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Old Apr 07, 2015, 10:54 AM
GrassCube is offline
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How to Choose The right Power System

Hi guys,
im bachelor's student for mechanical engineering, and currently im working on a project that involves a target homing robot that operates on a corrosive fluid (hypersaline water).
Given that the water is very corrosive, i want to avoid any moving part in the water itself so i figured that i should try an RC plane or quadcopter propulsion method (using an air propeller) instead of water prop.

I have absolutely no experience in this field , so im not even sure where to start and what questions should i ask.

I need power system to create thrust (parallel to the water surface) so it can float to its target.

So if you can help me to choose the right prop, motor and power supply it'll help me a lot.

Tnx!
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Old Apr 07, 2015, 12:59 PM
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Something like a air boat, swamp boat ?

To determine the power and prop size, we would need some sizes, expected speed etc, for the 'boat'.
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Old Apr 07, 2015, 01:24 PM
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As any mechanical engineer surely knows the power system you need depends on what you're trying to power (size, weight etc) and what performance you want from it (acceleration, speed etc).

There's probably someone here who can help but they'll need something to go on .

Steve
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Old Apr 07, 2015, 04:19 PM
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Well i just started working on the project so the specs of the robot are still being worked on, but i'll try to make some approximations to get it started

weight: i think about 4-5 kg in total, including the outer shell, floats ( to raise it above the water surface), Props (i was thinking of 2), motors, rudder (like on a airboat) power supply, a couple of servos/steppers, Arduino board (for all the monitoring and control), double dipole antenna (for the directional finding and homing), wiring a few other components.

Speed: the speed should be moderate, about 5-6 km/h (3.1-3.7 mph)

Acceleration: this factor will be controlled by the Arduino, and usually the acceleration from from a stand still will bee moderate as well, but i would like to have the option of a fast acceleration (but again this is optional)

Size: the robot must not exceed 300x300x300 mm frame, but if i can prove that this frame size is to small for the application requirements it can be larger that that.
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Old Apr 08, 2015, 04:56 AM
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Just some guesses -

Calculate the water displacement based on a 300x300mm platform and max weight of 6kg, (safety margin).
You should then be able to calculate the thrust required to push that 'flat fronted ?', (300mm wide x displacement), through the water at say 10km/h, (safety margin).
Once the required thrust is known, you stand a better chance of finding what size air prop and power system.

Consider whether the device will have enough steering using air rudders, (what about if reverse direction is required ?, air rudders will not function unless on both sides of the prop).
Perhaps even consider fully rotatable power units, (multi-directional).

No idea how tall the device needs to be above the water, or what it is expected to do, but 300x300mm is quite a small platform to support any superstructure.

A lot of work for you to do
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Old Apr 08, 2015, 05:24 AM
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Btw i found this Airboat, judjing by the specs of it, can i use it as a starting point?

I've seen the video of this boat on youtube and it looks to fast for what i need.
From what i've seen so far, i need a prop with a lower pitch so i'll get higher thrust force with lower top speed, but im not sure how to choose the right one.

Except the prop pitch what else can i change to get the performance i need, or can i just change the pitch and leave all the other components as is?
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Old Apr 08, 2015, 06:27 AM
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Quote:
Originally Posted by eflightray View Post
Just some guesses -

Calculate the water displacement based on a 300x300mm platform and max weight of 6kg, (safety margin).
You should then be able to calculate the thrust required to push that 'flat fronted ?', (300mm wide x displacement), through the water at say 10km/h, (safety margin).
Once the required thrust is known, you stand a better chance of finding what size air prop and power system.

Consider whether the device will have enough steering using air rudders, (what about if reverse direction is required ?, air rudders will not function unless on both sides of the prop).
Perhaps even consider fully rotatable power units, (multi-directional).

No idea how tall the device needs to be above the water, or what it is expected to do, but 300x300mm is quite a small platform to support any superstructure.

A lot of work for you to do
Tnx a lot! and we told to the faculty that this base of 300x300 is very small, but if i can prove that it wont be practical or enough i can exceed those measurements.

In case i figure out the force needed, how do i proceed from there to choosing a prop and power system?
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Old Apr 08, 2015, 07:06 AM
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Do yourself, and us a big favour, some reading for rainy/windy days.
Will prevent you from burning several controllers and/or motors and/or battery.

E-flight 101 by RCG member Ken Myers, will at least save you a ruined LiPo (or worse!), a burnt motor and a fried ESC:
The Ampeer
→ Electric Power Basics

followed by
The Ampeer
→ Everything youw wanted to know about e-flight (Ed Anderson)
Table of Contents
  • What You Need To Know About Receivers
  • What function goes on which stick?
  • Battery Basics
  • Amps Versus Volts Versus C
  • Lithium Battery Chargers
  • ... ...
  • Understanding the Electronic Speed Control (ESC)
  • the Low Voltage Cutoff Feature (LVC) Of Your ESC
  • The Role of the Battery Eliminator Circuit in Your ESC (BEC)
  • Sizing Power Systems for Electric Airplanes
  • Prop Versus Amps
  • What Do the Kv Numbers On Motors Mean?
  • Who Needs a Wattmeter/Power Meter? (everyone!, RvS)

www.scriptasylum.com
→ RC calculations
→ electrical
system wiring
respectively ...
LiPo pack wiring
respectively
chargers (2 menu items)
The other menu items and demos are also veeeeery handy/instructive for e-folk, add site to your favourites?

www.ezonemag.com
→ FAQ

Vriendelijke groeten Ron
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