Brutus

[Paul TParticipant @pault84577]

Looking good Bob

Its also nice to see that you have properly encapsulated the wire ends before putting them in that choc block……is this because you are a perfectionist or that you didn't want to be lambasted by our resident electronics expert.

Paul

[Bob Abell 2Participant @bobabell2]

Hello Paul

The motor wires were too few in number compared to the ESC cables, so I beefed them up with a few inserts

The JR/Futaba plug fit are a bit unreliable……Had to clamp them together

The weather has been bad all morning…….A bit like the D-Day weather, 70 years ago!

Can`t say when we can sail now……As you know the situation

Tomorrow is Raft Day at Etherow…….Car park will be heaving!

Bob

[Amy jane SeptemberParticipant @amyjaneseptember49770]

Good luck with the sailing, Bob. I'm itching to see her really go!

Aj

[Bob Abell 2Participant @bobabell2]

Thank you, Amy

Hoping to have a trial run before the show

Bob

[Bob Abell 2Participant @bobabell2]

Action shot from this mornings sail……..Via the IPad

Bob

[Bob Abell 2Participant @bobabell2]

Brutus video, just posted on YouTube…..Nice one, Duckie

I'll post a link shortly

Bob

[Paul TParticipant @pault84577]

Hi Bob

Just watched the video and I am over the moon with the result, the boat runs perfectly and creates a super fine bow wave.

I have to admit to a great deal of apprehension over this project as its the only one that I have ever published without having first built and tested a prototype.

All credit to you Bob as the build could so easily have gone disastrously wrong.

Thank you Bob for all of your hard work (and ability to understand my scribbling)

Paul

[mike farrellParticipant @mikefarrell21522]

Well done Bob ,your creation looks and sits well in water .Paul is a fine draughtsman and you read his drawings very well . So well done to Paul as well . Colour scheme makes it look angry and I imagine it can show an angry turn of speed

Michael

Now for Thor soon please

[Bob Abell 2Participant @bobabell2]

Thank you, Paul and Michael for your very kind words

Here is the video of Brutus, shot by Duckie this morning

**LINK**

It was going well, while it lasted!

Was showing a good turn of speed at times…..Then over heating took control!

Bob

[Bob Abell 2Participant @bobabell2]

Hello Paul

Just for reference, the MFA RX15 Plus motors are……….. 7.2v….20,000 rpm….190 watts

If we are thinking about the four motor drive, these must be as good as the larger common motors?

I`m only thinking about this idea, just for the visual effect, rather than the flat out crazy speed

The 50 dia props will have a quite an effect

Have ordered new beefier battery and fuse harness leads………Only one of the fuse harnesses shows signs of over heating, so I think we`ll be ok with the new wiring

Bob

[Dave MilbournParticipant @davemilbourn48782]

Ref connectors, you should be using at least 14AWG silicon-covered cable and Deans type connectors. The plastic Tamiya connectors are good only up to about 15A.

Suit yourself – you usually do.

Dave M

[Bob Abell 2Participant @bobabell2]

Thank you, Dave……….The usual friendly advice followed by a stab in the back, for good measure!

I know I`m living on the edge and I think it`ll be ok……Will have to be very careful on the water and limit the frantic dashes!……..And rely on the fuses to keep me safe

The new Tamiya plugs are mounted on 14 AWG wire and will be using blade type fuses….10 or 15 amp

Power supplied by two ABELL drives…..See below

Bob

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Oooo errrr Bob,

I can foresee problems with two motors on to a single drive, with the motors counter rotating – but I'll keep stum!! Looks very good though.

I use JST connecters in my PT Boat – rated to 60A – and they are common to either Li-Pos or 7.2 packs. Just soldered the appropriate end to the engine leads and ESC. Fuse is 5A below ESC max.

Kimmo.

Edited By Kimosubby Shipyards on 12/06/2014 10:00:01

[Bob Abell 2Participant @bobabell2]

Thanks Kimmo

Can you post a picture of your JST connectors, please….. I 've never heard of them?

Will have to build a working motor drive setup, before I go the whole hog!

I wonder if the variation in rpm will be a problem?…..There could be a conflict?

Bob

[Diede van AbsParticipant @diedevanabs87670]

I don't think you will have many issues with the two motors on one propshaft, the worst that can happen is that one motor takes a load when running out of the water. Any big difference in RPM should not be present anyway, or be taken up by the belts by slipping a bit.

As soon as the boat is in the water, the resistance will make sure both motors are loaded, although this will not be quite equally.

Is there any way you could prepare the MFA's for water cooling, if need be?

A speed difference between the two ABELL units is nothing different from having two single motors driving the propshafts, and you should correct that either using radio trim or the hard way using restrictors and other nonsense between motor and ESC…

I hope Kimmo means something else than JST's…, the JST connectors are the little red ones on small LiPo or Ni** packs and you should not run more than a couple A through that. Not nearly enough to cater for all the power you are going to draw. Better use XT60 or equivalent plugs.

[Bob Abell 2Participant @bobabell2]

Thank you, Diede

Thank you for the info

At the moment, I'll carry on regardless with my present gear, but run a few cautionary tests etc

Don't fancy getting involved with new plugs

Looking forward to tinkering with the twin drive unit!

Bob

[Diede van AbsParticipant @diedevanabs87670]

Hi Bob,

At least make sure you have a really decent fuse before the first Tamyia plug, as Dave definately has a point concerning the current draw limit of these. They do have a tendency to melt and cause mayhem / fire when being pushed too hard.

Either that, or take steps to prevent the current from running too high to start with, like running multiple packs in parallel. That way each plug will have to handle a lot less current. If you only use the plugs to connect the packs to the rest of the wiring, and solder everything else, you should be ok…?

[Bob Abell 2Participant @bobabell2]

Thank you, Diede

I could use some sort of heat sink on the plugs?

Don`t for get the constantly running cooling fans already fitted into the hull

Bob

[Paul TParticipant @pault84577]

Bob

Simply fit the correct gauge wire and appropriate batteries / connectors and you shouldn't have any problem, get that old coal fired ammeter out, dust it off and check what the maximum loaded current draw is.

Paul

[Colin BishopModerator @colinbishop34627]

Heat sinks on the plugs???? Whatever are you thinking of Bob? If your plugs or wiring are in danger of melting then there is something seriously amiss with the installation.

All heat in a model boat is a demonstration of inefficiency. You want the power to be directed to moving the thing not turning it into a mobile sauna!

If the current demand is too high then the motors are being overloaded and thereby running inefficiently. Gearing them down will certainly help but all the components interact with each other and your 'suck it and see' approach is not very scientific. The only times I have experienced melting wires is when I have had an inadvertent short circuit on a part of the circuitry not protected by a fuse.

Your adventures with Brutus are indeed entertaining, albeit possibly expensive, but good practice they certainly ain't and we don't want our readers to get into bad habits and start fires etc.!

As Paul advises, use test instruments to find out what is actually going on.

Colin

Edited By Colin Bishop, Website Editor on 12/06/2014 14:21:25

[Paul TParticipant @pault84577]

Do I get a gold star?

[Colin BishopModerator @colinbishop34627]

Only if he takes your advice….

[Dave MilbournParticipant @davemilbourn48782]

[Diede van AbsParticipant @diedevanabs87670]

LOL @ Bob fitting heat sinks to the connectors!

Not gonna work, sorry.

The Tamyia plugs generally overheat because of the poor contact between both connector halves, generating a transition resistance (overgangsweerstand in dutch – not sure if I translated correctly) which generates heat. The amount of heat generated rises exponentially as the amps increase (for P=I^2*R), and that will melt the plastic insulation at some point.

Heatsinks on the connector will not resolve that, because the root source of the heating problem is still there (and pretty deep hidden inside the plugs, so you cannot get close enough to the source).

Please do as Paul and Colin suggest; buy and use decent plugs, and measure the amount of current drawn.

[Paul TParticipant @pault84577]

I wonder how many people reading this discussion about overheating have encountered the same problem themselves….only they have been to afraid of looking foolish to ask for help.

I have been one of those stood at the lake side looking shocked with burn lines on my hand from red hot wires wondering how I got it so wrong……… and I am forced to admit to belonging to the twist the wires together and sellotape brigade

 

Edited By Paul T on 12/06/2014 15:33:46

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