You have multiple issues going on. First, your motor model is problematic because it violates the Modelica modeling concept. It is more like a Simulink model -- it is one direction only -- you put a current into the motor and it responds by accelerating its inertia, however, if I were to spin the inertia, it does not generate a current. The problem with this is that external torques are not making it back into your motor so your motor is independent of the system (which violates physics).

Is there a reason you do not want to use one of the built-in motor models? You can then control that motor with any control system you develop. (The control system can be all mathematical). If you want to make your own motor model, you need to have the output be a rotational flange and not a numerical output. If its a flange, then you have both speed and torque communicating through the flange and the motor behaves as you want.

As far as the Gyroscope models. I can explain them:

The first model is

This sets an initial rotation rate in the revolute joint so that bodyCylinger2 is spinning about its axis and gravity will move the body so that it causes rotations due to gyroscopic effects (no surprise). The second model is more subtle:

Here the second body is modeled with two blocks instead of one. bodyCylinder4 is a rigid body with no rotation that is attached to the swinging arm. The gyroscopic torques are provided by the rotor1D element. The rotor is given the same rotary inertia as the bodyCylinder (J= bodyCylinder4.I[1, 1]). It is spun up to the desired speed. By moving the base frame around, the appropriate torques are sent back to the rest of the structure. You can imagine the cylinder at the end as two concentric objects, one fixed and one rotating. While this appears less intuitive than the first example in which the body is modeled as one object, In some circumstances there can be some advantages with splitting it up and considering the torques separately.

My suggestion is to use either gyroscope model and hook your motor to the model: (file attached)

You can put a control system around the motor with blocks and sensors. Note: I chose completely random numbers for the motor so it is not what you want but it should give you a starting point.

I also put the motor on the second gyroscope example model but note that I needed to put the reaction force of the motor back into the frame or the model would not be correct.

Is this what you are looking for? Why do you want to use a "mathematical motor"? If you need a "Mathematical Motor" can't you output your motor to a rotational flange so it is more physical? (If this is what you want, I can show you an example).

Regards,

Neil

Attachments:

GyroscopeExample.mo

I don't think I completely understand your issue. The flywheel motor model seems to work fine.

Although you have a problem in the way you are using the rotor and Body. Currently, the body is completely stationary throughout the simulation (is it supposed to be??). You are attaching it to the reference frame for the rotor1D, but you give it no motion or torque so it does nothing. For this reason it does not contribute to the simulation in any way (you can prove this to yourself by disabling it and connecting the rotor to ground -- the simulation results are identical.

Look at the GyroscopicEffects example in the Multibody library (Modelica.Mechanics.MultiBody.Examples.Rotational3DEffects). This should help you, but I am really not clear on how you want to use your flywheel model and connect it.

Regards,

Neil

Hello Neil!

Wow thank you as usual for your exceptional explanation and the examples.

To get to your questions directly:

Is this what you are looking for? Basically yes. My model as I said, will be a Cube satellite, with motor drive inertias, and as such (beyond the sphereical joint) what you've modelled is pretty much what each sub system (motor, controller and rotor) will end up being.

Why do you want to use a "mathematical motor"?

This probably requires some more explanation. To be frank, it's mostly because I don't know how to use those finished models.

In the real system, I am using a EC 45 Flat motor (251601) plus their current controller (see attached PDF) from maxon motor. With the controller, I can drive the motor with a current source. Their data sheet has quite a bit of information about the motor itself, however when attempting to use the built-in model SM_PermanentMagnet and the subsequent example SMPM_CurrentSouce which at the time I assumed would be a perfect starting point.

I am completely overwhelmed with how it's set up and how to give correct data compared to my real life motor and controller, that I can actually do anything with. Lmd and Lmq, LD and LQ values and most other variables which work in the example, are vastly different to the values from the data sheet and I have no current way to measure or figure them out myself, maxon as a company also refuses to give anything more than the public facing catalogue data.

However, my mathematical ODE model represents the motors with their controller quite accurately, which I've verified and used for this project (https://www.youtube.com/watch?v=Lzw3ZGTuMUU) (which is one of the walls of the cube sat), and since I already had a model that does what I wanted, I decided it was the fastest route, rather than trying to hack the examples together.

I would absolutely appreciate if you could show me an example of how to improve my model with the rotational flanges, or to make it more physical in any other way. When attempting myself, I realise now that mixing and matching different blocks isn't as easy as I'd hope. The rotational flange only accepts rotational connections it seems...

As as side question, Do you have any suggestions for material, tutorials or likewise for the 'modelica method' you mention? It's difficult to find literature that is suited for beginners for this modeling concept, and my only experience as you accurately deduced, is simulink, which clearly isn't appropriate.

Thank you again for the detailed answer, I very much appreciate the help.

Attachments:

maxonmotor.pdf