Motor/ESC combination for Amati Riva Aquarama

[JeremyParticipant @jeremy15845]

Hi

I have read John Parker's article on Going Brushless and followed Alan Hazel's thread on his Perkasa. All very helpful but every situation is unique and I would appreciate advice on a motor/speed controller/prop combination for my twin proped Amati Riva Acquarama model, still in it's early stages of contruction.

I used a Turnigy D3536-6 1250kv brushless outrunner with a 100amp HobbyKing reversible car speed controller on my 34" Vosper fire tender (maybe a bit of overkill with the ESC but I had started with a 45 amp unit and this was prone to cutting out – overheat protection?). With a 40mm twin bladed Graupner prop, this boat goes well.

I am tempted to go for a similar set up for the Riva which is about the same length but maybe quite a bit heavier. It would look much like the kit in Bob Abell's Slo-mo-2, illustrated in the Perkasa thread. I want the boat to plane well but not to leap out of the water. I am concerned about possible overheating as the engine room space will be more confined than in the Vosper – maybe a bit more like Slo-mo-2. The is no opportunity to introduce air ducts into the enclosed space.

I am aware that outrunners have a lower kv, eliminating the need for a gearbox. On the other hand, water cooling would be more difficult and the car ESC can not be water cooled.

I think I will have to use Lipo batteries as there would be no room for the 12v 10 cell 5000mah brick which I have in the Vosper. Finally, I would opt for M4 drive shafts.

Any thoughts or advice would be much appreciated.

Jeremy

[JeremyParticipant @jeremy15845]

[Dodgy Geezer 1Participant @dodgygeezer1]

I think that some kind of ventilation would be useful – even if it's not to the outside air and just to other parts of the boat's structure. Totally enclosing an engine space means that heat will build up fast, if it's a small one.

It might also be wise to allow for a water scoop. Outrunner motors can be cooled by using a water-cooled mount, and you can get simple watercooled 'plates' which you can mount an ESC (or anything else) on…

**LINK**

[harry smith 1Participant @harrysmith1]

Hobbyking have a nice slim water cool mount for a 35mm motor(code 9215000019-0).

The water pipes come in from the top and mount rails are parallel to the motor.

40mm props should be OK or a bit smaller 3 blade alloy ones would like nice.

Car ESC's have an electric fan on top, so no plumbing required.

Also they small about 60mm cube and are light weight.

Hobbyking Car 45A with reverse 2-3S (code HK-45A)(69grams)

60A with reverse 2-4S (code HK-60A)(91grams)

100A with reverse 2-4S(code HK-100A)(106grams)

I am running about same size boat with a closed in top, car ESC un cooled 3648-1450kv motor on a 4S 5600mah.

Runs for over 30 minutes motor runs only warm, Esc cool and battery warm.

[Malcolm FraryParticipant @malcolmfrary95515]

A very brief google found this – http://www.ebay.com/itm/Joysway-Cooling-Plates-for-60A-Water-Cooled-Brushless-Marine-ESC-/231588529589 – so cooling items for ESCs are available. On an outrunner, the bit that spins is not the bit that needs cooling, it is the coil assembly that is effectively part of the back plate. Depositing unwanted heat outside of the hull in cooling water must be better than stirring air around inside an enclosed space in the hope that enough heat will escape through the hull material.

[Dave MilbournParticipant @davemilbourn48782]

Jeremy

A 60mm cube isn't what I'd call small, especially when there are two of them going into a 34" open speedboat. I agree with Malcolm ref the effectiveness of a fan, which eventually will just be moving air of an increasing temperature around an enclosed space. That said, twenty six dollars a pop (delivered) for water-cooled mounts isn't cheap – and that "two of" thing crops up again. My limited experience with these little monsters is that they don't get hot if you don't overload them, and neither do the ESCs or the batteries.
I don't believe that you're far off what you need with the existing Turnigy motor setup, save that you might use a pair with slightly lower Kv and more turns, and fit three-blade alloy props – which tend to have less pitch than 2-bladers. If you buy ESCs which are already set-up for water cooling then you can use it if you need it. Here's one – I dare say you could get the same thing cheaper direct from ROC. **LINK**

Dave M

[Dave MilbournParticipant @davemilbourn48782]

This motor mount is all over E-Bay for about £11-£12 delivered in UK **LINK**

DM

[harry smith 1Participant @harrysmith1]

Overloading motors, etc. with big props or large pitch and over the years I see a number of these as many of you had also seen go up in smoke or fail.

I go for a small prop to star with, also other modellers and forum advice.

If you look at my pictures and setup on my grandson's test boat.

It's no light weight (7 LBS) and with no water cooling , also enclosed top.

The alloy mount with the drive line as a heat sink(also the fan on the ESC) this boat run a 5800mah 3S and a 5600mah 4S one after the other.

It was driven flat out to see if heating would be a problem, but, no.

The temperature that today was 20 degrees C. and the kids went swimming after!!!

[JeremyParticipant @jeremy15845]

I have decided to go with the Turnigy outrunners on water cooled mounts with Turnigy water cooled 60 amp ECS's. The props will be 3 bladed 40mm. Dave M recommended a slighly lower kv than the 1250 I have on my single screwed 34" Vosper fire tender. The Turnigy motor is available in 1000 kv versions and 910 kv wirh respective max powers of 432 watts and 370 watts (the 1250 has a max power of 496 watts). Which should I go for? Batteries will be 11.1 volt Lipos.

The Turnigy has a 5mm drive shaft and I used a coupling to mate this to an M4 prop shaft on the Vosper. Should I do the same on the Riva or use M5 shafts? Would there be any advantages of using larger diameter shafts?

Sorry to ask so many questions but the response and advice given on these forums is so helpful that it is always tempting to ask more.

[Dave MilbournParticipant @davemilbourn48782]

Jeremy

I doubt if there's much noticeable difference between the two motors so I'd go for the slightly more powerful ones – on the basis that you have speed controllers anyway.
I'm not 100% sure about the shafts but only because I'd not considered it before. I've always used electric motors and until the advent of brushless ones there wasn't much that would strain a M4 shaft. On balance – using the belt-and-braces approach – I'd say use M5 as long as you can get the appropriate props with that thread. BTW I'd always recommend flexible couplings over the Huco U/J types.

Dave M

[harry smith 1Participant @harrysmith1]

If using 40mm 3 blade prop I go for the 3639-1100kv 800watts.

The props have a bit of bite to them and require a strong motor.

One of our members is running twin 3639-750kv 600watt on 3S with 2 blade 45mm props.

It runs a good speed but with the above setup it would give you a nice bit extra.

[JeremyParticipant @jeremy15845]

I am getting thoroughly confused! Kv's, watts and prop sizes are whirring around my head.

My 34" Vosper fireboat has one Turnigy D3536 1250kv 496 watt motor with a 2-bladed 40cm prop. It goes fast!

Bob Abell has two of these on his Slo-mo-shun 2 which looks to be no slouch.

It has been suggested that these same motors (or maybe the slighly slower 100kv 432 watt version) with a 3 bladed prop (less pitch than the racing 2 bladers) would do for the Riva.

Now Harry suggests two 800 watt motors, partly because the 3-bladed prop needs more power.

I recognise that the profile of the Riva is blunter than the Vosper but I will fit spray rails and I hope that it will plane at realistic speeds.

But do I need 800 watts for this? Also what amp ESC's would then be required?

I am very grateful for all the advice but is there any consensus on what would be best?

[Dave MilbournParticipant @davemilbourn48782]

Harry
My 23" Huntsman 31 has one 28mm dia 17-turn 1100kv brushless motor running on 11.1v. It turns a Prop Shop 32mm 3-blade scale bronze prop very nicely indeed – I've actually had to restrict the top speed on the Tx to 80%. There is a link elsewhere on this forum to a video of it performing . It's no slouch, but even if it's working at the very limit of its 18A ESC (which it isn't, or it would get very hot) that is an absolute maximum output of 160 watts. Are you suggesting that a prop just 25% bigger needs five times the power, and that a model boat not quite 3 feet long will benefit from over 2 brake horsepower??
Good luck to you, Harry.
I think Hobby King are flogging you Chinese watts as well as Chinese amps.

Dave M

Edited By Dave Milbourn on 25/06/2015 10:30:18

Edited By Dave Milbourn on 25/06/2015 10:42:09

[Paul TParticipant @pault84577]

Dave

Does this mean that if I buy a Chinese motor I also have to purchase a bag of Chinese amps as well?

Confused Confucius

[harry smith 1Participant @harrysmith1]

I am only going on their specs.

But I still would not run 3 blade 40mm props with the original motor quotes.

I am running a 37mm x 1.4 pitch 3 blade on my grandson's test boat with a 3639-1100kv and a car 60A ESC.

I have no motor cooling and it runs for a good 1/2 hour, no problems.

[Dave MilbournParticipant @davemilbourn48782]

No. Chinese amps are 100% state-subsidised and frequently included as free-of-charge items – hence their popularity in Australia. You can use British Standard Amps instead, but you will need far less of them. As a rule-of-thumb One Chinese Amp = 200 British Milliamps.
If you order from the UK warehouse (in Rotterdam) then you will probably get Euro-Amps. These vary in value depending on whereabouts in the EU they were either manufactured or imported and re-packaged.
Amps originating in Mexico or the Philippines are suspect in quality and will either fail immediately or wear out very quickly.
Does that help?
DM

(NB. This is very silly. If you don't understand it then I'm not at all surprised. Blame Paul – he started it).

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