Can anyone confirm or destroy my theory of how a Motion Magic go to position is actually performed on the talon. My theory is it that it is exactly the same as a motion profile execution but the trajectory points are generated by the talon instead of externally calculated. Is there anyone in this chat or reading this post that can confirm or deny this statement ?
If the above statement is true and you run motion magic with a Kf value only and no PID values (all zero), wouldn’t the controller output be zero at the end of the move (as the projected velocity is zero at the last trajectory point).?
And if the mechanism had any external force on it like gravity, wouldn’t it just drop at the end of the motion magic move? Our robot is an a bag inside a crate on the way to Houston, so this is something we can’t test.
When we are working on Motion Profiling we tweak our Kf values on the drive train using the method of zero for PID value and adjust Kf until the robot drives the approximate distance of our test profile. We always start so low that the robot doesn’t even move and then adjust up until it roughly makes the distance. Then we start ramping Kp until we get oscillations during the path and then back off Kp a bit. We mark the wheel with a highlight pen, position this mark at the top and then execute a profile that does exactly 5 turns. And with only Kf and Kp set this will execute exactly 5 turns to the mm every time. We don’t use Ki or Kd at all in drive train motion profiles. Then the team keep recompiling the motion profile to be faster and faster until the wheel slip starts to effect the repeat ability of the profile. And this gives them an indicative Max Acceleration and Max velocity to use in all of their auto paths. This work really well and I would recommend this to anyone that want to explore Motion Profiles.
We are using motion magic for our arm that goes from one side to the other, going over the top in the middle of the motion (16 different positions on a button board for all the different spots cargo and hatches can be placed), but we didn’t know about arbitrary feed forward until I read this post, so our arm is not tuned well at all and is running rather slowly in order to keep the movements smooth.
We are now in the same situation as some other people in this post. Do we pull it out of the bag at Houston and add an arbitrary feed forward that is continually updated with respect to arm angle (and I suppose you could even adjust for wrist angle because this varies the twisting force of the shoulder joint) and then re tune our Kf, Kp, Ki and Kd in the motion magic setting which could potentially destroy our shoulder mechanism and destroy gearboxes that drive it or do we just run with it as it is because it works and it got us this far. Any advise from experienced teams would be greatly appreciated here. Or if anyone wants to find us in the pits and come and offer some advise we would be forever grateful.