# Rotate BodyGyro in local CFrame

I’m working on creating a Mario Kart themed game, and I’m working on programming the hovercar, so you can drive around on sideways or upside-down grounds.

It’s working well enough, although I can’t get the car to turn on its local axis.

I’ve tried a few things, looked for similar posts on the DevForum, looked at CFrame and Vector3 on the Developer Hub, and even looked on a few other websites too. I’ve done all I can think of to do this, but I’ve never done anything specifically like this before so I have no examples to help me.

As said in the title, the car is set up with Body Movers. I have a single script called ‘Engine’ that runs the whole thing. In the car’s seat is a BodyGyro and BodyVelocity. My problem is with the BodyGyro, since it uses a global CFrame to function.

Image:

Code:

---- Body Mover Goals (section of setting physic variables)
local xv = velocity.Velocity.X
local yv = velocity.Velocity.Y
local zv = velocity.Velocity.Z
local xg = base.Orientation.X
local yg = base.Orientation.Y
local zg = base.Orientation.Z

``````local hoverTurn = function() -- This is the function for turning the car
yg = yg + turn -- This turns it on the global axis, when I want the local axis.
turn = turn*0.9
end

while wait() do
if not script.HoverWheels.Value then
--(Code for normal car)
else
-- Float
hoverFloat()
-- Accewhilellerate
hoverAccellerate()
-- Turn
hoverTurn() -- Here's the turn function
-- Gravity
hoverGravity()
-- Apply
velocity.Velocity = Vector3.new(xv, yv, zv)
end
``````
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I ran into a similar problem when making my hoverbike adapt to the ground’s surface normal. Check this out if you haven’t already!

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This looks like it would probably work, but since that post is solving a different problem, and providing examples for your code, could you help explain where what lines go and all? It’s getting very confusing dealing with 3 problems right now in this game.

It could also be that I’m newer to Roblox Lua than you are.

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Okay! So the code snippet given by sircfenner there lets you construct a CFrame given a forward vector (in this case the camera’s LookVector), an upwards pointing vector (the ground surface normal, which you can get from raycasts) and a right-pointing vector, which you just get by crossing the look and up vectors as shown there.

Here’s an example:

``````local camera = game.Workspace.CurrentCamera
local ray = Ray.new(cartChassis.Position,-cartChassis.CFrame.UpVector*32) -- Create a ray from the kart chassis that points downwards relative to the cart to check for ground. Shorter raycasts use less resources.
local hit,position,upVector,material = game.Workspace:FindPartOnRay(ray)
if upVector then -- Make sure there is a normal, and thus also ground.
local lookVector = camera.CFrame.LookVector
local rightVector = lookVector:Cross(upVector)
local gyroGoal = CFrame.new(
0, 0, 0
rightVector.x, upVector.x, -lookVector.x,
rightVector.y, upVector.y, -lookVector.y,
rightVector.z, upVector.z, -lookVector.z
) -- Credit to sircfenner for this!
cartChassis.Gyro.CFrame = gyroGoal
end
``````

Of course, you can substitute the camera’s LookVector for the mouse’s pointing vector instead. If you want a better explanation, just say the word.

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Just make a raycast under the seat or whatever your car base is and get the CFrame normal which will be the BodyGyro.CFrame. I think that should work.

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@Auhrii and @ADUPS, thanks for the help, but I must not have made the title specific enough. What I need help with is making the car turn (as if with a steering wheel) on the car’s local axis instead of the game’s.

The info you have already given me was good though, I used it and it is a lot better than what i had already!

Sadly, while using it I have encountered another problem other than the inability to turn the car. Now, when the car hits a wedge, it stops and does not turn to go up. I have tested in run mode with having the car above a wedge, then fall onto it, and it does change to the ground’s surface. So, at least we know it works and I typed it correctly.

So now I have to problems (which are pretty relative, if I figure out one I could probably do the other in a similar way) which I would like help with. More specifically, I need help with turning and moving the car on its local axis using a BodyGyro and BodyVelocity.

Here’s the updated hoverFloat function:

function hoverFloat()
``````local hoverFloat = function()
local ray = Ray.new(base.Position, -base.CFrame.UpVector*32)
local hit, position, upvector, material = workspace:FindPartOnRay(ray)
if upvector then
local lookvector = base.CFrame.LookVector
local rightvector = lookvector:Cross(upvector)
local gyroGoal = CFrame.new(
0, 0, 0,
rightvector.X, upvector.X, -lookvector.X,
rightvector.Y, upvector.Y, -lookvector.Y,
rightvector.Z, upvector.Z, -lookvector.Z
)
gyro.CFrame = gyroGoal
end
end
``````
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Ah, I see! There are functions you can use to convert a world space CFrame into an object space CFrame and vice-versa, as luck would have it! Check here, under Functions - specifically you’re probably after CFrame:ToObjectSpace and CFrame:ToWorldSpace (the latter to convert your object-aligned rotation to world CFrame for the BodyGyro):

https://developer.roblox.com/en-us/api-reference/datatype/CFrame

I’m a little pressed for time right now, but if you need anything further, don’t hesitate to ask!

3 Likes

Thanks! Those will probably work. I started trying to use them earlier, but I’m still finding problems I can hopefully solve on my own.

Thanks for verifying I’ve found the right thing.

1 Like