The J4-P3501 is the secondary propulsion for the EM-J4. It was added then it was realized that the drone would have problems performing its jobs beyond its physical reach. The P3501 allows the drone to ascend or descend freely to perform its operations. It is capable of lifting the drone, plus up to 50 kg / 110 lbs. It is classified as a high power system, so the drone uses it sparingly to conserve power.
The J4-P3501 can also be used to stabilize the drone on steep grades, or to fly over the grade.