How the Linear Motion Calculator Works
The FIRGELLI Linear Motion Calculator is an engineering tool designed to help you determine the exact force and stroke requirements for any application where a linear actuator pushes, pulls, or slides a load along a surface. Unlike our Lid & Hatch Calculator which handles rotational motion around a hinge, or our Panel Flip Calculator which models panels that rotate and flip, this tool is specifically built for straight-line linear motion — where the load travels in a direct path along a track, rail, surface, or guide.
The calculator accounts for all the real-world forces that act on a moving load: gravity on inclined surfaces, surface friction based on material type, external resistance from seals or springs, and the geometric effects of angled actuator mounting. It computes both the push force (extending the actuator) and the pull force (retracting), because on inclined surfaces these values differ significantly — gravity assists one direction while resisting the other. The actuator must be sized to handle whichever direction demands more force, and the calculator identifies this automatically.
Understanding the Physics
The force required to move a load along a surface is the sum of three components. The gravity component equals the load weight multiplied by the sine of the incline angle — this is zero on a flat surface and equals the full weight at 90 degrees. The friction component equals the friction coefficient multiplied by the load weight multiplied by the cosine of the incline angle — this represents the resistance between the load and the surface material. Finally, any external resistance from seals, gaskets, springs, or cable drag is added directly to the total.
When the actuator mounts at an angle to the direction of travel — for example, when the actuator base sits below the surface and connects to the load above it — only the horizontal component of the actuator’s force does useful work along the surface. The required actuator force increases by the factor 1/cos(θ), where θ is the mounting angle. A steeper angle means a larger force multiplier and a longer stroke requirement, since the actuator must travel a greater distance through its angled path to achieve the same horizontal displacement. The calculator derives this geometry automatically from the base Y position and connection height you specify.
Typical Applications
This calculator is ideal for any project where a linear actuator moves a load in a straight line rather than rotating it around a pivot point. Common applications include:
Sliding doors and gates — Barn doors, sliding security gates, pocket doors, and industrial access panels where the actuator pushes or pulls a door along a track. The friction coefficient varies depending on whether the door runs on wheels, roller bearings, or slides directly on a rail.
Drawer and tray automation — Server rack trays, kitchen drawers, tool cabinet slides, cash drawers, and medical equipment drawers where the actuator extends and retracts a tray on linear slides. Drawer slides typically have low friction coefficients (0.05–0.15) when using ball-bearing slides.
Push-out TV and monitor lifts — Television lifts that push a screen up from a cabinet, desk, or piece of furniture. These are often vertical (90° incline) where the actuator must overcome the full weight of the TV when pushing up and the load returns by gravity when retracting.
Conveyor and material handling — Pushing products, packages, or materials along a conveyor belt, sorting chute, or assembly line. External resistance from belt friction, product drag, or guide rails adds to the base friction force.
Window and vent openers — Skylight windows, greenhouse vents, louvre systems, and clerestory windows that slide open along a track rather than hinging. Often mounted at angles with the actuator base offset below the window frame.
Vehicle and marine applications — Tonneau cover slides on pickup trucks, sliding boat hatches, RV slide-out trays, and wheelchair ramp extensions. These applications frequently involve inclined surfaces and exposure to vibration, which adds to external resistance.
Agricultural and greenhouse automation — Sliding feed troughs, automated chicken coop doors, irrigation gate valves, and greenhouse panel openers. Environmental conditions like dirt, moisture, and ice significantly increase friction coefficients.
Industrial positioning systems — CNC machine tool tables, workpiece positioners, jig and fixture slides, and assembly station positioning. These require precise travel distances and often involve heavy loads with low-friction linear bearings.
Hidden compartment and safe room mechanisms — Bookcase doors that slide on concealed tracks, hidden wall panels, under-floor storage access, and security barriers. These often have high external resistance from concealment mechanisms and locking hardware.
Solar panel positioning — Single-axis solar trackers that push panel arrays along a track to follow the sun’s path. Wind loading adds significant external resistance, and the incline angle changes throughout the day as the panel tilts.
Choosing the Right Friction Coefficient
The friction coefficient (μ) has a significant impact on the force calculation, and selecting the right value for your surface materials is important for accurate results. Lubricated or ball-bearing slides have very low friction (0.05–0.10). Steel on steel without lubrication sits around 0.15. Wood on wood is approximately 0.25–0.30. Rubber on concrete is much higher at 0.50–0.70. If you are unsure of your friction coefficient, it is better to estimate on the higher side to build in a safety margin. The calculator also provides a separate safety multiplier (default 1.5×) that is applied on top of the computed force to account for real-world variations in load, friction, and environmental conditions.
Push vs. Pull Force — Why Both Matter
On a flat surface with no incline, the push and pull forces are identical because friction is the only resistance and it acts equally in both directions. But the moment you introduce an incline, the forces diverge. On a 30° uphill slope with a 100 lb load and 0.30 friction, the push force (extending uphill) is approximately 76 lbs while the pull force (retracting downhill) is only about 24 lbs. The actuator must be rated for the higher value, which is 76 lbs in this case. At steeper angles the difference becomes even more dramatic — at 90° (vertical), the push force equals the full weight plus any external resistance, while the pull force may be near zero since gravity returns the load for free. The calculator shows both values separately so you can understand exactly what your actuator faces in each direction of travel.
When to Use Multiple Actuators
For wide loads, heavy panels, or applications where stability is critical, the calculator supports configurations of 2, 3, or 4 actuators operating in sync. When using multiple actuators, the total force is divided equally among them, reducing the force requirement per actuator. However, synchronized multi-actuator setups require a feedback-capable controller like the FIRGELLI FCB-2 Controller paired with feedback-equipped actuators to ensure all units extend and retract at the same rate. Without synchronization, one actuator may lead or lag, causing binding, uneven loading, or mechanical damage to the load or guides.
Selecting an Actuator from the Results
Once the calculator determines your force and stroke requirements, you can switch to the Selector tab to find actuators from the FIRGELLI product range that meet or exceed your specifications. The selector scores each actuator based on a weighted 60/40 split between force capability and stroke match, and ranks them from best fit to least suitable. You can further filter by feedback capability (required for multi-actuator sync) and compare up to three actuators side-by-side in the Compare tab to evaluate force range, stroke options, speed, and IP rating before making your final selection.
For applications involving rotational motion around a hinge point rather than straight-line travel, use our Lid & Hatch Calculator instead. For panels that rotate and flip from one position to another, our Panel Flip Calculator handles the unique torque and geometry calculations required for those applications.