I don't think you can simulate this unless your motor component is a close simulation of the real thing and you can control the load on the motor and the way it impacts the speed. Power = torque (aka Amps) x Revs (aka Volts).

 

You would have to also control the load on the motor.

In a typical DC motor (like a permanent magnet motor), the voltage is primarily related to the speed of the motor and the current is primarily related to the torque of the motor. So as you change the current, you change the torque. But to keep the voltage the same, you need to then change the load so that the new torque value results in the motor spinning at the prior speed.

Be very careful running these types of motors with a constant current source, you can get a catastrophic overspeed condition pretty easily.

I found this out the hard way when I was a junior. A friend and I were working on a demo in which we bounced a laser beam off of two rotating mirrors and onto a screen, producing Lissajous patterns. The patterns weren't too stable, so I got the bright idea of running them in constant current mode instead of constant voltage mode. As I slowly turned up the current limit, nothing happened until the developed torque became sufficient to overcome the static friction. At that point, within just a second or two, the motor spun up so fast that the mirror grenaded, sending glass shards everywhere in the plane of rotation. A few minutes reflection was all it took to realize our mistake.

You would have to also control the load on the motor.

In a typical DC motor (like a permanent magnet motor), the voltage is primarily related to the speed of the motor and the current is primarily related to the torque of the motor. So as you change the current, you change the torque. But to keep the voltage the same, you need to then change the load so that the new torque value results in the motor spinning at the prior speed.

Be very careful running these types of motors with a constant current source, you can get a catastrophic overspeed condition pretty easily.

I found this out the hard way when I was a junior. A friend and I were working on a demo in which we bounced a laser beam off of two rotating mirrors and onto a screen, producing Lissajous patterns. The patterns weren't too stable, so I got the bright idea of running them in constant current mode instead of constant voltage mode. As I slowly turned up the current limit, nothing happened until the developed torque became sufficient to overcome the static friction. At that point, within just a second or two, the motor spun up so fast that the mirror grenaded, sending glass shards everywhere in the plane of rotation. A few minutes reflection was all it took to realize our mistake.

Thank you very much for your reply. As far as I understand, I should instantly check the voltage falling on the motor. Then, if it falls below the value I want, I should increase it, or if it exceeds the value I want, I should decrease it. In short, I need to balance the voltage going to the motor. Do I understand correctly?

 

if it falls below the value I want, I should increase it, or if it exceeds the value I want, I should decrease it. In short, I need to balance the voltage going to the motor. Do I understand correctly?

Isn't that what a standard voltage regulator circuit does.?

 

Thank you very much for your reply. As far as I understand, I should instantly check the voltage falling on the motor. Then, if it falls below the value I want, I should increase it, or if it exceeds the value I want, I should decrease it. In short, I need to balance the voltage going to the motor. Do I understand correctly?

I don't think you do understand yet.

You are saying that you want to control the current through the motor.

Fine.

But then that is what you are controlling -- the voltage will be what the voltage will be. If the voltage is lower than you want, you will need to either decrease the load on the motor (which you have given no indication that you are in a position to have control over), or you will need to increase the current. But if you increase the current, then you are no longer maintaining the current at the point you are trying to hold it at.

Another way of understanding what is going on is to consider just how you are trying to control the current through the motor. Whether you are using a current mirror or some other circuit, the underlying mechanism for how it sets the current in the motor is by adjusting the voltage across the motor until the desired current is obtained. Any change to that voltage, and the current will change. Under a given set of conditions, there is one voltage across the motor that will yield the desired current. If you want that current, then that is the voltage you have to live with.

 

I don't think you do understand yet.

You are saying that you want to control the current through the motor.

Fine.

But then that is what you are controlling -- the voltage will be what the voltage will be. If the voltage is lower than you want, you will need to either decrease the load on the motor (which you have given no indication that you are in a position to have control over), or you will need to increase the current. But if you increase the current, then you are no longer maintaining the current at the point you are trying to hold it at.

Another way of understanding what is going on is to consider just how you are trying to control the current through the motor. Whether you are using a current mirror or some other circuit, the underlying mechanism for how it sets the current in the motor is by adjusting the voltage across the motor until the desired current is obtained. Any change to that voltage, and the current will change. Under a given set of conditions, there is one voltage across the motor that will yield the desired current. If you want that current, then that is the voltage you have to live with.

I understand a little bit, please excuse me, but I'm a little inexperienced in these matters. My aim is to adjust the current passing through the motor to different values without changing the voltage falling on the motor

 

I understand a little bit, please excuse me, but I'm a little inexperienced in these matters. My aim is to adjust the current passing through the motor to different values without changing the voltage falling on the motor

This is like saying that you want to adjust the amount of water in a glass without changing the depth of the water.

The only way you can do this is to change the shape of the glass as you add or subtract water.

The same with the motor.

The only way you can change the current without changing the voltage is to change the conditions under which the motor is operating -- namely to adjust the load on the motor.

Unless you are in a position to dynamically change the load on the motor, you are on a fool's errand -- just like you would be if you insisted on adjusting the amount of water in a fixed glass without changing the depth of the water in the glass.

 

This is like saying that you want to adjust the amount of water in a glass without changing the depth of the water.

The only way you can do this is to change the shape of the glass as you add or subtract water.

The same with the motor.

The only way you can change the current without changing the voltage is to change the conditions under which the motor is operating -- namely to adjust the load on the motor.

Unless you are in a position to dynamically change the load on the motor, you are on a fool's errand -- just like you would be if you insisted on adjusting the amount of water in a fixed glass without changing the depth of the water in the glass.

I agree 100% with what you said. After all, we have a formula called V=I.R. However, this is part of the project I took for my control systems course. Our teacher asked us to adjust the current with a rotary encoder. He also said that the voltage on the motor should not change when adjusting the current with the rotary encoder. I have been thinking and researching how this is possible for almost 1.5 weeks. I did a lot of experiments on Proteus, but in all of them, as the current changed, the voltage also changed. I still thank you very much. for helping

 

I agree 100% with what you said. After all, we have a formula called V=I.R. However, this is part of the project I took for my control systems course. Our teacher asked us to adjust the current with a rotary encoder. He also said that the voltage on the motor should not change when adjusting the current with the rotary encoder. I have been thinking and researching how this is possible for almost 1.5 weeks. I did a lot of experiments on Proteus, but in all of them, as the current changed, the voltage also changed. I still thank you very much. for helping

Have you talked to teacher about this?

It's possible they just had a brain fart and didn't realize the implications of what they were asking for --it's easy to overlook some pretty obvious things when putting together an assignment without actually performing it. Or it's possible that they had something different in mind (such as adjusting the load). Or it's possible that they have never worked in the real world and don't really understand what they are teaching (that happens a LOT). It's also possible that they intended for you to run into the issues you are facing and to come to the conclusion that what was being asked for makes no sense and to report that.

Give them the benefit of the doubt and discuss your concerns with them and given them the opportunity to either clarify what they had in mind, or make the necessary corrections.

 

The fact that the prof mentioned a current mirror to do this makes me think he is simply incompetent, he does not know that it is impossible. I would not want to be in your position. The only way to avoid failing your assignment is to prove to him that it cannot be done.

 

Maybe we could offer the professor a "peer review" for homework and exam questions, so in the future he could avoid – ahh...embarrassment.

 

Have you talked to teacher about this?

It's possible they just had a brain fart and didn't realize the implications of what they were asking for --it's easy to overlook some pretty obvious things when putting together an assignment without actually performing it. Or it's possible that they had something different in mind (such as adjusting the load). Or it's possible that they have never worked in the real world and don't really understand what they are teaching (that happens a LOT). It's also possible that they intended for you to run into the issues you are facing and to come to the conclusion that what was being asked for makes no sense and to report that.

Give them the benefit of the doubt and discuss your concerns with them and given them the opportunity to either clarify what they had in mind, or make the necessary corrections.

Have you talked to teacher about this?

It's possible they just had a brain fart and didn't realize the implications of what they were asking for --it's easy to overlook some pretty obvious things when putting together an assignment without actually performing it. Or it's possible that they had something different in mind (such as adjusting the load). Or it's possible that they have never worked in the real world and don't really understand what they are teaching (that happens a LOT). It's also possible that they intended for you to run into the issues you are facing and to come to the conclusion that what was being asked for makes no sense and to report that.

Give them the benefit of the doubt and discuss your concerns with them and given them the opportunity to either clarify what they had in mind, or make the necessary corrections.

Our teacher explained the details of the homework online via MS Teams. First of all, I will watch the replay of that video. After all, I might have misunderstood too. But I don't think I'm wrong because I've already watched the video 2 or 3 times. Then I will consult my teacher and ask if this is really possible. Thank you very much for your help. If my teacher shows me a valid method, I will come here and tell you.

 

Our teacher explained the details of the homework online via MS Teams. First of all, I will watch the replay of that video. After all, I might have misunderstood too. But I don't think I'm wrong because I've already watched the video 2 or 3 times. Then I will consult my teacher and ask if this is really possible. Thank you very much for your help. If my teacher shows me a valid method, I will come here and tell you.

Sounds good. Interested to hear what happens.

 

Give them the benefit of the doubt and discuss your concerns with them and given them the opportunity to either clarify what they had in mind, or make the necessary corrections.

@meshcurrent And then report back as I'm intrigued at what your teacher was thinking. Could you share the video?

Also V/I = R doesn't apply to a motor except under stall conditions...

 

@meshcurrent And then report back as I'm intrigued at what your teacher was thinking. Could you share the video?

Also V/I = R doesn't apply to a motor except under stall conditions...

Today I asked my teacher about the project details. But he didn't answer me. Because we had to create the circuit ourselves. He just shot a short explanation video and wants us to benefit from that video. We really don't have enough detail. Approximately 100 people are doing this project including me. However, no one could produce a circuit as our teacher wanted. Apparently we will get 0 project grades.

 

can you share the video?

 

can you share the video?

I'm not sure I can share the video. Because we view it through the university microsoft account. Anyway, the video consists only of text and a few small hand drawings. Also, it consists of articles in Turkish, which is my native language, so it is not in English. But if you want, I can briefly explain to you what is in the video. That is, what the project wants in general. This won't take very long. Also maybe I misunderstood and we can fix that

 

Apparently we will get 0 project grades.

Will you be giving your teacher a '0 setting-a-project' grade?

 

Will you be giving your teacher a '0 setting-a-project' grade?

I don't think we can give any grade to our teacher xd. I really think he didn't explain well to us exactly what he wanted. How will he react when he sees that the project he has given cannot be done by anyone on the project delivery day? I am very curious.

 

I don't think we can give any grade to our teacher xd. I really think he didn't explain well to us exactly what he wanted. How will he react when he sees that the project he has given cannot be done by anyone on the project delivery day? I am very curious.

It'll be interesting to see how he reacts.

I gave a project one time that, as it turned out, had specs that couldn't be met because of a tweak I did at the last minute. Each team had to design a power amplifier that could take a 1 Vpp input signal and deliver 5 W into an 8 Ω load, powered from a supply with +/- 30 V rails. The power supply values were based on what was available in the lab, but also resulted in the students having to deal with thermal issues in their design, so that decision was partly made with malicious aforethought. Since the course had only covered dominant-pole analysis, the skirts of the bandpass region had to be first order. Originally, the spec'ed band for everyone was 20 Hz to 20 kHz. But at the last minute I got the bright idea to split this up amongst the teams so that each team had a different one-octave band such that, taken together, the system formed a crude equalizer. What I hadn't realized was that it is not possible to place the -3dB points of a first-order bandpass response one octave apart. I realized this after I handed out the assignment when I was modifying my circuit. You could get close, but not quite get there. I thought about changing the assignment, but instead chose to keep my mouth shut and just see how the teams handled it. I'm glad I did. All of the teams realized that they were having trouble meeting the spec. Only one of the teams did the analysis to show that the spec couldn't be met. All but one of the other teams came to the conclusion that they couldn't meet it and gave varying descriptions of what was causing the problem. One team never realized that the spec couldn't be met and just doggedly kept trying -- and they ended up coming the closest to meeting it of all of them.

 

Incidentally, how good is the motor simulation in your chosen simulator? Were you given that motor or is it some default settings?