Vintage Gentleman’s Cruiser

[Paul TParticipant @pault84577]

Bob

I'm not exaggerating: the reason for the depth of water at the transom is to prevent propeller cavitation. This would happen in choppy conditions when the water level falls below the transom and the propellers become exposed.

These are the technical questions that you were waiting for

From your readings

One 7.2v battery driving one 850 motor, with the other motor being back driven, gave a reading on the Watt Meter of 17.5 amps…….With the prop running in fresh air, the amp reading was about 8 amp

What was the reading with both motors connected and both driving the prop at full speed?

One 12v battery driving one 850 motor, with the other motor being back driven, gave a reading on the Watt Meter of a whopping 32 amps!

Running at 12v a reading of 32 amps is alarmingly high……..did you double check the readings?

What is the amp/hour specification of your 7.5v batteries?

With a 10 minute flatout runtime which will probably span out to nearly 20 mins when the other motors share the load, is ok by me

Sorry Bob but it doesn't work like that…. twice the motors means twice the load not half the load.

Paul

Edited By Paul T on 10/04/2015 19:56:52

[Bob Abell 2Participant @bobabell2]

Hello Paul

The props are well down in the water……Sailing in choppy water sounds great fun

The Watt Meter can only read one motor …..If the second motor is powered up, it will only reduce the Amp figure on the first motor

The purpose of the running trials was to read the Max amp figures

We checked the 12v test quite a few times……..Same reading every time

The batteries are from the original Slo Mo Shun and are quite old……..5 to 6 years in fact…….Could they be suspect?

The 7.2v battery ran for a good 10 minutes…….That's good enough for me…….With skilful sailing they should be acceptable

Don't know what the amp/ hour figure is?

I've run two motors driving one prop and all is well

Do you think a 40 amp ESC can handle two motors?…….I certainly won't be doing any racing starts!

I suppose, I could try one 40 amp ESC and see how it performs in the pool?…….That will be great fun

Bob

[CookieOldParticipant @cookieold]

Hi Bob, She looks GREAT and dont let that designer get to you as nice as he is.

Best Regards Dave

[Bob Abell 2Participant @bobabell2]

Welcome back, Cookie

We missed seeing you at Ellesmere Port Show…….(We are aware you've had a personal problem)

Paul is only being over helpful, he likes to highlight any possible problem, that he can foresee on the horizon…..How we respond to them, is up to us

Bob

[Bob Abell 2Participant @bobabell2]

Finally ordered the ESC`s……40amp…….With fingers crossed!

Taken a leaf out of Ralph`s MSC book and added stripes to the Canopy

Bob

[Paul TParticipant @pault84577]

Hi Bob

The Amp/Hour rating on the battery basically indicates how many amps per hour the battery is designed to deliver.

The rating is given in mAh, the battery above is rated at 3300mAh which in lay terms means the battery stick can provide 3.3amps per hour.

So on a motor that draws 3amps this battery would last for approximately 1 hour but for a motor that draws 6amps the battery would only last 30 minutes.

This is one of the reasons why the maximum motor amp consumption figure is a necessary requirement as you have to balance the motors need to the batteries ability to supply.

The general rule of thumb for ESCs is to take the maximum amp reading when the motors are running in a fully ballasted boat and then double it. For example your reading of 32amps would indicate that you would need a minimum 64amp speed controller.

I'm sorry but at the moment you haven't provided enough information for me to recommend either batteries or speed controllers.

Paul

 

Edited By Paul T on 11/04/2015 10:27:32

[Bob Abell 2Participant @bobabell2]

Hello Paul

Your post dated the 10th April……"Twice the motors….twice the load etc"…….. Is not correct

One motor can run for 10mins…..Flat out…….With careful driving, it could last 20 mins….Possibly?

The second motor will run in a similar manner, because it has got it's own battery……and No1 motor is not back driving it either

The model has got four motors for appearance only……For general sailing they will be only purring over

Once on the water, motor management will be an interesting learning curve

Bob

[Ralph PinchParticipant @ralphpinch41762]

Hi Bob,

She looks great in the raft, glad to see you have striped the canopy, enhances the classic look.

[Paul TParticipant @pault84577]

Bob

A little confusion here:

Way back in the mists of this thread you did say that one battery would be running a pair of motors, hence the question about wiring in series or parallel.

Are you now saying that each motor will have its own battery and ESC

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

One 40 amp ESC will power two motors, but each motor will have a 7.2v battery stick

Don`t remember one battery powering two motors?

So each pair of motors could power the boat in succession, thus prolonging battery life…..With the occasional four motor power run

All great fun coming our way!

Bob

[Paul TParticipant @pault84577]

Bob

I am completely confused now and must have the wrong end of the stick.

Can your new ESC take two separate power supplies and maintain the power split whilst independently controlling the two motors. I must be wrong as I always assumed that to have a separate power supply then each motor would need an independent ESC.

Paul

[Bob Abell 2Participant @bobabell2]

Paul

To save a lot of confusion……It's now…..One motor….One battery and one ESC per motor

It's been my mistake……Thanks for drawing my attention to the situation

Bob

[Bob Abell 2Participant @bobabell2]

Something has been bothering me lately, regarding the motor drives

I had the Wattmeter and battery on one motor to read the amps

i then disconnected the battery, but left the Wattmeter in place

I connected a battery to the second motor and it ran ok

Then I noticed the Wattmeter had lit up!………Which means that number two motor is also a generator

I quickly switched off

When the boat is wired up correctly, both motors are driving the prop

Do I have a problem somewhere, without realising it?

Bob

[Paul TParticipant @pault84577]

Hello Bob

We discussed the possibilities of number 2 motor becoming a generator when you first broached the idea of the Abell Drive.

Usually such setups are created with 'matched' motors, which in layman's terms are absolutely identical not just is size and shape but also in current draw, turning (revolution) speed, acceleration and braking.

After some thought you decided to use a pair of MFA 850 with suitable ESC on the basis that its only a model boat and that any discrepancy in current draw or shaft speed would be absorbed by the drive belts.

I agreed with your decision on the basis that the 850s are big ugly brutes and would probably work together in this arrangement and absorb any minor shaft speed inconsistences and variable current draw, especially so as model boats seldom do anything faster than potter around the pond.

The only real concerns that I have about the Abell Drive is what the amp draw is for one pair of motors (ie one Abell Drive) that are connected to the propeller and are tested in a fully ballasted boat, inc all batteries, cookers, sinks, anchors, dolls, teddy bears and superstructure.

With the answer to the question of maximum amp draw to each Abell Drive we can then confidently predict how the hull will perform and which ESC and battery combination will be required.

I am sorry to bang on about this but I am very worried that a loyal and trusted dear friend is about to spend a chunk of cash on expensive electronic equipment only to see it burst into flames as soon as he shoves the stick forward.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

Thank you for your comments

The motors run happily together when in the DOL configuration……There`s no cause for concern………Each motor is pushing out 8 amps each

In the water, a single motor pushes out 17amps, using the Wattmeter

I assume that with two motors driving, they will push out about 15 or16 amps apiece

Whether we use two ESC`S or a single unit doesn`t matter

The problem I imagine that will happen is that, when one battery goes flat, the other motor will start sending a charging current into the dead motor drive setup…..into the battery and also the ESC?

That is why I mentioned the electronic non return valve……..A Diode?

I will talk about your last post, shortly

Bob

[Colin BishopModerator @colinbishop34627]

Oh Gosh! If any of my boats draw anywhere near 5 amps at full whack then I reckon I am an environmental vandal! But, to be fair, they are a lot smaller than the Abell behemoth and don't feature ancillary wheels….

Colin

[Paul TParticipant @pault84577]

Hello Bob

This will be a long one but stick with me.

The motors run happily together when in the DOL configuration……There`s no cause for concern………Each motor is pushing out 8 amps each

Sorry but I don't know what DOL means

In the water, a single motor pushes out 17amps, using the Wattmeter I assume that with two motors driving, they will push out about 15 or16 amps apiece.

When using big amp hungry motors in this configuration you can not afford to make assumptions, the two motors driving a single shaft could draw anything from 15 to 30 amps, this is why it is essential to do the amp test using both motors at full speed in the water and with a fully ballasted hull.

Whether we use two ESC`S or a single unit doesn`t matter.

It does matter depending upon how the power transmission wiring is put together.

The problem I imagine that will happen is that, when one battery goes flat, the other motor will start sending a charging current into the dead motor drive setup…..into the battery and also the ESC?

How can this happen if you are using a single battery?

That is why I mentioned the electronic non return valve……..A Diode?

I don't know….. this is a question to take up with the ESC and Battery suppliers.

Paul

[Bob Abell 2Participant @bobabell2]

Thanks Paul for your timeless help and advice

One motor powered by one battery, with a Wattmeter attached…..Dragging the boat about the pool , is the worst case scenario?…….Which draws 17 amps

Do you agree?

Bob

[Paul TParticipant @pault84577]

One motor powered by one battery, with a Wattmeter attached…..Dragging the boat about the pool , is the worst case scenario?…….Which draws 17 amps

No Bob

I don't agree because there are two motors on the Abell Drive and connecting both motors to a single battery will draw more than 17 amps

If you were only using one motor per propeller shaft to drag your boat through the water then I still wouldn't agree because the boat isn't fully ballasted………..the extra weight WILL make a difference to the amp draw.

Sorry Bob but you cant argue with physics.

Paul

[Bob Abell 2Participant @bobabell2]

Paul

You are assuming that we are using one battery?…….We could use two batteries, but we would have the regen problem again

How about this?…….One 12v Jelly….+….Wattmeter….+ two wires and two motors

Bob

[Paul TParticipant @pault84577]

Bob

Its not about the quantity of batteries………….its all about the Amps.

We can talk about jellies, NiCad, lead acid until the cows come home because it is irrelevant.

You need to decide how many motors you intend to use and take everything from there……..which will include Amp tests in a fully ballasted hull and the possible changing of batteries to some more beefy types and possibly changing the ESCs to more beefy types.

At the moment we are putting the metaphorical horse before the cart

Pau

[Bob Abell 2Participant @bobabell2]

Paul

Are you saying, you do not agree with my proposed two motor amp test?

Bob

[Colin BishopModerator @colinbishop34627]

This is what happens when you move away from the conventional one motor, one shaft one prop configuration which has much to commend it.

Colin

[Bob Abell 2Participant @bobabell2]

Colin……Don't be an old stick in the mud……This is new technology and the answer to the current problems will soon be sorted

I know a man in the club, who has these problems for Breakfast!

It's a good job we realised the problems before jumping in with both feet and a fire extinguisher!

Bob

[Paul TParticipant @pault84577]

Bob

Sorry but no I don't agree with your method of testing as it depends upon guesswork and fingers crossed.

It's a good job we realised the problems before jumping in with both feet and a fire extinguisher! …..We?

Colin

I think its actually a clever idea and could have some potential especially for the tug builders, Like any inventor Bob is 'testing' his notion by feeling his way around the problems.

Paul

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