Can I find the input voltage of a servo using this equation?

[zelreedy1]

Hello. I've posted two other posts about my project designing and controlling a Ball and Beam system, with links attached below. As I'm doing it for an engineering project, I'm supposed to model the system mathematically, calculate the PID parameters, etc. A step of modelling the system is to find the input voltage of the servo. I've come across many research papers using this equation to find it:

This is a general motor equation, with I being the armature current, Ra being the armature resistance, Km as the motor torque constant, etc. My question is: Is there a way, if they exist, to find thsese values for a servo motor? The other question is, does a servo motor even have varying voltage input, or is its input a constant one, i.e. the rated one in its datasheet?

The two other topics about the same project:

Inaccurate IR Sensor Reading

[Mod edit: Please note that @zelreedy1 has 2 topics open about the same subject. They are linked in the sense that they are about the same project, but are different questions. The other one can be found here Ball & Beam System Target Landing ] I'm using the GP2Y0A21YK Sharp IR Sensor in a ball and beam system where I'm trying to balance the ball in the center of the beam using the IR Sensor as a distance locator and a servo motor to tilt the beam. I'm using a PID Controller for the system. Ho…

Ball & Beam System Target Landing

[Mod edit: Please note that @zelreedy1 has 2 topics open about the same subject. They are linked in the sense that they are about the same project, but are different questions. The other one can be found here Inaccurate IR Sensor Reading ] I'm working on a ball and beam project where I'm using an IR sensor to find the distance of the ball along the beam and use a PID controller to control the servo motor and balance the ball in the center of the beam. However, I'm now trying to achieve another…

[jremington]

@zelreedy1

does a servo motor even have varying voltage input

Hobby servos do not.

Please do not keep creating new posts on the same topic. Flagged.

[zelreedy1]

It is the same project, NOT the same topic. It is evidenced by your reply in each one that they do not talk about the same thing. I had had this discussion already with a moderator and was advised that I should leave links to other related posts, shall I decided to ask separate questions about the same project, which is what I did. Yet, I have already received my reply, so I wouldn't mind it being closed. Thank you for your assistance.

[Railroader]

I understand Your approach. However criss crossing through 2 other topics make it a lot more heavy and time consuming. Helpers will turn their back to this topic.
Post facts, links to the motor etc. here in this topic. Reading data sheets ought to be within Your capacity at Your position in the company...
The PID constants depend on a lot more then the motor. The mechanism attached to the motor is highly important to know. What play, what hysteresis are there? Torque needed versus motor torque...

[anon57585045]

@zelreedy1

My question is: Is there a way, if they exist, to find thsese values for a servo motor? The other question is, does a servo motor even have varying voltage input, or is its input a constant one, i.e. the rated one in its datasheet?

Question 1 - yes, you can place oscilloscope probes on the motor. Apply a step response and back calculate using best fit techniques.

Question 2 - you get this information the same way, scope it. It's verification though because the answer is "constant".

[zelreedy1]

The issue is that I'm using a servo motor, not a DC one. Therefore, its datasheet and operation is completely different. That's why I was wondering if I was able to extract the variables in the equation from a servo motor, because I never saw the equation parameters mentioned in their datasheets.

[zelreedy1]

Ah, I see. I think this is difficult to do as I haven't got an oscilloscope. However, that's an interesting technique. Thank you!

[anon57585045]

Actually you would need an accurate measurement of RPM too. So some kind of rotational sensor.

However, I don't see the relevance of the equation unless you will actually be driving the motor directly. A servo has it's own internal feedback loop.

[zelreedy1]

Might as well just buy myself a regular DC motor, haha!

[anon57585045]

For the purpose that you've mentioned, as an academic exploration, a motor makes a lot more sense than a servo... A PID produces a variable drive signal, the servo can't accept or use that.

[zelreedy1]

I see, thank you!