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How to make bottom of part constantly face point?

Asked by
thebayou 441 Moderation Voter
5 years ago
Edited 5 years ago

I'm trying to make a parachute, and in order for it to be realistic I want the bottom of the chute to constantly face a point no matter the position of the chute itself.

I know that CFrames can be initialized with a lookVector so the CFrame faces a certain position, but the problem is I don't want the front of the parachute to face the point, but rather the bottom of it.

I've tried multiplying the lookVector by a bunch of Vector3s but I wasn't really sure what I was doing and it didn't help at all. I've also tried doing cross products to get a perpendicular vector, but I don't know what to multiply. (point.Position - chute.Position).Unit and what?

EDIT: Ok, people want code. It's not going to help, but here you go:

local runService = game:GetService("RunService")

local parachute = script.Parent
local base = parachute:WaitForChild("Base").Value
local dragBF = base:WaitForChild("Drag")

local resistanceCoefficient = 10
local parachuteDistance = 10

runService.Heartbeat:Connect(function(step)

    -- Compute the parachute's drag force
    local drag = -base.Velocity * resistanceCoefficient 

    -- Compute position and direction of parachute
    local chutePos = base.Position + base.Velocity.Unit * parachuteDistance
    local chuteLV = ????

    parachute.CFrame = CFrame.new(chutePos, chuteLV)

    dragBF.Force = drag
end)

I don't know what to do for chuteLV

0
post script please. we can't help without it. maybe you're doing something wrong User#19524 175 — 5y
0
It's less that I'm doing something wrong and more that I have no idea what to do thebayou 441 — 5y
0
Chute is a meshpart (the parachute) and I want it to constantly face the parachute's payload, which is the point that I'm trying to face thebayou 441 — 5y
0
ChuteLV has to be perpendicular to the Velocity vector thebayou 441 — 5y
View all comments (3 more)
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Actually if I were to cross product would the second vector even matter since there's more than 1 solution thebayou 441 — 5y
0
Or am I doing this completely wrong and I shouldn't even use a look vector? thebayou 441 — 5y
0
Try using CFrame:inverse() LostPast 253 — 5y

1 answer

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Answered by
thebayou 441 Moderation Voter
5 years ago
Edited 5 years ago

OMGOMGOMG I FOUND A SOLUTION FINALLY

Ok this is dead, but in case anyone else encounters this problem, what you have to do is basically construct a CFrame from scratch, using the Rotation matrix to correctly orient the part.

I was actually pretty close to start with, I just didn't realize that what you cross product-ed the Vector3s with didn't matter.

Basically, if you want the upVector to point AWAY from a spot, you set the upVector of the CFrame to be the (beingAligned.Position - beingAlignedTo.Position).Unit.

Then, you cross product that upVector with basically any other unit vector at all, as long as the two are unique. That would yield another perpendicular vector (the thing I was missing). You can use this one as either the frontVector or the rightVector - it doesn't really matter.

For the final, missing vector just cross the first two.

Use the last CFrame.new constructor ... and VIOLA! Problem solved.

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