# Help to simulate step-by-step using simulator class

**URL:** <https://tech-community.robotics.abb.com/t/help-to-simulate-step-by-step-using-simulator-class/6715>\
**Category:** Developer Tools\
**Created:** [July 15, 2015, 8:49am UTC](https://tech-community.robotics.abb.com/t/help-to-simulate-step-by-step-using-simulator-class/6715 "2015-07-15T08:49:18Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![federico\_gentile](https://avatars.discourse-cdn.com/v4/letter/f/5f8ce5/32.png) [@federico\_gentile](https://tech-community.robotics.abb.com/u/federico_gentile)\
**Post date:** [July 15, 2015, 8:49am UTC](https://tech-community.robotics.abb.com/t/help-to-simulate-step-by-step-using-simulator-class/6715/1 "2015-07-15T08:49:18Z")

</div>

Good morning all,

I’m trying to simulate a RAPID program (simple path with two targets) using the Simulator methods Start/Step/Stop. While the Start method works nicely by starting the simulation of the whole program, Id’ like to perform a step by step simulation in order to perform some additional computation during a trajectory execution (i.e. collision check). I tried the Simulator.Step method; but once called it throws an Invalid Operation Exception with the additional info on the ‘Invalid Simulator State’. This means, I think, I miss some previous initialization of the simulator state machine or, at least, I have to tell the Simulator I’m going to use it in a step-by-step fashion through some property. Do someone could help me understanding which are the steps to successfully run a step-by-step simulation?