Add gear_ratio parameter

[Tacha-S]

I added the gear_ratio parameter to enable combining gears.
Since the default value is set to 1.0, there will be no changes to the existing behavior.

• fix Enabling gear ratio functionality #94

[Tacha-S]

@ijnek @youtalk or other maintainer, could you review it (and #96 , #98 )?
Or is this repository already out of maintenance and no longer maintained by anyone?

[ijnek]

Sorry for the delay @Tacha-S. I try to keep this repo maintained, but I appreciate the @mention, because it can get lost sometimes.
Could I ask, is it necessary to handle this in the hardware interface? What is the advantage of putting the gear ratio in the hardware interface, compared to using a URDF transmission tag?

[Tacha-S]

@ijnek Thank you for the review.
It is true that mechanicalReduction is defined in the transmission tag of URDF.
However, as far as I know, there has not been a way to send commands while considering these definitions, which is why I had prepared parameters separately.
Upon investigation, I found that in ROS 2, there is an approach to reflect transmission into the hardware interface, as demonstrated in the following example:
https://github.com/ros-controls/ros2_control_demos/tree/master/example_8
While this is not directly implementing the transmission definition itself, it seems to introduce it in a way that aligns with the intent of the definition to some extent.

What do you think about making the dynamixel_hardware capable of handling mechanicalReduction, similar to the method in this example?