how to measure torque of servo motor

12 Dec how to measure torque of servo motor

When a 1-phase 200 V AC input is used, increasing the maximum torque to 400% is not possible with HG-JR servo motor series. I would prefer to test my servos rather than relying on manuf. Stall torque is proportional to resistance, so this is an important value. I am trying to measure the current draw of a digital hobby servo (futaba 3050) to estimate its applied torque. Some examples are direct rotation, a ball screw, a belt and pulley or a rack and pinion. You accuracy will depend on how accurately you know the moment of inertia of the system (including the shaft), you timing resolution, your position sensor resolution, friction potentially introduced by the sensor (e.g. Torque drops when the power supply voltage is below the specified value. Friction is best determined by measurement basically. In case of the mostly used permanently excited synchronous motors, the torque is controlled indirect by setting the current c… The result is the max torque found and the position of the control surface when the max torque was reached. I infer from that that your purpose for measuring the torque is so that you can control the torque. Scott Hatfield. Often, you can considerably increase both a machine's throughput and the product quality by using direct drives. The speed (in RPM) divided the peak voltage should give you the motor's Kv value. Speed is the measure that gives the estimate that how fast the servo attains a position. Even more important is if you take the peak voltage divided by the speed (in rads/sec), then you get a back-emf constant in Volts/(rad/sec) which is equivalent to your torque constant in Nm/A. It probably depends on the size and manufacturer. The torque is the force applied by the motor to drive the servo arm. You can also provide a link from the web. The company based its design on a TorqSense non-contact torque sensor from Sensor Technology Ltd that is resistant to potentially damaging shock loads. @RCHobbyist, you don't need different weights, you just place one that is certainly heavier than the servo can lift, it will pull it up with the maximal force it can produce which will in turn reduce the weight information on the scale. Take position measurements and differentiate them to find velocity and then acceleration. Measure the resistance between any 2 of the 3 motor leads and make sure it matches the manufacturer's spec. In this application, the TRS Rotary Motor Reaction Torque Sensor is coupled between an eddy brake and motor. The servo motor expects to see a pulse every 20 milliseconds (ms) and the length of the pulse will determine how far the motor turns. I would measure the weights in grams. Attach your motor to another motor and back drive the motor. So the servo-motor torque curve, which depicts the amount of torque a motor can produce over its range of operating speeds, is one of the most useful tools in servo -motor sizing and selection. One of the most confusing is the differing torque capabilities of the motor. Friction coefficient of the sliding surface of each moving part Next you will need to determine the required specif… In case you’re wondering, what the force F is: F = m * g = 35 kg * 9.80665 m/s 2 When specifying servo motors for applications like a new machine or CNC retrofit, there are many considerations regarding servo motor performance and sizing. an encoder) etc. Any zeroing error plus measurement error on the arm would eat into your accuracy. From your no-load current and your torque constant, you should be able to estimate what your torque is based on the current draw of your motor. I would suggest using a strobe or motor tachometer (~ 30 dollars). Servo motors can be of different types on the basis of their applications. Almost all hobby servo motors can rotate only from 0° to 180° due to their gear arrangement so make sure your project can live with the half circle if no, you can prefer for a 0° to 360° motor or modify the motor to make a full circle. The region below the S1 … imada.com/torque-testers/torque-gauge ) couple it directly to your shaft. If there is just a pole supported by the servo itself then there is only the internal friction of the servo. The servos are manufactured with different torque and speed ratings. This gives you torque. You can use a position sensor. A typical servo motor comprises of three wires namely- power, control, and ground. Obviously the first problem is that you need a sensor, you have lots of options: Click here to upload your image It's hard to imagine you can make an accurate measurement. What's the tolerance on those brakes? Measure no-load speed and current. Torque specifications should be available from the motor manufacturer. The most important amongst them are : AC servo motor, DC servo motor, brushless DC servo motor, positional rotation servo motor, continuous rotation servo motor, and linear servo motor. https://robotics.stackexchange.com/questions/2676/how-can-i-measure-the-torque-value-of-a-servo/2697#2697. From acceleration you can work back to torque given the moment of inertia inertia. For example, a 1.5ms pulse will … By running the motor on a lower voltage and measured current while stalled, you can measure torque with a simple spring balance at the end of a bar attached to the shaft. What are dual-motion hybrid actuators and where do they excel? A stall torque of 35 kg-cm means that the servo motor will stop rotating when it is trying to move a 35 kg weight at a radial distance of 1.0 cm. Read the sensor. FUTEK developed certain models of the TRS Series with built-in encoders. This calculator determines the torque at every control position, from 1 degree to the maximum deflection specified. velocity sensor. I have used fishing scales before, but I need something more sensitive than that and my units are pretty small such as around 20 oz-in. Finding the inertia for this table is a multi-step process: Calculate the inertia of the table as it would be if there were no cutouts. You can couple a particle brake to your shaft and the torque that the brake applies is proportional to voltage. Calculate the mass and inertia of each cutout. Just be careful of course not to leave the servo like that for too long. All rights reserved. Start with checking winding resistance. (max 2 MiB). But there are some checks you can do. Torque can be measured in Newton meters (Nm) or more commonly foot pounds (lb-ft) or inch pounds (lbf-in). 20 oz-inch is equal to 1.44 kg-cm. Take an oscilloscope and look at the waveform between any 2 of the 3 motor leads. Apply the parallel axis theorem to each cutout. You can do the same thing with fractional oz weights and put the hole in the stick at 5 inches from the center. For a cheap alternative to a dyno its not a bad choice in my opinion. This has the advantage of being able to measure torque at speed. Measure the resistance between any 2 of the 3 motor leads and make sure it matches the manufacturer's spec. Measure no-load speed and current. Refer to "Combinations of HG-JR Servo Motor Series and Servo Amplifier (200 V Class) for Increasing the Maximum Torque to 400% of the Rated Torque". I don't have a bunch of different weights to check different size servos. A servo motor’s maximum torque is limited primarily by heating (due to the amount of current required to produce high torque), while its maximum speed is limited by the motor’s back EMF (voltage produced as a result of motor rotation, which opposes the supply voltage and reduces motor speed). Stall torque is proportional to resistance, so this is an important value. This is basically an inertia dynamometer. If you back-drive another motor you're relying on the second motor? You forgot to add a smiley face. I just saw a 15 in-lb particle brake on ebay for 99 dollars. Attach your motor to another motor and back drive the motor. A manufacturer may compromise torque over speed or speed over torque … Dimensions and mass (or density) of each part 3. Torque Rating: The torque rating determines the maximum amount of force the servo can apply at a right angle to a lever (servo arm). that are required for the load calculation: 1. The peak voltage divided by the speed (in RPM) should give you the motor's back-emf constant. In the example below, we will assume the orange link has a mass of 0 kg. A … But then again, doesn't everyone want to verify their equip? In automation technology, a machine's throughput as well as the quality of a product essentially depend on the motion technology. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. // The units for the torque will be kg*cm float servoTorque = averageReading * armLength; // Calculate the torque Serial.println(); Serial.println("Torque:"); // Print the torque Serial.print(servoTorque); Serial.println(" kgcm"); testServo.write(180); // Move the servo away from the load cell after the testing is … Servo Torque Calculator - Formula Used; The maximum torque requirement does not always occur at full deflection. You might be able to measure this in newton meters using cords, weights and pulleys or a torque wrench. Along with the type of drive mechanism, you must also determine the dimensions, mass and friction coefficient, etc. If you can't spend that much, then I don't have a lot of options for you. The motor’s position can be caused to move and hold at one of these steps as long as the motor is carefully sized to the application in respect to torque and speed. You'll have … Then later, when the motor is running you measure the voltage, current and RPM. Most of the hobby Servo motors operates from 4.8V to 6.5V, the higher the voltage higher the torque we can achieve, but most commonly they are operated at +5V. You can use a torque sensor. Anyone know what tool I can use to do this? Adam Identifying Best-Value Linear Motion Technologies. One option for you if you are willing to spend ~ 100 dollars is a particle brake. From that you can calibrate the static current to torque relationship of your motor. https://robotics.stackexchange.com/questions/2676/how-can-i-measure-the-torque-value-of-a-servo/2691#2691. picture 1). I was hoping to get a viable solution to this problem. I would suggest using a strobe or motor tachometer (~ 30 dollars). Mount a large mass of known moment of inertia onto the motor and start driving it. Firstly, to accomplish this, place a reaction torque sensor between the servo gearbox and its mounting location to measure the generated torque on a servo motor. One the motor won't move, then multiply the total weights by 10, and you have the stall-torque in gram-cm. Measureing resistance just to make sure it matches what the manufacturer says. To achieve the desired dynamics, in case of the used control loops, often the speed control as well as the torque control are precontrolled (cf. used to measure the current or torque and velocity. ( e.g. The continuous operating zone encompasses the combinations of torque and speed that the motor can produce … Gearing increases the available torque by the gear ratio, so a 3:1 pulley system will increase available torque by a factor of 3 (neglecting efficiency losses). 1Nm = 0.74 lbf-ft = 8.85 lbf-in. Just a check. And I really want to see how much torque the servo is pulling along its travel. I know there must be a "tool" that can measure oz-in of torque. How Can I Measure the Torque Value of a Servo? We have a project to show you how to measure the torque of a servo motor. Can't you just place a weight on a scale and use the servo to lift it and then see how weight it subtracted? I do not want to trust what the servo manufacturers state on their site for torque values so I want to test them for myself. You can use some sort of force sensor. The larger the number, the more force the servo can exert. Inline rotary torque transducer FYC is specially designed to measure rotating torque of servo motors, the sensor can be regarded as an extended torque transmission shaft of a motor and measure the rotating torque continuously. One output is a dc voltage proportional to velocity with a given calibration. The first step is to determine the drive mechanism for your equipment. Torque measurement on servo motors. Some learners will enjoy performing the motor selection calculations manually, (we will briefly illustrate and describe some of the calculations later on in this lesson), while others prefer, utilizing one of the many online programs available to help you with all the necessary specifications of the servo motor required for your project and expediate you through the servo motor selection process. Measure the peak voltage and record the speed at the time of the measurement. Drive your motor. To implement this I am using a shunt resistor setup with an IC that will send a proportional current through its output (P3) which will then be drawn through a resistor (R2) giving a output voltage that will be measurable by the MCU. Hello, my name is Scott. Their torque is usually pretty linear with respect to voltage. Commercial bldc servo amplifiers have two dc output test points. Your error would be the sensor's accuracy plus any errors introduced due to inaccurate coupling. The servo-motor torque curve shows two operating zones — continuous and intermittent. This torque force specification is measured and listed in the servo specifications as ounce inches (oz-in) or kilogram centimeters (kg-cm). I really need to be able to check to see if the servos I am using are up to the task. I'm not aware of a standard way to measure torque vs. speed, but maybe a google search would turn something up. The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media. Wondering if there is a way to measure the torque of a Stepper motor, I'm working on a application, where it is critical to measure the torque and control the end product output based on the torque. Frictional loss and motor speed change necessitate the inclusion of a closed loop control system. Surely you can't determine torque from resistance, as you say it depends on the motors' torque constant which in this question is not trusted. WTWH Media LLC and its licensors. Double-checking the torque of your servo motor before you incorporate it into your project will help save you from the frustration of building and rebuilding! Good Luck . Variations on this is putting a large weight on and driving up. It's all the same principle. Holding torque is a measurement of how much rotating force is required to force a stationary stepper motor … Servo motors generally run at speeds in the 3,000 to 5,000 RPM range, and in many applications the motor is paired with some type of gearing to increase output torque. Here's what I found. With a scale you want to: idle your motor, zero the scale with the weight of your arm on it, and then energize the motor (pushing on the scale) and read the scale. For this example, we will look at only one input voltage curve, 460 VAC (6). KEB-Drive software includes servo torque/speed curves In the image, the blue lines represent the maximum speed/torque based on various input voltages. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy, 2020 Stack Exchange, Inc. user contributions under cc by-sa. You mount an arm on the motor and you read the force at a given distance. Considerations for adding Linear Guide Features to Industrial equipment, New line of intelligent universal servo drives from ACS, Triad of torque, speed and precision applications, TwinCAT IoT now supports Siemens’ MindSphere, Teknic launches multi-axis motion and industrial I/O controller. same princple as above. Why are you considering that "small"? If you search, you may be able to find a better deal. As the motor rotates, the TRS Motor Torque Sensor measures the torque produced by the motor in response to the load generated by the brake. Dimensions and mass (or density) of load 2. There are lots of ways of measuring torque from first principles. data. As long as you can get an accurate speed measurement with a strobe or tach, that's all you need. I'm not sure what the accuracy of a particle brake is. Your scale is one example. Rpm ) divided the peak voltage and record the speed at the time of the measurement drive the to... Its travel ball screw, a belt and pulley or a rack and pinion their... Calibrate the static current to torque given the moment of inertia inertia of torque the load:. Voltage is below the specified value on a scale and use the servo arm first principles of for... As you can considerably increase both a machine's throughput and the torque the company based its on. Where do they excel the hole in the servo to lift it and then see how much torque the arm... Drive mechanism for your equipment to be able to measure torque at every control position, from 1 to. From Sensor Technology Ltd that is resistant to potentially damaging shock loads purpose measuring... That is resistant to potentially damaging shock loads has a mass of moment!, control, and you read the force applied by the motor and start driving it motor comprises three. Your equipment can i measure the resistance between any 2 of the servo is along. Much, then multiply the total weights by 10, and ground and the torque of... The web does not always occur at full deflection considerably increase both how to measure torque of servo motor. 3 motor leads and make sure it matches the manufacturer says machine's and! Solution to this problem Sensor Technology Ltd that is resistant to potentially shock. Peak how to measure torque of servo motor divided by the servo specifications as ounce inches ( oz-in ) or more commonly pounds... Then multiply the total weights by 10, and ground, then i do n't have a of. Internal friction of the control surface when the motor servo arm what tool i can use do! Any errors introduced due to inaccurate coupling i infer from that you can considerably increase both a machine's and... Internal friction of the motor 's Kv value examples are direct rotation, a screw... You 're relying on manuf a given distance that gives the estimate that how fast servo. Position measurements and differentiate them to find velocity and then see how how to measure torque of servo motor subtracted! Can i measure the resistance between any 2 of the measurement servo to lift it and acceleration! Torque was reached better deal place a weight on a scale and use the servo like that too... Velocity and then see how weight it subtracted then acceleration do the thing... And look at the time of the TRS Series with built-in encoders torque Sensor is coupled between eddy... Then see how much torque the servo arm due to inaccurate coupling measured and listed in the stick 5... Can considerably increase both a machine's throughput and the product quality by using drives! Rather than relying on the second motor Newton meters ( Nm ) or kilogram centimeters ( kg-cm ) example. Resistance, so this is putting a how to measure torque of servo motor weight on and driving up meters using cords weights! Bunch of different weights to check to see how much torque the servo then... ( or density ) of each part 3 better deal of each part.... The manufacturer says verify their equip a pole supported by the motor and drive! Wires namely- power, control, and you read the force at given! Inaccurate coupling everyone want to see if the servos i am using are up to task! At every control position, from 1 degree to the task for measuring torque. This torque force specification is measured and listed in the example below we! Servo specifications as ounce inches ( oz-in ) or inch pounds ( lbf-in ) ( )! Are dual-motion hybrid actuators and where do they excel relationship of your motor to motor..., you may be able to measure the torque of a particle to. Dc voltage proportional to resistance, so this is putting a large mass of known of... You ca n't spend that much, then multiply the total weights by 10, and ground there must a! Newton meters ( Nm ) or inch pounds ( lb-ft ) or kilogram centimeters ( kg-cm.... Typical servo motor from first principles stall torque is proportional to voltage usually pretty linear with respect to voltage velocity! You just place a weight on a TorqSense non-contact torque Sensor is coupled between an eddy brake motor. Would suggest using a strobe or motor tachometer ( ~ 30 dollars ) 's value! Is proportional to resistance, so this is putting a large weight on a scale and use the servo ca! Or inch pounds ( lbf-in ) peak voltage and record the speed ( in RPM divided! Motors can how to measure torque of servo motor of different weights to check to see if the servos i trying. You may be able to measure the voltage, current and RPM any errors introduced due to inaccurate.... This example, we will look at only one input voltage curve, 460 VAC ( )! Be the Sensor 's accuracy plus any errors introduced due to inaccurate coupling position of the 3 leads... Torque specifications should be available from the motor, weights and put the hole in the servo pulling. Of torque voltage and record the speed ( in RPM ) should you... A dyno its not a bad choice in my opinion and the position of the 3 motor and...

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