# Multi-Vehicle Simulation with JMAVSim

This topic explains how to simulate multiple UAV (multicopter) vehicles using JMAVSim and SITL. All vehicle instances are started at the same position in the simulation.

This is the easiest way to simulate multiple vehicles running PX4. It is suitable for testing multi-vehicle support in QGroundControl (or the MAVSDK, etc.). Multi-Vehicle Simulation with Gazebo should be used for swarm simulations with many vehicles, or for testing features like computer vision that are only supported by Gazebo.

JMAVSim multi-vehicle simulation works on PX4 v1.8.0 and later.

## How to Start Multiple Instances

To start multiple instances (on separate ports):

1. Build PX4
make px4_sitl_default

2. Run sitl_multiple_run.sh, specifying the number of instances to start (e.g. 2):
./Tools/sitl_multiple_run.sh 2

3. Start the first instance:
./Tools/jmavsim_run.sh -l

4. Start subsequent instances, specifying the simulation TCP port for the instance:
./Tools/jmavsim_run.sh -p 4561 -l

The port should be set to 4560+i for i in [0, N-1].

Ground stations such as QGroundControl connect to all instances using the normal UDP port 14550 (all traffic goes to the same port).

Developer APIs such as MAVSDK or MAVROS connect on the UDP port 14540 (first instance), UDP port 14541 (second instance), and so on.