Jon's Place

Wednesday, October 28, 2009

NanoSeeker Update

So, things are back to normal here, and I can post about NanoSeeker again. To the right is what it looks like right now, with the shell opened. At the very front (right side of the picture), is the compass - its a Honeywell HMC6343, a 3-axis, solid state compass, with an integrated 3-axis accelerometer (tilt compensation), and a nice I2C interface.

Immediately behind that is the thruster h-bridge - a Sanyo LB1836. Nice little chip - two channel one amp per channel surface mount h-bridge, that can handle low voltage signals and motors.

Beside the h-bridge is the thruster motor connector, and behind it is the processor, an ATmega328. I was originally using an ATmega168, but I ran out of RAM with my extensive debug menu, so I swapped in the 328, which is pin and source code compatible.

Under the AVR, on the top-side of the bottom board, is a Roving Networks Bluetooth module. This module is great - just plug it in, and I have an instant wireless serial port. No muss, no fuss.

Behind the processor is the 6-pin programming header, an oscillator for the SPI depth sensor, and the second h-bridge, which controls the dive plane and rudder linear actuators. Moving back again we see the plug for those two motors, and then the motors themselves. The motors are Solarbotics GM15 pager gearmotors. Glued onto the end of the motor shaft is a brass lead screw for the linear actuator, threaded to #2-56. The lead nuts are printed on my Dimension uPrint, and they slide the actuator arm, a piece of 1/32" brass rod. Those rods slide inside a brass tube, and are "sealed" with grease. The seal is good enough for a couple feet of depth, with is all I need at this stage, to test things.

Each actuator lead nut has embedded in it a 1/16" diameter, 1/4" long rare earth magnet. Under each lead nut, on the PCB, is an analog hall effect sensor, which can measure with nice accuracy the absolute position of the actuator.

Finally, the thruster motor is tucked in at the back. It is also a GM-15, and drives the custom-printed 7-blade propeller. The propeller shaft is sealed with a small o-ring.

The rudder and dive plane are at the very back, and are pivoted with the actuator arms.

At the bottom, underneath the bottom board, are a pair of 200 mAh Lithium Polymer batteries. They are connected in series, to provide 7.4 volts nominal voltage. The electronics are all running at 3.3 volts.

Here's a video showing the dive plane actuator working. Be sure to choose "HQ" for greater detail:



Here's a second video, showing the whole thing put together, testing both actuators and the thruster:



And here's the first wet/pool test:



The black bands around the sub are electrical tape, which I find is handy for doing temporary buoyancy adjustments without having to open the sub up to add weights.

More to come...