The servo tester and controller can be used as a signal generator for electronic speed controllers.   If you are looking for a low-cost way to get a servo up and running without any programming, you can plug directly into the servo tester.    

There are 3 modes that can be use:

Manual mode - By turning the knob, you can control how faster or slowly the servo arm moves.

Neutral mode - Sets the servo back to the neutral position.

Automatic mode - Like a windscreen wiper this will make the servo swing back and forth to its largest angle.

Up to 3 servos can be connected simultaneously.

 

Specification:

• Voltage consumption: DC4.8-6V 
• Size: 46 x 32 x 16mm ( approximately )
• Original box: NO
• Color: Blue
• Item size: 46*32*16 mm ( approximately )
• Net weight: 9g