Testing the Accuracy of ROBLOX Physics with Potato Cannons

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Potato Cannon ScreenshotROBLOX is built on a comprehensive physics engine, and our developers are constantly optimizing it so it can handle interactions between more physics objects and players, in an increasingly accurate and consistent way. We recently put our engine to the test with a new projectile-motion simulator – and most satisfying armament – the ROBLOX Potato Cannon. According to the results, which we describe in this article, we’re on the right trajectory.

The ROBLOX Potato Cannon mimics its real-world counterpart, a contraption traditionally constructed using a pipe and some means of generating air pressure. The difference is our potato cannon automatically performs the calculations you need to hit your target. We constructed the potato cannon so it computes the launch angle and, with the velocity at a constant 300 studs/second, the correct trajectory for your now-deadly potato. If your target is outside its range, it defaults to the maximum distance it can shoot.

Let’s look at how we calculate a potato’s trajectory for maximum distance and how the ROBLOX Potato Cannon stacks up against real-world physics.

Potato Cannons: ROBLOX Vs. Real World

In ROBLOX, one real-world meter is 20 studs. We can use that conversion to determine ROBLOX’s acceleration due to gravity. In the real world, acceleration due to gravity is 9.81 meters / second^2. When we multiply that number by 20 studs, we arrive at the acceleration due to gravity in ROBLOX: 196.2 studs / second^2.

With the muzzle velocity of our Potato Cannon at 300 studs/second, we can determine the Maximum Distance, Maximum Height and Time Traveled (twice the time it takes to reach the maximum height, assuming there is no air resistance) for the projectile.

Maximum Distance Equation

Maximum Height Equation

Time Traveled Equation

θ (Theta) is the launch angle of the projectile. The projectile will reach peak distance when θ = 45° – see the Wikipedia article on projectile motion for more information.

When we plug in our values for velocity (300 studs/second), launch angle (45°) and acceleration due to gravity (196.2 studs / second^2), we can compute the Maximum Distance, Maximum Height and Time Traveled as:

Maximum Distance Calculation

Maximum Height Calculation

Time Traveled Calculation

We can compare these calculations to the in-game performance of the ROBLOX Potato Cannon. Our results show that its trajectory is almost exactly what we calculated in the above formulas.

Potato Cannon Trajectory Test Output

You can see that the distance, height and time traveled, as simulated by ROBLOX’s physics engine, are very close to the real-world values. We suspect the marginal error in Maximum Distance is probably due to the “touch” events not polling fast enough and the discrepancy in Maximum Height is due to the Lua-side polling performed by the script.

Sure, the ROBLOX Potato Cannon is an intimidating piece of virtual gear you can tote around with your character. But it’s also a physics lesson in disguise — one that verifies the accuracy of ROBLOX’s engine.

147 thoughts on “Testing the Accuracy of ROBLOX Physics with Potato Cannons”

  2. yeah, potato cannon was good and now it doesn’t work right. I want a refund or a fix, which ever comes first.

  3. RIGHT TRAJECTORY? Well, then. Explain to me why you guys haven’t fixed hardly any bugs and not resolved exploiting. When you’re finished with that, you have a right to say “right trajectory” about anything in the ROBLOX physics engine.

  7. When i think about potatos it reminds me of when glados was a potato in portal 2

  8. Before yesterday, the potato cannon was OP, doing 294 damage instead of 49. Have you fixed this since? if not, plz do.

  9. lol we r small nice if roblox was motion controlled like connect, but if roblox ppl were in the real world, we would pwn lego. :3

  11. Finally an interesting blog post. Although that’s similar to my (dumb) friend’s physics homework… Only easier.

  12. I understand why we’re so small. We’re a “plastic building brick game.”

  13. ROBLOX has to take place in an alternate dimension or else the developers have to make all the games into little round planets.

  14. I wonder if someone in real life could make a potato cannon. Or a patato catapult, but they do have something in the old, country west places called: The spud gun so i guess its just the same

  19. Wait, If Robloxians are 25 inches tall, how tall is Lord TheReal (My LArgest RPG monster)?

    20 studs = One meter

    Lord Thereal = 15 studs

    robloxian = 25 cm

    Lord thereal = 75 cm

    O_O

  20. So tripping over everything is accurate physics? Not being able to stand up in a moving vehicle is accurate physics? >_> Rediculous.

    • Uh huh. You go ahead and develop a physics engine with complete accuracy and uses minimal computing power. -.-
      Point is, they’re trying to make it better, but they can’t be 100% accurate.

  21. I thought ROBLOXians wern’t even to scale of real life. Now I Know ROBLOX, thanks!

  22. I always thought we were tiny plastic people.

    As for the article, it’s interesting how real the physics are in a kid’s game.

  23. Lol. ROBLOXians in real life would be an endangered species (If we didn’t have respawn).

  25. So technically, if the ROBLOX Characters are 25cm, if it happened in real life, it would be larger than Lego sets.

  26. Great, your potato canon fires at the same speed a normal one does. Did you really need a blog post and a bunch of unnecessary formulas to do this?

    • Omg roblox really this means we are midgets or that your math is just bad..

      • The blog post shows the accuracy of the physics engine. There are still imaginative aspects to the game.

  28. The brickbattle slingshot also does these calculations, on a smaller scale.

  29. So, if 20 is one meter, then we travel at about .75 meters per second and are .25 meters tall Which would equal out to us being only 25 centimeters tall.

  30. So if 1 meter is 20 studs, does that mean ROBLOXias are only 1/4 mete tall? o.O

  32. Very cool doing those formulas, but what is this post about? Not a lot, I can test this stuff too. And the math isnt even that hard :/

  33. That makes since, because the trajectory of the potato goes about one meter.. And we’re so tiny. To me those codes look like things that they worked hard on. And the made it so at least some people, (Me) can understand it.

  34. You know, if you actually read the formula, the math is only about my Science Homework…

  36. This is very intresting but, i’m also waiting for 2 more updates to come known as: In-game wardrobe
    and the official Trade System

  38. ROBLOX, U NEED TO GIVE US MORE GAME TO REAL LIFE CONVERSIONS LIKE 20 STUDS = 1 METER. IT IS AWESOME TO CONNECT THOSE THINGS!!!

  39. You lost me at the first ‘The’ in the second paragraph… I dont do maths o_o

  40. So easy to understand, I don’t get why people don’t.

    20 studs = 1 meter?
    Character = 5 studs?
    5 studs = 25 cm?
    ._.

  41. if i put my foot on the computer screen all of the robloxians would die….a robloxian is only like an inch tall

  44. One real-world meter is 20 Roblox studs? So we be dwarfs? ROBLOX HAS PRANKED US!! WE’RE ALL LITTLE PEOPLE! RIOT!!!!!

  45. I think this is quite impressive yet will it be like minecraft when you shoot an arrow in the air above you will it land on you and kill you?

  47. Amazing, no wonder my experiments had missing information (I only looked at the lua side).

  48. i got all the gravity computations and how you multiplied it and got the numbers for that too, but no matter how much i get, its still confusing D:

  50. Amazing mathematics I understood the math more than the words a little =D

    • HOLY COW THIS HOLE TIME I HAVE BEEN CALCULATING ALL OF THIS WRONG! I didn’t know I had to find the square root of 2x (z)

    • yeah me too thats to much math to do and im in the morning so im too lazy and tierd to look at that

    • My normal footsteps are about half a meter each. I would’ve thought a meter in roblox is 2 studs xD

    • Impressive calculations, ROBLOX. Yet I am slighty worried about how 20 studs is a metre, O_o

    • Point=Robloxians are smaller than people, therfore to robloxians if they were as big as us, one stud would
      be a meter, therfore ROBLOX must equalize and caculate
      the exact number of studs to the same number meters
      in the real world. So lets say a real time rocket would fly
      400 M (mini Rocket) In Roblox that would be 200,000
      (two-hundred-thousand) STUDS. Roblox must break that down to 400 Studs to match the real world. To do that they must use this matimaticle stage, 200,000 divided by 400=Y, Y=5.0. By doing this Roblox has taken a step up in REAL TIME PHYSICS.

    • You sir, have a point. We’re only 5 studs tall, a fourth of a real world meter.

      We’re tinier than midgets.

  62. We did a potato cannon in physics class, that’s probably why they’re doing it here on ROBLOX

  64. All those complex computations for Three-Dimensional with 3D angles and trajectory… all for shooting a potato.

    Epic Win.

  65. Cool canon. Also, first comment. And I hope to be a soon-to-be image moderator for ROBLOX :D

  66. Hahah funny how their testing physics with a potato cannon but hey , its physics can’t argue with it