Vintage Gentleman’s Cruiser

[Bob Abell 2Participant @bobabell2]

My proposed test setup is not guesswork

It will give us the amp reading for running two motors………As you keep asking for!

The only problem, which we need to solve right , if we intend to use two batteries, is the regen of the flat battery enigma and I feel a Diode in each line will solve the problem

Just waiting for our club expert to return off holiday, sometime today

Bob

[Paul TParticipant @pault84577]

Hello Bob

Why are we now discussing using two batteries and diodes?

You are putting the cart in front of the horse again as the whole purpose of the test is to establish the maximum amp draw so that you can make informed decisions about batteries and ESCs.

Your proposed test will only work if undertaken in a fully ballasted hull.

Paul

[Bob Abell 2Participant @bobabell2]

Paul

The battery and Diode idea is only for interest now

I would just like to know if the idea would work……It may be handy later on

We will use one 12v Jelly per two motors with none of the regen problems?

Will do more motor tests when the weather improves in the pool

Bob

[Bob Abell 2Participant @bobabell2]

Paul

Why have a fully ballasted hull, when the hull is simply driving against the pool wall for max amp reading?

Last weeks 32amp reading was achieved with a 12v stick battery

It should be a lot less with a 12v jelly?

Bob

[Paul TParticipant @pault84577]

Bob

Great………..now all I have to do is convince you to fully ballast the boat for the test.

Paul

[Paul TParticipant @pault84577]

Bob

The test should be done in free water so that you can see how much power it takes to move the boat from a standstill to full speed.

Pushing against the pool side wont provide the true reading.

There will be no difference in readings between a stick or gel battery as they both provide 12volts.

Paul

[Bob Abell 2Participant @bobabell2]

A bit of light relief from all that heavy motor talk

Working on the cabin section again

Air vents………Which are actually furniture feet……Supplied by the intrepid Duckie

Bob

[Paul TParticipant @pault84577]

Hello Captain Bob

Back to the heavy motor talk

The weather is set fair tomorrow which will be perfect for testing in your paddling pool.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

Do you agree with the wiring diagram I proposed the other day?

Bob

[Paul TParticipant @pault84577]

Hello Bob

To prevent any further prolonged debate perhaps we should follow a simple diagram.

I think that the following is what you are talking about.

Remember that the boat must be fully ballasted or you will just be wasting your time

Paul

Edited By Paul T on 13/04/2015 15:43:31

[Bob Abell 2Participant @bobabell2]

Hello Paul

Thanks for the diagram

I propose the battery wires are extra long so that the Wattmeter can be hand held and then the wires can go back to the boat in the pool

We will do the test….As is……Then repeat it with the extra ballast and see what the difference is!

And repeat the test…..Pushing against the pool wall

Bob

[Paul TParticipant @pault84577]

Hello Captain

How much extra ballast are you going to add?

Bearing in mind that the all up design weight is approx. 70lb (a standard clay house brick weighs 5lb)

Paul

[Bob Abell 2Participant @bobabell2]

Why do we need all this ballast?

Bob

[Paul TParticipant @pault84577]

Captain Horatio Bob

There is a long and complicated answer to your question which we wont bother with, lets just say that the boat was designed to sit at a certain height in the water to give it the best hydrodynamic shape.

As a kind of explanation you might of heard of the phrase 'a boats swim' the swim is the way the hull moves through the water and a boat with a good 'swim' glides through the water causing very little disturbance.

The VGC has a long and thin hull profile (just like a destroyer) and needs to sit at a certain level in the water to gain the best advantage.

The way that you have built the boat will have had an effect on the optimum amount of ballast required.

Paul

[Gareth JonesParticipant @garethjones79649]

I have been trying to avoid getting involved in this debate as there is a lot of misleading and irrelevent information flying backwards and forwards. However I just could not resist joining in.

Bob,

Do the test as Paul suggests, one battery supplying two motors in parallel with the wattmeter reading the supply voltage and total current taken by both motors. This will give you your highest current, worst case load on your speed controller. Assuming that your VGC is currently ballasted so that the propeller is fully submerged and does not cavitate at max power, I am willing to bet there will be no significant difference in the wattmeter reading for your three test conditions, i.e.

1 Static pushing against the side of the pond

2 Accelerating from a standstill along the pond

3 With an extra half a dozen bricks for ballast.

What will make a difference, contrary to what Paul says on the previous page, is what type of battery you use for the test. If you use a 12 volt gel cell it will not be capable of delivering a high current because the voltage will fall off rapidly as the current drawn by the motors increases. If you use a 12 Volt NiMh or NiCd stick, it will be capable of sustaining a higher voltage as the current increases and you will be able to reach much higher current values.

I await your test results with interest. I am betting no more than 10% difference between all three tests and probably less than 5%

Gareth

[Paul TParticipant @pault84577]

Kevin

Please note that the basic circuit drawing indicates a basic ammeter rather than a fancy wattmeter.

[Colin BishopModerator @colinbishop34627]

Surely if the model is basically going to be sitting in the water in a static condition then the hydrodynamics are irrelevant as all you are measuring is the load on the props pushing water out the back. As long as the props are immersed to the designed depth that is all that matters. You don't need loads of house bricks – just push the stern down if necessary until the model sits at the designed waterline.

Under these conditions the loading will be significantly greater than if the model is free to move on the pond as a proportion of the stern thrust will be compensated for by forward movement.

Power consumption on a moving model will always be less than when it is static and this has commonly been held to be a useful safety margin when working out onboard power requirements.

The amount of ballast only becomes a significant factor if the model is moving as the overall weight of the model has a specific mass upon which the forces obtained from the propellers will act upon.

This is the same principle as in space exploration in zero gravity. Everything may be weightless but a greater mass requires a lot more force to change direction/speed than does a lower one.

Colin

[Andy CParticipant @andyc56856]

A Kevin's eye view of things (i.e. Very, Very simple, lots of diagrams and single syllable words), OK maybe not the last bit, but simple is good. As a Kevin, I can understand Pauls diagram,

1. Motors in Parallel – Got it.
2. Meter in the circuit to read, Volts, Watts or Amps, which ever takes your fancy, All three if necessary – Got it.
3. Wanting base line figures to make sure using correct ESC (it's all about the AMPs, about the AMPs, – No Treble) – Got – too small an ESC is a bad thing, not sure about too big an ESC, is there such a thing or is bigger better?

As a Kevin, you lost me at the first use of Hydrodynamic whatyathingamiebob. Too complicated for me. Off to lie down in a dark room till my head stops hurting.

Cheers (Kevin (Andy) (who knows anymore)

Keep up the good work Bob – nice use of odds and bobs for fittings. Very inspiring.

[Bob Abell 2Participant @bobabell2]

Thank you, Gareth…….I agree and welcome your common sense comments

But I still think the 12v Gels will be ok…….The Tugboat Boys use them and can sail about….All day long!

Thanks to Colin also for his logical comments

Thanks to Andy C for more common sense comments

Many thanks to Paul for his high tech advice and I'm sure he feels his advice has good intent, but I can't fill the boat up with 40lb of lead……Just to overload the motors?

I prefer to run light and never mind the Hydrodynamics!

Bob

[Paul TParticipant @pault84577]

I give up

[Gareth JonesParticipant @garethjones79649]

Bob,

If you plan to use a 12 volt gel cell battery in the final installation then measure the current with that supplying the motors. However if you are planning to use one gel cell battery to supply all four motors (or even just two) it will become the limiting factor in how much power you can get out of the whole system.

For the benefit of Kevin and the rest of us why not do the whole set of tests twice, firstly with a gel cell battery and then with a 12 volt NiMh or NiCd stick and we will all be so much wiser and you will have definitely covered the worst case. It only takes a few minutes to do each test if you are organised with compatible connectors.

Gareth

[Bob Abell 2Participant @bobabell2]

Come on Paul………Just lower our sights a little…….We are nearly there……….I think

We need you to Chair the meetings and keep a jaundiced eye on things

Gareth……. I`m very cautious of using the 12V NiMH batteries

We got a reading of 32amps on one motor last week…….So two motors will double it

I`m also thinking about the wiring now

I hope to use one Gel with two motors……..But two sets

Bob

[CookieOldParticipant @cookieold]

Hi Bob , Please dont get stressed with all this info , just take a step back and try all options and use whats

best for you .

Best Regards Dave

[Bob Abell 2Participant @bobabell2]

Hello Cookie

Thank you, for your concern…….I`m not getting stressed at all!

I`ve just turned my back on some of the nonsense as per my last post!

I only want to make a pretty boat and float it about some day

The way the thread is going at the moment, we could make it into a Soap Opera!

Bob

[Bob Abell 2Participant @bobabell2]

Have you thought about this, chaps?…….Just had a "Gerron with it" Email!

With one 12v Gel battery driving four 850 motors………It's almost a short circuit!

Luckily, we are only driving two motors, but we can still expect a few fireworks and hot wires?

I never realised the power involved, when ganging up big motors

Comments please, Paul?

Bob

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