NL bands are larger and almost impossible to fit in. FYI, NL bands are 8mm wide and 1mm thick. (might be the same for the whole of europe, don't know that)

It is possible to get these bands in, but I damaged the band during insertion. So I hope it will hold up during use.
Has anyone tried printing the pennies to shoot with this?
Had a problem printing, the carriage for the penny broke free from the pad. Can you post the file as individual pieces?
 I can't fit all of the pieces in the 140 mm by 140 mm area on my Up! Plus. Is it possible to get a zip of the separate pieces so I can print them out separately?
zheng3 - in reply to
You might want to take a look at the Short-Stock ballista. It's made for a 120x120 platform.

thingiverse.com/thing:23545

I think MeshLab or Netfabb basic (both free as in beer) should let you break up the STLs into their component parts until I can get around to making that zip for you.
 Many printings!

flickr.com/photos/albill/8270218295/in/photostream/

(Pardon my color balance being off.)
 Thanks. I saw the short stock just after this and am printing it now.
For this Seej game, are rubber-band powered, penny-tipped battering rams allowed?
Yes! See Core Rule #2 at s33j.net

As long as your opponent agrees to play against you with whatever strange device you bring to the table, it's legal.
When i was creating the gcode for this with slic3r, it came up with the error "This model has overlapping or self-intersecting facets" and "the input file was not marnifold near edge 122.000000-121.000000." When i printed it then it started printing from the layer above the front arch of the ballista. Any idea why this is happening? I printed the catapult the other day and its fun as hell, so i'm dying to get this one printed! Thanks!
EDIT! There's now a model that works with slic3r! There was some nonmanifold geometry around the bow that made slic3r choke but ReplicatorG let through.

I left the original version in place because if it ain't broke, don't fix it. Slic3r users should download zheng3_penny_ballista_slic3r.stl.
FYI both models have sections that are inside out (normals facing the wrong way) Also something weird about the D shaped keys.

You can fix them by sending them through cloud.netfabb.com
What are you using to make the models?
Thanks cyclone for bringing that to my attention. I've fixed the normals and tracked down the funky n-gons in the locking keys. It's now zheng3_penny_ballista_clean.stl

I left the older versions up for continuity.
I'll look into it. I've been using ReplicatorG to generate my gCode... maybe's it's a little less touchy than slic3r for this model.
Great thanks! i tried the shorter version of the ballista too and had the same issue.
I really wanted to print this but it is just barely too large to print without scaling on my 120mm x 120mm Thing-O-Matic heated build platform.
Here you go:

thingiverse.com/thing:23545/

Let us know how it turns out!
When I go to generate code it says it is still too big but I think it should actually print. I'll let you know how it comes out.
Thingiverse needs more office-weapons. :)
I'm workin' as fast as I can, cap'n!
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