How do I disable hinges if they are under too much load?

I’m making a bridge builder game, and i need bridge joints to break if they are under too much load, like Poly Bridge

Bridge = workspace.Bridge
Hinge = Bridge.HingeConstraint

MaxStress = 100

	if Bridge.Stress.Value > MaxStress then
		Hinge.Enabled = false

Things that need to affect the hinges are;

  • Heavy objects
  • Gravity
  • Mass
  • Stress
  • etc

How do i go about creating this?

Iv’e tried using SpringConstraints to do this, as you can get the length of the spring, but the bridges have way to much flex and are extremely glitchy. And hinges make the bridge look much more natural.


To detect the total amount of force being applied downwards on Hinge, you can add up the forces of the various items that push downwards. In terms of parts, you can multiply their mass by their velocity downwards.

For example:

Part1 = HingeConstraint.Attachment0.Parent
Part2 = HingeConstraint.Attachment1.Parent

while true do
    Stress = 0
    TouchingPartsMass = 0
    TouchingPartsVelocity = 0
    Gravity = workspace.Gravity

    --collect the parts that are currently touching the HingeConstraint parts
    TouchingParts = Part1:GetTouchingParts()
    for _, item in pairs(Part2:GetTouchingParts()) do
        table.insert(TouchingParts, item)

    for number, item in pairs(TouchingParts) do
        if item:IsA("Part") or item:IsA("MeshPart") then
            TouchingPartsMass = TouchingPartsMass + item:GetMass() + Part1:GetMass() + Part2:GetMass() -- collect those parts mass plus the mass of the HingeConstraint objects
            TouchingPartsVelocity = TouchingPartsVelocity + item.Velocity.Y --collect those parts velocity downwards

            if TouchingPartsVelocity > 0 then
                TouchingPartsVelocity = 0

    Stress = Gravity * -1 + TouchingPartsMass * (-1 + TouchingPartsVelocity) --add these values together to get the stress
    if Stress > MaxStress then
       HingeConstraint.Enabled = false

This is just a concept, and you would have to tinker with how much each force affects the total Stress.

It is also not going to be completely accurate, since there are a few other factors involved, but it can give you an idea.
Hope the above helps!

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are these suppose to be negative values?

I was thinking in terms of force downward onto the hinge, so yes. Just invert Stress to get it in it’s positive form.

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So, iv’e done some experimenting with your system, and wow am I impressed. This is by far the best custom roblox physics engine iv’e ever seen! I mean this is just an example, and its good.

And like you said it does need a bit of tweaking, but this will work. Thanks!

And keep up the good work my man!

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This is by far the best one! but…

stress doesn’t change when there are linked bridges. Stress will only change when there’s weight on it.

Also supports don’t decrease stress.

How should i go about that?

I would add on to the preexisting script to look for other truss’s that are connected, until they hit an anchor point. The more you have, the more stress is added because of weight. For supports you can do the same, but decrease the Stress for all that are connecting

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