You could directly set the Value property of the Gauge in a MATLAB App. In my opinion, this is the simplest way to pass the data to a GUI designed using MATLAB App Designer.
Assuming that you have a variable named motorSpeed, you can create a simple GUI using MATLAB App Designer named myApp.mlapp as shown below:
This app only has a Guage inside it. The Value property for this Guage is a public property. You just need to have the handle for the app when it is started. Following steps should get you started:
1) Open the app from script or command line using the following command
>> handleApp = myApp
2) Change the Guage Value
>> handleApp.Guage.Value = motorSpeed;
You could do this update whenever you have a new motorSpeed Value.
Please refer the following link to more about sharing data within apps: