Rules for player inventions

Question

To illustrate what I mean, let me give a quick example:

In the-dark-eye, there is a Staff Ritual named Hammer des Magus (No idea what the term is in english). Its effect is that everything non-organic you touch with the tip of your mage staff will be thrown back with a pretty nasty force (the force depends on the stats, but at some point, we knocked over old trees with it, so you get the idea).

One of my players joked that he should get a metal tube, fill it with stones from one end and push the staff in from the other, building a primitive shotgun.

Now, luckily, he did not try to sneak that past me (the current GM), but if he would try, I have no idea if I should allow it.

The questions in this case (and in most similar cases as well) is:

• Is it plausible that a character in a medieval setting, knowing nothing about modern-day science, will start building something like that?
• If yes: Would you include any skill checks for it? There are some things that might fit in TDE, but they are usually so unbearably useless that no-one ever skills them (Which might be a good reason to ask for skillchecks on them)
• Again, if you allow it: How do you balance it against existing game items / mechanics?

This is supposed to be a general question, not specifically about this scenario.

I'm interested in your opinions.

Answer 1

Since you asked for a general answer, and not one specific to your example, I'll put in my two cents:
^{(You didn't tag a system, and I don't know what "TDE" is, so I answered this medieval D&D-style.)}

The Invention Process

Human ingenuity is unbounded, especially when it comes to new ways to kill people. The problem is that we as residents of the twenty-first century have a much greater knowledge of physics and math than most people in the medieval world. People knew how battering rams and slings, but not about Newton's Law that explained them. Archers could predict the trajectory of an arrow, but nobody could do the math to explain it. If a player can relate their idea to a well-known item in their current setting, let them do it. If what they're trying to replicate hasn't been invented yet, still let them do it, but have it require maybe a DC 15 Int check and/or 1d4 months of research. (In your example, it's pretty easy to look at a sling and think "stones moving fast hurt." It's harder to come up with the idea of directing the stones via a pipe - that might take a check or some trial-and-error "research".)

Using the Invention

Generally, MacGyver-ing weapons wouldn't require any sort of skill check, but the resulting weapon will almost always be improvised or exotic and take a penalty to its use. Maybe let the character gain proficiency with it, but only after a long time training. The exception is siege engines, which already have a Profession skill associated with it. Otherwise, require Craft checks—either as generic Int checks or in some specific associate skill—to successfully operate. I wouldn't create a whole new skill just for a player-devised invention. If anything, create a new Craft or Profession subskill.

Balancing Player Inventions

Balancing player inventions is even harder and more subjective. Note, though, that unbalanced things tend to tip over. If your 1st level PC figures out how to make a shotgun that destroys everything you throw at it, blow it up in his face. Don't be malicious about it, but make it clear that the character simply isn't skilled enough to use the powerful item reliably. Maybe in a few levels, if the character has invested a little more time into it, a better system can be developed. "But for now," say, "you can tell this particular invention has a high chance of failing catastrophically." In your example, maybe require a Dex check not to touch the staff to the pipe itself, which would throw the pipe and probably injure the character's arm (Dex or Str damage.)

Another good way to balance player inventions is to simply make them impractical. If the player isn't putting a lot of thought into actually developing something new, but simply says "wouldn't this be cool?", it's probably impractical already. In your example, it would probably be a full-round action to load the stones into the pipe, and another standard action to insert the staff into the pipe, firing it off. Let them do it, but they'll quickly learn that the combination of terrible rate of fire, poor range, and unreliability simply isn't worth it.

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If, however, the player's putting a lot of thought into it, and their character actually invests time and money into it's development, totally let them do it! Maybe delay their research til it's a little more level-appropriate, but let them know it's feasible, just not right now. Balancing this is a little harder, and basically comes down to rewarding role-play. One trick I found is to make sure that the invention benefits the party, and not the character. If the entire party becomes slightly unbalanced, you can just up the encounters a little bit, and everyone has fun. If it's a character that's unbalanced, they take center stage and everyone else feels left out.

Once, I convinced my GM to let my high-level Gnome Wizard invent a telepathic network by creating a massive intelligent item which could scry and cast telepathic bond. (Basically Skynet.) I got government funding for it and developed it in my and my character's spare time, (our campaign had several skips of multiple years between sessions,) and they used it to communicate with their army's general and special task forces (including our party.) The GM balanced it by saying that my character couldn't become rich off of it—all profit was reinvested in what became a medieval CIA—and that it benefited the whole party. Plus it made a great plot point when Skynet decided it knew better than the government...

Answer 2

Answer 1: Probably, especially if your game is more of a late middle ages game. The middle ages lasted until the 15th century, and Europe had primitive guns in the 14th (and china had the idea in the 8th). I think it's very plausible that someone might think of the idea of using a tube to focus some shot.

Answer 2: I don't know TDE, but personally I would use whatever combat skill made the most sense.

Answer 3: Honestly, I feel like this particular firearm would be really, really bad. Think of how awkward it would be to shove a long stick into a shorter tube. Also, since he wouldn't have any of the technologies that made guns much better in later years, like rifling, the effective range of the gun would be very short. In addition, it's firing rocks instead of proper shot, which means what little accuracy he would have goes out the window. If I were running this in D&D 3.5, I'd give it ~1d10 damage in a 15 foot cone in front of the player. If you don't know the system, that's enough to probably kill a normal person, and enough to slightly injure a player character.

Answer 3

1. Depends on the specific medieval period you're trying to model. Late medieval periods did have black-powder firearms. Projectile weapons were known (crossbows) to well-known (bows, assorted siege machinery), so the idea of launching small rocks from a tube using magical force doesn't strike me as being horribly out of reach. Would you react similarly to a PC wanting to launch large rocks, using the same spell?

2. Yes, I'd require a new skill ("aim gravel-tube" or whatever the name turns out to be) starting from "abysmal", skill-level growing as a medium-difficulty skill (IF there's the concept of various skill difficulties) to centre the effect-cone on a certain point.

3. As far as balance goes, there are a few things you can do. It's using already-existing "throw things using a mage's staff" mechanics, that probably drains spell-slots or spell-power of some sort and that doesn't go away. Damage-wise, let it be the same as rocks/gravel of the same size dropped from 30-odd metres, minus one metre of fall height for each metre of vertical distance between the tube and the target (I am blithely assuming that your system already has rules for falling rocks, it may well work to just substitute plain falling damage here). The specific height may need a bit of tweaking, I picked a number that gave some range, while still being effectively-lethal at point blank.

Answer 4

I would invoke the 'Rule of Cool'. Is it's cool and awesome to turn a magic staff into a Shotgun? If the answer from your players is yes, then go for it!

Now, if you are playing a game with a high level of combat balance, rule that the 'shotgun' tube does not have the proper barelling to work perfectly as a gun, and then treat it as a shorter ranged but higher powered bow appropriate to your group's level. You could also bump up the damage by a step and rule that it takes an extra round to reload. This should leave the awesome, without screwing up combat balance.

Answer 5

by Malexmave Is it plausible that a character in a medieval setting, knowing nothing about modern-day science, will start building something like that?

YES And with Mages WHO DO NOT! live in Dirt Hovels and soldiers who posses even Bronse metal swords? YES. Concept from existing Tech's:

Any witnessed of a Bow or Crossbow or Ballista, or tapestry of a siege catapult used/seen before the characters. Any applied Use of "Hammer des Magus" into water at any Floating valid target (splash) rocks from lake/rive bed go up in your face. Any Use of Any armor type to Shield any party member from arrows or thrown rocks or "shrapnel" from Hammer des Magus.

THE First Test: touching an arrow that did not fire strait. The Desire NOT to Touch the Cross-Bow with TIP.!! The Desire to think "hay this could push 5+ arrows as easy if we could kept them on track". The Use of a Hallowed out U or V -ed Plank/Log. UP-Scailed to needing a chok-block to Arch it. Now, A Clay-JAR filled with Rocks.

Second TEST: "A round Metal Base Under A Clay Jar" Filled. The minimal Int Score to use a shield and fear that mages stick. The Desire to Use a Longer Tin sides on that Metal Base-plate & thin-Jar. Next: The Thought, Hey! IF Two Half U Tubes WERE tied together, We Could move this around Loaded. Then, Hay a Tin-metal tube is Lighter then Wood.

AMMO: Tin side-curved Bottom plate on ANY jar. Any Clay or Glass Pot/Jar/Vessel With a Seal-able top. Loading: Rocks Go in Jar, Arrows/Quarrels held tight in flax put in a book/Magic Scroll length Jar.

I've taken all this at a TL3-4 Tech level point of view, about Early Middle Roman/empire of era simple tech (if even that much adv.), using only Market grade and (semi-cheap) palatial house building products, for even the Ammo!..

Shoping list: Stick tech, One " Hammer of the Magi, aka 'de Force'Spitter" Stat powered, per Bearer & user of arcana Magica ect. 1 hammered tin-metal tube, Mildly expensive, indoor fountain pipe w/ Very thin copper poured on tubes "wield" spot, Variable size's SEE: Ammo. If you have a Even a Tin metal Sword the tech exists for the tube making -- with out magic effort assistance. Sand open air molds, A Hammer And Rock to bend it onto rounded shape, a smaller rock for the tighter shape smaller is desired.

by Malexmave If yes: Would you include any skill checks for it? There are some things that might fit in TDE, but they are usually so unbearably useless that no-one ever skills them (Which might be a good reason to ask for skillchecks on them)

Aiming? Arch Angle trajectory Only for extra MAX range (mild experimental). Not needed at under 40 feet, Aiming Skill is more based on Trusting the Mage (fear check) As he touches the staff to the JAR. (IF STAFF TIP TOUCHES THE TUBE, PEOPLE GET HURT!) Tube on your shoulder. Now Armor Penetration is based on Shape, Arrows and spear tips are known...

by Malexmave Again, if you allow it: How do you balance it against existing game items / mechanics?

*WHAT is this NEW ITEM HE Proposed? A ROCKET LAUNCHER Zero Recoil, Zero internal "tube" Pressure from (gun powder) gasses. No need for Rifling Tech on a single or multi Shrapnel/Quarrel/Spear Rocket/missile. Encumbrance Based on Diameter and thickness choices of Loaded Wood/Metal Type Mass.

Dangers of Use? Well.. Depends on the PHYSICAL Weight of mass Being displaced (ammo) By the Confident User of Said staff-tip, Hour to Hour Consistency of his Magic Stats (or magic power input into Staff-tip force) And a Steady Hand.. & the Longer from Tube rear Ammo sticks out, the safer for all. ADD a small Wood notched pegged lever in the tube to hold ammo from backside on the Jar, most Basic of lever concepts.

Damage: Is by number of shots per load, TYPE OF AMMO/Ammo Mix, ODDS of STRAIT FIRING ARROWS/Spears IS Kinda HIGH for upto 1-5 items, as it could Start to spread a bit More depending on how wide the barrel/tube is bigger then the loading end. Player: "OF Course, 2 Different tubes Types is better then 1." Pretty much Make a Missiles Hit Spread Table per Target (Battle Tech style), likely the first 20-30 feet is strait and after that, spread. Unless they go Wide-Bore Cannon right off the bat. Then the D&D Cone-Shaped spell structure works on both Hexagonal and Square maps. Force to mass, Distance per mass.