If the vertical shoulder holds position for a short time and then gradually sags, this usually indicates a load, mechanical, or protection-related issue rather than a software error.

In most cases, this behavior is caused by one of the following:

1. Mechanical resistance or friction

• Over-tightened screws
• Misaligned joints
• Missing or worn bearings
• Poor print tolerances causing binding under load

2. Excessive load on the shoulder joint

• The shoulder is operating near or above its torque limit
• Even if it initially holds position, sustained load can cause gradual failure

3. Thermal or internal servo protection

• Some servos may reduce torque or disable output after sustained high current draw
• This can appear as a sudden “sag” after several seconds of holding position

Recommended steps:

• Check for friction in the shoulder assembly and reassemble if necessary
• Reduce load on the joint during testing
• Verify that the servos are not operating near their maximum torque for extended periods
• Ensure the power supply is stable and correctly rated

If the issue persists even under low load and with free-moving joints, consider testing with a higher-torque motor variant or upgraded hardware configuration.