# How to get odometry from propeller rotation signals knowing that they can rotate to maximum value?

m trying to get Velocity in order to control underwater swarm ROV. I can use the acceleration and to Euler integration but the error will be accumulated over time. As we are having a swarm (many small robots) Im limited with sensors on board. So in order to get more accurate Velocity estimation was thinking of sensor Fusing of IMU and odometry. As don't have any odometry sensors came to some out of the box solution

So as I have access to the motor (thruster- propeller) signals and the robot can move to maximum and constant speed. Means the rotation of the propeller have a maximum limit and when they reach that limit they can maintain that maximum. So was thinking of some mathematical model that can be used to provide me with odometry and than use some of the ROS packages for sensor fission(robot_lokalization orh ector_pose_estimation) to get accurate Velocity.

The propeller revolution curve looks like something like this

So I need a help in that mathematical model how to get odometry from the motors-thrusters. Any help with that and possible ROS node (C++) implementation?

• I don't understand what you're asking - are you trying to count propeller revolutions to get a distance, or are you trying to use propeller speed to get robot speed?
– Chuck
Oct 13, 2021 at 18:39
• yes the propeller revolutions to get distance, so the propeller serves like encoders so can get odometry topic. It require some mathematical modeling for that
– bob
Oct 13, 2021 at 19:17
• I edit how the propeller revolution curve looks like with a tau inclination.
– bob
Oct 13, 2021 at 19:46
• What are the axes on the plot? I don't understand what I'm looking at. There are two curves - what are they?
– Chuck
Oct 13, 2021 at 20:57
• You've got a simulator, so you have perfect knowledge of the vehicle and what it's doing - you should do some testing here to characterize the relationship. Vehicle speed, prop speed, vehicle position, prop rotations, etc. Do it for a variety of speeds and see what looks good. That said, all of this will largely be a waste of time if your simulator doesn't accurately reflect the motion characteristics of your actual vehicle.
– Chuck
Oct 14, 2021 at 12:22