I purchased a remote payload drop for one of my drones. I can use this to release the placards for testing. I could of used a servo but I have to tap into the drones power and put a switch on the ground controller (station). hopefully I can do some testing at the beginning of November.
Here are the things you need to measure during your drone drops:
1. The size of the placard, specifically the height and width. Presumably, the thickness can be ignored.
2. The weight of the placard in ounces. You may need to visit a post office and use their scales assuming they have some with sufficient accuracy. You may ideally need to be able to measure fractions of an ounce and less than one ounce.
3. The height of the drone when the placard is released and the time until it hits the ground measured in seconds. A stop watch is ideal for this timing.
4. Ideally the wind should be calm. But the horizontal distance that the placard travels is not particularly important in these drop tests.
5. After the tests, call or check online with your local weather bureau to get the atmospheric pressure (preferably in inches of mercury) corrected to sea level.
6. Video tape the drops if possible so that the placards behavior can be observed.
Then please post the information here.