MATLAB Help - Adding Current Used in Reaction Wheels for CubeSAT Simulation

Here I take the ADCS Seminar Series code and compute the total current running through the reaction wheels.
All code is still here:
github.com/cmo...

[@user-by6xf8qe8q]

Man you're the best! Thanks for the video :)

[@user-by6xf8qe8q]

Looking forward to the video on disturbance torques. Cheers!

[@SA-ys8eg]

Thank you for the video. In the previous reactions wheels code, the angular velocities of tumbling rate reaches zero and the curve is smooth but after the addition of total current control in the code , the initial angular velocities never reaches zero. Altough they reach values close to zero but the satellite is still in tumbling state. could you please give us some insights as to why that is happening and how to completely stabilize the satellite

[@SA-ys8eg]

I assume its because of adding the disturbing forces and moments to the simulation? is It possible to fully stablize the satellite even having all the disturbing forces?

[@CarlosMontalvo251]

Great observation. That is a timestep issue. In the video I changed the timestep = 1.0 so the code would run faster. In order for the RK4 integrator to converge properly for attitude control you really need the timestep = 0.1 or lower. That will increase simulation time but increase accuracy and make the curves smoother as you say. Hope that helps!

[@SA-ys8eg]

@@CarlosMontalvo251 Thank you for the response Sir. I tried extremely low values but the spacecraft is still not completely detumbling.

[@CarlosMontalvo251]

@@SA-ys8egDo you still have sensor errors and biases turned on? Because it will never go to zero if you have errors turned on.

[@SA-ys8eg]

@@CarlosMontalvo251Sir, I will send an email to you showing plots with the same parameters but different codes. The previous code is able to detumble the satellite completely while the new code (after adding the total current calculation for reaction wheels) has chattering even if the simulation is run for 20 orbits with timestep of 0.01. And yes I turned of sensor errors biases. I also removed the affect of disturbance forces which I suspect were causing the satellite to keep tumbling but that was not case. Thank you for the response.

[@tahaansari4036]

To calculate the current in RWs, you used the MaxAlpha (rad/s^2) to get the Amps2alpha ratio and multiplied that by rw_alphas to get the current. Is there a specific reason you did not use the MaxSpeed (rad/s) to get the Amps2omega ratio and multiplied that by rw_omega to get the current.

[@CarlosMontalvo251]

Well torque is equal to inertia times angular acceleration. So I made an assumption that current was proportional to torque since that's energy put into the system and this proportional to the angular acceleration.

[@tahaansari4036]

Alright, thanks for your response. Also, the attitude control demonstrated in this seminar series is only for stationary desired attitude. If we want to perform non-stationary attitude control such as nadir pointing, do we have to use a different control law/equation.

[@CarlosMontalvo251]

I'm pretty sure the equations are the same but you'd just have to change the commanded angle.

[@tahaansari4036]

So compute desired quaternion everytime and convert it to Euler Angle as ptpcommand in the control block? By using angles in the control block, do we face risk of singularity issues.

[@CarlosMontalvo251]

Well yes. Converting from quaternions to Euler angles introduces the risk of singularity. Better to do a control scheme that creates an error signal with quaternions