Motors - 3/99 - Motion Control Tips

Hygienic, stainless gearmotor designs improve fish-processing plant

December 6, 2018 By Miles Budimir Leave a Comment

Processing fresh fish necessitates a hygienic environment with regular washdowns, followed by frigid temperatures for freezing final products. That’s why machinery in such settings must be extremely rugged — and why one fish supplier has used motors from Bauer Gear Motor for the last few years.

Van Der Lee Seafish processes approximately 200 tons of fresh fish every week. Fish is subject to conveyor-driven sorting, filleting, breading, freezing, and packaging processes. Drives for these conveyors must meet strict food-industry hygiene requirements.

Building reliable processing lines for hygienic environments subject to -43° C temperatures is challenging. One fish supplier recently upgraded its conveyor drives to stainless-steel variants for top reliability. Its fish-processing lines can be reconfigured for different products.

“Product quality is paramount, so fish must be processed quickly and efficiently,” said technical director Willem Van der Lee. “We can have seven processing and five packaging lines operating at any given time, and each one employs many motors and drives. That necessitates spare parts be kept to minimize downtime should a breakdown occur.”

That’s why Van Der Lee Seafish standardized on Bauer’s gearmotors throughout its food-processing facility a few years ago. The AsepticDrive from Bauer Gear Motor (of Altra Industrial Motion Corp.) has a hygienic gearmotor design with smooth surfaces and no cooling fins that can promote bacteria accumulation. Standardizing on the gearmotor minimized spare-parts inventory. What’s more, the permanent magnet synchronous motors (PMSMs) have high energy efficiency, especially under partial load. Plus the synchronous nature of the PMSM motors maintains constant speed independent of load. That means as long as the mains frequency is held constant the motor speed doesn’t vary, even under overloading or voltage drops.

Standardizing on the AsepticDrive units improved overall food-processing facility energy efficiency.

The gearmotors delivered the promised level of performance on almost all counts. One exception was on some motors subject to mechanical damage from other equipment. On these units, degradation of the hygienic coating threatened to compromise the hygienic design. So for certain locations in the plant, Bauer engineers supplied a newer gearmotor — a stainless-steel HiflexDrive variation with maximum mechanical resilience and the ability to withstand harsh washdowns.

VFDs run the gearmotors to allow precise control of conveyor speeds.

“The AsepticDrive has let us trim spare-parts inventory, and the HiflexDrive in stainless steel is a direct replacement for running in frozen storage areas,” added Van der Lee.

Bauer’s HiflexDrive comes in a modular design allowing gearbox, electric motor, and external finish selection. Motors rated up to IE5, according to IEC TS 60034-30-2, offer top energy efficiency, while pairing with variable speed drives allows exact conveyor-speed setting. Including a PMSM in the drives reduces heat losses from the rotor by 100% and total losses by approximately 25% — plus boosts total efficiency by 10% or more. Such savings are significant especially for stainless-steel motor variations that dissipate heat less efficiently than those built with aluminum or cast-iron housings.

HiflexDrive system flexibility lends itself to the food and beverage industry. The stainless-steel construction eliminates hygiene risks posed by mechanical impacts or extended operation subject to rigorous cleaning. Ingress protection is to IP69K — a washdown designation for applications subject to high temperature and high-pressure water.

A new stainless-steel gearmotor variant is now employed where the fish processor needed maximum machinery ruggedness.

Flexible designs also mean Van der Lee Seafish can move its conveyors around to various areas and not worry about drive reliability. Stainless-steel HiflexDrive units ensure maximum productivity.

PowerPlus stepper motors from Moons’ Industries — high-torque replacements for NEMA 23, 24, and 34 motors

December 4, 2018 By Lisa Eitel Leave a Comment

To upgrade machine performance or address stalling problems, manufacturers often resize motors with greater torque to reach greater accelerations for proper operations. Retrofitting a stepper motor, however, is time-consuming and expensive as it requires machining new mounting brackets and increasing the drive size and power supplies. PowerPlus Hybrid Stepper Motors from MOONS’ Industries eliminate the hassles of resizing motors by providing 25% to 40% more torque across the entire speed range of a motor. With the same physical dimensions as standard NEMA 23, 24 and 34 stepper motors, PowerPlus Hybrid Stepper Motors often drop into place to minimize upgrade costs while improving performance.

The increased torque of the PowerPlus technology is the result of higher motor efficiency. In a conventional stepper motor, some of the torque-producing flux that links the rotor to the stator is formed outside the stator teeth. The stray flux wastes power and adds little to motor torque.

A higher magnetic flux density within the motor increases the performance of the PowerPlus Stepper Motor, enabling it to generate up to 40% more torque than conventional motors. Magnets placed between the stator teeth redirect and refocus most of the stray magnetic flux into the stator teeth to produce additional torque with the same input power.

Retrofitting existing motors with PowerPlus technology offers a quick path to producing new machines with improved performance.

Because the motor size, drive, and mechanical parts remain the same, PowerPlus Hybrid Stepper Motors:

Reduce engineering costs
Expedite new product introductions with an easier production phase
Reduce spare parts inventory
Provide a quick solution to stalling machines due to unexpected field conditions such as low temperature, dirt, wear of mechanical parts or lack of maintenance

Application for PowerPlus stepper motors

In a typical application upgrading stepper motor performance with PowerPlus technology, a manufacturer of CNC cutting systems wants to produce a high-performance version of its current machine to increase cutting speeds by 75% to 100% and improve move speed.

Machine specs of current machine

Machine specs of high-performance machine

· Rapid move speed: 300 rpm

· Cutting speed: 150 rpm

· Power supply output: 24 Vdc @ 5 A

· Stepper drive output: 1.5 A

· Motor holding toque: 210 oz-in.

· Rapid move speed: 600 rpm

· Cutting speed: 300 rpm

· Power supply output: 24 Vdc @ 5 A

· Stepper drive output: 1.5 A

· Motor holding toque: 330 oz-in.

Engineering this new product, the CNC manufacturer wants to minimize engineering time while limiting parts inventory. A PowerPlus Stepper Motor provides twice the additional power over the existing motor needed for the new CNC machine without redesigning new parts or changing drives, power supply or the control program. In fact, by using PowerPlus motors, the machine builder can possibly use a smaller size motor and drive system to reach the same performance in a smaller and more cost-effective package.

For more information on the PowerPlus motors, visit moonsindustries.com/c/powerplus-hybrid-stepper-motors-a020102 or email chuck.leonard@moonsindustries.com.

MOONS’ Industries is a manufacturer of key components for motion control, intelligent LED lighting control, and industrial equipment management. MOONS’ cooperates with leading companies to provide creative solutions and high quality products focused on efficiency and performance. For more information, visit moonsindustries.com.

New Physik Instrumente reference on precision motion control and positioning systems for electronics manufacturing

December 1, 2018 By Lisa Eitel Leave a Comment

PI’s new brochure gives an insight on advances in standard and custom motion systems designed to satisfy the needs of industrial test, inspection, and manufacturing engineers in the electronics and semiconductor industry.

With decades of experience in the semiconductor market, the technological diversity and the high vertical range of manufacturing enables PI (Physik Instrumente) to offer motion systems that address the needs of OEMs, integrators, and end users and react flexibly to changes in the market. PI’s new brochure contains examples of high-performance systems for different productions steps, including piezo based nanopositioning systems, air bearings, beam steering systems, XY and XYZ gantry stages, granite-based multi-axis systems, parallel-kinematic hexapods, fast silicon photonics alignment systems, and high-end industrial motion controllers with EtherCAT connectivity.

Applications include aligning fibers and optical components; tactile and optical testing of electronic devices; processing large printed circuit boards; inspecting complex structures; and placing components and tools.

Download the brochure at this deep link on pi-usa.com.

PI has in-house engineered solutions with more than decades of experience working with customers to provide products that meet application demands … and can quickly modify existing product designs or provide a fully customized OEM part to fit the exact requirements of the application.

When do you need a soft starter for an AC motor?

November 21, 2018 By Danielle Collins Leave a Comment

Image credit: WEG Electric

The traditional method of starting an AC induction motor “across the line” results in full voltage, current, and torque being applied immediately when the motor is started, and likewise, being removed immediately when the motor is stopped. While this is the most simple starting method, the high inrush current (often 6 to 7 times the motor’s rated current) and peak starting torque can damage the motor, driven equipment, and product. Across the line starting also causes high peak power demand, which can trigger peak demand fees from the utility company.

A soft starter can eliminate these problems by gradually increasing voltage to the motor terminals during startup, providing a controlled ramp-up to full speed. This lowers inrush current and controls starting torque, reducing mechanical shocks to the system and to the product.

In a soft starter, three pairs of SCRs control voltage to the motor during startup.
Image credit: WEG Electric

Soft starters are also known as reduced voltage soft starters (RVSS).

A soft starter relies on three pairs of SCRs (silicon controlled rectifiers) — one pair for each phase of power — that are applied gradually for portion of each voltage phase, limiting the voltage provided to the motor. In turn, current is reduced proportionally to the reduction in voltage. Torque, however, is proportional to the square of the voltage, so even a small reduction in voltage results in a large reduction in torque. For example: a 50 percent reduction in voltage yields a 50 precent reduction in current and a 75 percent reduction in torque.

Where:

T₂ = Torque at reduced current/voltage

T₁ = Torque at locked rotor current

I₂ = Reduced current

I₁ = Locked rotor current

V₂ = Reduced voltage

V₁ = Full voltage

Once the motor is up to speed, the soft starter is bypassed and the motor is connected across the line, allowing full power to the motor terminals. Soft starters introduce almost no harmonics into the system and typically have efficiencies of 99 percent or better.

A soft starter (solid-state starter) allows current to be limited (top) during motor starting. The corresponding torque reduction (bottom) is proportional to the square of the reduction in voltage.
Image credit: Eaton Corporation

It’s important to note that a VFD (variable frequency drive) can provide the same controlled starting and stopping functions that a soft starter provides, albeit in a different way — by varying the frequency of the voltage, rather than by controlling the amount of voltage, supplied to the motor. VFDs offer other benefits over soft starters, the most significant being the ability to control motor speed throughout the operating range. VFDs can also provide holding torque (full torque at zero speed), which is critical in applications such as elevators and cranes.

For applications such as conveyors and fans that require speed and torque control or current limiting during starting and stopping — but run at constant speed otherwise — soft starters provide a simple, economic solution in a small footprint.

What is DC injection braking and how does it compare with other methods?

November 15, 2018 By Danielle Collins Leave a Comment

Many variable frequency drives (VFDs) include DC injection braking functionality.
Image credit: Galt Electric

AC induction motors excel at driving high-inertia loads at high speeds — in fans, saws, conveyors, and mills, for example — and variable frequency drives make it possible to match the motor speed to the application requirements by varying the frequency of the supplied voltage.

But when quick stops are needed — whether for safety reasons or to prevent wasted time and lost productivity waiting for the load to come to a standstill — high speeds and high load inertia make it difficult to brake the motor and stop the load.

In an AC induction motor, three-phase AC power is fed to the stator windings, creating a magnetic field that rotates. This magnetic field induces a current and a corresponding magnetic field in the rotor. The interacting magnetic fields of the rotor and stator cause the motor to turn.

DC injection braking works just as its name implies — by injecting DC voltage into the motor windings. Before DC injection braking can begin, the AC power to the motor stator must be disconnected — typically by the opening of a relay. In turn, a relay controlling motor braking closes, allowing DC voltage — sourced by the DC bus — to be applied to the windings. To prevent the braking current from exceeding the drive and motor ratings, circuitry in the VFD or in an external braking module controls the amount of voltage applied.

DC injection braking begins when AC voltage is removed (S1 opens) and DC voltage is injected into the windings (S2 closes).
Image credit: KB Electronics, Inc.

When DC current is applied to the motor windings, it creates a fixed (rather than rotating) magnetic field. Braking action is produced by the rotor working to align to this stationary field. The higher the DC current, the stronger the braking force.

The energy generated during braking is dissipated as heat by the motor (particularly the rotor) and the controller, so thermal limitations of these components dictate how much braking current can be applied and the amount of time for which it can be applied before overheating occurs. If DC injection braking is used frequently, the additional heating created during braking must be taken into account when sizing the motor.

Although DC injection braking can be used to hold a load stationary, it’s not generally recommended due to heat generated in the motor. And because DC injection brakes require a constant power supply, they’re not considered fail-safe devices.

DC injection braking is just one of several electrical methods of bringing an AC induction motor to a stop. Two other forms of braking — dynamic braking and regenerative braking — convert mechanical energy generated as the rotor slows down into electrical energy.

During motor starts and stops, or when the load is overhauling, an AC induction motor functions as a generator and produces electrical energy from mechanical energy. This electrical energy can be fed back to the AC power source.
Image credit: Bonitron

In a dynamic braking system, this electrical energy is released as heat through a voltage regulated resistor. In regenerative braking, this electrical energy is fed back to the power supply or to a common DC bus. Dynamic braking is best for applications that require only periodic braking without high heat dissipation demands, while regenerative braking is best for applications with frequent stops and starts or overhauling loads.

A drawback of both dynamic braking and regenerative braking is that the braking force decreases as the motor (rotor) slows down. DC injection brakes are often used in conjunction with dynamic or regenerative braking systems to provide the final braking power required to fully stop the motor and load. And because DC injection brakes can cause thermal problems for the motor and drive, the use of dynamic or regenerative braking in the beginning, together with DC injection braking at the end of the stop, reduces the risk of overheating while providing fast, complete stopping for high-inertia, high-speed AC induction motor applications.

Conveyors with direct-drive motors offer key advantages to Pa. facility

November 11, 2018 By Lisa Eitel Leave a Comment

American Axle Manufacturing (AAM) is increasing the functionality of its St. Mary’s, Pa. manufacturing operations with conveyors sporting advanced drive technology. Small yet powerful direct-drive motors from Electric Torque Machines actuate Dorner conveyors that move small parts around the AAM facility.

AAM designs, engineers, validates, and manufactures an array of driveline, metal-forming, powertrain, and casting technologies — and is known for manufacturing large components such as axles and differentials. However, the AAM St. Mary’s facility manufactures many of the small and lightweight parts that go into AAM drivetrains. Transporting these parts from station to station and within workcells requires small and precise conveyors. The challenge is that the compactness of such conveyors is degraded by the bulk of traditional gearmotors. That’s what prompted AAM to specify conveyors driven by Dorner’s Universal Drive offerings — with direct-drive motors from Electric Torque Machines at their core.

Dorner Conveyor and Electric Torque Machines helped improve the material handling setup inside the Pennsylvania facility of American Axle Manufacturing.

The direct-drive motors have high continuous torque density (particularly at lower operating speeds) to eliminate the need for a bulky gearbox. Integrated into Dorner’s 2200 Universal Drive — which includes the motor, configurable motor mount, and controller — they reduce the conveyor-drive size by nearly 70% while boosting functionality and maintaining required output torque.

“We chose Dorner’s Universal Drive for its unique motor,” said AAM facilities engineer Michael Vandervort. “The motor is smaller and lighter than traditional ac motors … and can run in designated working areas unguarded, because the motor runs cool. In contrast, traditional ac motors are too hot to touch.”

ETM’s direct-drive motor imparts advanced functions to simplify automated tasks.

Vandervort also cited the wide speed and torque ranges of the Dorner Universal Drive as key benefits. “The drive lets us use the conveyors for applications such as slow pass-under vision tasks; heavy accumulation tasks; and high-speed part transfers.”

The on-conveyor inspection function is especially challenging. “At our facility, we use a lot of small conveyors to move light loads. Electric Torque Machines developed motor tuning functions to help stabilize our vision imaging on pass-under applications with very low torque requirements. We really appreciate ETM working with us and developing solutions for our specific needs,” Vandervort added.

“It was energizing to work with industry leader AAM — and encouraging to see the industry ready to adopt new technologies. AAM’s application illustrates the advantages of direct-drive motors,” added ETM V.P. of engineering Scott Reynolds.

What do IP ratings really mean, and how do they differ from NEMA ratings?

November 9, 2018 By Danielle Collins Leave a Comment

Image credit: Kollmorgen

Electrical enclosures, such as those for motors, sensors, and HMIs, are often given what is known as an IP rating, consisting of the two letters, “IP,” followed by two numeric digits — IP65, for example. This IP rating indicates the amount of protection the enclosure provides against the ingress of solid particles and liquids.

Unlike other designations that are often applied to industrial equipment, such as “high torque,” or “waterproof,” IP ratings are specific and internationally accepted. Both the rating system and the testing process are defined by the International Electrotechnical Commission in standard IEC 60529.

The initials “IP” are often taken to mean “Ingress Protection,” but according to IEC 60529, the correct term is “International Protection.”

Decoding the IP rating system

The first numeric digit in the IP rating specifies the protection level against foreign objects, based on the size of the object (12 mm versus 1 mm, for example). The higher the number, the better the protection, with the maximum rating being 6, which indicates a dust-tight enclosure. An enclosure that meets a stated degree of protection against solid objects must also meet all the lower degrees of protection. For example, an enclosure rated IP4x must also meet IP3x, IP2x, IP1x, and IP0x requirements.

The second numeric digit specifies the protection level against the ingress of liquids, based on the amount of liquid and the direction of its approach to the object. The test to determine protection against liquids is time-based, and where applicable, includes specification of nozzle size, distance from object, and delivery pressure.

Image credit: Techathlon

It’s important to note that for protection against liquids, an enclosure must meet all the protection requirements below its rated designation, up to and including level 6 protection. Enclosures rated IP-7 and IP-8 do not have to comply with IP-5 and IP-6 requirements for water jet exposure.

If a device has not been tested or rated for one of the criteria, that digit is replaced with an “X.” For example, IPX4.

An important extension of the IP ratings comes from the DIN standard 40050-9 (which has been rolled into the ISO standard 20653:2013). This DIN standard adds an additional letter, “K,” to indicate environmental sealing. This additional specification applies only to IP6- ratings, which means the device must be dust-tight before the environmental sealing (“K”) designation can be applied.

An IP6-K rating, such as IP69K, means the device can withstand high-pressure cleaning and steam cleaning, with the test consisting of 80° C water delivered at pressures of 8 to 10 MPa (80 to 100 bar) at a rate of 14 to 16 L/min, with the nozzle located 10 to 15 cm from the device at angles of 0, 30, 60, and 90 degrees for 30 seconds each. Food processing and pharmaceutical applications often require electrical equipment that meets IP69K standards, due to the use of high-temperature, high-pressure liquids and steam for cleaning.

How are NEMA enclosure standards different?

NEMA — the National Electrical Manufacturers Association — also provides a standard, referred to as NEMA 250-2014, that defines an enclosure’s ability to provide environmental protection.

While the NEMA and IEC standards have the same general purpose, the protection requirements and test standards specified by NEMA 250 are, in some cases, more rigorous. For example, the NEMA 250 standard addresses environmental conditions such as corrosion, icing, oil, and coolants — none of which are addressed by the IEC 60529 standard.

Protection ratings in the NEMA 250 standard are categorized by whether the equipment is constructed for indoor or outdoor use, and whether it is applied in non-hazardous or hazardous locations. For example, NEMA enclosure Types 1, 2, 4, 5, 6, 12, and 13 are applicable to enclosures constructed for indoor use in non-hazardous locations. Types 3, 4, and 6 apply to enclosures constructed for outdoor use in non-hazardous locations. (Note that there is some overlap between indoor and outdoor use in Types 4 and 6.) Types 7, 8, 9, and 10 apply to enclosures in hazardous locations.

The table below is a simplified description of the NEMA enclosure ratings. For the full definitions and specifications, see the NEMA Enclosure Types document.

NEMA Enclosure Types Guide
Image credit: Marshall Wolf Automation

Can IP and NEMA enclosure ratings be cross-referenced?

In some cases, it is possible to convert NEMA Type ratings to IEC IP ratings, but because NEMA ratings include requirements not covered by IEC, it’s not possible to convert an IP rating to a NEMA Type rating, as the IP rating would not cover the same conditions as the NEMA rating.

The chart below, provided by NEMA, can be used as a guideline for converting NEMA Type ratings to IEC IP ratings.

A shaded block in the “A” column indicates that the NEMA Enclosure Type exceeds the requirements for the respective IEC 60529 IP First Character Designation. The IP First Character Designation is the protection against access to hazardous parts and solid foreign objects. A shaded block in the “B” column indicates that the NEMA Enclosure Type exceeds the requirements for the respective IEC 60529 IP Second Character Designation. The IP Second Character Designation is the protection against the ingress of water.

Feature image credit: Unmanned Systems Source

Applied Motion Products customizes integrated motor for better package handling on conveyor

November 8, 2018 By Lisa Eitel Leave a Comment

Integrated STM/SWM stepper motors from Applied Motion Products help save space, wiring, and cost on advanced conveyors.

For one conveyor handling packages of various configurations, the integrated steppers form part of an assembly to position as rapidly as the analog control updates target position — every 4 msec. Here, the motors also address changing requirements for sorting, alignment, and singulation.

Combining a motor, drive, and control, STM/SWM motors are capable of automatic stall detection and prevention … and include an encoder for feedback on motor position.

Q Programmer motion control software on the STM/SWM integrated stepper-motor controls simplifies configuration to specific conveyor requirements. In addition, EtherNet/IP communications replace noisy analog signals … and eliminate the need to run long signal wires from as many as 100 motors to a central PLC. That lets even the most advanced conveyors coordinate high-speed maneuvers with precision.

For more information, visit applied-motion.com/products or fill out this contact form.

Applied Motion Products specializes in high-precision, cost-effective motion control products including stepper and servo motors, drives, controllers, gearheads, and power supplies. The company serves a diverse industrial and OEM customer base with both standard and customized products. With in-depth motor and control expertise, Applied Motion Products works with customers from initial concept and design through finished product and production to provide the best motion control solutions to a range of markets.

Most efficient vehicle in the world uses brushless motor in drivetrain

November 8, 2018 By Lisa Eitel Leave a Comment

One little hydrogen fuel-cell vehicle holds the Guinness world record for the most efficient vehicle … and uses a slotless brushless 60L-H-175-A from Koford Motors to drive its rear power wheel. This year, the tiny car from the Duke Electric Vehicles team beat the 12,600-mpg efficiency of the PAC CAR 2, in turn designed by a student team at the Eidgenössische Technische Hochschule (ETH) in Zürich, Switzerland.

The Duke vehicle’s conversion of chemical energy (stored in hydrogen gas) to mechanical energy is maximally efficient.

According to Patrick Grady (president of the Duke Electric Vehicles team until he graduated this year) their fuel-cell vehicle Maxwell (in its final World Record iteration) has a 15-mph design speed and 40.8 W of total power (sourced from hydrogen chemical energy). During redesign based of a Maxwell predecessor, the team saw that with a nominal fuel-cell efficiency of 58% average electrical energy from the fuel cell (used by the motor) couldn’t exceed 23.6 W. With a motor and drivetrain efficiency of 87% or so, mechanical power dissipation couldn’t exceed 20.6 W.

The Duke team used the 23-W target extensively to make quick decisions on what components to swap for better.

“For Maxwell prototypes, our Teensy 3.2 microcontroller of choice drew about 300 mW when powered from 5 V … so had we used the Teensy in the final Maxwell design, we would’ve lost 1.3% efficiency just powering the microcontroller,” explained Grady.

Another key to ensuring efficiency was calculating the average power level and then optimizing the fuel-cell system for top efficiency there. But average motor load over a representative race is 23 W … and the Duke team’s original design used a motor most efficient at 80 W.

Yet another wrinkle: To maintain speed during races, the driver cycles the motor on and off. So to allow this mode of operation, the team considered a few system architectures:

No load levelling — with the motor controller directly connected to fuel-cell output with no energy storage between the two

Passive load levelling — with a large supercapacitor bank connected to the fuel-cell output

Active load levelling — with a custom DC/DC converter between fuel cell and supercapacitor bank for total fuel-cell control

Fuel cells are more efficient under constant load than dynamic load. This fact (and how a larger fuel-cell stack to output 80 W has higher leakage and auxiliary losses than a stack sized for 23 W) meant the Duke team needed something to modulate draw from motor off stack.

The first approach would’ve required the fuel cell to supply full motor power … and optimization around 80-W motor power instead of the car’s nominal 23 W. Making matters worse, such a design would’ve necessitated “optimization” for 0-W conditions — requiring low gas leakage and latent current draw in such situations. So the team vetoed this design.

The second method was one the Duke team used on their Gemini car — for a 2018 Shell Eco-Marathon race. This setup employs a dc/dc converter to actively control power with software to stepup fuel-cell voltage to higher supercapacitor and motor voltage. The configurable converter drew constant power from the fuel cell and into a supercapacitor bank for efficiency. This entirely decoupled the fuel cell from the motor and was the theoretically cleanest option. But in the 2018 Eco-Marathon, the Duke team only got 96% efficiency from the converter. Plus it (and associated software and hardware) introduced complexity and design issues.

So for Maxwell’s world-record run, the Duke team employed passive load levelling. Here, a supercapacitor bank connects in parallel to the fuel cell and motor controller. The fuel cell continuously trickles power into the supercapacitors … and then motor discharges the bank in high-power bursts. Supercapacitor size was chosen to hold voltage and power draw off the fuel cell constant over a lap. The supercapacitors added about 2 kg to the vehicle weight, but their simplicity made the car design more robust — and losses from the dynamics of the fuel cell were smaller than the losses from dc/dc converter to boot.

Shown here is the energy flow on Maxwell’s powertrain.

More specifically, supercapacitors run at better than 99% efficiency (with losses from internal resistance) … and that of Maxwell vehicle’s supercapacitor bank is only about 10 mOhm — far lower than that of comparable lithium-ion solutions.

Shown here is Maxwell’s 1200F supercapacitors next to a lithium polymer (LiPo) unit of comparable capacity.

Electric motors do their part maintaining the car’s efficiency

Critical to Maxwell’s efficiency is having an efficient electric motor that’s also light and reconfigurable to myriad input voltages.

“Few motor manufacturers list their motors’ theoretical efficiency, and still fewer have measured dyno results. Unfortunately, most vendors focus on optimizing power density or cost … so we struggled to find resources focused on efficiency,” said Grady. “Our team ultimately chose Koford Motors to power Maxwell. Their data sheets very helpful and their motors highly efficient — with dyno results to quantify that efficiency.”

More specifically, the team picked a Koford 60L-H-175-A motor — with a peak efficiency of about 92% and well-suited sizewise for Maxwell.

Shown here (black, in background) is a Koford 60L-H-175-A motor with a sprocket to engage a chain — which ultimately propels the power wheel on the world’s most efficient vehicle.

Paired to the brushless motor is a chain transmission — to transfer power from the motor shaft to Maxwell’s rear wheel. On the final record-setting Maxwell powertrain, a #25 chain runs on a 14T sprocket coupled to the Koford motor …and then a 120T sprocket drives a freewheel on Maxwell’s rear wheel. The chain transmission let the Duke team easily change gear ratios to let the motor run at peak efficiency … which was helpful, as the motor and drive are most efficient at 100% duty cycle (near top speed).

The Duke students built an inertial dynamometer to measure the efficiency of purchased motors themselves. Results partially masked in red here cover inaccurate results due to an incorrectly programmed motor controller misreporting low-speed efficiency. True efficiency curves are flatter … and the high speed results shown here are more accurate. The students got their efficiency results after the chain transmission (which taxes peak efficiency by 3 to 4%).

Direct-drive option? Not for this efficient design

The Duke team considered using a direct-drive hub motor in Maxwell, as such motors are theoretically more efficient than electric motors connected to power-transmission components. But the team only found hub motors that were heavy, poorly documented, or designed for low-cost electric bikes.

Maxwell’s motor controller uses Hall-sensor feedback for simple block commutation. The team tried out a blended Hall and back-EMF commutation for more accurate timing but found its implementation didn’t match the performance of classic Hall commutation.

To save power, Maxwell was programmed to shut off most electrical systems when the motor wasn’t running. The car’s driver was given just a button control the motor — not the more standard throttle potentiometer. Upon depression, the button triggers a wake-up sequence and throttles the motor at constant current. Removing the driver’s throttle control boosts consistency and performance by keeping the electric motor running near its optimal point.

Visit this blog deep link on duke-ev.org for more information from Patrick Grady about the Maxwell fuel-cell vehicle — and on challenges related to getting top performance out of Maxwell’s off-the-shelf Horizon H-100 PEM fuel cell. At the blog, Grady also explains the advanced analysis the team performed on various racetracks to pick one that would give Maxwell the best odds of beating the world record for vehicle efficiency.

AutomationDirect adds SureStep stepper system motors, encoders and inertia dampers

November 2, 2018 By Miles Budimir Leave a Comment

New stepper motors, encoders and inertia dampers have been added to the SureStep system of step motor control. SureStep series high-torque industry-standard NEMA 14, 17, 23, and 34 stepper motors now provide holding torque from 8 to 1,288 oz-in. The new smaller frame size NEMA 14 motors (1.4-in. wide) start at $22.00 and are available in single and dual shaft versions.

The SureStep family has options for open loop control (no encoder), position monitoring (external encoder feedback), and position verification (integrated motor/drives with internal encoder). Replacement and optional encoders (starting at $42.00) are available for standalone dual-shaft motors and standard integrated motor/drives in all NEMA 14, 17, and 23 sizes.

Fixed resolution encoders are available in 400 pulses per revolution (ppr) and 1,000 ppr; new configurable encoders allow resolution selection from 48 to 4,096 ppr (the default is 400 ppr). A free downloadable configuration utility autodetects the encoder and allows ppr selection.

New step motor inertia dampers (starting at $13.00) smooth out steps in a typical step motor, resulting in a quieter and smoother motion when rotating between steps. The dampers also reduce resonance and possible micro oscillations when moving from step to step and can be used as a hand wheel to directly rotate the position of the rotor when power is removed from the motor.

SureStep Stepper System motors, encoders and dampers are CE approved and backed by a one-year warranty.

For more information, visit www.automationdirect.com/stepper-systems.