Thanks for uploading the test data and videos on the servos.
I think the OSR2 should have a heatsink as it only has 2 motors to spread the load, modifications and heatslinks like this might be what’s required, also it has room to add one as they are horizontally mounted.
The SR6 has 2-3x motors with up/down load. Due to the mounting of the servos there is not much room to add heatsinks, however it can be done.
