Confusion with turning

I want to program with LabView this year, so I started learning it online. During the simple autonomous lesson where you set the speeds for the motor, I am really confused about the x and y speed inputs. If x=0.25 and y=0.5 then it turns right and if they are reversed, it turns left??? This doesn’t really make sense. Is it turning with no forward movement or still moving forward, just turning a little?

turn right.JPG

turn right.JPG

The y value tells Arcade to move forward at half speed while the x tells it how much to turn (quarter speed) and in what direction (left or right), so the robot will move forward in an arc as it turns. To turn in place, make y=0.

To overcome the mass and friction of the robot it takes a little bit of the low-end power, so maybe 20% (.2) of the forward power will simply get the robot moving slightly (depends on the robot).

To turn the opposite way leave y alone and make x negative, i.e., x=-0.25

Make y negative to backup while turning.

If you use Tank Drive instead of Arcade, then you might reverse the two inputs to get the opposite effect, but the inputs would typically represent two y joysticks, rather than the single joystick of Arcade. In autonomous of course there are no joysticks, but many people still like to think of it as if a driver were controlling the robot.

I think you have the x and y interchanged?


Yes, thanks. I made that and other corrections.

I’m a bit distracted by the NASA Grant emails flying around this morning.

so, which one is the forward movement? x or y?

x axis is for movement left and right,
y axis is for movement up and down

oh ok, so it is just like a graph. Thanks, got it now.

Rather then changing both x and y at the same time, it would have been better to only change one value while keeping the other the same. I would probably try five different tests (see below). That may seem like a lot, but it allows you to fully characterize the behavior and is a lot faster then changing multiple values at once and guessing which one caused what change. Once you’ve done those, you should be able to predict what would happen for any other combination.

x=0, y=0
x=0.25, y=0
x=-0.25, y=0
x=0, y=0.25
x=0, y=-0.25