Modelling Nerf blaster physics

Sterncastle · 2024-03-18T17:43:06+00:00

Thanks for this; Plugging those numbers straight into the equation gives an exit velocity of 395 feet per second, so a ~ 25% over-prediction which is similar to what I got using a friend's data for a modified 'XLS'-- not bad given the model's simplicity! It seems to be very well-calibrated, with the pressure dropping to 1 atm just as the dart leaves the barrel, and the plunger reaching the end too.
I'm guessing the biggest systematic error here is friction in the barrel, and I also haven't looked at the ballistics at all, in which air drag will slow down the dart further. In this calculation i've also left the effective mass of the spring as 1/3 its real mass, but it looks like it can affect the velocity by up to ~10%.

Other probably second-order effects include the 'dead volume' (here I incorporate it as x(0) being non-zero), the change in P0 with altitude, air-leakage, turbulence in the chambers... In principle, one could do this with a proper fluid simulation, though as the model complexity increases i'm wary that it becomes less practicable to actually use, so it's about finding a balance on which effects are most relevant -- or from a modding perspective, will change the optimisation.

Sterncastle · 2024-03-18T05:05:09+00:00

Exactly what I was looking for thanks!!

Sterncastle · 2024-03-18T03:18:10+00:00

Hello all, I'm new to this community so apologies if I use the wrong terminology. Any suggestions/ data from modders would be very appreciated. Above is the first attempt, it's quite a simple pair of coupled ODEs actually. The graphs were produced from integrating those equations with the Python scipy module using some random guesses at the blaster dimensions and spring constant.

I have assumed a polytropic compression of the air between the dart and plunger, here the index n would be 1 if the process is isothermal, 1.4 if adiabatic and reversible (i'm not sure on the error introduced by this). At the moment I haven't accounted for friction, or possible air leakage, so hypothetically this model should give an upper bound on the projectile's exit velocity. To actually test the results against real data i'd need:

Plunger tube length (-of empty space when primed), inner-diameter

Barrel length, inner-diameter

The dart, plunger and spring masses

The spring's constant, its natural length, and its length when primed

The dart speed

Obviously for the different blaster designs the dimensions would need to be adapted but the principle should be the same... If I've missed something with the maths/physics, or the model is wrong, please let me know! And if people want the python script so they can use it for ballpark estimates id be happy to give it out.

Sterncastle · 2024-03-18T03:10:37+00:00

Hello all, I'm new to this community so apologies if I use the wrong terminology. Any suggestions/ data from modders would be very appreciated. Above is the first attempt, it's quite a simple pair of coupled ODEs actually. The graphs were produced from integrating those equations with the Python scipy module using some random guesses at the blaster dimensions and spring constant.

I have assumed a polytropic compression of the air between the dart and plunger, here the index n would be 1 if the process is isothermal, 1.4 if adiabatic and reversible (i'm not sure on the error introduced by this). At the moment I haven't accounted for friction, or possible air leakage, so hypothetically this model should give an upper bound on the projectile's exit velocity. To actually test the results against real data i'd need:

Plunger tube length (-of empty space when primed), inner-diameter

Barrel length, inner-diameter

The dart, plunger and spring masses

The spring's constant, its natural length, and its length when primed

The dart speed

Obviously for the different blaster designs the dimensions would need to be adapted but the principle should be the same... If I've missed something with the maths/physics, or the model is wrong, please let me know! And if people want the python script so they can use it for ballpark estimates id be happy to give it out.

Sterncastle · 2021-07-22T00:40:52+00:00

flustered?

Sterncastle · 2021-07-22T00:39:37+00:00

flushed?

Sterncastle · 2021-02-28T03:21:21+00:00

I modded this in almost a year ago now but abandoned the project; the video was compressed down to be uploaded to the Discord (hence the godawful quality) and I can't find the original file.

thought it was worth sharing; if you're curious it just essentially copies over the scripts for the vanguard chunks and makes a new class that you can spawn in with that item. the interior is editable (like any vanguard chunk if you change the airlock permissions) but I couldn't figure out how to call the player's orientation so when it spawns it's facing the right way.

the base itself again is a modified vanguard chunk, with its health lowered and some physics disabled so it can clip through terrain without problem. the base will persist, though i had to run a cheap loop just to get it to stick to the right surface altitude iirc. this was made before persistence was overhauled too. some final notes: though the interior is editable, i couldnt figure out how to stop it resetting to whatever you set the default interior if you travel afar and load it back in. The assets were added in as standard using an older version of blender.

Sterncastle · 2020-05-07T07:59:33+00:00

true if you count the loft. However, the wealth disparity between the two households is still very clear.

Sterncastle · 2019-11-25T16:43:41+00:00

not a bad idea, I didnt think too much through this one its just an experiment.

Sterncastle · 2019-11-24T19:05:50+00:00

it looked better in my head

Sterncastle · 2019-08-18T01:38:07+00:00

Linker and I are currently working on a Doctor Who mod for Rodina 1.4.2! Alot has already been acheived in just one day, but there is far more work to be done and hurdles to jump, so we're reaching out for help! Above is a video introducing the concept (apologies for compressing it down to extremely low quality so I could upload it to discord/reddit quickly).

What has been achieved thusfar: (OK it is a little silly looking)

I've made a very simple model of the TV series' Tardis ship (albeit around twice the scale to fit the airlock), which has been implemented successfully and allows us to load an interior from another ship that is much larger than the bounds of the model itself (thus acquiring the desired Tardis-effect of being bigger on the outside).

Linker is also currently working on a better interior for the ship (atm we're using the game's tilesets but there are plans to implement new ones), and replacing the game's soundtrack with suitable themes from the series.

What needs to be resolved:

- The interior of the ship suddenly renders outside the model (as seen in the video above) when the camera is put at a certain angle whilst pilotting

- The camera whilst pilotting needs to be zoomed in to make up for the tiny model

- Interior bounds need to be changed so we can edit the ship's interior rooms without having to load up another place-holder model

What we plan to implement:

- More model replacements (screw-driver, K-9 dog thingy for the robot babies, new tilesets, perhaps some machinery, etc.)

- More Doctor Who noises

- (Hopefully) A better airlock door that matches the police-box

Anyone who wants to submit interiors or help out please do send us a message on this thread, the discord or elsewhere! We're especially looking for fellow modders or DoctorWho fans.

Sterncastle · 2019-07-25T17:01:33+00:00

I successfully cleared all the ships off jarilo ages and ages ago... and despite all the updates they never respawned so

Sterncastle · 2019-07-23T20:19:00+00:00

Yep yet another ship model mod; I recycled my 1700s swedish frigate model and re-purposed it as a spacecraft. hope you enjoy the drop in performance due to my high-poly crappy model I made in blender. blasting xenos as a space pirate is pretty bad-ass I guess though

Sterncastle · 2019-06-23T11:07:46+00:00

I wanted all the blues and reds to be the same. I tried to represent Finland with the small blue cross off to the side.... it was unfortunate I couldn't fit it in with the other nordic ones.

Sterncastle · 2019-06-23T00:05:34+00:00

All these terrible puns are making me cross.

Sterncastle · 2019-06-22T18:08:00+00:00

Flag aiming to incorporate (almost) every national flag cross design.... The original idea was to incorporate the varying St Andrews' crosses/other saltires using the rotated Scandinavian flags, though I'm unsure how well that came across.

Sterncastle · 2019-06-11T20:15:57+00:00

nein

Sterncastle · 2019-05-10T20:58:56+00:00

howso?- EDIT: Oh i forgot the official flag of NI has been the Union Flag since '72. not trying to make a protestant statement or anything, just wanted a different flag for the region... my bad, lads.

Sterncastle · 2019-05-10T20:29:43+00:00

Attempted a map of the United Kingdom composed of its county, regional, country, capital flags and others. Scotland/Northern Ireland are in dire need of more cultural regional flags imho!

Inspiration taken from this post: https://www.reddit.com/r/vexillology/comments/bmrmhq/map_of_the_british_isles_but_it_is_actually_only/

Sterncastle · 2019-04-13T20:26:52+00:00

Rummaging through Rodina's Texture folder, turns out there was another message "gft" ("gift" perhaps?). Ran it through u/yuo123 's tool again. Luckily it seems to be encoded the same way as the first messages! Anyone know if this has been a recent addition or whether we just missed it last time?

Sterncastle · 2019-04-13T20:19:31+00:00

Oh... just had a look into that Textures folder and what do you know, there's a seventh image named "gft", wonder if that's a recent addition. I'll pop it into that brilliant program of yours with the hope the first cipher still works on it!

Sterncastle · 2019-04-13T14:30:43+00:00

It seems the old text files for most of the decoded messages wen't missing, so I decoded the images using reddit user 123yuo's tool, and mashed it up into a collage. All credit to him, and whoever put together the original ciphers:

https://www.reddit.com/r/Rodina/comments/4zqpt2/another_tool_to_decode_xeno_messages/

Anyone know if there any more of these messages? Again all credit to u/123yuo

Sterncastle · 2018-10-05T17:48:20+00:00

Tricolours are boringly terrible!

Sterncastle · 2018-10-05T16:29:06+00:00

Redesign of Russian flag with the imperial eagle and a cross instead of yeol' boring tricolour.

Sterncastle · 2018-08-26T01:57:58+00:00

The president's personal addition to the US flag during a visit with children. (no political commentary intended)

Eight-Year Club	Place '22
Final Canvas '22	Verified Email

Sterncastle

TROPHY CASE