Problems with using 330's goal tracking code

[Joe Ross]

Originally Posted by windell747

When I ran the code out of the box from the team 330 posting, I figured that since our bots are similar in size, mass and drive configuration (tank drive) that their PID gains would be close to what I would want. So when I saw the bot oscillating, I immediately thought that it was a code problem. Just for confirmation, the out of the box gains in the program was proportional=0.5, derivative=integral=0.0.

The out of the box settings were 0.05 for P, 0 for the others. Due to a few mistakes, the settings in the code didn't match the settings from the video. I think the gains might have been the very, but the maximum output values were higher in the code then the video. I figured that most people would have to tune the values anyway, so I didn't spend the extra time to recreate the ones from the video. Sorry for leading you down the wrong path.

[windell747]

No worries, Joe! Thanks for the reply! is it possible to get an example set of gains from you so that I have something to start with that will tell me weather or not the code is correct and that the problem is only with tuning? Maybe not your best set of parameters, but something that converges to no error over time. That way if mine doesn't converge then I know something is wrong.

I'm a fulltime engineering student and although I would like to mentor the team all day and get things just right, I have to do my studies too so it is hard sometimes to find the time to tune things from scratch. Again im not asking for competition gains, but something that will guarantee converge. Thanks!

[windell747]

Thanks for your help! It looks like I was able to get the response to converge. here are my gains for anyone interested. x-axis0.003,I0.5. y-axis: P0.015,I0.70. derivative terms 0. max x=0.45,max y=0.7

I'm trying to plot the x and y axis outputs to a graph but im having some trouble. I'm using the plot waveform and feeding to the input a get waveform time array, but im not getting the correct data types. Can anyone briefly explain the process to do this?

Thanks!

[airnate]

One of the easiest ways to do this is to:

1. Go to your Front Panel
2. Select Express->Graph Indicators->XY Graph (aka Express XY Graph)
3. On the block diagram, wire your X and Y inputs
4. Double click the Build XY Graph on the block diagram and turn off Clear Data on Each Call.

-Nate

[windell747]

how do you put time values for the x variable each iteration? I guess I could just put a counter that increments, but im not sure how to do this either. I would like to not use a for loop. Any suggestions?

[airnate]

Sorry, I assumed you wanted an XY plot (plotting one variable against another). If you have two independent variables to plot, then use a Chart.

Bundle the two values (presumably X and Y) together and then wire to the Chart terminal.