Vintage Gentleman’s Cruiser

[Gareth JonesParticipant @garethjones79649]

I think you are all overcomplicating the problem for the average boat builder. The only simple and practical way of measuring the power taken by the motor and the speed of the propeller is with the boat static in the water, tethered to the bank where you can read the values on the wattmeter and tacho at maximum forward throttle setting. (or in the bath if you prefer)

If you are using an established make of speed controller, eg Mtroniks, use the next size up above your measured current so you have a margin to cover any transient effects. If you are using a cheap chinese import use one with a rating about 100% bigger than your measured current.

This will give you a good enough feel for the operating conditions of your model. All this business about size mass, inertia and whether the boat is accelerating forwards or backwards is just second order stuff you dont need to worry about.

Gareth

[Diede van AbsParticipant @diedevanabs87670]

Amen, Gareth.

[Dave MilbournParticipant @davemilbourn48782]

Bob

A Newton is the unit of force in the SI (metric) system. Its equivalent in the Imperial system of measurement is a Poundal, which is defined as the force required to accelerate a mass of 1 pound by 1 foot per sec². A Poundal is equal to approx 0.138 Newtons.
As Gareth says, there is little if any point in worrying about these matters when designing or sailing a model boat. It's only old pedants like me and Paul who use them to stir up the Kevins.

Dave M

[ashley needhamParticipant @ashleyneedham69188]

All this calulating and prevaricating is of course the reason you have purchased a wott? meter Bob. it hopefully has a max current setting (so it captures the maximum current taken, on a run, for instance) and there will be no mystery, no magic, no argument.

A `bollard` static test would be the best bet for an initial reading I say.

I have an optical tachometer now and am curious to see if it will pick up on the outer casing of an outrunner (if some lines are painted on in white) as then we would have not only current draw but actual prop speed to go on.

Ashley

[Paul TParticipant @pault84577]

It's only old pedants like me and Paul who use them to stir up the Kevins.

I resemble that remark

 

Although I stand by my statement that the mass must be part of any amp calculations especially when it weighs in excess of 20kilos

Paul

Didn't Newton team up with Ridley and start a brewery  

 

Edited By Paul T on 25/03/2015 17:33:03

[Bob Abell 2Participant @bobabell2]

Hello Paul

All this silliness has given me an idea!

I could gear the props down, quite easily……….With the timing belts!……….Since we won`t be dashing about!

I could use the Brutus ESC`s then?

Just a silly idea

Bob

[Dave MilbournParticipant @davemilbourn48782]

Go on, Paul – show us your equation. Don't be shy, m'duck.

Newton was most noted for his invention of the pastry delicacy, filled with figs, which bears his name (the Isaac biscuit) while Ridley was a playwright and later actor, most remembered for playing Private Godfrey in Dad's Army. Newton and Ridley's only brews cold tea. Trust me – I did the tour……………………

DM

[Paul TParticipant @pault84577]

Hello Bob

I cant remember what the Brutus ESCs were…..it might work …………..but you will have to do the amp test to check the loadings.

Paul

[Colin BishopModerator @colinbishop34627]

I have just ordered a Wattmeter myself as recommended by Dave. My Daughter will give it to me for my forthcoming birthday.

I thought Newton was all about apples….

Colin

[Paul TParticipant @pault84577]

 

"Do not give what is holy to the dogs; nor cast your pearls before swine, lest they trample them under their feet, and turn and tear you in pieces."

Edited By Paul T on 25/03/2015 18:45:34

[Bob Abell 2Participant @bobabell2]

When the Newton first appeared on the scene, can't remember when that was, we used to consider it the weight of an apple!

We assumed this was the basis of the 0.22 lb

"No' a lo' o' people know that"

Bob

[Colin BishopModerator @colinbishop34627]

Ah, but was it a Bramley or a Golden Delicious? I think we should be told.

Colin

[Bob Abell 2Participant @bobabell2]

Ah!…. That's the question!

Lets throw open, your question to the wits?

Come on boys…..I'll start the ball rolling with……..It was a Macintosh……….As it was raining apples at the time!

Bob

[Mark Jarvis 2Participant @markjarvis2]

HI Bob

Toffee apples

Mark

[Mark Jarvis 2Participant @markjarvis2]

Ashlee

No need to paint lines on your outrunners to get a reading on an optical tac. It shoud pickup on the U/J. Check the distance range you may not have to be that close to get a good reading

Mark

[Dave MilbournParticipant @davemilbourn48782]

1687 – Philosophiae Naturalis Principia Mathematica was published. Probably the most important book in history. The young Newton was raised by his Granny*; it's not known for sure if her name was Smith**.

DM

* True
** Apple joke

[Bob Abell 2Participant @bobabell2]

Nice one, Dave……Newty would be proud

Newton really was an exceptional man

He was years ahead of his time

I am impressed with his ability to dream up Calculus and Logithirums and his Laws of Motion

He gets on me pip!

Bob

[ashley needhamParticipant @ashleyneedham69188]

Shame he didnt do anything for BOATS eh??

All this theoreticising….. STICK IT IN THE WATER with a wott?? meter.!!!

Ashley

[Diede van AbsParticipant @diedevanabs87670]

Oh, but Newt did something for boats: Action = reaction. Translating in: Thrust towards the back of your boat will cause said boat to move forward in an amount that equals said thrust. Some say this is what your boat causes to go places..

[Bob Abell 2Participant @bobabell2]

The 120amp watt meter still hasn't arrived, chaps

Not looking forward to the water test….Full belt at Max throttle?

It seems extremely drastic?……..Think of the poor timing belts!

Bob

[Diede van AbsParticipant @diedevanabs87670]

Bob, the timing belts are designed to cope with that stuff. And they are not your mom, so get over it and hammer it already

[Colin BishopModerator @colinbishop34627]

I received my 100 watt wattmeter from the link Dave gave yesterday, overnight delivery!

Colin

[Bob Abell 2Participant @bobabell2]

My Watt Meter is 130 amp…..and Amps are heavee!

Bob

Correction……It's just turned up!

Edited By Bob Abell on 27/03/2015 12:58:12

[Bob Abell 2Participant @bobabell2]

Some time ago I devised a method of drilling wheel rims reasonably accurately……It`s in Eureka Moments, if you can find it!

To drill eight holes in a rim, with any form of accuracy, is quite a tricky job without a dividing head

My lathe has a 40 tooth sprocket inside the headstock, mounted on the spindle……It`s behind the pulley

I made a pivoting arm, with a single gear tooth, shown white, which engages with the sprocket teeth

To drill eight holes in the rim, the sprocket is indexed round every five teeth

If I wanted 20 holes, the sprocket would be indexed every twp teeth and so on

In the tool post is a length of Ali channel, which is used to guide the hand drill

To be continued

Bob

[ashley needhamParticipant @ashleyneedham69188]

Mark. That will be fabbydozo if it picks up on the u/j, as it will then be possible to clock the revs on all and any boats. Very useful.

Will be playing at the pond on Subday with it.

Ashley

[Author]

Posts