# How to calculate velocity for a tracked robot

Hi to all,

I've built my own skid-steering tracked robot and I wrote a simple ROS node which allows me to control it by using my keyboard. Since I'm using encoders for both motors, I would like to be able to calculate the tracks velocity and displacement so I can publish these values as ROS topics.

The problem is that I'm not able to find the correct formula to use, can you help me please?

The total tracks length is 275 cm. After a full driving wheel rotation, the rubber tracks displacement is 125 cm. The tracks rubber footprint is 85 cm. Encoder pulses for a full driving wheel rotations are 200.000. Max output driving wheel RPMs are 51, but I think this is not relevant.

What kind of formula do I have to use if I want to calculate velocity and displacement for each track?

I know I should use the classical formula V = S / T and S = V x T but I can't understand how to use these relations for my robot since it uses tracks instead of wheels. Is it possible to calculate the overall angular velocity for the robot?

I hope you can help me..