Torpedo Activation Circuit

On a small scale machine, it is not always practical to activate components using mechanical/contact means. In the case of a torpedo launching from small AUV, it is ideal not to have any physical connections such as wires or connectors between the vessel and the projectile. A reliable light source and a light dependent resistor (LDR) can easily replace a momentary contact switch. The figure below illustrates the simplicity of the circuit:

For the given circuit, the trigger is connected to a voltage divider. In the dark, the LDR is measured to be at least 33k Ohms, providing a minimum of .75Vs to the trigger. As the LDR is exposed to light, its resistance drops, increasing the voltage going into the trigger. For a 10k Ohm pull up resistor, the resistance of the LDR should drop to around 5k Ohms to bring the voltage down below 1/3Vs, activating the 555 timer. At this point, the output, which powers the transistors controlling the motor to the torpedo, is driven high to Vs until the reset pin is pulled below .7Vs.

To stop the torpedo, the reset pin is connected to a momentary switch. This switch is connected to the tip of the torpedo. When the torpedo runs into an obstacle such as a wall, the reset pin will drop down to 0V, shutting off the output, and consequently, the motors.

A 555 timer in this configuration is known as a bistable circuit. It maintains its current output state until interrupted by the reset or trigger pins.

Image source: http://www.kpsec.freeuk.com/555timer.htm#bistable
Image modified by: Author

Friday april 18th meeting

Here is the overall result of our meeting on friday, may 18th.
As where we are today, we have a water proofed chassis that drives around. Both cameras are working sufficiently. Compass needs some work but it is functional. Tether seems like it works properly and we have some manipulators but they require more work.
Next we laid out what we need to do for short term goals.

 Next there was a discussion on what cables go in and out of the computer box and the oterbox.

Then the missions were reviewed and we decided in what order we want to approach and take care of the tasks.

Missions:
#1 Visual: Square Gate.
#2 Id 9 inch Colored Buoys(Red, Green, Yellow) and in order
#3 Visual: U-Shaped Bridge.
#4 Dropping markers in bins
#5 Shooting Torpedo
#6 Manipulation of two cylinders horizontally and vertically.
#7 Capture Laurel at depth and surface inside an octagon.

We grouped the tasks that were at the same level of difficulty. From simplest to most difficult.
Group1: Tasks # 1and 3.
Group2: Task # 2.
Group3: Task # 4.
Group4: Tasks # 5 and 6.
Group5: Task# 7.

Following is a table of what we pan on accomplishing by the stated date given that we have 8 weeks to the competition.

Ethernet Discoveries

After hearing some advice and following up with research, the team learned that the Fast Ethernet (100Base-T) only uses 4 out of the 8 wires in an Ethernet cable. After tearing apart an old Ethernet cable, pins 4, 5, 7, 8 were clipped and have been confirmed to work as intended. For Gigabit Network Interface Cards (NIC), Ad-HOC is auto-detected, eliminating the requirement of a crossover cable.

Python Submarine Class

A class for controlling the submarine has been completed. Using the functions turnLeft, turnRight, goStraight, ascend, descend, clawopen, clawclose, and stop, a Python program can autonomously control the onboard motors.

Submarine( port, baud, cmd_size ):
This is the class constructor for the Submarine. The port is the serial port to which the motor controller is connected. The baud is the baud rate for the serial port. cmd_size is the length of the commands to be sent to the motor controller. The default for cmd_size is 8.

turnLeft( int ):
Taking a parameter between 0 and 100, the RoboSub will turn left using the appropriate number of thrusters. If the power is between 1 and 50, the left motor will move in "reverse." For power levels greater than 50, the right motor will push forward. At 100, both motors are operating at full power in opposite directions.

turnRight( int ):
Identical to turnLeft, except the motor roles are reversed.

goStraight( int ):
This takes a parameter between -100 and 100. At -100, the left and right motors will be at full power in reverse, and at 100, the motors will be at full power forward.

ascend(  ):
This forces the climb motor to draw the RoboSub toward the surface.

descend(  ):
This brings the RoboSub lower into the water.

clawopen(  ):
This will open the claw and shut off the motor after a brief moment.

clawclose(  ):
This will close the claw and shut off the motor after a brief moment.

stop(  ):
This shuts off all motors and the robot should start floating if it is positively buoyant. Depending on time, this may change to allow the climb motor to counteract the buoyant force and maintain its current depth. ( Ideal )

Usage is as follows:

import submarineclass
import time

RoboSub = submarineclass.Submarine( 9, 2400 )
RoboSub.turnRight( 25 )
time.sleep( 1 )
RoboSub.goStraight( -90 )
time.sleep( 5 )
RoboSub.stop(  )
RoboSub.clawopen(  )
RoboSub.ascend(  )
time.sleep( .4 )
RoboSub.stop(  )
RoboSub.clawclose(  )

This should turn the RoboSub right for 1 second, then move backward at 90% power for 5 seconds, open the claw, move up a bit, then close the claw.

New Sub Designs

A few hours of hacking away at AutoCAD Inventor led to this design for the robosub chassis. Notice the rendering and exotic tundra. I do not think that the sub will be effective on land, but it had much more dramatic shadows in this location.

I have generated some drawing file for the above components and we will attempt to cut them as soon as possible. The next step is to make sure that the motor controllers are working.

Corrosion test

After the thrust profile test was completed, I did not have enough time to dismantle the experimental set up, so I left it in our lab for a day until I could return to it. Upon extraction, I was much surprised to find the level of corrosion present on the DC-DC converter and 2 of the 3 shaft couplers on the motors.

 Corrosion on the DC-DC converter

Corrosion on the shaft coupler

The rate of corrosion is really the interesting part of this test. The parts were likely submerged for 36 hours and look as if they are starting to grow barnacles. In order to prevent this, I believe we should apply a coat of acrylic paint to surfaces which will be continuously exposed to the water.

If it works for ships, it should work for us.

Thruster with new power supplies

We exchanged the original power supply: (see photo)

 

For two, also old but better power supplies:

 The difference lies in the current ratings. The Cenco power supply is only rated to provide 3 amps at 50 volts, whereas each Lab-Volt can handle up to 10 amps. The reason the two are wired in series is because the Lab-Volts can only provide up to 36 Volts. Neither power supply can provide for all of our needs in the thruster profile, so two in series is the way to go.
 

Like last time, the thrusters were immersed in water to simulate the load the will experience while in operation. Unlike last time, the DC-DC converter unit was also submerged for the duration of the test.

Instead of varying the voltage on this trial, I merely set the Lab-Volts to generate a potential of 48 Volts, and then connected the motors.

Here is a summary of the results:

Interesting differences compared to the previous experiment include that the sag voltage at the source is the same for each configuration (40V) and the current changes only marginally from two motors to three. If the resistance in the cable is approximately 5.5 Ohms, as was previously calculated, the power lost to the cable is 30, 38 and 43 Watts respectively.