Quote:
Originally Posted by wesleyac
Just want to point out that this is probably easier than you think to control - you can do feed forward by applying voltage proportional to the cosine of the angle of the arm to cancel out gravity, at which point it becomes a (approximately) linear system, that is fairly easy to control (Although there are still some considerations to be taken with the difference between going up and down). A FF + PID arm is much easier to control than one with surgical tubing or a gas shock, imo.
The point that programming can only do so much is definitely valid, I just wanted to point out that arms aren't too difficult, as that's what we spent our season doing  |
There's another compounding factor that isn't apparent here. The efficiency of a gearbox removes power regardless of if you are accelerating the arm or decelerating it. So, if you apply a torque at the motor to accelerate the arm, you will see a reduction in torque. If you apply torque at the motor to decelerate the arm, you will see an amplification of the motor torque. (Look at what conservation of energy says to verify) This year, for our shoulder joint, we had to gain schedule based on whether or not we were accelerating or decelerating to compensate for this. It took a couple weeks of hard work to figure that out.
In the end, yes, you can compensate for a lot of nonlinear junk in software, but the more you do in hardware, the better you are off. 971 robots move like they do both because the software lets them do that, but also because we go to great depths to do things like reduce backlash, reduce friction, increase stiffness, etc, to make it easier to write the software.
/end tangent...