Precedent 34″ Huntsman

[BarzoParticipant @barzo]

Dave,s mod to the P98 was impressive, the motor ran noticibly cooler.

The three bladed, 45m brass prop was a disappointment, the boat was considerably slower but it did seem to run more smoothly. I reverted to the two bladed, plastic prop, 50x mm at the pond side and restored the excitement.

I have acquire the Action rc Electronic P101 ‘Noisey thing’ and have started to consider how to install it. My problem is that the total weight of the P101, P100 and loud speaker plus extra batteries to power the amplifier is heavier than the existing ballast I can sacrifice.

I can reduce the weight of the copper motor cooling coils, by using aluminium tube, which is one third the weight of copper. The next problem was to find some aluminium water cooling coils for the 52mm diam motor can – not easy -. Most thin walled aluminium is supplied work hardened and is difficult to anneal without the use of a temperature controlled furnace. As luck would have it, and some painful web searching, I found a post in model boat mayhem. The reference was to aluminium tubing used for ‘pilot light’ application. This can be found in PlumbCentre/Part Centre shops. It is 3mm ID and 6mm OD, (catalogue #555557) the length approx. 1250 mm. This is not particularly thin walled but it is annealed and can be bent on a former. There is also a 1mm ID and 3mm OD version.

With the weight of the cooling coil being reduced from 160gm to 38 gm I can now install the extra kit without increasing the weight overall.

I have some new video shots but they are being edited at the moment.

Cheers Barzo

[Mark Beard 1Participant @markbeard1]

Alan,

 

Copper and aluminium are the materials of choice in electronics thermal management because both have excellent thermal conductivity. Copper is marginally better at conducting, but is heavier, as you say. So in weight-critical applications (such as yours), aluminium is an excellent choice.

 

I would avoid narrow bore tubing, such as the 1mm ID stuff, this will restrict the flow of cooling water. Use something no smaller than the intake tube.

 

As an alternative, if you are comfortable with fabricating a water jacket from thin copper sheet, by soldering or using epoxy resin, then a particularly light solution can be made. You can use thin sheet as this is a low pressure system. Make the exit port to the jacket at the top of the motor, to prevent an airlock inside the jacket.

 

Remember to include the weight of the water within the circuit for your calculations, as the system should be full when in operation!

 

Best wishes,

 

Mark

[kgurdParticipant @kgurd]

Hi Barzo,
This has been a great post. I find at the end of the day
it all comes down to power to weight. My 34″ Huntsman was fitted with a
MFA 850/12V/x45mm prop. It was surprisingly fast. Basically it was
built as light as possible, the motor was also water cooled which is
certainly a necessity to prolong the life of the motor on hot summer
days. Of course if the voltage was increased so would the performance
but then again so would the stress on the electronics. At the end of
the day its always going to come down to a compromise but i must stress
again the issue of weight.
Again thanks for a great post. I will see if i can upload a video on YouTube when my model was running on 7.2volts.

Kevin

 

Edited By kgurd on 29/04/2011 12:00:30

[kgurdParticipant @kgurd]

Here is the link. Video was taken at Fawley some time ago.

 

http://www.youtube.com/watch?v=gXMCTNuNEt4

[BarzoParticipant @barzo]

Hi kgurd

Many thanks for your comments and the opportunity to see your boat in action.

This thread started out with a request for help in choosing a suitable electric motor.

The consequence of going down the brushed motor route has been interesting.

To reflect on the experience – the request was set against the original motor – an HP40 ic engine, which delivered approx 1 hp. weight of the engine + silencer and fuel was probably in then region of 530 grms, giving a hp/kg of 1.89. My current boat batteries + motor weighs 1.73 kgs., giving a hp/kg of .31.Clearly the brushed motor electric version can never match the ic engine performance.

From scale point of view the model should weigh in the region of 3.82 kgs. my model at the moment weighs approx. 3.18 kgs. The actual model speed has not yet been measured, but I suspect it will match its scale speed.

If I had taken a different approach and rebuilt the boat as light as possible and used brushless motors and Lipo batteries, I might have approached the ic engined boat speed, how ever the battery versions could not run all afternoon without multiple battery sets and/or poolside quick chargers (more expense!), where as I could run the boat all afternoon on a half gallon of fuel. As you say its all a matter of compromise.

Still at my age I’m not sure I could take the stress induced by running the model at massively over scale speeds.

Cheers Barzo

PS for BillyS, I have uploaded a photo of the aluminium cooling coil. Because of the greater OD than the copper version, I have had to cut away a portion of the motor mount to enable it to fit – still it has saved me 100grms.

PPS Ah well, it never stops, such is the fascination of our hobby.

Edited By Barzo on 01/05/2011 15:51:44

[BarzoParticipant @barzo]

Yeough! – as in ‘dough’

The following video shows the boat with a 50x mm two bladed plastic prop. after approximately 25/30 mins of bimbling around in the pond.

http://youtu.be/L5AJ17IgMiA

Cheers Barzo

[Mark Beard 1Participant @markbeard1]

Looks like pretty impressive performance to me (and she looks beautiful on the water). If you’ve got half an hour running at that pace, it seems like you’ve got a good efficient match between hull, prop and motor with that 50mm 2-blader. Is this what you wanted? How’s the motor temp when you bring it back alongside?

[BarzoParticipant @barzo]

BillyS,

Thanks for the comments.

As to ‘is this what I wanted?’ – that is a difficult one.

I started out wanting to have the boat go as fast as the IC version. It became clear early on that brushed motors and NimH batteries were never going to provide the power density required to drive the hull at IC engine speeds. It would probably be possible to make it go faster with brushless motors and LiPo batteries, but the cost I suspect would be very high. I have no idea what a 100 amp ESC would cost.

As I said to kgurd, it is all a matter of compromise.

I think that my goal is now to optimise the prop. characteristics to give me good balance between duration on the pond and boat speed. The hull is being driven at a good scale speed and I will play with extending the scale functionality with the implementation of the Action rc Electronics engine noise module and may be some other sound effects.

Thanks again for your interest and encouragement.

Cheers Barzo

PS I have just received a three bladed, brass 50mm prop. something else to play with tee hee!

[BarzoParticipant @barzo]

Tried the new prop. this week end – the effect was amazing!

The wake was smooth and even the bow wave seemed cleaner. There might also been some contribution by the reduction in weight of the aluminium water cooling coil, in the bow.

The only unfortunate event was the loss of the prop.. I have never had a prop. come adrift before, It happened to be a right handed prop. and no doubt I must have failed to tighten the locknut enough.

Some advice would be appreciated, regarding some water ingress, which I believe is pumped into the boat when going astern. Has any one got any advice to mitigate this effect?

Cheers Barzo

[BarzoParticipant @barzo]

Perhaps the last post.

It crossed my mind that some one may be looking for a way to put customised print details on their boats eg, names, instrument decals, logos etc.. For what its worth I have found a supplier of inkjet water-slide decal paper. The water-slide paper is supplied as either suitable for white backgrounds or suitable for dark backgrounds.

The supplier is ‘Crafty computer paper’ – http://www.craftycomputerpaper.co.uk -.

It has been very useful for me. Having found a Fairey Company logo, I was able to scale it using an image processing application.

Cheers Barzo

[BarzoParticipant @barzo]

Greetings ffolks

I see that it is nearly a year ago that I had reached a a point of equilibrium with my Boat/Engine combo.

However in the intervening period a terrible itch has developed, to just see what a brushless motor might do! The nagging problem was the weight of the existing motor and battery combination mitigated against a truely exciting performance. The rationalisation of achieving scale speeds has finally proved to be unsatisfactory.

I have purchased a Turnigy 35-42 motor (1000kv) which will reputedly handle 700 watts.. I also acquired a 60amp ESC and intend to run the motor on 2 x 5000ma 3s lipo batteries in parallel. The weight saving is amazing with the combo coming out at just over a third of the existing weight.

My biggest concern, at the moment is what sort of heat will the out runner generate and what is the best way of dissipating it. My current advice, from a brushless devotee is to bolt the motor onto an aluminium mount together with an aluminium block that has been drilled to provide an internal matrix of channels, through which the water will flow. It does seem that the suface area of the motor that comes into contact with the motor mount is quite small, still nothing ventured nothing gained.

If any one has experience of out runner motors in boats then I would really appreciate their comments.

Cheers Barzo

[Mark Beard 1Participant @markbeard1]

Sounds like you have some powerful kit there!

You have come up against the biggest downside of outrunners: the fact that the heat is generated on the inside and needs to get to the outside. This is the equivalent thermal problem to brushed motors.

In a brushed motor, the windings where the heat is generated are on the rotor on the inside. To dissipate, that heat must pass through the bearings to the stator and either free air or a water jacket.

In a brushless motor, the windings are on the stator not the rotor. The outrunner has the stator on the inside. So the heat still has to pass through the bearings to dissipate. The other complecation of the outrunner is that you can't put an effective water jacket on a spinning outside rotor. Some outrunners, (and the Turnigy 35-42 seems to fall into this category) have non-rotating cases around the rotor. This adds an enclosed layer of insulating air to the outside which makes thermal management harder still.

The inrunner brushless motor has the stator on the outside and here the windings are coupled to the outside by a thermally conductive metal sleeve. This allows heat to dissipate very easilly to air, or better still to a water jacket.

As far as I know, the only practical and effective way to cool an outrunner is a high flow of air over and (if possible) axially through the motor. I guess that's why they're used so much in model planes and helecopters!!! So if you can engineer forced air cooling over the motor, then this will probably be the best plan.

Mark

[BarzoParticipant @barzo]

Hi Ffolks,

After many trials and tribulations and I must say, one of the benefits of belonging to a model boat club, has been the great help from fellow members, my Huntsman is now on the water.

The biggest delay was with The Royal Mail and their procedure for lost deliveries. Despite using the Recorded Delivery facilty it took nearly a month and a half to have the delivery to be acknowledged as lost and to get a refund.

The configuration mentioned in my previous Post has stood the test. The only difference is that the Lipo was changed to 20C.

The water cooling device has been a success and it enabled me to use the MMB900 bracket to mount the Brushless motor withut any changes.

I have been able to lose 1.5 kilos of weight and together with the consequent reduction in wetted area the boat is almost upto IC speeds.

The increase in temperature of the engine/ESC/Batteries is barely perceivable. I have managed to rampage around the lake for a good hour and still have a respectable performance.

It is now too fast for me to 'sail?' in the small lake in Clevedon, the turning circle, to turn without the bow digging in at full speed is too big for the width of the lake. Still there is a three acre lake adjacent.

The youtube clip gives an indication of the performance – can go faster if I so choose. The prop is a plastic, two bladed 45mm x1.4. I am going to try a 40mm three bladed, brass prop. – an inveterate fiddler!

 

Youtube clip:–   http://youtu.be/3AjTFvDdtj0

 

Cheers

Barzo

 

 

 

 

 

 

Edited By Barzo on 31/08/2012 11:49:38

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