How to Perfectly Synchronize Two Linear Actuators

 

Why do two identical linear actuators drift out of sync?

Synchronizing two linear actuators means keeping their extended positions matched in real time across changing loads — and the only reliable way to achieve this is closed-loop feedback control, not matched power.

Building a project that requires two linear actuators working in perfect unison seems straightforward on paper. Whether you're constructing a TV lift mechanism, a custom hatch system, or a large-scale platform that demands balanced lifting, the assumption is simple: buy two identical actuators, wire them to the same power source, and they'll move together. Unfortunately, this assumption leads to one of the most common frustrations in motion control projects.

In synchronized motion, the actuator isn't the source of accuracy — the feedback loop is. Wiring and control logic carry as much of the design as the motor does.

The reality is that no two electric motors—and by extension, no two linear actuators—are truly identical. Manufacturing tolerances, even within the same production batch, create subtle variations in internal resistance, gear mesh efficiency, and motor winding characteristics. These microscopic differences compound over time, causing one actuator to extend or retract faster than its partner. The result is a system that drifts out of alignment, creating uneven loads, mechanical binding, and potentially catastrophic failure of your entire assembly.

This synchronization problem becomes particularly acute in applications where precision matters. A custom standing desk that lifts unevenly creates an unstable work surface. A horizontal hatch that opens at different rates on each side will bind against its frame, overloading motors and wearing mechanical components prematurely. In worst-case scenarios, the misalignment can damage the load being moved or even pose safety risks if the application involves overhead lifting. Understanding why standard actuators drift apart—and how to properly synchronize two linear actuators—is essential for any serious motion control project.

Why doesn't parallel wiring keep two actuators synchronized?

The intuitive solution for most DIY builders and even some experienced engineers is to wire two actuators in parallel to a single power supply. The logic seems sound: if both motors receive the same voltage simultaneously, they should move at the same speed. This approach works reliably for simple lighting circuits or heating elements, so why wouldn't it work for linear actuators?

The fundamental issue is that DC motors don't behave like resistive loads. When you connect two actuators in parallel, they don't simply share the current equally. Instead, the actuator with slightly lower internal resistance will draw more current and consequently move faster. As it moves faster, its back-EMF (electromotive force) increases, which partially self-regulates its speed. However, this self-regulation is insufficient to maintain true synchronization. The faster actuator continues to outpace its partner, and the speed differential accumulates over each cycle of operation.

Load distribution compounds this problem significantly. In real-world applications, loads are rarely perfectly balanced. If one actuator carries even slightly more weight than the other—perhaps due to mounting geometry or an uneven load distribution—it will move more slowly under the increased resistance. The parallel-wired partner, experiencing less load, speeds ahead. This creates a feedback loop: as one side lifts higher, more weight shifts to that side, while the lagging side experiences even less resistance and should speed up, but by then mechanical binding may prevent any movement at all.

Temperature differentials introduce another variable that makes parallel wiring unreliable. As actuators operate, their internal components heat up, changing electrical resistance. If one actuator is positioned in better airflow or operates in a cooler part of your assembly, it will exhibit different electrical characteristics than its thermally-stressed partner. Over extended operation periods, these thermal variations can cause drift even in systems that initially appeared synchronized.

The mechanical tolerance stack-up in the driven load itself presents yet another challenge. Even if you could achieve perfect electrical synchronization, mechanical play in mounting brackets, slight differences in stroke length calibration, and accumulated wear in mechanical components mean that "electrically synchronized" doesn't guarantee "mechanically aligned." This is why professional motion control systems—including those used in aerospace and automotive manufacturing—never rely on simple parallel wiring for critical synchronized applications.

"Two motors are never truly identical. The moment you put load on a parallel-wired pair, the side with lower resistance pulls ahead, the side with more weight falls behind, and you end up fighting the geometry of your own mechanism. Feedback isn't a luxury here — it's the only thing that holds the system together over thousands of cycles." — Robbie Dickson, Founder and Chief Engineer of FIRGELLI Automations

How does feedback control synchronize two linear actuators?

The professional solution to synchronize two linear actuators relies on closed-loop feedback control, a fundamental principle in precision motion systems. Instead of assuming both actuators will move identically, a feedback-based system continuously monitors the actual position of each actuator and makes real-time corrections to keep them aligned. This approach transforms an open-loop system vulnerable to drift into a closed-loop system that actively maintains synchronization regardless of load variations, temperature changes, or manufacturing tolerances.

At the heart of this solution are feedback actuators equipped with internal position sensors. The most common feedback mechanisms include potentiometers, Hall-effect sensors, and optical encoders. Potentiometric feedback uses a variable resistor mechanically coupled to the actuator's extension, providing an analog voltage signal proportional to position. Hall-effect sensors detect magnetic field changes as the actuator extends, offering excellent durability and resistance to environmental contamination. Optical encoders provide the highest resolution but are typically reserved for ultra-precision applications due to their cost premium.

Sensor type	Typical resolution	Environmental tolerance	Relative cost	Best fit
Potentiometer	1–3 mm	Moderate (analog signal, susceptible to wear)	Low	General DIY and commercial sync applications
Hall-effect	Sub-millimeter	High (sealed, contamination-resistant)	Medium	Outdoor, marine, RV, dusty environments
Optical encoder	Tenths of a millimeter	Low (sensitive to dust and moisture)	High	Lab, medical, precision industrial positioning

The feedback signal from each actuator feeds into a synchronized control board that compares positions in real-time. When the controller detects that one actuator has extended further than its partner—even by fractions of a millimeter—it modulates power delivery to correct the discrepancy. The leading actuator receives reduced voltage or pulse-width modulated power, slowing its advance, while the lagging actuator receives full power to catch up. This correction cycle happens hundreds of times per second, maintaining alignment far tighter than mechanical tolerances alone could achieve.

The beauty of feedback-based synchronization is its adaptability to changing conditions. If your application involves variable loads—such as a platform that sometimes carries heavy equipment and sometimes operates empty—the feedback system automatically compensates. When one actuator encounters increased resistance, the controller detects the position lag and adjusts power distribution accordingly. This dynamic compensation is impossible with parallel wiring, where any load imbalance immediately translates to position error.

Modern synchronized control systems also incorporate safety features that parallel wiring cannot provide. If one actuator fails mechanically or electrically, the controller can detect the resulting position discrepancy and immediately halt all motion before damage occurs. Many systems include adjustable synchronization tolerance bands, allowing you to define acceptable position variance based on your application requirements. A large agricultural gate might tolerate ±5mm variance, while a precision laboratory platform might require ±0.5mm synchronization.

For DIY builders and engineers working with Actuator synchronization controller or similar microcontroller platforms, implementing feedback-based synchronization is increasingly accessible. Reading analog feedback signals, comparing positions, and generating PWM outputs for motor control are well within the capabilities of even entry-level development boards. However, for reliability and ease of installation, purpose-built synchronized control boards offer significant advantages over custom programming solutions, particularly in permanent installations where long-term reliability is paramount.

How do you set up a synchronized control board?

Installing a synchronized control system requires careful planning and methodical execution, but the process is straightforward for anyone comfortable with basic electrical wiring. The first step is selecting appropriate feedback actuators for your application. Ensure both actuators are identical models with matching stroke lengths, force ratings, and voltage specifications. Even small differences in nominal specifications can complicate the synchronization algorithm and reduce overall system performance.

Begin the installation by mounting your actuators using appropriate mounting brackets that ensure rigid attachment to both the fixed frame and moving load. Flexible mounting arrangements introduce mechanical slop that no amount of electronic synchronization can overcome. If your application involves side-loading or off-axis forces, consider track actuators that incorporate guide rails to constrain motion and reduce lateral stress on the actuator shaft.

Wiring a synchronized control board involves connecting power, feedback signals, and motor outputs. Most synchronized controllers accept 12V, 24V, or 36V DC input from a dedicated power supply. Size your power supply to handle the combined current draw of both actuators at their rated load plus a 20-30% safety margin. Undersized power supplies cause voltage sag under load, which can introduce synchronization errors or trigger undervoltage protection circuits.

The feedback connections typically use three-wire configurations: power, ground, and signal. Potentiometric feedback requires stable reference voltage—usually 5V provided by the controller—and returns an analog signal proportional to position. Route feedback wires separately from motor power cables to minimize electrical noise interference. Even brief signal corruption during a position reading can cause momentary synchronization errors, so proper wire management is not merely cosmetic but functionally important.

Calibration is the critical final step that many builders rush through, resulting in suboptimal performance. Begin by manually extending both actuators to their fully retracted position. Some controllers include an auto-calibration routine that sweeps through the full stroke range, mapping feedback voltage to physical position. Others require manual entry of minimum and maximum feedback values. Record these calibration parameters—you'll need them if you ever replace a controller or troubleshoot synchronization issues.

Set your synchronization tolerance based on application requirements. Tighter tolerances provide better alignment but may cause the system to "hunt" or oscillate as it attempts to maintain unrealistically precise synchronization. For most applications, a tolerance band of 2-5mm provides excellent practical synchronization without excessive servo activity. Test your installation under various load conditions, including maximum rated load, to verify synchronization performance across the entire operating envelope.

Integration with user controls is typically straightforward. Most synchronized controllers accept standard momentary switch inputs for extend and retract commands, compatible with common rocker switch configurations. Advanced controllers may offer remote control compatibility or integration with home automation systems. If your application requires automated operation, many controllers provide logic-level inputs suitable for connection to PLCs, Actuator synchronization controller systems, or other industrial control equipment.

Where are synchronized actuator pairs used?

• TV lifts and media cabinets — two actuators lift a heavy panel evenly to prevent racking.
• Standing desks — synchronized columns keep the work surface level under uneven keyboard and monitor weight.
• Horizontal hatches and hood lifts (RV, marine, automotive) — twin actuators on either side prevent binding in the hinge line.
• Agricultural gates and barn doors — wide gates synchronized at both posts.
• Platform lifts and stage equipment — multi-actuator coordination for level lifting of heavy distributed loads.
• Laboratory and medical positioning systems — sub-millimeter synchronization for sample stages and patient platforms.
• Industrial machinery — coordinated motion in presses, clamps, and indexing tables.

What usually goes wrong with synchronized actuator setups?

1. Parallel wiring drift. Two actuators on a shared supply diverge because of small differences in motor resistance, gear mesh, and back-EMF. Drift compounds every cycle.
2. Load imbalance amplification. The side with less load speeds up while the loaded side lags, creating a feedback loop that ends in mechanical binding.
3. Thermal drift. One actuator runs hotter than its partner (poor airflow, enclosed mounting) and its electrical characteristics shift mid-duty.
4. Undersized power supply. Voltage sag under load triggers undervoltage protection or introduces synchronization errors that look like controller faults.
5. Controller hunting. Synchronization tolerance set too tight causes the controller to oscillate around the target position instead of holding it.
6. Feedback signal noise. Routing feedback wires next to motor power cables corrupts position readings and produces erratic correction behavior.
7. Mounting slop. Flexible brackets or loose pin joints let the load shift independently of the actuator rod, so the controller chases a moving reference.

How should you test a synchronized actuator pair before trusting it?

1. No-load full-stroke test. Run both actuators from fully retracted to fully extended several times with no load. Confirm both reach the end stops within the controller's tolerance band.
2. Rated-load cycle test. Apply the maximum expected load and cycle the pair at least 20–50 times. Drift or hunting that wasn't visible no-load shows up here.
3. Asymmetric load test. Deliberately bias the load to one side. The controller should compensate without stalling. If the lagging actuator can't catch up, the supply is undersized or the tolerance is too tight.
4. Mid-stroke pause test. Stop the pair at multiple intermediate positions and measure the position differential. The hard part of travel — where loads change direction or geometry binds — is where misalignment usually appears.
5. Thermal soak test. Run continuous cycles until both actuators reach steady-state temperature, then re-check synchronization. Drift that only appears warm points to thermal asymmetry in mounting.
6. Power-interrupt recovery. Cut power mid-stroke and restart. Confirm the controller re-acquires position correctly on the next command.

Shop Firgelli Synchronized Actuator Kits

For builders seeking turnkey solutions that eliminate the guesswork from synchronized motion control, complete actuator kits provide significant advantages over piecing together individual components. These kits bundle matched feedback actuators, synchronized control electronics, appropriate power supplies, and all necessary wiring in a single package engineered for reliable operation.

The primary advantage of purchasing a synchronized kit is the assurance of component compatibility. Every element—from actuator feedback voltage range to controller input specifications to power supply current capacity—has been verified to work together. This eliminates the common pitfall of selecting components that are individually excellent but incompatible when integrated. The time saved on research, troubleshooting, and potential component returns typically justifies any price premium over sourcing individual parts.

Synchronized kits also include pre-configured control boards with tested synchronization algorithms. These controllers have been calibrated and validated across thousands of installations, incorporating lessons learned from real-world deployments. The difference between a purpose-built synchronized controller and a generic PWM motor controller is substantial—professional controllers implement sophisticated position tracking algorithms, adaptive compensation for load variations, and safety features that protect your investment.

Documentation quality in complete kits provides another significant benefit. Professional kit packages include detailed wiring diagrams, installation instructions, and troubleshooting guides specific to the included components. This targeted documentation is far more valuable than generic actuator datasheets when you're in the middle of an installation and need to verify a wire color or understand a specific controller behavior.

When selecting a synchronized kit, prioritize specifications that match your application requirements. Consider the total stroke length needed—kits are available with strokes ranging from compact 100mm options suitable for small cabinets to extended 600mm+ configurations for large lifting applications. Force rating is equally critical; calculate the actual force required using an actuator calculator rather than estimating, as undersized actuators are a common cause of premature failure.

Operating voltage deserves careful consideration based on your power infrastructure. While 12V systems offer easy integration with automotive electrical systems and common power supplies, 24V systems provide better efficiency at higher power levels and are standard in industrial environments. Higher voltage systems also reduce current draw, allowing the use of smaller gauge wiring and reducing resistive losses in long cable runs.

Conclusion

Successfully implementing synchronized linear motion requires understanding why simple parallel wiring fails and embracing feedback-based control as the professional solution. The investment in feedback actuators and synchronized control electronics delivers reliability, precision, and safety that open-loop systems simply cannot match. Whether you're building a custom automation project, upgrading an existing mechanism, or designing a commercial product, proper synchronization protects your investment and ensures years of trouble-free operation.

The key takeaway is that attempting to synchronize two linear actuators without feedback control is a false economy. The hours spent troubleshooting drift issues, the cost of damaged components from misalignment, and the frustration of unreliable operation far exceed the modest investment in proper synchronized control. Modern feedback systems are more accessible and affordable than ever, bringing industrial-grade motion control within reach of serious hobbyists and professional engineers alike.

Frequently Asked Questions

Can I synchronize actuators with different stroke lengths?

While technically possible with advanced control programming, synchronizing actuators with different stroke lengths is not recommended for most applications. The control system must scale feedback signals differently for each actuator, adding complexity and potential points of failure. More importantly, different stroke lengths usually indicate different internal gearing or screw lead specifications, which means the actuators will have different speed and force characteristics even under synchronized control. For reliable operation, always use identical actuator models with matching specifications.

What happens if one actuator fails during operation?

Quality synchronized control systems include safety features that detect actuator failure through position feedback monitoring. If one actuator stops moving while the controller continues commanding motion, the position discrepancy rapidly exceeds the synchronization tolerance band. The controller detects this fault condition and immediately halts power to both actuators, preventing the functional actuator from forcing the system into a damaging misaligned state. This fail-safe behavior is one of the key advantages of feedback-based synchronization over simple parallel wiring, which would allow one actuator to continue moving unchecked if its partner failed.

How precise is feedback-based synchronization?

Synchronization precision depends on feedback sensor resolution and controller update rate. Potentiometric feedback systems typically maintain synchronization within 1-3mm under normal operating conditions, which is sufficient for the vast majority of applications. Hall-effect sensors can achieve sub-millimeter precision, while optical encoders can maintain synchronization to tenths of a millimeter. However, absolute precision is limited by mechanical factors including mounting rigidity, load deflection, and actuator internal backlash. For most practical applications, the precision of modern synchronized control systems far exceeds what mechanical tolerances alone would allow.

Can I add more than two actuators to a synchronized system?

Many advanced synchronized control systems support three, four, or even more actuators operating in coordination. Multi-actuator systems use the same feedback principles as two-actuator systems but require more sophisticated control algorithms to manage position relationships between multiple units. Common applications include large platform lifts, multi-panel hatch systems, and complex automated machinery. When designing multi-actuator systems, ensure your controller explicitly supports the desired number of outputs, as not all synchronized controllers can manage more than two actuators simultaneously. The electrical infrastructure must also scale appropriately—power supplies must handle the combined current draw, and wiring must be carefully organized to prevent signal interference.

Do I need special actuators, or can I add feedback to existing units?

While aftermarket feedback sensors can theoretically be added to standard actuators, this approach is rarely practical or cost-effective. Installing internal position sensors requires disassembling the actuator, machining mounting provisions, and routing signal wires through sealed housings—modifications that void warranties and compromise environmental sealing. The sensor must also be mechanically coupled to the actuator's movement with minimal backlash and drift, which is challenging without precision manufacturing capabilities. Purpose-built feedback actuators integrate sensors during manufacturing, ensuring proper sealing, reliable signal quality, and warranty coverage. For any serious application, starting with factory-equipped feedback actuators is the only practical approach.