P16229: Robofish 3.1 - Navigation

Integrated System Build & Test

Table of Contents

Team Vision for Integrated System Build & Test Phase

In this phase, our team worked to bring all the subsystems of the electronics together as well as constructed the tail to be used on the Robofish platform. Our next major milestone is still to incorporate the entire electronics system with the tail through the valves and muscles.

Test Results Summary

I/O Board Design & Development

As discussed in the last phase, the need arose for a third PCB to carry out the electronic functionality for P16229 Robofish operation. The board was deemed an I/O board based on its functionality of preparing singals or power for use elsewhere in the system. The contents of the board can be found in the last phase documentation. The PCB layout was created in Eagle software and sent to OSH Park for manufacturing. We currently have the physical PCB and have installed the components upon the board. An important aspect of the board is the mounting area for the 24V buck converter which will bring the battery voltage down to 24V for the valve. The DC-DC converter fit nicely unto the OSH Park board and functions properly. The sonar sensor circuitry on the board has yet to be tested. The board also incorporates a switch which will be mounted through the wall of the electronics water proof box as a way to easily turn the power on and off to the robofish from the batteries.

Water Proof Electronics Container

The water proof electronics box was obtained for use on the robofish. The box incorporates and water tight lid with a gasket seal. The box was tested briefly by submerging it in a small bucket and examining for leaks into the box. None were found. The box also includes mounting slots on the corners of the interior. Acrylic mounting plates were manufactured to slide within these slots with holes to support the various circuit boards. The acrylic plates were sanded as to not interfere with the box lid. In addition, a cardboard slice was placed at the bottom of the box to create a flat surface for the batteries to rest on over the protrusions on the bottom of the box. The box was also tested for leaks with the mounting plates inside. The batteries are to be placed slighty offset from the center of the box as to create extra space for the mounting boards and plates to fit. The batteries will be tied to the cardboard slice and box through a velcro strap which extends around the entire battery pack. This is necessary since the box will actually be mounted upside-down upon the robofish.

Battery Pack

Once the missing single battery holster was ordered and acquired, the battery pack was completed. The battery pack is comprimised of 4 parallel sets of 9 batteries in series to create a 30V to 38V power bus with the energy capacity desired. The battery pack was created using execlusively 36 single battery holsters. As discussed previously, this enables for an effective battery swap precedure in which the batteries are removed and replaced individually. This circumvents the design and usage of a battery management system since the batteries are charged individually on a commerical charger. The individual cells of 9 series batteries were connected in such a way that the pack is able to unfold in an acordian-like fashion to easily access all of the batteries. Once the battery swap has been made, the pack folds back up and is held together by multiple velcro strips. Hot glue was used to cover the holster terminals to prevent accidential contact with other conductors. The individual battery holsters where glued together with epoxy, although, this is proving to be a fairly fragile method of structure. Instead, the plan is you use popsicle sticks and expoxy to glue multiple holsters togther for extra structural support. The full electronics system was tested with the assembled battery pack and functioned properly. At this point, the battery pack is expected to be used for all future testing and during Robofish operation.

System Electrical Wiring

In order to make connections between the circuitry internal to the waterproof box and the other electical devices outside the box, a system was devised to protect the wires from water exposure and effectively deliver the power and signals necessary. Previously, the Robofish wiring had be accomplished by running regular wires through open water. While electrically insulated from the water, having only the wire insulation protection is not the best solultion especially so extended use due to insulation wear and broken insulation could casuse serve power loss and/or signal integrety issues. The proposed system would bundle multiple wires in a rubber or flexible tube which would run to the desired device. In order to accomplish this presumably water-proof technique, a cable gland will be used to interface any water tight box with the associated tubing. The cable gland works by clamping a tight seal around the perimeter of the tube through a large locking nut. A hole will need to be drilled in the electronics box and the pump box for these glands. The number of wires leaving the box was approximated and used to size the tubing appropiately. Note that the tubing will all have to be the same type and size dur to the nature of the joints, glands, and other connectors. In the electronics box, all wires leaving the box will travel through this cable gland discussed. In order to re-route certain cables to different devices throughout the fish, "Y" joints will be used to create a path for certain wires to split off from the main bundle while remaining in their own, seperate tubing. Eventually the tubing will need to terminate close to certain devices (valves, camera, and other sensors) It will be required and important that the tube is back filled with epoxy or other material to create a water tight seal. The amount of naturally-insulated wire exposed to open water will be minimized. In addition, push-to-connect ports may be placed in series with some of the branches of the tubing and wiring for ease of service and repair. This will enable certain devices to be disconnected from the main tubing. Otherwise once the tubing and wiring network is constructed, the configuration would be permanent. The push-to-connects would be a water tight connecter which simply feeds the electrical signals through the connector and is able to be disconnected, breaking the signal/power path.

Arduino Code Update

As previously discussed, the Arduino was presumed to have been broken and a new Arduino was ordered. While working for a reasonable period of time, eventually the new Arduino experienced the same connectivity issue. The original Arduino was investigated and through reinstallation of drivers, the Arduino was returned to a functioning state. The Arduino code was updated so that a turning sequence is not executed as soon as the command to do so is recieved. Previously, the program waited untill the end of the swimming period to transition to a turning maneuver. With the instant turning capability, the Robofish will have a much faster response time from detecting objects to turning.

Integrated Raspberry Pi Testing

A Raspberry Pi is used by P16029 team to carry out image processing and provide direction for the Arduino and associated valves. A milestone test was conducted in which the Raspberry Pi was used to send left and right turning directions to the four tail valves. Previously, to create a turning command, a wire was physically moved to bring the node to a high or low level via other Arduino ports. In this test, this was replaced by commands from the Rapberry Pi and asscioate camera. An object was moved from the left to right sides of the camera field of view. This resulted in the valve switching pattern adjusting. When the object was in the left hand side field of view, the valves executed a left turn pattern. Similarly, a right turn procedure was seen on the valves for the time the object was in the right hand side field of view. When the object was not in the field of view, the valves executed a striaght swimming pattern. A video of which is shown below.

Raspberry Pi & Camera Integration Test Video

Robofish Tail Construction

The Robofish tail was constructed from stock Delrin material one half inches thick. The pieces were drawn in SolidWorks and prints were created. These prints were coupled with the models and sent to the machine shop to be cut using the water jet CNC machine.

Holes were drilled into the parts to attach the pulley wheels as well as to place the shafts for rotation. Additionally, islets were screwed into the pulley wheels as guides for the line which will transfer the force generated by the muscles.

The whole tail apparatus was assembled. Spacers were needed to prevent unnecessary movement between the pieces, both between the body and the first half as well as between the first half and the second half. The whole tail was attached to the body with the 3D printed piece that interfaces with the body parts.

Valve Attachment

Holes were drilled in the body plates in order to attach the valves for the muscles that actuate the tail to the body. The valves that control the first half of the tail are to be attached to the top of the fish body while those that control the back half of the tail will be attached to the bottom of the fish body. The valves that control the ballast tank will be attached to the front vertical part of the fish body. Holes were also drilled for this part and the valves will be zip tied through these holes.

Muscle Placement and Hydraulic System

The muscles that power the first half of the tail will be directly attached to the valves that control them. The valve itself will act as the rigid attachment point for the muscle. The muscles that power the second half of the tail cannot be attached to the fish body. This realization came as a result of testing with the tail apparatus. The distance between point of attachment and the origin for the line changes dramatically between the extremes of the swimming pattern. That being said it became apparent that if the muscles were attached to the first half of the tail there would be much less of a difference.

A handful of three way push to connects were used to route lines from the pump box to the valves both on the top and the bottom of the fish body. A single line will leave the pump box in order to minimize the number of times we have to compromise the integrity of the box for the hydraulic component. The pump box itself will require three holes; one for the inlet with a filter, one for the outlet, and one for the electrical connection to power the pump.

Inputs & Source

  1. Test Plan
  2. Subsystem fabrication

Outputs & Destination

  1. Test Results
  2. System integration

Risk and Problem Tracking

Electrical Risks

  1. Porting wires though various water tight boxes. System critical and also very risky. It is imperitive that the joints do not leak or the entire electrical box and its contents may be comprimised. Lithium-Ion batteries are very sensitive to water.
  2. Still a large work effort to be put into the programming and tuning of Robofish. Most of which can not be effectively performed until the fish is water tight and can swim well.
  3. Fitting all of the electrical components into the water proof box may prove to be a challenge, the batteries take up a large amount of space.

Functional Demo Materials

Electrical Team

No extra demo materials are necessary.

Plans for next phase

Electrical Team Plans

  1. Install cable gland in electronics box and test for water resistance.
  2. Perform tail testing including timing and tuning the Arduino swimming algorithm for optimal swimming style.
  3. Working with P16029 to create interfaces for camera, Rapberry Pi, and Bluetooth return-to-home system.
  4. Underwater sonar sensor testing and functionality. Will it even work underwater?
  5. Pray to the electical gods and scramble to finish before Imagine RIT. Just over a month left...

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