# How do I determine the right actuator size for my unwind or rewind web guide? > Actuator sizing starts with one question: how much force does the actuator need to produce to move your guide or shifting stand reliably? The answer depends on more than just the weight on the bearings. Roll-2-Roll Technologies uses a 6-term force model that accounts for every significant… **Last updated:** 2026-10-08 **Source:** https://r2r.tech/resources/faq/how-do-i-determine-right-actuator-size-my-unwind-or-rewind-web-guide --- ## Question How do I determine the right actuator size for my unwind or rewind web guide? ## Short Answer Calculate the total force from friction and inertia, apply a safety factor of at least 2.0, then compare against the RLA thrust ratings. ## Detailed Answer Actuator sizing starts with one question: **how much force does the actuator need to produce** to move your guide or shifting stand reliably? The answer depends on more than just the weight on the bearings. Roll-2-Roll Technologies uses a **6-term force model** that accounts for every significant resistance the actuator must overcome: - Bearing friction — the dominant term for heavy loads on linear bearings - Inertia — force to accelerate the mass at your target correction rate - Web tension lateral component — the sideways pull from web wrap angle on guide rollers - Umbilical drag — hoses, cables, and air lines that resist carriage motion - Floor grade — gravity component if the travel axis is not perfectly level - Misalignment friction — additional drag from rail or bearing misalignment Our [actuator sizing calculator](https://r2r.tech/resources/actuator-sizing-calculator) offers two approaches: - Simple mode — enter load weight and bearing type for a quick estimate. Uses a factor of safety of 2.0 or higher to compensate for forces not explicitly modeled. - Detailed mode — model all six force terms individually for a precise result, typically with a factor of safety of 1.5 to 1.75. If you want a reality check before running the calculator, try a **spring-scale pull test**: attach a calibrated spring scale to the carriage and pull horizontally at a steady, slow rate. The peak reading gives you the actual installed friction force — often 2 to 5 times the catalog bearing friction value. For a deeper walkthrough of the force model and worked examples, see the full [actuator sizing technical article](https://r2r.tech/articles/how-to-size-an-actuator-for-unwind-and-rewind-web-guides). **Category:** Technical --- ## About Roll-2-Roll Technologies Roll-2-Roll Technologies designs and manufactures patented fiber-optic web position sensors and advanced web guiding controllers — the precision measurement and control core of modern roll-to-roll manufacturing. Spun out of Oklahoma State University's Web Handling Research Center and trusted by Fortune 500 medical, battery, and nonwovens manufacturers, our patented sensors work without recalibration, with 0.0635 mm resolution and ±0.127 mm repeatability at line speeds up to 760 m/min — typical customer outcomes are 50%+ less downtime and payback under six months. Headquartered in Stillwater, Oklahoma, our team of PhDs, controls engineers, and industry veterans extends the sensor + controller core into complete web guide systems including stepper-motor-based linear actuators (RLA, BLA, LHS). - Website: https://r2r.tech - Phone: +1 (888) 290-3215 - Email: sales@r2r.tech