Airboat – brushless or brushed motor???

[Alan GregoryParticipant @alangregory61043]

Hi everyone

 

I’ve nearly completed my scratch built Florida airboat from plans obtained from  ww.cajungatorairboats.com, the model is 24 inches long, 11 inches wide and the hull 2 inches deep made up of 1/8th ply and a balsa deck. Motor mount is 5 inches above the deck, so perhaps a 6 inch aircraft prop would be ideal.

 

Would you suggest I go brushless or brushed motor and use lipo batteries???

 

Thanks for any help or light you can shed on this matter

[Alan GregoryParticipant @alangregory61043]

[Dave MilbournParticipant @davemilbourn48782]

If you mean 6″ diameter then it doesn’t sound enough. I built a Glynn Guest all-balsa airboat which wasn’t much more than half that size and was powered by a Speed 400 motor…………with a 6″ prop. What size prop is shown on the plan, anyway?

If you want to go brushless+LiPo then read up as much as you can about operating and maintaining LiPo batteries first. You probably won’t need reverse so a cheapo aircraft brushless ESC would do the job.

Dave M

[ashley needhamParticipant @ashleyneedham69188]

I would probably choose a brushless for this, as you get more power for yer amp (hour/battery).

 

I agree with DM, 6 inches is a bit small I would have thought for your airboat, 8 or 9 inches perhaps. Brushless motors are well established in the model aircraft world, so  decide on your prop size and call an established aeromodel shop and they would advise on the type of brushless for your craft….possibly an outrunner at a lowish rev/volt rating.

 

I would hesitate before going LiPo , there are questions regarding longevity and certainly they dont take mistreatment. As you are not really weight strapped I would personally stick to NiMh.  But others wouldnt of course.

 

There is a difference in mounting brushed/brushless in-runners and brushless outrunners….so you need to decide these bits before sticking lumps of wood together really !

 

Ashley.. sudden expert after buying completely the wrong brushless for next project !

[Alan GregoryParticipant @alangregory61043]

Hey Ho …. spot the donkey …..

 

What was I thinking when I said 6 inch prop ….. if the motor is mounted at least 5 inches above the deck, then that gives me clearance for a 10 inch prop …. so have decided to go for a 10 x 4 prop … I really must try to agitate the grey cells once in a while.

 

I have practically made my mind up on a motor, so will go down the Emax 2815 /09 route, the model without radio or any electrical gear weighs in at 700 grams …. it should fly …. thinking about it seriously, it probably will fly … straight up … maybe I should have joined a model aircraft club?

 

 

I’m also considering using 2x 3S packs wired in parallel to give double the running capacity and duration. Doing this can work out cheaper than buying a stonking big battery…..as I am oft reminded….” you are a tight bugger”!

 

Speed controller only has to be forward as Dave so correctly stated…. so might save a few pence with that.

 

Thanks again for your comments lads, when funds allow and my financial adviser (Wife) says yes, I will order the relevant bits and pieces and let you know if I have built a boat or a plane.

 

I might even try this gear in my LCT6 and get that up on the plane ….

 

Alan

 

PS: Might even consider fitting the engine out of my motorbike ……

 

 

 

 

 

[Dave MilbournParticipant @davemilbourn48782]

I haven’t read much about them but I know enough to say DON’T WIRE LIPOs in PARALLEL! The current these things can put out is frightening and if you have them even slightly out of balance you’ll get a huge back-charge surge current which could melt anything in its path explosively, including the model and you.

Now, to pre-empt the predictable macho “I’ve done this and it works OK” posting, all I have to say is matey – you have been very lucky. These things are potentially lethal and not to be mucked about with “because it does no harm to my NiMH packs”. Our Aussie agent calls ’em “Napalm Bombs” and for good reason.When you’ve seen one go up you’ll think twice about mistreating them.

I’m not joking here – this is serious.

If you want longer duration then fit a larger-capacity pack or, as Ashley says, use a  NiMH pack instead (my own personal choice, this). We don’t sell either type so I’ve no trader’s axe to grind here.

Dave M

 

[Glenn Howcroft 1Participant @glennhowcroft1]

Hi all…

 

I’d like to point you to this article on Lipo’s http://www.astecmodels.co.uk/lipos.htm .

 

Lipo’s used correctly with the right equipment are NOT napalm bombs, they ARE different from Nicads and MiMh cells and as such require a different approach.

 

 Lipo’s can be used easily and safely in paralled IF BOTH packs are discharged and balanced to the same level BEFORE charging as a parallel pack. If you are using the pack from that point on as a paralel pack then normal cahrging and balancing of the pack is all that is needed.  

 

 This next bit is a copy of a post on the parallel pack question , from the same auther of the Lipo information in the link above …

 

”

Re: LiPo – 2s1p x 2 or 4s1p for Hydro 2

I try to keep things as simple as possible.

1) discharge both packs separately to 3v per cell.

2) charge them together with either a charging balancer or a balancer from maverick made for the job of balancing double packs.

I have several packs I do like this but I tend to use the packs together all the time.
I dont like mixing packs for different things

My
2p x 10s (made up from 4 x 5s packs) packs can be either charged
through my schulze balancing system. They actually make an adapter for
doing the Job. Have at on the schulze web site. However that can be an
expensive system if you have to buy their charger as well.
Have a look on the site. Maverick(http://www.li-po.co.uk)
will make up one of their low cost balancing cards to do the job for a
lot less. Card for 6s £15 plus the leads for doing what you want. so if
you have 2 x 2s, it will come with 2 connectors for you just to connect
to.

My 1/8scale hydro was first charged with the maverick system
and it worked very well charging the 4 x 5000mah Maverick pack. Even at
discharges over 4kw the packs worked great.

 

“

I hope the above helps to dismiss some of the bad press about Lipos .. MODERN LIPO’s much, much better.

 

Glenn

[Dave MilbournParticipant @davemilbourn48782]

Glenn

 

Point taken, and thanks for the links, but the crux of your message lies in the phrases “used correctly with the right equipment” and “discharged and balanced to the same level…..”. They are NOT fit-and-forget items, as you so rightly say, and I’m afraid that with the best will in the world most modellers are ignorant of the potential dangers of mistreating these things. Indeed, they probably wouldn’t know if they were mistreating them or not because LiPos are much different from the other types of power source that they use.

I’ve have been asked some truly amazing questions by customers e.g. “Can I use a mains-powered car battery charger to charge my NiCADs if I put a resistor in there to limit the current?” was one asked only last week. If you know what you’re doing and are aware of the potential hazards then most things can be done – it’s ignorance that causes accidents (not just stupidity – they are different).

I make no apologies for what I said and would strongly urge anyone to read up all they can about the use of LiPo batteries before deciding to go that way. You clearly have.

 

If you’re tight-fisted like Alan then maybe the cost of the right equipment will put you off anyway!

Dave M

[Alan GregoryParticipant @alangregory61043]

OK …. that’s really scared me ….

 

Fires …. Model’s exploding … rather large bangs !!!!

 

I’m really going to be popular down at the local pond ….

 

Me thinks I’ll do a lot more reading before choosing the final power supply.

 

Oh, and Dave, I ain’t really tight-fisted, I’m retired and my good lady wife is my financial advisor …. Nuff said.

 

Thanks again for the reading links and advice chaps.

 

Alan

[Glenn Howcroft 1Participant @glennhowcroft1]

Hi all ..

 

Your spot on Dave .. it’s the not knowing that usually causes the problems ..

 

Check out this link .. excellent information. Don’t be put off with the model flying part .. the information is essential to all users of Lipos !!. Electric flight is probably the fastest growing user base for Lipos in models, new kit coming along almost daily,  and I know a lot of model boaters who use model aircraft kit in thier boats ..

 

 

http://www.modelflying.co.uk/forums/postings.asp?th=31198 

 

 

Charging Lipos from anything other than a charger designed for the purpose is just asking for trouble. Never, ever charge them from your old charger, ’cause thats what you’ve used for years. CHECK that it’s capable of charging LiPos .

 

Saying all that, a new charger that will charge ALL your cells, be it Lead acid, gel cell, Nicad, Nimh, Lipo etc and balance the Lipo’s isn’t going to cost you an arm and a leg, and is well worth the outlay. After all we spend hundreds on our models, most of us have several adding up  to many thousands, but for some strange reason most people don’t seem to want to spend on a reliable, versatile charger .. 

 

They don’t cost all that much  .. check this charger out http://www.giantcod.co.uk/icharger-106bplus-250w-balancecharger-p-404527.html . I mean all  this and just £67. Even includes a temperature probe that when activated will stop the charging when the cells get too hot, and a USB connection for your PC so you can keep a log of battery charge data. To see if any cells are getting lazy over many charges, thus needing changing etc.

 

My own charger isn’t that advanced and cost me a lot more 2 years ago !!

 

Glenn

 

[Len OchiltreeParticipant @lenochiltree67043]

Hi Alan and all,

Why is there a need to have the fastest and cost most?.

The original AirBoats were built out of what was lying about and cheap,like my model ones.

 

 

This one was built around a Action Man and made from Styrene,there is another one in my Gallery,also on the front page of the Forum.

Len.

[George Papandropoulos 1Participant @georgepapandropoulos1]

“>” width=”350″ alt=”” />

Hi Alan,

 

a lot of educated and knowledgable opinions after, I feel like adding my salt, though irrelevant to the model world….

 

I powered mine with a 1400 cc VW engine and imported the prop from some serious company in Texas. The plans were mine and I ended up married to the white clothed girl (then),

 

Sorry to cut in like this but we old people live mostly with memories…

 

George

 

[IMG]http://i200.photobucket.com/albums/aa77/papandropoulos/boatipg.jpg[/IMG]

Edited By George Papandropoulos on 21/01/2010 23:15:43

[George Papandropoulos 1Participant @georgepapandropoulos1]

Hi Alan,

 

a lot of educated and knowledgable opinions after, I feel like adding my salt, though irrelevant to the model world….

 

I powered mine with a 1400 cc VW engine and imported the prop from some serious company in Texas. The plans were mine and I ended up married to the white clothed girl (then),

 

Sorry to cut in like this but we old people live mostly with memories…

 

George

 

[IMG]http://i200.photobucket.com/albums/aa77/papandropoulos/boatipg.jpg[/IMG]

[ashley needhamParticipant @ashleyneedham69188]

George, great picture, and not at all irrelevant to the model boating world.

 

I bet virtually all the airboats built by modellers follow the same “florida” design, and yet here we have a real life airboat of a much different type.

 

I like seeing different sorts of craft as it gives you IDEAS for something, well, different.

It would be a good project for instance to replicate your boat in scale. Be a challenge!

Ashley

[Alan GregoryParticipant @alangregory61043]

Thanks for the information George and also the picture, I reckon that turned a few heads when you took it for a spin.

 

As Ashley says, seeing a one off like that certainly gets the old grey matter working, perhaps you should build a replica model?

 

Alan

[Andy CParticipant @andyc56856]

Hi All

 

Just to say, I used a lipo on my hovercraft as it was lighter.  Once you talk to the guys who know about these things, and buy the correct charger and balancer, they can make a difference when it comes to weight.  In point of fact I bought two, as when putting the connetors on, they touched and shorted the battery, I am still here to tell the tale as well.

 

Regards

Andy

[James ThomasParticipant @jamesthomas81838]

 I have a set of Charging Leads from Graupner, from around 1982, for charging a 6 cell 1200 Nicad pack, direct from a Car battery. Instructions tell you to charge for 20 minutes or” until pack is hand warm” Now that is really delicate judgement.!! ( I don’t use them now!!)Posted by Dave Milbourn on 14/01/2010 08:56:12:

Glenn

 

Point taken, and thanks for the links, but the crux of your message lies in the phrases “used correctly with the right equipment” and “discharged and balanced to the same level…..”. They are NOT fit-and-forget items, as you so rightly say, and I’m afraid that with the best will in the world most modellers are ignorant of the potential dangers of mistreating these things. Indeed, they probably wouldn’t know if they were mistreating them or not because LiPos are much different from the other types of power source that they use.

I’ve have been asked some truly amazing questions by customers e.g. “Can I use a mains-powered car battery charger to charge my NiCADs if I put a resistor in there to limit the current?” was one asked only last week. If you know what you’re doing and are aware of the potential hazards then most things can be done – it’s ignorance that causes accidents (not just stupidity – they are different).

I make no apologies for what I said and would strongly urge anyone to read up all they can about the use of LiPo batteries before deciding to go that way. You clearly have.

 

If you’re tight-fisted like Alan then maybe the cost of the right equipment will put you off anyway!

Dave M

 

[Tony OLIVERParticipant @tonyoliver44792]

I’ve just come across this thread.

I’ve been operating brushless/LiPo airboats ( see http://www.rcgroups.com/forums/showthread.php?t=1530921) for three years or so. It’s based on the Skimmer. I’m using the same LiPos I started with 1300mah 3S (3S means three cells in series making 11.1v in total). But I removed the heavy 400 brushed motor almost immediately and haven’t looked back since. It’s been dunked, swamped, and totally filled with water including the radio. I’ve been able to crack open the throttle while it was inverted in the water and drive it back to shore. Amusing the onlookers and disbelievers alike.

They do not explode, catch fire or have any ‘here be dragons’ experiences. However they do need some sensible and careful thought as they are not brushed motor with lead/acid batteries which can be mistreated and not be too harmfull. (What? shorting out a 20mah 12v battery isn’t harmfull?).

As an earlier contributor pointed out, to get the best and safest use from LiPo you need to charge and discharge them properly. You can’t be casual about it. You must use a LiPo charger. That will ensure the battery will not discharge below or charge higher than the limits they will stand. Either excess and they are dead. Very expensive. LiPo compatible chargers may have a balancer to check each cell is treated separately (multicell packs have the normal two power leads plus a separate lead and plug to use in the checker ). If the LiPo charger doesn’t have this, a separate balancer to go inline between the charger and battery pack is needed to keep track of each cell. Normally the cells are charged at a rate to charge from empty to full in 1 hour. Cut off on full charge is automatic, but it’s sensible to monitor charging in the same way NiXx are at high rates.

 

As an example of what’s possible, my small 50watt outrunner motor drives a 3 blade 5x3prop at around 14000rpm at about 5amps. There’s more about it here :-

 

http://www.rcgroups.com/forums/showthread.php?t=1530919

I hope it might inspire others to look at brushless as an alternative.

 

At the moment I’m looking for information on comparisons in brushless terms between Graupner Race 600BB motors (about 150 watts I believe) which will do around 24000rpm in a mini-jet. A brushless’s revs need to be the same so in/outrunners are readily and cheaply available but I have no experience of what power (in watts) is needed in the minijet to get equivalent revs without moving into too high power territory. My gut instinct is to do what I do with my boats – put in an overkill motor and run it at lower power (volts). But can that work in brushless? Luckily most brushless are measured in revs per volt. If it’s over powered it will do the job at lower consumption, if underpowered it will just try harder and gulp down the amps until it does it’s job. Props for aircraft use are no problem, but I haven’t a clue about the energy a small 19mm impeller will absorb in a Graupner mini-jet.

 

Has anyone got any idea? My Visby corvette’s waiting for the motors.

Any comments or suggestions will be very welcome.

 

Tony

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