Quick Answer:
Actuator sizing depends on load mass, bearing friction coefficient, and desired acceleration—not just total weight. Low-friction linear bearings reduce thrust requirements significantly.
Sizing an unwind actuator requires more than knowing the total load weight. The key factors are:
- Breakaway Force: The actuator must overcome static friction to start movement. This depends on the bearing type:
- Low-friction linear rail bearings (coefficient ~0.01): A 10,000 lb load requires only ~100 lbf to start moving
- Sliding shaft bearings (coefficient ~0.25): The same 10,000 lb load requires ~2,500 lbf
- Acceleration Requirements: Higher acceleration for faster response requires proportionally more thrust
- Safety Factor: Include 20-30% margin for binding, misalignment, and wear
Recommendation: Always use low-friction linear rail bearings. The cost savings on a smaller actuator typically exceeds the bearing cost difference, plus you get better dynamic response.
Roll-2-Roll Technologies BLA and RLA series actuators provide nominal thrust from 150 lbf to 2,000 lbf. The BLA-067 moves about 10,833 lb on rolling bearings at μ 0.06 (6,500 lb at μ 0.1); the RLA-200 moves about 33,333 lb at μ 0.06 (20,000 lb at μ 0.1). See the BLA and RLA load tables.