Motion Profile Turning

CR7 · April 13, 2020, 2:29pm

When I tried point turning during motion profiling, the robot just stayed there and didn’t move. I read the article about motion profiles not being able to generate sharp paths, and I was just wondering if there were some alternatives to point turning during motion profiling?

rpm · April 13, 2020, 3:05pm

PathFinder does not do point turns. It creates “S” paths.
use turnAngle to accomplish that.

here is an example mixing the two

github.com

timeconfusing/OkapiLVGL/blob/1c1a593e9662687de003dffd9282a36322867840/src/mab.cpp#L57


      
          profileControllerM->removePath("B");
          profileControllerF->generatePath({{0_in, 0_in, 0_deg}, {24_in, 0_in, 0_deg}}, "D");
          profileControllerF->waitUntilSettled();
          
          profileControllerF->setTarget("D",true); // true means to use the path in reverse
          profileControllerF->removePath("C");
          profileControllerM->generatePath({{0_in, 0_in, 0_deg}, {12_in, 0_in, 0_deg}}, "E");
          profileControllerF->waitUntilSettled();
          
          chassis->setMaxVelocity(gearing*.66); // set the turn to be slower for more accuracy
          chassis->turnAngle(-270_deg);
          chassis->setMaxVelocity(gearing); // set veolcity back to full cartride value
          
          profileControllerM->setTarget("E");
          profileControllerM->waitUntilSettled();
          profileControllerM->removePath("E");
          }
          
          void mabl2() {
          info_printf(1,"in mabl2");

LouisDotA · April 13, 2020, 3:24pm

Sorry for being pedantic, but Pathfinder (what OkapiLib uses to generate the motion profiles) doesn’t only generate “S” paths, it can be paths of other shapes as well. I believe it cannot generate profiles for point turns because Pathfinder cannot generate negative velocities.

rpm · April 13, 2020, 4:33pm

Correct. I’m pretty sure it generates splines, which can be an I, C, S or complex curve paths (when using waypoints). I used “S” b/c I think that is more understandable w.r.t. to the conversion.

LouisDotA · April 14, 2020, 1:31am

One thing to note is that motion profiling (at least in the default OkapiLib sense) is all open-loop, which means that sensor feedback is not used at all. It blindly feeds precalculated wheel velocities to the motors. That’s obviously an inferior way of doing turns when you can at least use the IMEs (integrated motor encoders), which is what the chassis->turnAngle does. Even if Pathfinder could generate point turns, it isn’t really the best option.