For example, OPTI has a built-in Optiflow Sensor (a downward facing sensor), which functions by picking out the patterns on the ground to ensure that the drone maintains a straight position.  ATTI, conversely, works a bit differently. With the ATTI, the drone employs other techniques apart from the external sensors to keep the drone in the right orientation and altitude. Thus, the drone can hover in place, or drift slightly around with the wind serving as a push. You will also find a GPS in some drones, and they help the drone to maintain coordinated and precise flights and landings.
As it is for every gadget out there, a buyer must set realistic expectations when buying a cheap drone (or other devices).  If you set expectations that are too high, chances of being disappointed ultimately are high, and this may ruin your drone flying experience.  Instead of the high standards, expect far less from the device and let it surprise you instead while providing you with so much excitement in the process.  You may consider buying a spare drone also.
The weight of the Holy Stone is about 14.1 ounces and a dimension of 12 x 12 inches. The range of the transmitter is 330 feet, with the ability to stay up to seven or ten minutes of in air at a go. Despite the weight, it is still in line with the FAA’s regulations, and you will not require a license. The drone has a slow rotation around the vertical axis, i.e., yawn, although you will still do some tricks conveniently with it. The resolution of the photos taken by the drone is not so bad. However, there is reduced stabilization during flight times. 
Many manufacturers mount cameras inside the body of the drone. This is acceptable for casual photography, but if you want more professional results, consider adding an external camera mount, or gimbal. Gimbals allow you to place your video or still camera in front of the drone body, away from the vibrating motor and rotors. Gimbals can swivel and pivot, providing you with additional control over your imagery.

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