I designed this bait release mechanism specifically for my ZMR 250 for fishing but it could fit other quadcopters if you can have the same mounting holes or don't mind drilling new holes in your bottom plate.
It has clearance holes to match 30.5mm flight controller mounts allowing it to fit flush with the bottom plate.
The release has been angled so that the weight being carried is as close to the center of the quadcopter as possible.
On a ZMR 250, the bait release is mounted to the frame using the same holes as the inner standoffs and slightly longer screws.
You will need:
1 x 9g Servo controller.
1 x paperclip or thin gauge wire to connect the servo to the release pin.
Don't have a 3d printer? You can purchase this model from my Etsy shop.
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