Sea Sampler: Midwater Plankton Tow for OpenROV




Introduction: Sea Sampler: Midwater Plankton Tow for OpenROV

Dive. Sample. Share.

We know more about outer space than we do about the oceans on our own little planet--and funding for ocean research is dwindling. Our midwater plankton tow is a low-cost, customizable tool for researchers, students and citizen scientists to gather samples with an OpenROV. Our oceans are in trouble--and we can all help by taking a closer look.

From the surface to the seafloor

Scientists around the world use plankton tows to sample tiny animals and plants from the sea's surface. As you go deeper, collecting gets complicated—and expensive. Our midwater plankton tow is simple and easily attaches to an OpenROV--so you can sample at any depth! For best results, find a microscope (check out for a friend's awesome smartphone microscope invention) or make one to examine specimens.

Start your own sampling

- Every ocean, lake, and stream is bursting with tiny plants and animals. Collect and study your own miniature menagerie!

- Tiny bits of plastic are everywhere--but often hard to see. Start sampling and share your results with local lawmakers and groups advocating for plastic bag or microbead bans.

- Help monitor local water bodies for invasive species, like zebra mussel larvae--or recovering species, like sea stars on the west coast of North America.

- Just start sampling! You never know what you'll find until you start looking.

Share your results

- Share what you've found on OpenExplorer, a collaborative community that allows scientists and enthusiasts to share information and build a greater understanding of our planet. Together you may notice a larger pattern or trend and learn more about what's going on in our oceans.

- Swapped out the plankton mesh size? Modified the specimen collection tube? Let us know! With OpenROV, we want to help make ocean research tools like this simple, inexpensive and accessible.

Step 1: Gather Material and Files


1. File: OpenROV Plankton tow_Laser parts quarter inch acrylic.eps (use this file for cutting the 1/4" parts)

2. File: OpenROV Plankton tow_Laser parts eighth inch acrylic.eps (use this file for cutting the 1/8" parts)


1. File: OpenROV Plankton tow_Vinyl mesh pattern.eps (use any color of vinyl you prefer, clear transfer paper is available at TechShop)


1. O-rings:

2. Quick release pin:

3. Bolts:

4. Nuts:


1. Waterproof servo from OpenROV

2. 4" x 6" piece of desired mesh material

Step 2: Fill Your Squeeze Bottle With Solvent

The majority of the assembly work will involve using a needle tip bottle for applying acrylic solvent. Acrylic solvent is not a glue, it slightly dissolves the acrylic when it comes in contact with it and bonds both acrylic components. In order to start bonding your acrylic you need to fill your bottle (bottles are available from Tap Plastics, you will be looking for the small BD-25/2 squeeze bottle). Do not attempt to fill the bottle directly from the solvent container, it is thin like water and will go everywhere.....huge mess, don't even think about it. Instead, fill a cup with the solvent and then pinch the cup to form a spout and fill your squeeze bottle.

Step 3: Servo Chassis Assembly

Now you need to assemble the servo chassis. This will secure the servo and this entire assembly will slip over the acrylic collection tube. The chassis allows for the servo to be easily removed if necessary. Here is how to build the chassis:

  1. Place the base plate on a clean flat surface and insert one of the vertical supports into the appropriate slots.
  2. Carefully apply a thin bead of solvent right at the junction between the acrylic parts. (If you have never used acrylic solvent before, the key is moderation and control as very little solvent is needed to create a strong joint. Capillary action will suck the low viscosity liquid into the joint so the solvent can be applied with the joint in place. A thin needle nose bottle is suggested for application.)
  3. Place the next vertical support into the appropriate slots.
  4. Carefully apply a thin bead of solvent right at the junction between the acrylic parts.
  5. Insert servo between vertical supports.
  6. Align top plate so that vertical supports and servo integrate through slots.
  7. Insert bolts through holes in vertical supports to secure servo. Nut side goes away from the collection tube. Tighten bolts slightly beyond hand tight.

* Note only the middle four cut parts that are needed for the main chassis assembly.

Step 4: End-Cap Assembly

At the end of the collection tube a filter end-cap must be placed. this ensures specimen collection while maintaining water flow through the tube.

  1. Place mesh over the base ring.
  2. Place inner ring over mesh. This sandwiches the mesh between the base ring and the inner ring.
  3. Use the inner ring placement jig to ensure proper placement if needed.
  4. Apply bead of solvent around inner ring perimeter.
  5. Cut around inner ring with utility knife to remove excess mesh material.
  6. Place assembly in outer ring placement jig to ensure alignment of outer ring.
  7. Apply solvent to junction between outer and base rings.

Step 5: Vinyl-Mesh Wrap Preparation

This hexagon pattern was created on a CNC vinyl cutter (pattern attached). This will give the mesh wrap some additional structure. If you do not have access to a CNC vinyl cutter, the pattern could be cut manually with an exacto knife or it could be omitted all together and the mesh alone could be affixed to the tube with adhesive, O-rings or some other method. To create the vinyl-mesh filter wrap the vinyl must be applied to the mesh by following these steps:

  1. Remove vinyl from backing paper by pulling up the transfer paper. The vinyl should come with the transfer paper.
  2. Place vinyl over mesh and apply when desired placement is achieved.
  3. Using the collection tube burnish the vinyl onto the mesh to ensure adhesion.
  4. Start removing the transfer paper slowly. Remove the transfer paper sideways in the same plane as the vinyl, do not pull up like you would remove making tape. You may need to hold a corner of the vinyl once you have some of the transfer paper removed. This can be tricky to get started but should be easy once you get the vinyl to stick.
  5. Set the transfer paper aside adhesive side up as you will use it in the next step.

Step 6: Collection Tube Preparation

Now it is time to prepare the collection tube. The idea here is that we want to drill a hole pattern that will allow water to flow freely through the tube as the OpenROV is performing collection operations. The tube will later be wrapped in a mesh/vinyl to keep our specimens in the tube. The attached files can also be used as a print out drilling template if you do not have clear transfer paper. In this case we are using the transfer paper from our vinyl. Follow these steps to prepare the collection tube:

  1. Apply the transfer paper to the tube. Be careful to align it squarely.
  2. The witness mark of the hexagons will be visible on the clear transfer paper. Mark the hexagons with a cross hair pattern quickly as the impression of the hexagons will disappear over time.
  3. Drill marked holes with a hand drill or drill press.
  4. Drill hole for quick release pin all the way through the tube. Hole will be placed so that the pin lands in front of the rear ring of the servo chassis and holds the chassis on securely. This hole should be located at about 1.75" from the open end of the tube. Do not drill this hole until the chassis with tube gate has been placed on the tube and then mark and drill hole. (not pictured)
  5. Optional- Counter sink holes to remove burrs and to create a cleaner look.

* Note that tube is a standard OpenROV part

* Note that geometric pattern left on adhesive transfer sheet will disappear once you removed from vinyl sheath so you should remove transfer sheet immediately wrap tube and draw circles to be drilled all in one step.

Step 7: Install End-cap on Collection Tube

The end-cap filter assembly must be installed on the end of the collection tube to ensure specimen collection and water flow through the tube during collection. Follow these steps to install end-cap:

  1. Apply a small amount of solvent to the end cap
  2. Place end cap on tube and hold in place for 15-30 seconds to ensure adequate bonding.
  3. An additional bead of solvent can be applied if needed once the end-cap is in place.

Step 8: Collection Tube Gate Assembly

Assembling the collection tube gate is simple. Basically all that needs to happen is to bond the spline washer to the tube gate body. The photos show usage of jigs for alignment. This is optional, the pieces can be aligned with the small hole in the tube gate body being aligned concentrically with the hole int he spline washer. If using the jigs follow the steps below for assembly:

  1. Place the tube gate body inside the nesting jig.
  2. Place the gate body alignment jig inside the nesting jig as well. When you laser cut the gate body alignment jig leave the paper on the back of the acrylic to ensure acrylic does not bond to the gate body.
  3. Place a small bead of solvent in the hole and on the spline washer.
  4. Firmly place the spline washer in the hole and apply pressure until parts are bonded.
  5. Remove jig components as soon as possible to ensure they do not bond with tube gate assembly.
  6. Place the tube gate over the servo by integrating the spline washer with the spline on the servo. (not pictured)
  7. Screw the tube gate down with the screw provided with the servo. (not pictured)

Step 9: Final Plankton Tow Assembly

Now that your components are assembled it is time to wrap it up and put a bow on it. The next steps are to install the mesh and the servo chassis.

  1. Wrap the mesh around the tube taking care to align hexagons with the holes in the tube.
  2. Use the o-rings to attach the mesh to the tube. 4 evenly spaced o-rings will secure the mesh adequately.
  3. Place the chassis over the tube and carefully push the assembly onto the tube.
  4. Place the quick release pin in the hole for quick sample tube removal. (not pictured)

Step 10: Plankton Tow Attachment to OpenROV

All that is left is to attach the plankton tow to your OpenROV. to do this use the large rubber o-ring and first attach the o-ring over the rear ring of the servo chassis and feed it under the threaded rod on the ROV. Attach the other end of the o-ring over the top of the end cap. The tension of the o-ring will secure the plankton tow securely for collection.

You're almost ready to field test your plankton tow--you just need power! By connecting the servo wires to the external auxiliary wires of the OpenROV, you can power and control the plankton tow from the same laptop interface as the other OpenROV controls. Steps may differ for each generation of robot--we're working on another Instructables to explain that process!

Once your plankton tow is build and powered, you're ready to go! And please share your findings on OpenExplorer!

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    6 Discussions


    4 years ago on Introduction

    Thank you for this. My engineering skill is too poor to build it, but I greatly appreciate your concern for the ocean and taking meaningful action. Nothing is more depressing than seeing massive death in the sea because the people above do not know the world they are destroying. We can help by showing where just past the beach there is a world where experience is like nothing on land.


    5 years ago



    5 years ago on Introduction

    Very cool!

    That ROV looks really neat. About how much does something like that cost?


    Reply 5 years ago on Introduction

    The parts for the Plankton Tow are around $20 for hardware, although I don't have an exact price for the waterproof servo, OpenROV ( should be producing them soon. The OpenROV itself is a kit you can purchase for $899 (