Underwater Robotics Chapter 7, Moving and Maneuvering Sections 2, 3, and 6

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Motor Shrouds – MATE Required Primary Purpose of the Motor Shroud is Safety

Spinning propellers and fingers are a bad combination. Plastic spinning propellers are just as dangerous as metal

propellers. The Students get this and yes propellers do cut fingers.

A well designed shroud can slightly increase ROV

performance while a poorly designed shroud can significantly decrease performance.

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3D Printing -a big Impact on ROV Shrouds

This shroud motor mount combination excels at protecting fingers however is missing safety markings. The concentric rings increase frontal area and will throw off eddies, negatively impacting ROV performance. The front guard will decrease forward thrust and metal bolts add weight.

This shroud combines printed supports with a straight metal protective cylinder resulting in nice clean flow paths and good safety markings. A shorter cylinder might increase performance by allowing easier water flow. Metal bolts add weight.

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3D Printing -a big Impact on ROV Shrouds

Nice red safety color while the tulip shape is attractive and protects the fingers; being all plastic is light weight. Nice hydrodynamic shape especially the final downward curve. The slots maybe too small and hamper water flow into and out of the shrouds. Shroud may be too long increasing weight; glued to motor so must be replaced together. Overall pretty good.

This is a well designed shroud, the cylinder shields the propeller while not be so long to hampering water flow in either direction. Safety markings are clearly visible. The flexibility 3D printing allowed for offsetting mounting needed to ameliorate motor placement issues.

Downward curve

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Shrouds & Propellers combination can Significantly increase Performance

This shroud propeller combination is called a KORT nozzle and can increase motor thrust around 15%. The inside of the shroud is shaped like a wing and the propeller tip is flat with a very precise clearance to the shroud. Most ROV teams do not have the tooling or manufacturing skill to make these. Tight Clearance between propeller

and shroud are required for the nozzle to work properly.

Underwater Robotics, pg. 328 5

What makes a Good Motor Shroud? Safety - Protects fingers and is well marked

Allows for easy water entrance and exit in either direction Straightens/guides (ducts) the water flow Light weight Sturdy and does not move around hitting the propeller

Will standup to students reconfiguring the ROV

Hydrodynamic Shape to decrease drag, low frontal area

Easy to make and inexpensive

6

Handmade Shrouds

Tube made by rolling aluminum, screwed into an ABS coupling that was fitted around the bilge pump motor. Nice straight flows though one needs metal working tools and experience. Wobbling may hit propeller and decrease performance.

The all PVC shroud provides nice clean flows, is light weight, and inexpensive. It is the easy to make and can be glued directly onto the MATE provided PVC motor mount.

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Readily available Materials 2 inch ABS (black ) or PVC (white) pipe couplings require

minimal preparation and are inexpensive.

1 ½ inch PVC or ABS pipe couplings can be used but requires a fair amount of sanding to get the propellers to fit but will give you better performance

Remove inside ridge Cut in PVC coupling in two to decrease length

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So ABS or PVC….Depends Both can use PVC glue and are easy to work with Rigid material so shroud will not move around Cost per coupling is similar but you get TWO shrouds out of

the PVC coupling so cost for PVC shroud is ½ cost of ABS. Though ABS is lighter…remember 1 per motor

There is no right…..

37 grams

50 grams

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So how do you fit these together

MATE Provided Bilge pump motor mount is 1 ¼ inch ID PVC

Coupling is 2 inch ID

Want the Propeller in

middle of coupling

So there is a difference of approximately ¾ inch between the Motor mount and the coupling…..

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Not all PVC is Round

You can buy flat sheets of PVC at the plastic store Solid PVC Sheet or Foam Board At least 1/8 inch thick Comes in different colors Check out the scrap bin to save $

The good part is it easy to cut, glue, and bend.

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Cut pieces and glue them together to build up the gap

Here foam PVC Board is being use

Though Solid PC strips could also be used

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Or Use Heat to Bend SOLID PVC

When using this method use the solid PVC not the foam board

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Use PVC glue to attach

For glue to set, the pieces must be firmly held together in a vice or use clamps

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Finished Demonstration shroud

This demonstration shroud illustrates two different techniques for attaching the shroud to the motor coupling.

Shroud

Motor coupling

Fill the gap with built up foam

pieces

Fill the gap by bending solid

PVC strips

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How would you make this design better?

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