Understanding Kinematics for Inertial to Body Conversion

[Pikapi]

Hey Everyone,

I basically need a crash course on kinematics as I am trying to model this in simulink. I am given an intial set of position, velocity, ECI to Body Quaternion and suppose to convert into rotational rate and linear acceleration. Can anyone explain what i need to do? I tried looking it up but honestly the equations are above me. It seems that I am also suppose to convert from inertial to body but i am not sure why and how i am suppose to do this. I'm an EE and not mechanical so please bear with me, it's been a while since i worked with this.

 

[Pikapi]

I guess I should also explain that this is to simulate an inertial navigation system.

 

[K^2]

If you don't understand how quaternion rotations work, you have two options. Either learn linear algebra, which will take a while, or find someone else to do the work for you. There is no shortcut for this problem.

 

[Pikapi]

Actually i do know how to work with linear algebra, but I'm confused on what steps I need to take. For example, when given an initial position and velocity, do we need to first transform them into inertial coordinates and why do we need them in inertial coordinates?

 

[K^2]

It's always easier to work with these things in inertial coordinate system. For one thing, you have conservation laws on your side. For another, no fictitious forces.

So what exactly do you have, in terms of running variables, and what exactly are you trying to do? Usually, INS gives you body accelerations and you integrate these to inertial position and orientation. Is that what you are trying to do, or are you trying to solve the reverse problem? Given coordinates/orientation try to simulate what INS is going to measure?