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Moving and Maneavering
Transcript of Moving and Maneavering
MOVING AND MANEUVERING
Build Your Own Thruster !
An object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force.
The vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration vector a of the object.
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
F = m.a
TRANSLATION, PLEASE !!
For a vehicle to maintain
, all of the forces acting on it must be
, so their effects cancel.
For a vehicle to
, there must be an
in the forces acting on it, so the net force is not zero.
To push a vehicle in one direction, you must push something else equally hard in the opposite direction.
FORCES ON UNDERWATER VEHICLES
Estimating Thrust Requirement
Cd : Drag Coeff.
A: Frontal Area
V: Relative Speed Through the Fluid
How to determine the drag coefficient for our ROV in SolidWorks ?
How to calculate the Surface Area using SolidWorks ?
Nearly finished vehicle.
The need for: Spring Scale, long string, a stopwatch, tape measure.
Access to a swimming pool where the vehicle can move straight for 15m.
String length = 5m and pull horizontally.
Check if the spring scale measures horizontally accurately.
Give 5m before measuring speed.
Measure 2 above and 2 below the max. speed.
Paddles and Oars
Impeller-driven water jets
Reciprocating fish-like tails
Magnetohydrodynamic drives (MHD)
Magnus effect drives
DC Brushed Motors
The least expensive.
The most common
DC Brushless Motors
Need complex driver circuit
Gear box attached to motor shaft
Increase the torque without drawing more current
Used for precision control of motor shaft rotation angle
Precise angle control
Commonly, 0-180 deg. only
Has built-in circuit
Number of blades
Method to attach prop hub to shaft
Ducted props or not
How it works ..
Forward and backward thrust
Impeller-driven Water Jets
1. Choosing a Motor
2.Waterproofing a Motor
3.Attaching the Thruster
Provide strong support that won't flex or vibrate when the thruster is at full power underwater.
Minimize blockage of the thruster water jet in forward and backward.
Resistant to snapping.
Allow some adjustment of position and angle.
Allow for easy removal and reattachment of the thruster.
4.Selecting and Attaching a Propeller
5.Matching Propeller to Motor
Too large or too small !
Optimal DC Motor Speed.
How powerful (required force) does each motor has to be ?
How much voltage and current can you realistically and safely provide for them ?
How much can you afford to pay (especially since you'll need 3 of 4 motors) ?
Do you want to use brushed or brushless motors ?
Do you need a gear motor ?
How will you waterproof the motors ?
How will you attach the propeller to the motor shaft ?
How important is it to be able to replace the motors quickly and easily ?
Under optimal conditions: 1N per 3W
Usually, homemade thrusters produce 1/2 or 1/3 this value
Look for 12V motors which produce 4N for 3A
Commercial thruster produce from 44.4N - 133.4N
Brushed VS Brushless
Gearing and Gear Motors
Gear motors as thrusters
Motors are more efficient when spinning at high speed not high torque.
Planetary Gear Motors
Ready-made Waterproofed Housing
Bilge Pump Motor
Small Commercial ROV Thruster
Build Your Own Thruster Housing
Cordless Drill DC Motor
Cordless Drill Gearbox
RC Cars Brushless Motor
Sealing The Shaft !
Brushed VS Brushless Again !
Connecting Prop to Motor Shaft
Can be: Section of PVC Pipe.
Work best when ?
Little space between the blade tip and the duct.
Must be exactly centered.
How to connect the duct to the thruster or to the ROV ?
The wrong diameter -_-
Tight friction fit
Thruster Test Jig
Interpreting the Results
and calculate the
in a table.
For each propeller, do the test for 4 different voltages (i.e 3, 6, 9 and 12V).
Plot the results.
Notice the thrust at lower powers.
Notice the power at the maximum thrust and if it exceeds the rated power of the motor.
Choose the propeller that gives you the maximum thrust within the range of the motor's rated power.
THE DANGERS !!
Splattering water can make the wires get wet and make shorts.
Wear Eye Protection because the mechanical connections are temporary and can fly at the face !
Too big props can get the motor extremely hot and burn wires, skin and make fire.
If you think you find good combination, test it in water for at least 5 minutes to make sure nothing overheats.
Design a test jig mechanism that can be used to measure both pushes and pulls at low cost and with easy construction steps. The best design will be fabricated and utilized.
More Elaborate Thruster Arrangement
Obstacles to flow
Unwanted Turning Moments
Counter rotating props
Thruster Spacing for fast turns.
Impact of thrusters on circuits
Any Questions ?!