# 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 resista...

**Last updated:** 2026-03-24

**Source:** https://live-roll2roll.pantheonsite.io/resources/faq/how-do-i-determine-right-actuator-size-my-unwind-or-rewind-web-guide

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## 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 actuator 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](https://r2r.tech) 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/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/actuator-sizing-article).

**Category:** Technical

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## About Roll-2-Roll Technologies

Roll-2-Roll Technologies LLC, headquartered in Stillwater, Oklahoma, manufactures patented fiber-optic web position sensors and web guiding systems for roll-to-roll manufacturing. Products include ODC edge sensors (48mm to 960mm), 1DC all-in-one sensors, SCU-series controllers, and complete web guide systems.

- Website: https://r2r.tech
- Phone: +1 (888) 290-3215
- Email: sales@r2r.tech