# Restricting "active" joints in RigidBodyDynamics.jl

**URL:** https://discourse.julialang.org/t/restricting-active-joints-in-rigidbodydynamics-jl/70829
**Category:** Modelling & Simulations
**Tags:** question
**Created:** [November 2, 2021, 10:19pm UTC](https://discourse.julialang.org/t/restricting-active-joints-in-rigidbodydynamics-jl/70829 "2021-11-02T22:19:15Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![benjamin-macadam](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/benjamin-macadam/32/29024_2.png) [@benjamin-macadam](https://discourse.julialang.org/u/benjamin-macadam)
#### Post date: [November 2, 2021, 10:19pm UTC](https://discourse.julialang.org/t/restricting-active-joints-in-rigidbodydynamics-jl/70829/1 "2021-11-02T22:19:15Z")

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Hi there,

I have been using RigidBodyDynamics.jl to do some simulations with robotics for about a month or so. I’m finding performance for some of my simulations really suffers when I use the full collection of joints in the robot, while everything works quite well when I use an URDF that has most joints set to fixed. It seems like it should be possible to “switch off” joints from my state so they will be treated as a fixed joint (and also to create linear/affine relationships between pairs of states, in the case of a mimic joint).

Does anyone know if this is supported by the library (or if it would take less than a couple of days to implement)?