Building an EEZYBOTARM MK1 My bot arm building is complete, I'm using it with Arduino and 2 joysticks with 4 servos ( mg90s), running with the 9v battery, but still, the servos could not lift the bot arm once it is going down and the servo keeps fluctuating. It is a 3d printed bot so it is not so heavy. please help?
Even if your device is not so heavy, a 9V battery has a maximum practical current draw in the 10s of milliamps. It's not a good choice for operating motors.

A better choice would be AA, C, D, or Lithium-Ion/Lithium-Polymer batteries, wired in series to produce the desired voltage.