Inertial sensor programming

[weilin]

These topics have helpful discussion:

VEXcode, motor groups and drivetrain example

There have been quite a few requests for instructions on how to use motor groups and creating a drivetrain with more than 2 motors in VEXcode. I’m going to discuss these classes a little and provide a simple example. What is a motor group ? A motor group collects two or more motors together and allows control as if they were a single entity. Just about all motor class member functions (by that I mean spin, spinTo, setVelocity etc.) are available on the motor group class. We introduced motor…

@jpearman

A drivetrain that is created with a gyro or inertial sensor will use the sensor when the drivetrain is asked to make turns. The specific class member functions that use these sensors are turnFor, turnToHeading and turnToRotation.

Drivetrain.turnToHeading( 90 , degrees );

will turn the robot to a heading of 90 degrees (heading is like a compass heading now, 0 to 359.99 degrees). The robot will always take the shortest route to achieve the new heading.

Drivetrain.turnFor( 90, degrees );

will turn the robot 90 degrees starting at the current heading, that is, relative to the current starting position.

Drivetrain.turnToRotation( 500, degrees );

will turn the robot to an absolute rotation of 500 degrees, the robot may turn through more than 360 degrees to achieve this.

See VEXcode help for more information

@jpearman

The turnFor function in the smartdrive class is very simple, no PID or anything is used, all it does is slow down as the turn is getting close to the target and then stop when the error is less than 2 degrees. We may improve a little for a future release but we really want teams to write their own code for this and not rely on VEX providing everything for them, it already does more than some of the dev team would like.

Smartdrive (inherits from vex::drivetrain) api: VEX Help
Inertial sensor (inherits from vex::guido) api: VEX Help

New V5 Inertial Sensor Testing Video and Review

We messed around with the new V5 Inertial sensor and completed our turning code. Here’s a little peek at our turning testing: VRC Tower Takeover V5 Inertial Sensor Turning [1080P] - YouTube. As far as we can tell, the sensor seems to be a solid upgrade over the gyro. We made a custom PID function and used that in the video but we’ll test the sensor with both the stock PID and the custom one when we have access to a field. Nice work with this sensor Vex

Smartdrive Inertial Sensor Turning Video

As promised, the comparison video of the VEXCode smartdrive turnFor method and our PID turning method: V5 Inertial Sensor Turning Comparison Video Vex Tower Takeover [2.7K] - YouTube

90 degree turns aren't 90 degrees

We are using the Vex V5 Text editor and when we put in a 90 degree turn the robot turns more or less than 90 degrees…never a true 90 degree turn. Is that just the way it is and we need to compensate in our coding or is there some other issue at play?