# Measurement (sensor) of torque - ?

Hi! I'm working on a project in which you want exercise the power servo drive. To do this I need to measure the torque on the servo how can this be done? Are there torque sensors? Can I replace them with the measurement of electrical signals to the servo? Thank you in advance for your advice.

If what you want is a measurement of how much 'work' the servo is having to do to move the load it has attached to it, probably the easiest way is to try and measure the current load it's drawing. Either a hall effect current sensor on the power wire or a low side current sampling resistor on the ground wire could be used to measure the "work" the servo is doing.

More precise then that would involve mounting a load cell between the servo and it's mechanically attached load and read the instantaneous load Vs distance traveled to get ft/pounds or whatever units you are trying to calculate. I think that involves a integration formula or some kind, right?

Lefty

Thanks, in my project there is no linear relationship between rotation servo and torque. I need to ensure that its rotation is only when a certain force. Option to measure the current strength like You can read more about it?

Ok, I need to measure the torque moment(static) of the external force coming to the servo, I want to do this by measuring the voltage consumed by a servomotor, how is this possible? sorry for my English.

I use the metal gear digital torque servo (1 / 10 - format), which should turn only in the case when it is loaded with torque (I can calculate it separately.) I need to adjust some of the efforts will be spinning the servomotor. Greater accuracy of measurement is not required or I can do the calibration yourself. How can i measure the current and servo control with the Arduino? What are the details still need to tell? Thanks for your help.

How can i measure the current and servo control with the Arduino?
What are the details still need to tell? Thanks for your help.

This would involve wiring a low value resistor in series between the servo’s ground wire and the ground connection of the system. As current flows through the resistor there will be a small analog positive voltage developed that will be proportional to the current being consumed by the servo motor. This voltage would then be wired to a analog input pin and read by the software to determine how hard the servo is working at any given instant.

To properly size the resistor we would need to know the worst case maximum current draw of the servo under stalled condition.

Lefty

Thank you Lefty, but I don't quite understand, my servo has 3 input (+5 power, ground and management), grounding the system in common with the Arduino, then it turns out that I only measure the voltage on the ground? Or if I had to do a separate power supply for servo motor? Can you draw a diagram?

Please forgive me, but I badly speak English and therefore it does not matter explain its purpose. I'm going to use a servo MG996R, which I have. Torque is how I calculate the product of the force on the shoulder, where the axis is the axis servo. Actually I need to define a load on the axle actuator or not. If there is a certain load on the servomotor should I turn it a few degrees. What else should I tell?

pryschik: Thank you Lefty, but I don't quite understand, my servo has 3 input (+5 power, ground and management), grounding the system in common with the Arduino, then it turns out that I only measure the voltage on the ground? Or if I had to do a separate power supply for servo motor? Can you draw a diagram?

I can't draw it at this time. So instead of the servo ground wire going directly to system ground, it goes to one end of say a .2 ohm 2 watt resistor, the other end of the resistor wires to system ground, which is also arduino ground. Now if the servo was to draw two amps of current under load the servo end of the resistor would measure + .4vdc. That point could be wired to a arduino analog input pin and be measured with analogRead() statment.

Again the actual value of the resistor needs to be sized for the maximum current draw rating for the servo.

Lefty

Thanks, I'll try and sort out about my results will explain later.