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Spinning Algorithm: How do I do it?

Asked by

Minifig77 190

9 years ago

I'm trying to make a function that will spin a brick 360 degrees in a given amount of time. Or, an explanation in code:

function SpinBrick(Time)
    --Spin the brick 360 degrees in *Time* seconds.
end

I tried making a function that calculated how much the brick needed to spin per second by dividing the circumference of its spin by Time, but I ran into another problem: How many times do I need to iterate the spin distance to reach 360 degrees? In the end, I couldn't figure it out.

How do I make a function that spins a brick 360 degrees in a given amount of time?

2 answers

Answered by

BlueTaslem 18071

9 years ago

Instead of trying to wait a particular amount of time for each iteration, we can just wait as quickly/often/short as possible and figure out, based on the current time, how far along we should be.

E.g., if we're 8.2 seconds through a 10 second duration, we should be at 82% a full revolution.

Equivalently, if before we were at 8.2 seconds of 10, and we got to 8.3 seconds of 10, then we moved forward 1% in time; so we should rotate 1% of a full revolution.


-- for some `brick` a Part
-- for `duration` in seconds

function spin(duration)
    local time = 0
    local totalAngle = math.pi * 2 -- One full rotation

    local startCFrame = brick.CFrame
    -- Where the brick started
    -- (See after loop)

    while time < duration do
        local deltaTime = wait();

        local deltaPercent = deltaTime / duration

        local deltaAngle = totalAngle * deltaPercent
        -- "Unit conversion"

        brick.CFrame = brick.CFrame * CFrame.Angles(0, deltaAngle, 0)

        time = time + deltaTime
        -- Keep track of how much time is left
    end
    brick.CFrame = startCFrame
    -- Since we aren't exactly on
    -- in iteration count, we want to make sure it didn't get
    -- really slightly off.
end

Answered by

cjcool12345 58

9 years ago

Unfortunately, there is no actual way to get an exact time and Roblox does not offer any method of waiting a specific set of milliseconds (meaning that you can not get an exact time).

Your best option would be to use a for loop that rotates the brick a small amount and waits a fixed amount depending on your iterations (360) and the time you want to achieve (like you said, but in reverse, you divide the time by the circumference).

function SpinBrick(Time)
    local waitTime = Time / 360
    for i = 1, 360 do
        Brick.CFrame = Brick.CFrame * CFrame.Angles(0, math.rad(1), 0)
        wait(waitTime)
    end
end

If you need to get a closer accuracy, you will need to lower the amount of interactions by increasing the for loops increment (for i = 1, 360, 10) and by lowering the circumference in the division of the waitTime (Time / 36 due to 360 / 10 = 36).

Be careful; this implicitly requires that `Time` be at least 12 seconds (because `wait` can't wait quickly enough). BlueTaslem 18071 — 9y

Is there a way to make it spin faster? For my needs, the spinner has to accelerate. Minifig77 190 — 9y

You could either set the radians increment to a higher value every interation within the loop using a variable, or by decreasing the time every interation. How you go about this really depends on the effect you want to achieve. It may be worth looking into interpolation algorithms for this purpose. cjcool12345 58 — 9y

Spinning Algorithm: How do I do it?

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