Size the actuator against the worst-case moment about the tilt pivot, which occurs when the panel is partway through its arc with wind acting on the full face — not against the panel's weight. For a typical trailer-mounted message board, wind pressure at the specified rating usually exceeds the gravity load by a wide margin, and the actuator's lever arm at the start of travel is where the mechanism is weakest. Work the numbers at three angles, apply a safety factor of at least 2, and confirm the holding load with power removed.

This article is part of our guide to linear actuators for traffic signals and ITS equipment.

What a sign tilt frame does, and why it is actuated

A variable message sign (VMS) or portable changeable message sign (PCMS) must sit high and vertical to be readable — and must lie flat to be towed or driven. The tilt frame is what converts between the two states.

Real products and their published mechanisms:

Sources: Wanco, Wanco traffic safety, Ver-Mac TM-548, TecHome.

Two design notes worth extracting from those specs. First, Wanco uses two actuators for a 500 lb frame and one for its smaller boards — the split point is a real engineering decision, covered below. Second, Ver-Mac's sales sheet states that the actuator's "integrated limit switch prevents motor gear wear and tear," confirming that end-of-travel protection is treated as a functional requirement, not an option.

Step 1: Establish the load cases

Three loads act on a tilt frame. Only one of them usually governs.

Gravity

The panel's mass acting through its centre of gravity. Straightforward, and usually not the governing case for a sign of any size.

Wind

The dominant case. A message board is, structurally speaking, a flat plate held into the airflow.

The standard velocity-pressure relationship used in North American practice (ASCE 7) is:

q=0.00256×V²

where  $q$  is velocity pressure in pounds per square foot and  $V$  is wind speed in mph. Full ASCE 7 design pressure applies further coefficients — exposure ( $K_z$ ), topographic ( $K_{zt}$ ), directionality ( $K_d$ ), gust and force coefficients — so treat the bare formula as a first-pass sizing tool, not as a structural certification. Signs specifically are covered by ASCE 7-16 Section 29.3.

What wind speed to design to? There is no single industry-mandated figure. What is verifiable from published specifications: Ver-Mac's TLD-3612 G3 trailer and Superior Traffic Services' Truss Signal are both rated at 90 mph (Trafficsupply, STS). TAPCO claims 100 mph sustained and 110 mph gusts for the SQ3TS. Use the figure your customer specifies, and get it in writing before you size anything.

Dynamic and towing loads

Vehicle-mounted signs experience road vibration and shock in the stowed position. NEMA TS 2 Section 2.2 covers vibration and shock testing for traffic control equipment and is the reference agencies cite. The actuator must survive this in the retracted state — which makes a solid mechanical stop in the stowed position, rather than the actuator's screw, the right place to carry towing loads.

Step 2: Work the moment about the pivot

A tilt frame is a lever. The actuator does not fight the load directly; it fights the load's moment about the pivot, through its own moment arm.

Where:

• $W$ = the resultant force (wind + gravity component) on the panel
• d_load​ = perpendicular distance from the pivot to that force's line of action
• d_actuator​ = perpendicular distance from the pivot to the actuator's line of action

The critical insight: both distances change continuously through the arc. On most tilt frames the actuator's moment arm is shortest at the start of the lift, when the actuator is retracted and its line of action passes close to the pivot. That is where required force peaks — often two to three times the value at mid-travel.

Calculate at a minimum of three positions: fully stowed (0°), mid-travel (45°), and fully deployed (90°). Size for the worst of them.

Step 3: A worked example

Assumptions stated explicitly — substitute your own.

Given:

• Sign panel: 6 ft × 3 ft = 18 ft²
• Panel + frame mass: 200 lb
• Design wind speed: 90 mph
• Pivot at the panel's lower edge; panel centroid 1.5 ft from the pivot
• Actuator moment arm at worst position: 0.5 ft

Wind pressure:

q=0.00256×902=20.7 psf

Wind force on the panel face:

F_wind​=20.7×18=373 lb

Moment from wind about the pivot:

M_wind​=373×1.5=560 lb⋅ft

Moment from gravity (panel horizontal, worst case for gravity):

M_gravity​=200×1.5=300 lb⋅ft

Note that these two peak at different points in the arc — wind moment is greatest when the panel is vertical and facing the wind; gravity moment is greatest when the panel is horizontal. Combining them at full value is conservative, which is appropriate for a first pass:

M_total​=860 lb⋅ft

Required actuator force at the worst moment arm:

Apply a safety factor of 2:

F_design ≈ 3,440 lb ≈ 15,300 N

Interpretation. A single actuator at 15,300 N is a large, expensive component. This is precisely why Wanco uses dual electric actuators on its 500 lb tilt frames. Two options follow:

1. Split the load across two actuators — roughly 7,650 N each, which is within the range of an 8,000 N industrial actuator such as JDR's FY015C or FY011E. Requires synchronisation.
2. Improve the geometry — increasing the actuator's moment arm from 0.5 ft to 1.0 ft halves the force requirement. Mechanical layout is almost always cheaper than a bigger actuator.

Also note the operational mitigation: Ver-Mac's automatic lowering exists partly to reduce wind drag by stowing the panel. If the sign lowers automatically in high wind, the extreme wind case may apply to the stowed structure rather than to the actuator at full extension. Confirm that logic with your controls engineer before relying on it, and never let a control strategy substitute for a mechanical stop.

Step 4: One actuator or two?

If you use two, they must be synchronised. Mismatched extension racks the frame, binds the pivots, and eventually destroys both actuators. Hall-effect feedback with a synchronising controller is the standard solution — see How to Sync Two Linear Actuators.

The same one-versus-two decision applies to signal masts, where the geometry and energy trade-offs differ — see Portable Traffic Signal Mast Lift: Electric Actuator vs Hydraulic vs Winch.

Step 5: Stroke, speed and duty

Stroke

Determined by geometry, not by preference. For a 90° tilt with the actuator mounted between a fixed frame point and a point on the panel, stroke equals the difference between the extended and retracted mounting distances. Model it — a 2D CAD sketch swept through the arc takes minutes and prevents an expensive mistake. TecHome's TA2-P offers up to 1,000 mm stroke for roof-mounted sign duty, which indicates the scale involved on larger vehicle installations.

Speed

A 90° tilt in 20–40 seconds is typical and appropriate. Faster is not better: momentum in a large panel creates shock loads at the end stops, and slower travel gives an operator time to spot an obstruction. Industrial actuators in the 4–30 mm/s range suit this duty well.

Duty cycle

Two cycles per deployment, then long dwell. A 10% duty rating (2 min on / 18 min off) is more than adequate. As with mast lifts, the engineering risk is not thermal — it is weeks of stationary exposure followed by a demand for reliable motion. Prioritise sealing and corrosion resistance. See Linear Actuator Duty Cycle Explained.

Holding load

Once deployed, the actuator holds the panel against wind for days. Confirm the static holding force with power removed and the behaviour under reverse loading. A screw-driven actuator is self-locking, but the specific reverse-load figure is a number to obtain from the supplier rather than assume.

Step 6: Environmental specification

Ingress protection

Per IEC 60529, IP66 (dust-tight, powerful water jets) is the practical minimum for a sign mounted outdoors; IP67 adds temporary immersion. For vehicle-mounted signs that pass through wash bays, IP69K's high-pressure, high-temperature washdown protection is the relevant grade.

Ask for the test report. Our own explanation of what these tests involve is in Ingress Protection Testing of Industrial Actuators.

Temperature

The same constraint that governs mast lifts governs sign tilt frames. Agency specifications commonly cite the NEMA TS 2 envelope of −34 °C to +74 °C. JDR's standard catalogue rating is −15 °C to +45 °C, which does not meet that envelope — a limitation we would rather state up front than have discovered during qualification. Vehicle-mounted signs stored in heated depots are generally unaffected; roadside trailers in severe winter climates require an extended-temperature build with a measured cold-start report.

European market

EN 12966 covers variable message traffic signs, and Ver-Mac certifies products to it. Usefully for component suppliers, EN 12966 explicitly excludes gantries, cantilevers, posts, supports and foundations from its scope — the lifting mechanism is not certified by the VMS standard, so the burden of demonstrating structural and environmental fitness sits with the equipment builder and its actuator supplier.

Selection summary

Relevant JDR models with published specifications: FY015C (8,000 N, IP67), FY011E (8,000 N, IP67), FY015D (7,000 N, IP65), FY021D (2,000 N, IP66, brushless). The full Industrial Actuator Series offers Hall-effect and potentiometer feedback with customisable stroke.

Frequently asked questions

How do I calculate wind load on a message sign?

For first-pass sizing, use  $q=0.00256\times V^2$ to get velocity pressure in psf from wind speed in mph, then multiply by the panel area. For structural certification, apply the full ASCE 7 method (Section 29.3 covers signs) with exposure, topographic, directionality and force coefficients, or have a structural engineer verify.

Do I need one or two actuators for a sign tilt frame?

One is adequate for narrow, torsionally stiff frames within a single actuator's force range — Wanco uses a single actuator on its smaller truck-mount boards. Use two, synchronised, for wide or heavy frames; Wanco uses dual actuators on its 500 lb tilt frames.

What stroke length do I need for a 90-degree sign tilt?

It depends entirely on mounting geometry, not on panel size. Sketch the mechanism and measure the change in distance between mounting points across the full arc. Vehicle-mounted sign actuators are available with strokes up to around 1,000 mm.

Can the actuator hold the sign against wind without power?

A screw-driven actuator is self-locking and holds position with power removed. Obtain the specific static holding and reverse-load figures from the supplier rather than assuming, and size against the moment at your specified wind rating.

What IP rating does a VMS tilt actuator need?

IP66 as a minimum for outdoor trailer-mounted signs, IP67 where standing water or snowmelt is credible, and IP69K for vehicle-mounted signs subject to high-pressure washdown. Request the IEC 60529 test report rather than relying on the marketing figure.

Send us your geometry and we will run the numbers

JDR has manufactured electric linear actuators since 2004 in Wuxi, China, shipping to 78 countries under ISO 9001. We build to drawing — stroke, mounting eyes, feedback, voltage and sealing are all specifiable.

Send us your panel dimensions and mass, pivot and actuator mounting geometry, specified wind load, bus voltage and ambient temperature range, and our engineers will return a sizing calculation and a candidate model — including a straight answer on any requirement we cannot meet from the standard catalogue.

Request an engineering consultation →