# Novice trouble modeling a system in Simulink

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1. May 30, 2017

### Playbacknick

Greetings,
For the past 5 days i have been learning how to use simulink.I decided to try and model a mechanical system described by the equations in the picture below.I provide a second picture with my work so far.A couple of questions that i have are: a)How do i include the first equation? and b) how do i represent the tau(t) in the second equation? Any suggestions about mistakes are welcome!
Nick

2. Jun 3, 2017

### Dr.D

It would help a lot if you would tell us what this system is and perhaps present a system drawing (not just a block diagram).
When you say "the first equation," I presume you are referring to eq(4.26a), in which case, the answer is that it is represented in eq(4.31b).

As to how to include tau, who knows? You have not told us what tau is.

I might also suggest that you make your first attempt to use Simulink on something much more simple, something for which you already know what to expect at every part. How about a simple spring-mass-damper system?

3. Jun 9, 2017

### Playbacknick

In the following picture you can see the rotational system. Equation 4.24 describes tau.

Should τ(t) be represented by a step function?

4. Jun 9, 2017

### Dr.D

Eq(4.24) describes something called tau-sub-tau (or is it tau-sub-t?), but is that the same thing as plain tau? I would not expect it to be.

In Fig. 4.5, I see a tau on the end of the shaft. Who knows what this is supposed to be! (All of your text and figures are so small I can hardly read them; I'm about 4 times your age, and my eyesight is not all that great.)

I suspect that this problem is rather closely linked to the text where you found it, and consequently you are going to have to answer your own question based on re-reading the text material.

5. Jun 9, 2017

### Playbacknick

Thanks again it means a lot that you devoted some of your time to reply.
My understanding is that tau is the torque and i think it is the input of the system.Assuming that, i'm going to represent as a step function and run the simulation tomorrow.

6. Jun 9, 2017

### Dr.D

I would agree that your book uses tau for torque, but there seems to be more than one torque that is represented by that symbol (also tau-sub-t).

Your figure appears to show a clutch. If you think that tau is the torque through the clutch, then making it a step function amounts to snapping the clutch. Great for drag racing, but very hard on clutches!