Going brushless?

[Peter VintonParticipant @petervinton69315]

My 40cm depron Fairy Swordsman is currently running a 540 motor and a 29mm prop with a 7.2v Ni-MH battery. I'm looking at a 24/30 7200KV brushless outrunner with esc on the bay, could I expect a significant increase in performance if I took the plunge and made this conversion?

[Peter VintonParticipant @petervinton69315]

[Dodgy Geezer 1Participant @dodgygeezer1]

Would you be using your 7.2v battery? If so, and if it can provide the amps, you are looking at more than 50,000 rpm. With some wild guesses about the pitch of your prop and slip, that might be 25mph?

7200 seems a bit high for a sports boat. Something made out of depron ought to be very light. My EeZeBilt PT boat is 20" – around 50cm – but a similar light boat in balsa. Here is a shot of one running in a small pool, which lets it get up to about half-speed:

**LINK**

The motor there is an EMax CF2822 1200KV You can get one with a Chinese ESC for around £10 on ebay, and it can swing a 30mm-40mm prop quite happily. The problem with brushless motors – especially small ones with cheap escs – is that they are a bit 'all or nothing'. They start with a jerk and don't like running slowly. Going for 1200KV gives you a lower RPM range for manoeuvring and quite a sprightly performance. With 7200 I suspect that you'd be off like a rocket…

I find that, in practice, changing props can make a huge difference to a boat – more so than changing an engine…

[harry smith 1Participant @harrysmith1]

Hi Peter and Dodgy

That motor would hit 51840 rpm.

A 28 mm brushless motor 1200kv to 1700kv with a wattage about 600 will work on a 29 mm prop.

A car 45A ESC(brushless) with a Lipo battery Turnigy 2S 2650mah/30C (weight 139 grams) or a Turnigy 2650mah/30C (weight 250 grams).

These batteries are about the same size as Ni-MH batteries and is the same weight range.

The Hobbyking car ones (HK-30 to 100A) with program card are easy to setup and work great.

[Dave MilbournParticipant @davemilbourn48782]

I hope that the 7200kv was a typo i.e. it should have been 720kv. If not then it stands every chance of boiling the pond away without actually moving the boat. An average Speed 400 does around 19000RPM on 7.2v (no load) and that's more than fast enough for a 25mm 2-bl prop. The 24/30 7200kv motors on E-Bay are inrunners and designed to be run in 1/16 scale cars through a gearbox of around 9:1 (or higher).

DM

[Peter VintonParticipant @petervinton69315]

Thanks for the replies, it is a car motor and I hadn't realised it was an in runner. I'll look again for a more suitable motor.

[Dave MilbournParticipant @davemilbourn48782]

Peter

I think that this motor would be more appropriate, say with a 2S LiPo pack. BE2208-13 DYS Brushless Outrunner Motor 1400KV Brand New (Just 'Search' on E-Bay). I run 2817 and 2830 motors in my various Huntsmen and Huntresses but those models are 600mm long while yours is only 2/3 of that – and a lot lighter.

I've personally used this speed controller and would have no hesitation in recommending it. **LINK**

Dave M

[John.RedearthParticipant @john-redearth]

Peter

Why? I think there is a novelty value in going brushless but a '40cm depron Fairy Swordsman is currently running a 540 motor and a 29mm prop with a 7.2v Ni-MH battery' has a lot of power. I could understand going LIPO instead of NIMH, but why change? I personally prefer the 545 which has power and better low speed performance. What is your scale speed target?

John

[Dave MilbournParticipant @davemilbourn48782]

John

Much like Arduino microcontrollers, there is more to using brushless motors in the right situation than just "novelty value". I wouldn't fit a low-revving 545 in a Fairey model – low speed performance isn't what a Swordsman is all about.

Dave M

[Peter VintonParticipant @petervinton69315]

Why? The 540 motor is quite heavy and large, also I'm new to power boats as I've only built sailing models before (mostly scratch built), so I'm playing really. I've ordered an Emax 2822 with controller, it's only £10 so seems a cheap bit of fun. And yes, I'm not particularly interested in scale speeds, I want it to take off over a wave!

[John.RedearthParticipant @john-redearth]

What a good answer!

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Peter Vinton on 19/02/2016 16:36:08:

…. I've ordered an Emax 2822 with controller, it's only £10 so seems a cheap bit of fun. And yes, I'm not particularly interested in scale speeds, I want it to take off over a wave!

A major design consideration for EeZeBilts is 'a CHEAP bit of fun'!

I think that Emax offers a good introduction into the world of brushless motors but note that it's not only the motor that will give you the performance you want.

First, note that 7.2v is on the low side for this motor. It is designed for 2-3 cell Lipos – which is around 8-12 volts. So you can up the power quite easily, so long as you consider how the motor might be cooled…

Props really do make a huge difference, especially in small sizes. If you can experiment with different props you will see this…

'Talking off over a wave' is going to be dependant on weight as much as power. You may well find that swapping your NiMH for light Lipos (particularly a small cheap 3S) will make the boat into a rocket. At this point torque and stability start to become important considerations…

[John.RedearthParticipant @john-redearth]

G'day Dave

So I see you're attitude to arduino is softening. Yes I just googled Fairey Swordsman and note it is to be fast and light. I have just come from a long discussion with someone about going brushless as it seems to have turned his boat into a slingshot. I am a scale modeller so should stay in my box.

Cheers mate

John

[Dave MilbournParticipant @davemilbourn48782]

Hello John

My attitude towards Arduino was never 'hard' – I simply decided, on a purely selfish basis, that the technology didn't merit the time it would take for me to master it because the models I make are so straightforward.

As regards brushless motors I agree that there is a tendency for many people to overpower their models. It still seems like magic that you only need a brushless motor the size of an "old" 360 to produce the power of an "old" 540. As lower kv outrunners become more widely available, along with ESCs which do offer decent low-speed control, I think that the use of brushed motors will decline. As it stands today, it's becoming difficult to find a brushed-motor marine speed controller on the usual Chinese hobby websites.

We modellers are fortunate that industry still uses cheap brushed motors in their millions for domestic appliances, toys and vehicle applications. Once they latch on to brushless technology (e.g. the so-called "digital motor" in Dyson's latest cordless vaccuum cleaner) then brushed motors will become an endangered species. I hope that, by the time that happens, expertise in the use of brushless motors in model boats has become sufficiently widespread as to avoid the sight of Perkasas screaming round the lake with a scale speed approaching Mach 1. Some of those You Tube videos make me wince!

Keep the faith.

Dave M

[harry smith 1Participant @harrysmith1]

I found one on the Hobbyking site, but, it does NOT SAY that it has REVERSE!!!!

I matched the RPM for my old dune buggy car which had a HOT 540 motor and replaced it with a bolt in brushless motor.

I thought I would get a bit of extra performance from the brushless motor!!!!!

I did not look at the wattage of the motors and thought it Chinese watts were nuts!!!

BIG MISTAKE !!!

The motor I installed was about seven times more powerful and yes the car approaching Dave M's MACH 1 or MACH 2 !!!

So a smaller 100 Watt 28mm brushless motor at about the same rpm would suit a more scale speed.

Harry

[Peter VintonParticipant @petervinton69315]

The outrunner is now fitted and with the 7.2v nicad pack it goes really well, much faster than before and I'm really pleased with it. It ought to go, it only weighs 400g now without the battery! And I know I can up the voltage when I get the need for even more speed, although control might start to get a bit difficult then.

Many thanks for the advice on here

[Dodgy Geezer 1Participant @dodgygeezer1]

Glad to hear that!

The original EeZeBilts were designed around a KaKo 1 motor (a 280 or less!), a 5.5" prop shaft and a 15mm prop. The new 50+ Eezebilts vary in size, but the sporty ones are designed around an EMax 2822 1200Kv, a 9" prop shaft and a 35-40mm prop, It was the cheapest suitable outrunner I could find…

They run happily without cooling on 7.2v, but I suspect that some cooling will be needed if you go up to 12v. You could increase the prop size if a bigger one will fit….

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