I recently built a smaller buoy design while I continue to work on the IMU code. The previous buoy was approximately 150mm in diameter and had room for lights, GPS, a large li-po battery and a considerably bigger microcontroller. This latest version is based on the electronics from a previous post and only needs to house a trinketpro, Xbee, and BNO005 IMU from Adafruit.
Old vs new design.
The 95mm buoy is powered by x3 AA batteries which are housed in the lower hull. This design will not be getting wet until I complete the IMU code, so there was no need for an o-ring at this time.
Side note – future hull designs may eliminate the o-ring completely and opt for RTV or some other marine-grade silicone sealant since the o-ring requires considerable force for proper compression.
The four posts are for mounting the perfboard with the IMU, microcontroller, and Xbee. The two cavities are for mounting the battery pack and ballast weight. The ring around the edge is to help the top half of the hull stay aligned will installing the screws, and could also act as a barrier for adding a marine silicone sealant around the edge to form a simple gasket for testing in the water.
The smaller of the two cavities in the lower hull for holding ballast weight, the larger rectangular cavity is for the battery pack. I plan to use large washers for the ballast weight stacked onto of each other to get the desired mass, so there is a round hole with a post at the very bottom to keep the ballast centered. You could also machine a thick walled cylinder of appropriate mass for the ballast to fit snuggly in bottom of the hull.This is just a prototype, but helpful comments and suggestions are always welcome.