Apr. 14, 2025
An electric motor (E-motor) test stand (also referred to as a bench) is a test stand for reproducible testing of electric motors. In addition to the mechanical design, an electric motor test stand consists of accompanying measurement devices, sensors, and application software. The bus systems used to control and monitor the test objects are also included in the test stand. There are a variety of different types of test stands, such as developmental test stands, endurance test stands, end-of-line (EoL) test stands, and hardware-in-the-loop (HiL) test stands.[1]
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Testing of electric motors is generally done to determine characteristic curve points or entire characteristic curves. There is also additional testing that is done to characterize the electromagnetic behavior of the test object: e.g., generative measurements, measurements of cogging torque, and discharge measurements.
A typical test setup includes a load machine, clutch, and torque transducer. An externally applied load is used to strain, i.e., load, the motor. Using this method, simple characteristics can be directly mechanically acquired and the derived variables calculated. From the input current and input voltage, the absorbed power can also be recorded. Similarly, from the rpm and torque output values, the mechanical power output can be determined, and thus, the efficiency of the motor.
Using the test object-s own inertia to dynamically run through the characteristic curve: This method tests electric motors without a mechanical coupling and without torque and speed measurements. The test is carried out via the terminal voltage and current values. The parameters are determined by means of mathematical models.
Brushless motors are often used as a propulsion component for UAS (Unmanned Aerial System). In order to optimize your flight time or lift capacity, the brushless motor should be carefully selected by testing it. Different tests can be executed such as endurance testing, flight replays, reliability testing, or pass/fail tests for quality control. RCbenchmark (Tyto Robotics Inc.) is the main manufacturer of test stands specialized for UAS propulsion testing.
A noise analysis is performed by means of a suitable excitation function. The test function should be selected so that all the forces that produce noise can be analyzed by respective sensors. The most common sources of noise are rolling bearings, commutators, and electric forces.
Electrical machines, which are energized and driven from the outside, induce a voltage which can be measured on the connection lines of the machine. The induced voltage is proportional to the speed and excitation. The course of the induced voltage gives information about the windings and the characteristics of the excitement around the circumference. The measurement of the induced voltage provides a simple method to diagnose the electromagnetic behavior of the motor. Regularities are derived from a moving conductor loop in a constant magnetic field.
In rotating electrical machines, the number of poles in the rotor multiplied by the number of strands in the stator equals the number of preferred stable positions in which the rotor moves. The amount of cogging torque is significantly influenced by the structural design. Regardless of the type of measurement, the load machine drives the currentless test object. The cogging torque is measured with a torque transducer connected between the test object and the load machine. The cogging torque can be determined in two different ways: Measurement of the cogging torque at slow speed or measurement of the cogging torque with closed-loop position control. For both measurements, an active load machine is required to drive the test object.
A test bench is an assembly or system designed to test the functionality and performance of a motor or motor controller under various conditions. It simulates real-world operating scenarios to ensure that the motor controllers perform as expected, without needing to install them in a live, operational setup. Test benches help detect and resolve potential issues such as overheating, inefficiencies, and faults early in the development process.
A test bench is an integrated setup designed to evaluate motor controllers and motors under various conditions. Composed of core components like a desktop computer, controller, motor, feedback systems, and sensors, the test bench simulates real-world operating environments to measure performance, durability, and efficiency. Test benches provide a controlled environment where motor controllers can be stressed under specific conditions to detect issues before deployment.
In our laboratory, we primarily work with low-to-mid power motors that are compatible with SOLO Motor Controllers and can be tested against their datasheets. Our previously designed test bench allowed us to perform various types of tests, including endurance, load, and temperature tests. It was also instrumental in achieving multiple certifications for our controllers.
This motor test bench was redesigned for one of our customers to meet their specific requirements for testing new types of controllers. Some of their critical demands included an external DC power supply (as they already had one), a universal mount for different motor types, reliable power control capable of handling up to 200A, safety features, CAN and USB ports on one of the control panels, compact size and weight, and mobility.
In this chapter we’ll explain the design and control features which helped us to achieve the requirements. If you’re interested in our previous motor test bench please follow this link and subscribe to our channel.
One of the most critical and frequently used components is the motor/load bracket. Our experience shows that the more universal the bracket, the quicker the tests can be conducted, minimizing the need for additional machining and reducing time and cost inefficiencies. However, this approach has its limitations, as some motors have completely different mounts such as outrunners or mounting hole positions that deviate significantly from standard universal brackets.
Our solution accommodates motors with three- or four-bolt types mounting configurations, where the mounting holes are equidistantly positioned along a curve with a minimum diameter of 120 mm and a maximum of 210 mm. These brackets are compatible with M8 bolts or thinner bolts when used with additional washers.
The industrial approach used in designing the motor test bench ensured it is both robust and safe. However, the assembly is relatively heavy, requiring proper wheels to make it mobile and easy to transport. Additionally, damped stands are essential to ensure a stable and level horizontal platform for conducting tests.
This design incorporates a combined solution of wheels and stands, simplifying the construction and saving space while maintaining functionality and stability.
Testing motors or loads often carries risks of mechanical failures, increasing the likelihood of hazards. The powertrain includes components such as shafts, couplings, sensors, and other devices with wires and mounts, which, if improperly secured, can be ejected from the operating area. To address this, a safety cover made of 5mm plexiglass was designed.
The cover is mounted on two industrial hinges attached to aluminum beams using standard mounts. Additionally, air springs are installed on both the right and left sides of the cover to keep it securely closed or assist during opening. A safety limit switch detects when the cover is slightly opened and activates the Safe Torque Off function to ensure operational safety (page 49 of SOLO MEGA User Manual).
The second crucial component, after the operating area with high-power mechanical devices, is the electrical cabinet. A reliable contactor is required to handle the 200A current, controlled by other relays and buttons located on the operator panel. All electrical components must be housed in a closed, secure space where they can be safely wired and easily maintained if necessary.
In this case, an industrial approach helped create a simple electrical panel, which was later installed in the machine and wired in place, as shown in the following images.
A shaftless magnetic incremental encoder was used in this setup due to its compatibility with the motor’s back-side mount and its compact design. Below is some information from the encoder’s datasheet for reference.
The encoder is designed for mounting on electric motors or other devices to measure shaft position and speed. Its robust metal housing ensures top-level protection (IP68), high EMC immunity, an extended operating temperature range, and excellent resistance to shock and vibration. Output signals are provided in industry-standard formats, including absolute, incremental, analogue sinusoidal, and linear voltage.
The encoder with an external zeroing feature allows the zero position to be set using a zero pen and operates on a 5 V supply voltage. In its base configuration, the encoder offers resolutions up to 14 bits (16,384 counts per revolution), maintains an installation air gap of ±0.1 mm, and is priced economically.
The encoder supports binary resolutions ranging from 5 to 12 bits, features a wider installation air gap tolerance of ±0.5 mm, and is more cost-effective than the base configuration.
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The motor controller is one of the key components of the test bench. In some cases, the motor controller can be as crucial a testing unit as the motor or the load itself. In this project, we used two motor controllers with identical power ratings, as both the motor and the load sides are equivalent electrical motors.
SOLO MEGA is a family of high-power motor controllers that are designed for high-current applications. This product is designed to support various types of electrical motors like DC brushed, Brushless DC and PMSM motors up to 60V with the supply voltage and the continuous current of up to 120 Amps DC or 110 Amps RMS, this will enable SOLO MEGA to be utilized in wide range of products and projects and eventually speeding up the developments and time to market for its users.
SOLO MEGA can be commanded in two different ways, either by sending Analogue voltages or PWM pulses which is called Analogue Mode, or totally by sending Digital data packets through isolated UART, isolated USB or isolated CAN bus lines. This will give a high flexibility in terms of system setup to the users and they can choose the best way to wire up their systems using SOLO.
As explained earlier, the “Safe Torque Off” (STO) is a hardware-level protection mechanism that reliably disconnects the energy supply to the motor in your application. For proper operation of SOLO MEGA, providing STO wiring is mandatory.
The STO uses negative logic, meaning that when the STO lines are powered to a high state (e.g., +5V), the unit activates the power electronics controlling the motor. Conversely, when the STO pins are left open or grounded (e.g., connected to ground), the unit stops supplying current to the motor, causing it to stop according to its natural time constant.
In this project, the STO line passes through the control panel’s STO button (via Normally Closed contacts) and the safety cover’s limit switch (via Normally Open contacts). This setup ensures that while the cover remains closed and the STO button is not pressed, the STO function is disengaged, allowing the motor controllers to operate freely. However, if either of these elements changes state—such as the cover being opened or the button being pressed—the STO function engages, cutting the motor’s power supply and stopping the motors. Additionally this will be explained in the control logic and electrical diagrams chapter.
The AC power serves as the main supportive power source, supplying the actuating coil of the general DC power contactor and the AC-DC converter that generates 24VDC for other components. The AC power input features a standard IEC C14 inlet socket with a 2m power cord. For safety, the earth wire is connected to the aluminum frame and the electrical panel within the control cabinet and is not interrupted by the AC switch.
The AC switch controls both the live and neutral lines, which then pass through a circuit breaker equipped with a current leakage detection sensor. If an AC current leakage occurs anywhere in the circuit, the circuit breaker disconnects the power supply to prevent electrical hazards. The overall schematic is illustrated in the diagram below.
The 24VDC power supply is used in the machine as it is one of the most common standards in industrial applications. It provides electrical energy to activate the control relays for the fan, the STO functions of both motor controllers, and the secondary power contactor, which serves as the actuating unit for the main DC power contactor. Additionally, all control lamps and buttons on the control panels are powered by 24VDC, ensuring safety for operators, even if some control elements malfunction.
The 24VDC section of the electrical diagram, together with the previously discussed AC section and the self-holding relay logic, will be explained and illustrated in the paragraphs below.
The concept of self-holding relay logic can be divided into several key steps: activating the self-holding scheme, deactivating it, adding safety features, and providing state feedback (using indicator lamps). This concept is illustrated and explained using the sections of the diagrams provided below.
To activate Contactor 2, its actuating coil must be supplied with 24VDC, which is achieved by pressing the green button “Main DC On” on the operator panel. Once activated, the normally open (NO) contacts of Contactor 2 close simultaneously. Two of these contacts supply AC power to Contactor 1, while one of the remaining contacts supports the coil voltage of Contactor 2 itself, maintaining its engagement and holding both Contactors 1 and 2 in an engaged state by providing 24VDC to the actuating coil of Contactor 2.
An additional safety feature of this approach lies in the design, where the main power switch remains in the Normally Open position until the operator actively turns it on. This ensures that whenever the machine is turned off using the AC mechanical switch, in the event of a circuit breaker issue, or due to a general AC power line failure, the contactor responsible for the main power supply will automatically disengage its contacts, cutting power to the drive units. This mechanism provides an extra layer of protection against unintended power delivery.
The schemes above illustrate how the main power of the entire system is controlled. However, there are secondary elements that enable safe and convenient operation of the machine without disconnecting the main power supply. These features allow the operator to change data wires, measure temperature, or adjust mechanical components in the working area without unnecessary power interruptions.
For this purpose, the STO (Safe Torque Off) function of the SOLO MEGA controller is utilized. It ensures that no mechanical motion occurs when the STO button is pressed or the chamber cover is opened, providing an additional layer of safety during maintenance or adjustments.
The diagram can be divided into several steps to simplify the explanation. These steps include: connecting the STO relays for the two controllers, establishing the logic for the STO state indicator lamps, and integrating the fan control to prevent overheating.
In this machine, the STO function is wired to a safety relay using the internal +5V non-isolated supply voltage, as shown in the figure below. This internal supply voltage connects directly to the STO inputs. The safety relay can be controlled by external commanding devices for enhanced safety and reliability.
In our setup, these commanding devices include the STO Swift Release red button and the chamber cover limit switch, which are connected in series to supply the relays STO 1 and STO 2 and ensure proper operation and safety compliance.
The indicator lamps are connected to an additional relay that operates in parallel with the two relays dedicated to the STO function. This setup supplies +24VDC to the white lamp, which is connected to the relay’s Normally Open (NO) contact. The white lamp illuminates when the STO relays are engaged, indicating that the controllers are allowed to provide torque to the motors. Conversely, when the relays are disengaged, the orange lamp lights up to indicate that the Safe Torque Off (STO) function is active, preventing the controllers from injecting current into the motors.
SOLO Motor Controllers offer custom test benches designed to adapt to unique needs or Standard Solutions. From specialized hardware setups to advanced testing features, ensuring each solution is both practical and efficient.
A Solution That Fits
SOLO’s Test Benches are built with flexibility in mind, tailored to match specific applications. Whether for small-scale testing or more demanding projects, they combine reliability, ease of use, and precision.
End-to-End Support
SOLO takes care of everything:
With SOLO’s custom test benches, users can approach motor testing with confidence, knowing the tools are designed around their needs. Those interested can reach out to explore the possibilities of a tailored solution.
The final result is a compact, mobile motor test bench ideal for laboratory tests, offering the capability to control the process via CAN lines. This allows for parameter adjustments and data recording for further analysis.
A key component of this project is the Motion Terminal online software, which provides real-time monitoring of motor and controller behavior. It also allows users to record and export data for detailed analysis, including mechanical torque graphs.
Refer to the figure below for an example of the Motion Terminal in operation. Watch our video about the test bench, and don’t forget to subscribe to our channel to learn more about motor control.
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