What does the $ in the model definition xacro mean

[throwawayacco]

So in any of the model xacros, example f450.xacro all the intertia definitions are has a $ infront of them. The problem is that when using a precalculated value there is a huge difference between using the $ or not

So

Ixx = "0.1"
Iyy = "0.1"
Izz = "0.1"
and
Ixx = "$0.1"
Iyy = "$0.1"
Izz = "$0.1"
behave in completly different ways when simulated.

What does the $ sign mean and which definition is correct?

[throwawayacco]

I'm refering specifically to line 118,119 and 120.

An additional question, how has the inertia body radius and inertia body height in line 76&77 been determined/calculated?

[spurnvoj]

Hi, check the documentation for xacro http://wiki.ros.org/xacro ne 9. 5. 2021 v 3:56 odesílatel throwawayacco ***@***.***> napsal:

…

I'm refering specifically to line 118,119 and 120. An additional question, how has the inertia body radius and inertia body height in line 76&77 been determined/calculated? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#70 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AB34JKFYCOQ4DTQYNOJFVBTTMXTSZANCNFSM44OI24TA> .

[spurnvoj]

The Inertia of the body of the drone is simplified and it is represented using a cylinder.. how the inertia of the cylinder is computed is explained for example here https://scienceworld.wolfram.com/physics/MomentofInertiaCylinder.html. The parameters of the cylinder are specified in the same file (see https://github.com/ctu-mrs/mrs_simulation/blob/master/models/mrs_robots_description/urdf/f450.xacro#L76-L77)