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  1. This guide will walk you through upgrading your endcaps using the OpenROV 2.6 Endcap Upgrade Kit.
    • This guide will walk you through upgrading your endcaps using the OpenROV 2.6 Endcap Upgrade Kit.

    • This guide was created using a v2.5 OpenROV.

    • You will need the following tools:

    • Heat gun, Digital Multimeter (recommended), Painters or masking tape, Electrical tape, Soldering iron/solder/helping hands, Hobby knife, Tape measure with metric, Silicone grease or petroleum jelly for lubricating o-rings, Hot glue gun, Hacksaw Wire strippers/clippers, Acrylic cement and applicator syringe, 2-ton epoxy with mixing tube applicator.

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  2. Some parts of this guide are identical to the 2.6 Build Guide and steps that are the same have been re-used from that guide found here.
    • Some parts of this guide are identical to the 2.6 Build Guide and steps that are the same have been re-used from that guide found here.

    • I will be working on the pink ROV (#018, built and operated by the lovely, Meredith). There will be some differences in the visuals of the steps borrowed from the 2.6 guide so don't be alarmed if yours doesn't look exactly the same. Follow the step-by-step and you should be good to go!

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    • First we're going to remove the internal structure from the frame for easier access.

    • Remove the electronics chassis from the acrylic main tube and disconnect the DB25 cable

    • Cut away the zip ties that hold the wires to the internal structure.

    • Cut the tether away, leaving as much on the bundle or spool side as possible.

    • Cut the battery tube wires about 10cm from the rear end of the battery tube as shown.

    • Unscrew the motor mounts from the internal structure and set it aside.

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    • Cut the motor wires as shown. Be careful to not cut the wires on the motors so short that you cut away the enameled wire that is underneath the we will resolder this to the new wires.

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    • Carefully cut away the blue heatshrink and black adhesive-lined heatshrink from each of the motor wires. The goal to to expose the solder joint as shown.

    • This is best done with a very sharp razor blade or scalpel.

    • Using a soldering iron, de-solder each of the nine motor wires.

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    • You should have something looking like picture here, a free frame with nothing attached to it, two free battery tubes with 10cm wires, and three free motors with the wires cut

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    • Slightly different from the 2.6 build guide, but borrowing the images and instructions.

    • Next, cut a total of 19 pieces of one-meter long 20awg stranded wire. (Nine will be attached to the three motors, four will be attached to the two battery packs, and six will be used as auxiliary wires for external devices like the IMU depth/heading sensor.)

    • Strip a small amount of insulation off the ends of nine of the one-meter wires, tin them, and solder them to the motors.

    • After soldering each leadwire, inspect that the solder joint is smooth and shiny (not dull and rough, which would indicate a "cold solder joint" that won't conduct or hold well).

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    • Cut quantity 9 pieces of waterproof heat shrink tubing, length should be 2-3cm.

    • Apply a small amount of hot glue to the joint as shown.

    • With the hot glue still warm, slide the heat shrink tubing over the joint.

    • Make sure the pieces of shrink tubing are slid all the way up the wires so that each solder joint is completely covered.

    • Heat the tubing with a heat gun until the gel lining and hot glue inside oozes out from the tubing on both sides.

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    • Take four 1m lengths of wire and strip one end of each.

    • Strip the leads from each of the battery tubes and solder them to the 1m lengths of wire as show.

    • Apply the adhesive-lined heatshrink to each of the solder joints. Make sure to completely cover the joint plus a decent length of the wire to insure a good seal.

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    • Using some masking or painter's tape, label each of the bundles of wire. (e.g. port motor, starboard motor, vertical motor, port battery tube...)

    • Now is also a good time to mark which battery tube wire is positive and which is negative. You can test this with a multimeter by doing a continuity test on the button cap (positive end) of each battery tube and the bare wire.

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    • SAME PROCEDURE FROM 2.6 BUILD GUIDE (for the next couple of steps)

    • We're now going to build the endcaps for the electronics tube of the ROV. Although the pieces for each endcap are identical, you'll want to build the endcaps so that they are MIRROR IMAGES of each other (we'll go into that in more detail later).

    • Start out by removing the plunger from both syringes. We're going to cut the syringe tube in two locations to create a centering pin (which also acts as a purge valve) for the endcap pieces.

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    • Cut the syringe just past its plunger stop (the barrier inside the tube that the plunger butts up against when pushed in all the way) with a hacksaw. We want to keep the plunger stop in place so that the plunger can make a seal against it during dives.

    • We only want to cut off excess plastic (the part that a needle would normally screw into) in order to remove unusable length in the plunger.

    • Once the end of the syringe has been cut off, cut at (around) the 0.16mL mark.

    • Use medium-grit sand paper to smooth and square up the cut sides of the syringe.

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    • Using a razor, you can debur the inside edge of the syringe section, but be careful not to make any large gashes along the inside surface!

    • A paper towel or thin cloth can also be used to remove particles from inside the syringe tube.

    • If you have a Q-tip handy, you can also use that (wetted with water or alcohol) to clean the inside of the syringe section.

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    • Now we're going to start cementing the endcap disks together.

    • The first two pieces you'll cement together are the 3mm-thick disk and the 6mm-thick disk with a smaller hole in the center.

    • The 3mm-thick piece will end up being the inner-most disk of the endcap. Place the syringe section in the centering holes of the two disks so that the plunger stop-end of the syringe section is facing the inner disk.

    • You may also notice small notches extending from one side of the inner disk (a result of the laser-cutting process). Ideally these notches should face inward (away from the 6mm disk) as they may make it harder for the o-ring to seal properly.

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    • To make the endcap as strong as possible, we'll want as much surface area between the two disks to be cemented as possible. A good technique for cementing the disks together is to insert the syringe needle between the top of the two disks while pinching the bottom.

    • Allow cement to flow between the two disks so that it fills the gap between them from the bottom, up. (You may want to wear gloves, as some cement tends to leak out the bottom). Fill until the cement is about half way, then remove the syringe and squeeze the disks together so that cement is pushed across the entire interface between the disks.

    • You may want to rotate the disks about each-other slightly to spread cement around, but be sure that the two holes toward the edges of the disks are aligned before the cement sets.

    • Extra cement that drips out from the disks can be blotted up with a paper towel.

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    • Make sure the cut syringe is flush with the surface of the inner disk (the 3mm disk).

    • Cement the clear, 1.5mm-thick disk to the 6mm-thick disk in the same way the first two were attached. Visually inspect to make sure the disks are concentric (since the hole on the 1.5mm disk is larger then the syringe section.)

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    • Stack the remaining 6mm-thick disk (the one with a slot coming from the edge) on top of the 1.5mm thick disk that was just added. Make sure the inner radius of the slot and the hole from the other disks are aligned, and the disks are concentric.

    • After the disks have been cemented together, it's a good idea to allow a little more cement to run around the perimeter of each interface to assure no gaps are left on the outside edges of the disks.

    • One more disk (the white, 1.5mm-thick one) will be added later, but set that aside for now.

    • Once these parts are cemented together, you can repeat the same steps for the other endcap.


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    • Repeat the steps for building the previous endcap, but attach the 1.5mm, and second 6mm disks so that they make a mirror image of the other endcap.

    • Make sure you cement the second endcap so it its a MIRROR IMAGE of the other (not identical) as shown.

    • Congratulations! You have completed most of the electronics tube endcaps. Now, we'll check to see if they fit well in the main tube.

    • Don't cement the white endcap flange onto the endcaps yet!

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    • We'll now place syringe plungers into the holes for each main endcap. These plungers seal the endcaps during use, but can be pulled out momentarily to relieve pressure after the endcaps get seated (which pressurizes the air inside the main tube)

    • The stem of each syringe plunger should be cut so that it is flush with the outer surface of the endcap as shown. (This way it will be held in place when the main tube is placed inside the shell of the ROV)

    • Place a #340 o-ring (the medium-sized, fat one) in the grooves ("o-ring glands") of both endcaps

    • Since the o-ring will make a pretty tight fit with the main tube when pushed out to the right diameter, it is recommended that a lubricant be used on top of the o-ring (we like to use a commonly available lubricant called "MagicLube" which is available at many hardware stores) to assure the o-ring gets seated properly

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    • Place both endcaps into the main tube, and inspect to make sure that at least a 1mm-thick band of the o-ring is pressed against the inside of the main tube. Rotate the tube to make sure the o-rig engages along the entire interior perimeter of the tube.

    • VERY IMPORTANT: Because the tolerances of the pieces may vary slightly, it's possible that your endcap may not engage tightly enough with the main tube. (You can see an example of what this looks like in the second image).

    • If the endcap doesn't fit well, the band of engaged o-ring will be very thin or may even disappear in spots. If this is the case, send us an email at with an image of your endcap in the main tube (like the images shown) and we'll make sure you end up with parts that fit.

    • Once you've tested the fit of your endcaps, put them in a clean place (like a zip lock bag) so dust and particles don't get on the o-rings.

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    • Remount the motors.

    • Remount the battery tubes using the re-usuable zipties.

    • Run the remaining six 1m lengths along the same route. We're going to use these as auxiliary wires in case you want to connect any modules to your ROV.

    • If you have the IMU depth/heading sensor module (or any other modules) now is a good time to splice the wires just like we did with the battery tube wires.

    • Use some new zips or wire to make sure all the wire and cables are out of the way of the props.

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    • We're now going to re-pot the the endcaps. To do this, we're going to follow along with the OpenROV 2.6 build guide.

    • If you've been using the v2.5 or v2.4 OpenROV, you've hopefully got some of the 90-Minute Epoxy left. If not, we've done extensive testing and found that we can safely use 2-ton epoxy from the hardware store. The brand we like is Devcon, 2-ton epoxy "flowmix". The "flowmix" is important because it gives you a mixing tube applicator.

    • 5-minute epoxy is not apropraite, as it hardens before it can penetrate between all the wires and cables.

    • Either way, the next several steps show a new ROV in progress, but the technique is the same for us.

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    • Now we're going to route the yellow mesh sleeve material over the main wire harness. The sleeve material expands when it is compressed much like how a finger trap works.

    • Start by wrapping tape around the ends of all the wires in the main harness as shown. The purpose of this is to prevent the sleeve material from getting snagged as it is placed over the harness.

    • If only a few individual wires are left sticking out of the tape, and their labels are further down the wire, those ends can be snipped off.

    • Push the sleeve over the main wiring harness and slide it all the way down until its end goes past the bulkhead of the internal structure.

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    • To keep the sleeve material from fraying (beyond what it will have already done while putting it on) wrap both ends with electrical tape where the fraying stops.

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    • Use scissors to cut off left over frayed ends of the sleeve material up to the electrical tape.

    • Thread the wiring harness through the Port endcap. The harness should go from the outside of the endcap, inward. You can make sure you're going through the correct endcap by placing it in the position as shown. In this position, the flat edge of the endcap should face toward the port battery tube.

    • During this step, we'll measure out the right length of wiring harness so that it is not too tight or too loose when the endcap is in place.

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    • Once the tension of the main wire harness looks good, you can cement the white endcap cover onto the endcap. Be sure the endcap cover is pressed firmly against the endcap near where the harness passes through the assembly.

    • You'll also want to cement the other white endcap cover onto the other (Starboard) endcap.

    • Apply hot glue around the part of the endcap the wire harness enters through (the side with the rectangular opening- not the side with a circular opening). This hot glue will form a barrier that will prevent epoxy from leaking out when the endcap is potted.

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    • Insert wisdom here.The other (starboard) endcap can also be prepared for potting at this time. Create a barrier of hot glue at the end of the endcap channel to hold the epoxy in.

    • Apply a glob of hot glue to the end of each of the six auxiliary wires, then after each glob has hardened, bundle the ends together and apply hot glue to the bundle.

    • The six auxiliary wires can be used later to attach external payloads like sensors and actuators. While these are not being used, the ends should be sealed so water can't travel down the wires underneath the insulation into the the electronics tube (an effect known as "hosing"). To prevent this, we'll seal the ends of the wires with hot glue.

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    • Now, we're going to prepare the endcap to be potted. To start, we'll want to bundle the wires coming out of the endcap together.

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    • You can now start potting the endcap. It is important that all the gaps between the wires in the harness get filled with epoxy. When potting the harness, periodically insert the epoxy nozzle between random sets of wires and move the tip of the nozzle around. Also be sure to inject epoxy under the channel the wires pass through in the endcap.

    • To help remove voids in the epoxy filing the endcap channel, move the harness up and down (like a toilet plunger) and from side to side. This may cause the level of the epoxy to fall (as it fills voids). More epoxy can be added as needed.

    • Finally, you'll also want to fill the hole of the Starboard endcap with epoxy. Just as for the Port endcap, epoxy should come up to just below the rim of the endcap hole.

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    • Now that the epoxy in your endcap has had a little time to cure, we can get ready to add the DB-25 connector to the end of the wiring harness that passes through the endcap.

    • Start by removing the tape that was used to hold the bundle together

    • Next, measure a distance of 17cm from the inside surface of the endcap, and cut one of the wires from the bundle at that length. Measure twice, cut once- you don't want the harness to be too long or too short by more then about 1cm!

    • Use the one wire that you've cut as a guide to cut all the remaining wires in the bundle to the same length

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    • Now you can get ready to solder the DB-25 connector to the end of the newly trimmed wire harness.

    • Start by stripping off about 3mm of insulation from the end of each wire

    • Because each stripped wire will just barely fit in the solder cups for the DB-25 connector, it's easiest not to tin the wires before inserting them into their respective positions.

    • Look on the back of the DB-25 connector (the end with the solder cups) and identify pin 1 (labeled with a faint imprint in the plastic for the connector)

    • Use the guide shown to attach wires to the DB-25 connector. Be sure that battery polarity is correct by measuring for continuity between the forward (positive) terminal in each pack and the other end of the wire it goes too

      • The four I2C wires and the two AUX wires can be any of the extra six that were potted into the endcap- there is no order that need be put to them at this time. Following the photos later, the yellow strand on the tether line should be TETHER_A (18) and the blue strand should be TETHER_B (19)

      • There should be four pins that are left empty (TP22-TP25)

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    • Before hooking everything up it is crucial to not forget to epoxy the syringes in place.

    • Be careful not to allow epoxy to over-flow into the hole of the syringe as this will need to be clear for the syringe plunger (which acts as a pressure relief valve).

    • Make sure to keep for use later.

    • This needs to cure before we can flip it over and do the other side. 3 hours for the Hysol and 8-12 hours for the Devcon.

    • Once it is set, you can get back to testing and hopefully back in the water.

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    • This is a good time to check the connectivity and polarity of your battery connections with a multimeter. Check them at the DB-25 terminal before plugging it into your control board.

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    • Because the three wires from your motors likely have become swapped, its a good idea to check and make sure their direction is correct.

    • If not, you can change this from the OpenROV cockpit software OR you can switch any two of the three wires at the DB-25 connector for that motor.

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    • You're done! You've now got upgraded endcaps.

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Finish Line

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