How to Size a Linear Drive for Precision Positioning Applications

Reap the benefits of low noise and high precision with a properly sized linear drive system

If you design motion control systems, chances are you’ve worked with pulse width modulated (PWM) drives. Thanks to their stability, availability and familiarity, PWM drives are the default choice in most day-to-day motion control jobs. But PWM drives tend to be noisy, producing a degree of electromagnetic interference (EMI) that makes them less than ideal in some high- f idelity motion applications.

These noise-sensitive applications include advanced inspection and metrology tools used by the semiconductor industry as well as medical imaging and diagnostic systems. And that’s where linear drives come into play. Rather than the continuous voltage switching that defines PWM, linear drives scale an input voltage to arrive at a desired current or voltage output.

This constant gain approach results in fast, accurate current loops and also eliminates any deadband at the drive’s zero crossing, giving linear drives an edge in high precision motion control applications.

The price you’ll pay for the improved precision will mostly come in the form of heat. Linear drives typically maintain small amounts of power inside the drive circuits, increasing heat. Excess voltage not needed by the motor is also dissipated as heat. To manage these thermal conditions while meeting the application requirements, it’s crucially important that you size linear drives correctly. Here’s how:

1. Define System Requirements

Right-sizing a linear drive to match a motion control application is a multi-step process due to the many factors that influence system behavior. The most important system variables from a sizing standpoint are:

• Peak motor velocity in RPM

• Peak motor torque or force

• Average velocity and torque values

Load characteristics and friction effects are implicit in the motor, torque and force requirements. You’ll also need to take the motion profile into consideration when calculating both peak and average torque requirements. For example, a trapezoidal profile requires constant torque until peak velocity is reached. In contrast, an S-curve or parabolic profile requires gradually less torque as the move sequence approaches peak velocity. To obtain actual application values, torque must be calculated for each motion profile that will be executed—because average torque must be known in order to determine average power dissipation.

2. Select a Motor and Drive

Once the required motion parameters are defined, it is time to make the initial motor and drive selection. First, choose a motor family capable of satisfying peak torque and speed requirements. Next, calculate the required voltage and current for each motor in the system and look for a matching drive that can handle these voltage and current values. Note that the required voltage is based on the voltage constant (Ke) and peak speed, while the required current is based on the torque constant (Kt), peak torque and resistive losses. Consult the lookup chart or specification sheet of the linear drive being considered to see if there is a match. If not, either another motor or a different drive will need to be selected.

Consider the following example. From the desired motion profile, we know that:

Peak velocity = 400 mm/s (0.4 m/s)

Peak torque = 1344 N

Stage mass = 280 kg

Motor Properties:

Voltage constant (Ke) = 163.5 m/s/V

Torque constant (Kt) = 141.6 N/A

Winding resistance (r) = 9.5 Ω

Voltage and Current Requirements:

Peak current required (Ipeak) = Peak torque/Kt Ipeak = 1344 N/141.6 N/A = 9.5 A

Peak voltage (Vpeak) = (Ke × peak velocity) + (winding resistance (r) × Ipeak ) + drive overhead (10 V safety margin for the Trust Automation TA330/333 linear drive used in this example)

Vpeak = (163.5 m/s/V × 0.4 m) + (9.5 Ω × 9.5 A) + 10 V = 165.6 V

Bi-polar power supply requirement = 1/2 Vpeak = 0.5 × 165.6 V = 82.8 V

In this example, the calculated voltage and current values of 165.6 V and 9.5 A are within the TA333’s capability. (TA333 = 25 A and 200 V; TA330 = 18 A and 150 V). The voltage is slightly higher than the TA330’s capability (150 V), so the TA333 is necessary to meet the 165.6 V requirement. Note that this calculation exercise can be done to check the suitability of any linear drive.

3. Determine Safe Operating Area (SOA)

Once you’ve made the initial linear drive selection, the safe operating area (SOA) for the application must be calculated to ensure that the power does not surpass the drive’s capacity.

Although certain linear drives feature a reactive safety capability, if the SOA is exceeded significantly and quickly, the drive may not be able to shut down in time to prevent damage. Basically, a linear drive acts as a large variable resistor in the supply-motor-drive circuit. Supply voltage is divided between the motor and drive with the current in series, using a pair of power devices and the motor. It is important to be aware of two of the most common danger conditions—stalls and dynamic breaking and deceleration.

Following are examples and calculations of these two danger scenarios, one involving a stalled motor and the other illustrating a dynamic stopping motion. Note that the TA330 and TA333 used in these examples calculate wattage per power device. At least two power devices are on at any time, so the individual worst case wattage is half the total wattage.

Safe Operating Area (SOA)

Supply Current 500 ms max @18 A 18 10 6 1 400 W, 25 ms @ 70ºC the TA330 and TA333 used in these examples calculate wattage per power device. At least two power devices are on at any time, so the individual worst case wattage is half the total wattage. 600 W, 25 ms @ 25ºC 1 10 75 100 Drive Voltage

Danger Scenario I—Stalled Motor

Consider that the motor is stalled and pushing against a hard stop while the controller is commanding 9.5 A. Known values are as follows:

Vsupply = 192 V (total supply voltage)

Icommand = 9.5 A (commanded current)

Winding resistance = 9.5 Ω (motor impedance)

Temperature = 30°C (heatsink temperature)


Vmotor = 90.3 V (motor voltage = 9.5 A × 9.5 Ω)

Vdrive = 101.7 V (remaining voltage = 192 V − 90.3 V)

Wdrive = 966.6 W (total wattage the drive must dissipate)

W per device = 483.3 W (wattage for use in SOA chart; half of total wattage)

According to the TA333 SOA chart that covers wattage, time and temperature, 483.3 W at 30°C is within the continuous operation zone. Be sure to ask your linear drive manufacturer for the SOA chart or spec sheet that corresponds to the drive you are considering.

Danger Scenario II—Dynamic Stopping

Whenever motion is involved, wattage calculations become much more complex. This complexity is due to the kinetic energy involved in moving the load. When the controller sends a command to stop moving, kinetic energy must be dissipated. In a traditional PWM drive setup, kinetic energy is pushed back onto the power supply bus and a shunt regulator is typically used to dissipate this energy. With a linear drive, the kinetic energy is absorbed by the drive itself, but must be dissipated as heat. This energy must be added to the energy required by the drive to stop all motion.

The exact amount of kinetic energy to be absorbed is challenging to calculate, because system efficiency and friction are large variables that must be considered. For example, an ultra-low friction air bearing stage may retain close to 100 percent of this energy, while a high friction lead screw stage might only retain 5 percent of this energy.

In the following example, linear deceleration is assumed. Average kinetic energy over the stopping time is used in these calculations and is applied at the point when the motor stops, but the command current is still going:

Kinetic energy (KE) = 0.5 × mv2 (KE is expressed in joules)

Wattage = (KE/2)/time (assuming linear deceleration)

Adjusted wattage = wattage × friction factor


m = mass (Kg)

v = velocity (m/s)

KE units = joules (J)

t = time to stop motion

Friction factor % = estimated energy lost to friction (ff)

Known Values:

Mass = 280 Kg

Velocity = 0.4 m/s

Time = 0.1 s

f f = 90%

Calculated Values:

KE = 0.5 × 280 Kg × (0.4 m/s)2 = 22.4 J

W = (22.4 J/2)/0.1 s = 112 W

W adjusted = 90% × 224 W = 100.8

The kinetic energy value should now be added to the stalled wattage equation to obtain a rough estimate of the wattage the drive will need to dissipate when stopping. This energy must be added to the individual power device wattage because it is not shared energy. From the stalled motor calculations in the previous example, we take the 483.3 W and add the KE wattage of 100.8 W. The result is a 584.1 W thermal load on the drive. Not all linear drives are designed to measure kinetic energy. Nevertheless, it is extremely important for system designers to consider these calculations when setting up a motion system.

4. Calculate Continuous Dissipation

As the final step in choosing a correctly sized linear drive, it is important to calculate the continuous operating limits to ensure that average wattage is not exceeded, which could damage the drive and degrade overall system performance. Keep in mind that average velocity and torque are calculated in relation to time. To keep things simple, assume a trapezoidal motion profile and use half the torque and velocity during acceleration and deceleration.

Using these values, generate a timetable with the system’s torque and velocity for the move profile. Be sure to include all cycle times and dwell times. Multiply the time value by the torque value and sum all steps, then divide by the total time for the average torque value. Repeat with velocity to obtain the average. Next, use these average numbers to calculate wattage in the same manner as the first example described previously.

Average current required (I) = Average torque/Kt

Average voltage required (V) = (Ke × average velocity) + (winding resistance × average current required)

Average wattage dissipated = (Supply voltage – average voltage) × average current


Supply voltage = 192 V

Average torque = 247.1N

Average velocity = 0.18 m/s

Using the Selected Motor Properties:

Voltage constant (Ke) = 163.5 m/s/V

Torque constant (Kt) = 141.6 N/A

Winding resistance (r) = 9.5 Ω

Average current required (I) = Average torque/Kt Average voltage required (V) = (Ke × average velocity) + (winding resistance × average current required)

Motor I = 247.1 N/141.6 N/A = 1.74 A

Motor V = (163.5 × 0.18) + (9.5 Ω × 1.74 A) = 46.3 V

Total drive W = (192 – 46.3) × 1.74 = 254.2 W

The final step is to verify that the average heatsink wattage does not exceed 400 W with the heatsink at 20°C (for the TA330 and TA333 linear drives discussed here). Calculated results must be evaluated against the drive’s SOA chart. In the example used here, calculated peak wattage is 584.1 W for a duration of 0.1 s (100 ms).

According to the TA330 SOA chart, 584.1 W in continuous operation corresponds with a heatsink temperature up to 29°C. At 30-34°C, the controller would allow 61 ms prior to generating a fault. Note that the allowed time decreases as temperature rises. Therefore, if the heatsink temperature is allowed to climb above 29°C, driving for 100 ms, the drive could be damaged.

Studying the TA333 SOA chart, 584.1 W in continuous operation corresponds with a heatsink temperature up to 49°C. At 50-54°C, the controller would allow 84 ms prior to generating a fault. In this case, if the heatsink temperature is allowed to climb above 49°C, the drive could be damaged.

The tips and calculations described here are intended to help you make an informed choice when selecting a linear drive. Once the actual system is up and running, however, these values should be analyzed again to optimize drive performance. To learn how linear drives can improve positioning in your next motion control application, visit

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Trust Automation to Provide Cybersecurity Solutions for Legacy Industrial Control Systems

Trust Automation Inc., a leading supplier of automation technology for defense and industrial applications, has announced it will offer a novel new cybersecurity solution for industrial control systems (ICS).

Working through the United States Department of Homeland Security’s Science and Technology Directorate, Trust has obtained an exclusive license to the Autonomic Intelligent Cyber Sensor (AICS) technology developed by Idaho National Laboratories.

AICS brings autonomous, real-time cybersecurity measures to the legacy ICS networks that still control much of the United States’ critical energy, water and transportation infrastructure. “AICS is a key enabling technology in the protection of aging, yet still critical, infrastructure that wasn’t designed to withstand cyberattacks,” says Trust Automation CEO and CTO, Ty Safreno.

At its core, AICS technology employs autonomic computing techniques and a service-oriented architecture to discover ICS network entity information, deploy deceptive virtual hosts and identify anomalous network traffic with high accuracy. AICS is compatible with SerialTap™, a patented sensor that passively monitors the serial communications employed by most legacy ICS networks.

The exclusive license enables Trust Automation to use AICS to upgrade the cyber defenses of vulnerable legacy critical infrastructure systems—including natural gas distribution, water distribution and management, electrical grid systems and transportation. The move builds on Trust Automation’s extensive experience with control and power-management systems for semiconductor, defense and green technology applications.

For more information, visit

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Partnering with Cynash on Advanced Industrial Cybersecurity Platform

We’re excited to announce our recent partnership with Cynash on a next-generation cybersecurity platform that can detect and mitigate cyberattacks on the industrial control systems that run energy, water, transportation and industrial infrastructure.

The platform builds on Cynash’s SerialTap™ sensor that passively monitors the serial communications used by many of the world’s industrial control systems. SerialTap™ can now pass the monitored traffic to our AICS machine learning system—enabling us to solve more extensive security challenges using advanced techniques in anomaly detection and behavioral analysis.

Both technologies separately won prestigious R&D 100 Awards—SerialTap™ in 2017 and AICS for 2018.

They also started as applied research and development efforts by the U.S. Department of Energy’s National Laboratories. Their commercialization is the direct result of the Transition-to-Practice (TTP) Program—an initiative run by Dr. Nadia Carlsten at the Department of Homeland Security (DHS) that identifies emerging technologies that have national security applications.

To learn more about, read our latest press release.

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Trust Automation Contributes to the Development of Life Saving Drones Delivering Vital Medical Supplies to Rwanda

Trust Automation, Inc., known for standard and custom high efficiency motors and controls as well as support system solutions, today announced that it has designed and manufactured a custom system that contributes to the successful flights of drones that deliver lifesaving medical supplies to people who live in isolated territories of Rwanda. The drones have been developed by Zipline an autonomous robotics company based in San Francisco.

In Rwanda, medical supplies such as blood transfusions, antibiotics, vaccines, or antivenoms that are needed by patients in difficult to access areas take hours to deliver and sometimes can’t be delivered at all resulting in a significant amount of lost lives.

The founders of Zipline, are responding to this dire humanitarian need by developing a small launching hub and a fleet of 15 autonomous drones. With their pioneering aerospace solution; medical personnel can send Zipline a text message and a drone will respond with an airdrop containing the critical supplies within 30 minutes. The drone will send a message to the health center when it is two minutes away and the package, equipped with a parachute, will carefully float to the ground without the drone landing. The aircraft then returns to the launch site.

Trust Automation, known for inventing systems to meet complex challenges contributed to the Zipline system by collaborating with the team of engineers at Zipline with our motor control and system expertise.

“With the success of this project in Rwanda, we are looking forward to the many future possibilities this technology will offer,” said Ty Safreno, CEO and CTO for Trust Automation. “People in more countries can be saved, quality of life can be improved, and economic development opportunities can be supported with the expansion of this unique drone system providing access of materials to otherwise isolated areas.”

The Zipline drones will use GPS receivers to navigate and communicate via the Rwandan cellular network. They will be able to fly in inclement weather and winds up to 30 miles per hour. They are the most agile airborne alternative to automate supply chains.

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Solving the Most Complicated Military Needs

In today’s rapidly evolving security landscape of unconventional battlefields and irregular warfare, our soldiers need to quickly locate and neutralize mortar and rocket threats. The U.S. Army’s objectives call for custom engineered systems to take the lead in providing solutions that can be rapidly developed and deployed. These systems need to be both accurate and reliable to keep our troops safe and give them a technological advantage that is both flexible and field proven.

Trust Automation designed and currently manufactures the lift, level, and rotate technology for the AN/TPQ-53 (Q-53) produced by Lockheed Martin Corporation. This mobile platform’s counterfire target acquisition radar relies on the rugged and high tech vehicle automation system to provide soldiers with enhanced 360-degree protection from indirect fire. The AN/TPQ-53 is a new generation radar system with the flexibility to adapt to harsh environments and meet a broad scope of mission requirements.

Trust Automation has been providing industry leading power density, accuracy, and reliability for the electro-mechanical control systems needed for the next generation of DoD military equipment including the AN/TPQ-53 since 2008. Trust Automation has since been awarded sub-system design contracts for a number of Lockheed Martin’s ground based radar platforms. The AN/TPQ-53 system has been globally deployed and has proven its capabilities in harsh environments such as monsoonal rain, sand storms, subzero to extreme hot desert conditions, as well as the shock and vibration exposure common to in-theatre deployment.

Trust’s team of engineers design and develop custom solutions for MilitaryMedicalIndustrial, and Power applications involving high performance motorscontrollerspower generationpower storage solutionspower conversions and drivessystem assemblies, and servo drives to respond to needs for DoD, IARPA, DARPA and for all branches of the U.S. military.

Trust’s motion control solutions also contributed to the success of the Medium Extended Air Defense System (MEADS) FT-2 Flight Test. Trust Automation designed and developed critical motion control elements to the radar platform. During a demonstration of its 360-degree Air and Missile Defense (AMD) capabilities, the MEADS System intercepted and destroyed two simultaneous targets attacking from opposite directions. All system elements worked as planned. MEADS is a next-generation, ground mobile AMD system that incorporates 360-degree radars, netted and distributed battle management, easily transportable launchers and the hit-to-kill PAC-3 MSE Missile. Video footage can be seen at

Aurora Flight Sciences along with partners ThinGap and Trust Automation answered the need for safe, high power density electric lift fans, with specific interest in vertical takeoff and landing (VTOL) air vehicle applications. The team’s unique approach utilized a DC brushless ring motor, high switching rate controller, and a ducted fan design. The Defense Advanced Research Projects Agency (DARPA) funded contract produced a 32-inch diameter ducted fan powered by a 70kW electric motor capable of producing over 430 pounds of thrust. Trust Automation’s controller design leveraged high switching rates and Field Oriented Control to effectively manage the low inductance propulsion system. Continued development is planned to reduce weight and increase system efficiency as potential platform specific applications are pursued. This ducted electric lift technology has applications to vertical take-off and landing vehicles, helicopter tail rotors, and aircraft propulsion. EMP and nuclear events are an ongoing concern for electronic systems. Trust developed a high speed radiation hardened fan drive/controller capable of high shock and vibration conditions for missile silo ventilation systems.

UAV platforms have become increasingly important for both situational awareness and remote enforcement. However, the noise signature has been a challenge. Trust Automation successfully participated in the IARPA funded Great Horned Owl project to develop high efficiency systems converting fuel to electricity and electricity to propulsion with the goal of producing near silent flight capabilities.

In addition, Trust Automation is responding to the needs of our military for reliable and efficient energy storage by developing Agile Energy Management System™ (AEMS™). This highly flexible battery management system can be customized for land, air or marine applications. With a multitude of configurations, unmanned vehicles can be equipped to perform for extended periods while the soldier is safely operating the system from a remote location.

Field Service Engineering is provided globally to customers that require highly trained and experienced “boots on the ground” support for motion control or energy management systems.

Trust Automation is an AS9100 certified Women – Owned Small Business (WOSB) bringing high quality and reliability to motion control and energy management systems for the defense market. Well versed in Federal Acquisition Regulations (FAR), Trust can offer the U.S. Army COTS or full custom designed and engineered solutions.

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Good Selection of Product Creates Quick Turn Around at a Reasonable Cost

A startup mobile-robotic material handling company needed to test their first version of automated equipment. The most expeditious way of doing this was to draw from our stock product found at This website allows customers to select motion control, drive, motor, and gearbox and get immediate delivery. Since it is focused on low voltage, it fits the mobile robotic (typically battery powered) equipment perfectly.

Once they began testing the motor, they were able to characterize the load throughout the speed range. This allowed us to specify the exact motor they needed. The customer ordered a batch of custom wound motors, and 4 weeks later was able to prepare the machine for early marketing and sales. We won a long term customer, and they connected with a reasonable cost, quick delivery supplier capable of providing custom products.

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Gearmotor Supplies Multiple Speeds with Custom Features for Customer

Mach Motion Products markets a full variety of drives, motors and gears. As much as we try to show all offerings on our website, there is frequently something our customers need that is not listed. That does not stop our sales team from pursuing a project that has good volume associated with it.

A recent example is an assembly machine manufacturer that had been using a simple one speed gearmotor. They wanted to add the ability to allow the operator to adjust speed, and of course they did not want to pay significantly more money. This initially seemed an unlikely win for us until we found that the annual consumption was approximately 10,000 units.

Mach Motion Products sourced an equivalent gearbox with higher torque capability, then added a generously sized motor and a custom manufactured DC drive to create a new product that worked flawlessly.

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High Tech X-Y Couplings Offer Superior Performance

A high-tech company markets a machine that requires precise positioning. In it, they use zero backlash flexible couplings.

When their coupling supplier raised their price by almost 50%, they went looking for an alternative supplier. Mach Motion Products now offers drop in replacements for machined couplings that fit perfectly.

After a few months of testing, it was determined that performance matches that of the previous supplier. As a side benefit, the delivery from Mach Motion Products is always on-time since we inventory product dedicated to our OEM customers.

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Brushless Gear Motor Utilizes Many Options for Unique Client Needs

An industrial manufacturer that uses a precisely-controlled fluid pump was struggling with speed variations in their current system. They would adjust the drive to the correct speed before shipment, but since it was potentiometer controlled, temperature and time caused the speed to change. This of course changed performance on their system. Since they produced 6 different sizes of machines, they needed 6 different speeds for the fluid pump.

Mach Motion Products offered a brushless gearmotor along with a customized drive to solve their problem. The custom drive was configured with 6 dip switches allowing for the 6 different speeds. Additionally, the drive was programmed to use the halls in a manner similar to an encoder so over time, the speed variation is less than 0.01 percent which far exceeded the customer’s previous approach.

Since the customer had both 115VAC and 230VAC applications, a power supply was provided that automatically output the 24VDC needed for the brushless drive and motor regardless of what input voltage was provided. In the end, the customer was able to utilize just one series of products for every machine reducing inventory and providing the perfect solution.

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Ball Screw Increases Production Line Success

A manufacturer of a miniature CNC machine came to us asking for a low cost C5 precision ballscrew. The lead time from their current supplier had extended to 40 weeks. The OEM uses over 1000 units per year, so it required quick turn around to both allow them to test as well as to get production units in their hands in a timely manner so their production line was not interrupted. We received samples in 3 weeks, and sent them off for evaluation.

The customer measured and tested the screws to find they were of superior quality to the units they had been receiving. The customer placed a production order which was received in 5 weeks, and now there is no delivery issue because Mach Motion Products holds inventory for them. The lead time for their product now is one day.

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