Brush less motors

[Dave MilbournParticipant @davemilbourn48782]

Some considerable sense in there, Geoff. I guess that a 'norm' for these motors will gradually become established with time and as more modellers using them. Certainly for most models except water-jets and fast electrics there doesn't seem to be a need for more than about 10,000RPM – less for a warship and much less for a tug or other workboat. Outrunners are also a better choice than inrunners, which tend to run insanely fast and have little in the way of low-speed response. Forward and reverse ESCs will be a problem for a while yet. I think we'll have to look at what the car and truck guys are doing and maybe steal their technology!

Dave M

[Paul FreshneyParticipant @paulfreshney24971]

Hi all

If you look back at the Lubeck thread, this shows the Turnigy outrunner motor and the esc is a Hawk 30 amp.

http://www.modelboats.co.uk/forums/postings.asp?th=93498

With that combination, perfect slow speed control is possible – that is to say that the propeller is barely turning.

Experiments with my Sievers Pilot Boat this last weekend which has two slightly largely Turnigy motors and 40amp Hawk controllers showed that it to could move both forwards and reverse very, very slowly – more than good enough to cope with a steering course.

Hawk controllers are not cheap. but work perfectly forwards and reverse (full rpm range) and at around £40 are no more expensive than the popular Fleet controllers of the 1990's.

I have tried the cheap controllers from elsewhere and performance has often been poor, which confirms that you get what you pay for I suspect, although John Elliott has had success with a combination of :

Brushless motor: Turnigy SK3-280-920KV.

Brushless esc: Turnigy TrackStar 25 Amp Brushless Car forwards and reverse.

This combination has been used (and i photographed it on the water) in his forthcoming Deans Marine Bulwark ship's boat review in January 2015 MB.

Also, running time with a brushless motor can be much much greater than an equivalent brushed motor.

Paul Freshney

[Len Morris 2Participant @lenmorris2]

Hi Everybody,

Here's a question. Will a BM work totally submerged in water? Background – mi car died the other day. No fuel line pressure – new pump needed – where is it – in the fuel tank! Turned out that it wasn't so bad to extract and fit a new one. Pulled the old one apart and was quite amazed at what I found. An axial flow brushed motor and pump unit where the petrol flowed straight through the armature, motor brushes and everything! You just wouldn't do it would you in a petrol tank but apparently it's now universal practice!

Len

[Geoff SleathParticipant @geoffsleath41411]

Brushed motor are quite happy to run submerged. It was standard practice to run them in under water with a low voltage (usually a single NiCad cell) to bed the brushes in. Just tip out the water with all the carbon dust after an hour or so and relubricate the bearings.

Running them in a petrol tank sounds a bit risky because they're prone to sparks at the brushes but I suppose if they're fully submerged there's no air or petrol vapour to cause an explosion. I would think a brushless motor would work fine fully submerged too with less risk of sparks.

No guarantees with this opinion

Geoff

[Dave MilbournParticipant @davemilbourn48782]

I remember a friend built one of Glynn Guest's 400-powered airboats. The thing was screaming around the lake when it hit some wash and flipped right over onto its back, with the motor pylon totally submerged. To both our amazement he opened the throttle and sailed it sedately back to the bank – submerged motor, 6" airscrew et al!

O, yes – Christmas Thingies to all forum members.

Dave M

[Malcolm FraryParticipant @malcolmfrary95515]

Brushed, submerged in fresh water will work. In salt water the exposed metal bits will corrode rapidly. The brushed petrol pump in the tank – OK as long as the tank is full of fuel and petrol vapour – not so good if air joins in the party.

Inverting a boat – I suppose that the airboat motor survived because it had become water cooled. One of my members flipped his Sloopy many years ago (Venetian night, strapped a torch to the top of it). The tiny prop acted as a small airscrew, and he drove it in like that. Fortunately the torch was waterproof, so he could see where it was.

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