AlignPosition to HumanoidRootPart, changing Attachment shakes Character, because of ReatcionForceEnabled, and I don't know why


I was told to report this as a Bug by @kleptonaut a few days ago.

While I already had it set before they suggested me to use AlignPosition and AlignOrientation. To create a collision box that remains upright and etc. which is what I did way before.

They then suggested me to disable ReactionForceEnabled, which does solve the shaking issue, but now the Collision Box no longer acts as a collision box, it does not block path anymore. And to report the shaking as a bug.

The issue is that when I change the Attachment from AlignPosition, the character shakes up and down really fast, before the position is set.

This happens with this in Workspace as well.


Reproduction Steps

Requires test game that I uploaded on the PM.

  1. Start the game.
  2. Manually adjust the center Attachment
  3. Observe how the character shakes for a brief moment, everytime the position is changed. If you observe it on the server’s end you can see that the box moves up and down slowly, and while it does move up and down, it drags the character’s assembly down too as if the AlignPosition would have a weight.

Expected Result

Eventually this may be intended, but since I was told to report this as a bug.

What I wanted to achieve was something that I can offset the collision box, so that one can make the character crouch, lay down, etc. and adjust the scale and offset of the collision box.

But since I can’t have that box touch the floor anyways, it’s pointless to even bother trying with it anyways. Once it touches the floor it influences the movement of the character anyways

Actual Result

When changing the center attachment or RootAttachment, the character shakes up and down. Make sure you actually don’t make the box collide with the floor.

Videos are attached

A private message is associated with this bug report

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(You didn’t actually include the videos)

Is the collision box Massless Property checked True? Any item welded or attached to a player that has mass will affect the player’s physics.

If the box is CanCollide true (I’m guessing that’s the case because you don’t want it touching the floor) then it’s probably interfering with the player’s CanCollide true Parts.
Why not use Collision Groups to keep the box from hitting the player and the floor?

I attached them in the Private Message.

Without mass the character is slippery. Don’t get me wrong, it’s a default R15 character. Not a custom one.

Setting everything to massless makes the shaking worser. RootPriority won’t help me here either.


The box needs CanCollide with true, but all the other collisions are disabled or moved in a different collision group.

The Humanoid C++ is dank. An internal ray is being shot from the HumanoidRootPart apparently.


If the box can’t be told to be the movement controller, then it’s pointless. The floor is determined by the Humanoid and HumanoidRootPart.

SINCE it shoots a ray, the HumanoidRootPart needs to be in the same collision group as the floor, or the player will fall. And HipHeight 0 makes the player fall at all times, but would remove the offset of the HumanoidRootPart. The HumanoidRootPart, simply can not be used for this. There’s to many things tied internally about it, that would break.

Don’t make the character’s Parts Massless, just anything you join to it (tools, Parts, your collision box, etc).

Why does shooting a ray from the Humanoid to any other Collision group make a difference? The ray can be set up to include or exclude any Parts you choose in the game. I’m pretty sure rays don’t care what Collision Groups items are in since rays don’t have a physical “collision” Property.

Rays can have a optional collision filter.

For some reason, if the HumanoidRootPart is not in the same collision group as the floor, the default character falls.

You should be able to set which collision groups collide with each other.
Is the floor in the default group and if so is the Humanoid’s collision group set to collide with it? It should have an X in the box that aligns between the vertical list of groups and the horizontal list of groups.

Dang! Just sent this one to the team. Thank you for the report!

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