As usual my design has to do with water and something that my brother asked me to have a look at.
What he needed was a way to launch a probe with a controlled decent of 10m at 20-50m offshore. The device had to be light, cheap and easy to control as it might be carried by students into remote lakes.
The base of the raft is a 50mm dens foam board covered with a 6mm plywood sheet to have something to mount equipment on to.
At the center of the raft there is a 70x70mm cutout where the probe will enter the water. Over this ‘moon pool’ the 40RPM 6V winch is mounted. The clever bit here is that a lower limit switch is not needed. If the user wants the probe to go down 10m then this length of wire is spooled on to the reel. When the probe launches the motor will run only in one direction, when the probe is at its lowest position the winch will start pulling it up again.
To trigger the winch I used a cheap eBay remote like this http://www.ebay.com/itm/433MHZ-4-Channel-RF-Radio-Wireless-Controller-Remote-/350892509578?pt=US_Radio_Control_Control_Line&hash=item51b2d2c98a
To control the raft away from the shore I only needed a SPDP switch.
When the system is on, all the power goes to the motor. When the raft is at its correct position the switch is thrown and power is directed to the winch control.
To control the distance from shore a simple wire is used to stop the raft. Then the raft waits for a remote signal to launch the probe. As we have remote control over the winch the probe can be launched several times before the raft it pulled back to shore.
Back at shore the data can be downloaded and the system can move to a new location.
Some more images
The bottom board is only a proto board that holds a 5V regulator for the PICAXE PCB. This board is actually the first PCB I ever made https://www.robotshop.com/letsmakerobots/node/30611
The PICAXE 18M2 is way overkill but as I already had several boards it was perfect for this job. The program running is only 50 bytes of the 2048 bytes available.
The motor driving the propeller is from another project https://www.robotshop.com/letsmakerobots/node/28827
I designed and printed some brackets holding the motor in place. There is also some aluminum fins on each side to steer the raft as straight as possible.