MH12: Joint Limits in Datasheet vs XACRO/URDF

[dipendras]

in MH12 robot, the joint limits of U axis is different in datasheet compared to the one in xacro/urdf file.
In datasheet, the U-joint limit is -175/240 degrees. However in xacro file the limit is -85/150 degrees. Even-though the limits in xacro seems more correct than the one available in datasheet, is there an explanation for this difference?

[EricMarcil]

Yes, the -175/240 is the position that the U-axis can take relative to the ground, which is in reality the combination of the L-axis and U-axis. Where as the -85/150 degrees angle is relative to the previous joint. There are only a few datasheets that were publish that way. The practice has been dropped since.

[dipendras]

If we want to find the correct joint limits for U-axis then, we have to subtract 90 degrees from the maximum joint limits and add 90 degrees to the minimum joint limits taken from the datasheets.

For example, correct joint limits for U-axis of MH12 robot are:
Min: -175 (from datasheet) + 90 = -85
Max: 240 (from datasheet) - 90 = 150

Is it correct? Can we apply the same for other robots for which the joint limits are available in the similar way? @EricMarcil

[EricMarcil]

No, the -175 to 240 is more complicated because there are also some special mechanical interference between the L and U axis to account for.

If you want the range, you have to look at the range soft-limit for each axis. This is what was use to determine the URDF range. If a user adjust the soft-limit for his application, then he should also update the URDF range to reflect that change.