Brushless motors

[BRYAN ASTONParticipant @bryanaston57723]

Dave

I will take your advice,thanks

[Dodgy Geezer 1Participant @dodgygeezer1]

It's surprising how much a different prop can affect a boat, even if the different prop is nominally the same. If you can, get a selection of props and see what the difference is.

I thought apart from the amperage , all nihm batteries were the same….

It would be truer to say that all batteries are different!

Conceptually, a battery is two dissimilar plates with an electrolyte between them. In a simple battery. the electrons initially flow easily between the plates, but then they gradually slow down as the chemical close to each plate becomes locally depleted – this is called 'polarisation'. Leave the battery for a while and it will recover.

Modern batteries address this problem with clever chemical mixes, and clever internal physical organisation, optimised for the job the battery has to do – typically either long slow power delivery or short fast power delivery. The ability to accept fast recharging is also designed in, or not, depending on the battery. As are other features. So even batteries which use the same basic internal chemistry may have different characteristics, depending on their design…

[BRYAN ASTONParticipant @bryanaston57723]

Dodgy

Reading your message above, how do you know wether a battery is long slow power delivery, or a short fast power delivery, the ability to accept fast charging or not., are they marked somehow to show what spec they have?

[Dave MilbournParticipant @davemilbourn48782]

Bryan

ALL NiMH and LiPo batteries will accept a 'fast charge' – the maximum rate is often shown on the pack. Personally I never charge packs at more than the C rate (its capacity) so, for example, I'd charge a 2600maH pack at no more than 2.6A. I dare say that the model aircraft and fast electric boat modellers would scoff at such caution – but that's just me. There are certainly other articles which will tell you what limits others apply; take your pick and go with the one that suits. Whatever you do, never fast-charge a new pack for the first three or four charge/discharge cycles and bear in mind that continually fast-charging will reduce the effective life of the pack quite significantly.

The ability of a pack to deliver high current is shown as 'NNC', where NN is the maximum continuous discharge rate in Amps and C is the nominal capacity in Amp.Hours. Thus a pack labelled 2600maH (i.e. 2.6AH capacity) and 35C can deliver 35 x 2.6A = 91A.

Just as a caveat, the batteries I'm referring to are the ones which come from a reputable manufacturer and supplier e.g. Vapex/Component Shop. Some of the values quoted on cheap battery packs from oriental suppliers beggar belief!

Dave M

Edited By Dave Milbourn on 25/04/2016 11:10:34

[BRYAN ASTONParticipant @bryanaston57723]

Greetings Dave

Thankyou for the info, I must admit that apart from the amperage I have never read the small print on the nihm batteries, I agree with you that batteries from the PRofC have no info on them that I can see, the non PRofC packs do. As I have said before life is a never ending learning curve.

Onward and upward

[BRYAN ASTONParticipant @bryanaston57723]

Greetings all

Have fitted a TURNIGY 11kv motor to my big Huntsmam with 55 mm prop and Marine 60a v3 esc,it performed only slightly better than when it ran with a 600 Johnson Black and Decker drill motor, most disappointing, I gave up trying to program the the card, all I got was three red lines in the boxes, I asked the dealer who I bought it from for help, he had no idea ,but promised to ring me the next day, still waiting.

Anyway the motor seemed to run okay without any programming ,but after running for around 20mins. it started cutting out, but would start again then cut out again. The esc must be water cooled so I bought a kit online and connected it up ,the esc does not get hot to the touch, the power supply is two 7.2 newly charged batts in parallel .

Anyone got any suggestions about all my troubles, life should be simple.

[Dave MilbournParticipant @davemilbourn48782]

Connect your two 2S packs in series to give 14.8v. Your 7.4v batteries are turning over the prop at about half the speed of a 10cc glowmotor. It also sounds as if the programming might be improved. Three red lines doesn't sound hopeful, does it? Timing and number of motor poles are important for best performance.

DM

[BRYAN ASTONParticipant @bryanaston57723]

IThanks for the reply DAVE, the batts are nihm 7.2 volts,I have changed the prop for a smaller 3 blade one ,see what happens. The motor when it is running sounds a lot slower than the inrunner in the Sea Commander

I will check to see if the motor is compatible with 14.4 volts, if there is no improvement I will fit an inrunner around .3000 kv. like the Sea Commander, that goes like a rocket and is the roughly the same weight as the Huntsman.

What do you reckon about the cutting out,batts losing power?

Onward and upward

Bryan

[Dave MilbournParticipant @davemilbourn48782]

Just curious, but the Sea Commander is 34" long while the big Precedent Huntsman 31 (1/8 scale ) is 47"; the smaller one (1/11 scale ) is 34". Can we agree which Huntsman we are dealing with here? We may have our lines crossed.

A smaller 3-blade prop is a good idea but at 7200RPM you're not going to get much in the way of performance for a model that size. Inrunners are by their nature much faster but they draw more current and therefore the batteries won't last as long. The cutting out might well be due to low voltage circuitry, which will either cut or slow the motor when the nominal voltage is reached. You shouldn't allow NiMH cells to discharge below 1v each or fatal damage could result.

DM

[BRYAN ASTONParticipant @bryanaston57723]

Dave the Huntsman is the big one 47 inches in length with a plastic hull,the Sea Commander has a wooden hull scratch built by me as a first attempt ,it has a great deal of Halfords filler to correct my mistakes and around eight coats of Ronseal diamond hard varnish and it ain't light, but with the Etronix inrunner it moves very fast, as both boats are around equal weight it would suggest that an inrunner of the same kv as the Commander eg.2950 would obtain the same performance or thereabouts. I will see what happens with smaller prop and higher volts. Watch this space.

Bryan

[harry smith 1Participant @harrysmith1]

Hi Bryan

Decrease your prop size down I run 40 to 50mm props.

I use the HK-60A car ESC with a program card HK-Prog-Card (for HK45 to 100A ESC's).

Dam simple to use, I posted the setup in my Sea Hornet 2015 build and use the same in all my cars and boats.

The only change is for 2S,3S and 4S batteries for cut out voltage.

Harry

[BRYAN ASTONParticipant @bryanaston57723]

Greetings Harry

I have changed the prop for a smaller one, I will also use a 12v c pack nihm, I will have try it all out next Sunday assuming the weed has not taken over.

I have sent away for a 3100 kv inrunner motor if all else fails, I think I will stick with inrunners in future as they seem to be good for power consumption and performance ,the Sea Commander ran for well over an hour on two 3700mah 7.2 v c packs in parallel with quite a few flat out runs.Watch this space.

Dave you mentioned timing for brushless motors could you please explain this a bit more.

Bryan ( still on a learning curve )

[Dave MilbournParticipant @davemilbourn48782]

Bryan

Not 100% certain so I stand to be corrected on this. The motor consists of a number of wire-wound poles [in a small motor typically 12-14] which are switched on electronically in turn. This creates a magnetic force which attracts them towards fixed magnets around the casing of the motor. The 'timing' is the angular distance between the point where any particular pole is switched on and the next fixed magnet around the inside of the casing.

I'm still scratching my head about the efficiency of a standard prop trying to turn at 37,200RPM [that's a 3100kv motor on 12v]. I would have thought that cavitation would take over well below that sort of speed – unless it's in a top-line surface-piercing setup. Conventional wisdom says that for a submerged drive a big prop turning relatively slowly is more efficient than a small one turning quickly. I can only reiterate my experience with the prototype H31, which had a 1.5BHP [approx 1000W] glowplug motor turning an X55 2-blade prop at about 15,000RPM and went beautifully. At least you've avoided the '850+12v SLA' setup which turns a fast cruiser into a canal barge.

DM

 

Edited By Dave Milbourn on 09/05/2016 08:47:40

[BRYAN ASTONParticipant @bryanaston57723]

Dave I was going to use the 12v c pack on the outrunner already fitted, if I change the motor for an inrunner,the I will go back to two 3700mah c packs in parallel for power, it will all come right in the end.you don't always have to go flat out it depends on the length of the pond./ lake and how many boring yachts are taking up space that I need to use, that's why I go early

Regarding timing I will investigate this

Thanks

Bryan

[BRYAN ASTONParticipant @bryanaston57723]

Dave I was going to use the 12v c pack on the outrunner already fitted, if I change the motor for an inrunner,the I will go back to two 3700mah c packs in parallel for power, it will all come right in the end.you don't always have to go flat out it depends on the length of the pond./ lake and how many boring yachts are taking up space that I need to use, that's why I go early

Regarding timing I will investigate this

Thanks

Bryan

[BRYAN ASTONParticipant @bryanaston57723]

Dave I was going to use the 12v c pack on the outrunner already fitted, if I change the motor for an inrunner,the I will go back to two 3700mah c packs in parallel for power, it will all come right in the end.you don't always have to go flat out it depends on the length of the pond./ lake and how many boring yachts are taking up space that I need to use, that's why I go early

Regarding timing I will investigate this

Thanks

Bryan

[ashley needhamParticipant @ashleyneedham69188]

I am not sure, but I think that the very high KV motors are generally intended for geared operation. Certainly the 2900Kv tiny motors in my Ecranoplans are, and ungeared they turn only a very small (air) prop…which is ok in my case as I only wanted a small one.

In something like a large boat, like wot u have, a much larger prop spinning relatively slowly must be best. Lower Kv motors put out much more torque to turn a larger prop.

Peter, on out pond, had a whopping great boat (cabin cruiser, 5 foot or something) and this goes very very nicely on a big brushless of about 750Kv, and 14V turning a lovely big brass prop, 60mm or so (guessing here). Not only that, but the boat is very quiet, no screaming and thrashing.

Ashley

[harry smith 1Participant @harrysmith1]

Hi Bryan

I am using Turnigy 5800mah 3s 25C on my D3648/4 1100kv or a Zippy Compact 5800mah 4S 40C.

I do not batteries other than Lipo's can deliver the power brushless motors require.

The motor on 2S=7920rpm

3S=12210rpm

4S= 16280rpm

5S=20350rpm

That's unloaded, but, these beasts like to rev!!!!

On U tube check out Spearfish on.(50mm prop)

This is a mates boat on 750kv 3S and 1100kv 4S.

Also one run with a XK 3674-B-1900kv on 4S with a Hobbyking 3 blade 37mm prop!!!!

[harry smith 1Participant @harrysmith1]

Hi Ashley

One of our club member's has a Fantome Large Cabin Cruiser with a 500kv on 6S(twin 5800 mah 3S) and a 4 blade 70mm prop.

With GoPro camera etc. this thing is dam fast and quiet !!!

I call it Beaufighter(whispering death)!!!

Harry

[Dave MilbournParticipant @davemilbourn48782]

Bryan

1. There is a world of difference between a 1100kv outrunner and a 3100kv inrunner. I personally would not favour the latter unless it was driving through reduction gears, as Ashley says, but suit yourself.
2. I would strongly recommend fitting a budget wattmeter into the model to monitor the maximum current drawn before deciding whether or not to change from NiMH to LiPo. Here's the one I have, which will also serve as a low-voltage alarm. There are several other similar types available **LINK**
3. IMHO a scale powerboat going too quickly looks just as ridiculous as one plodding round the lake like a coal-barge.

One of our club member's has a Fantome Large Cabin Cruiser with a 500kv on 6S(twin 5800 mah 3S) and a 4 blade 70mm prop.

That's around 11,000RPM, which I'd say sounds about right for that size of prop and model. Note the use of a low kv outrunner.

DM

Edited By Dave Milbourn on 09/05/2016 11:18:12

[BRYAN ASTONParticipant @bryanaston57723]

Dave and Ashley

I charged up the 12v c pack and connected it to the outrunner in the Huntsman, the speed the motor turned seemed to be double previously obtained

I have neve seen the need for a gearbox in a model boat ,the only exception perhaps is in a tug with a very large prop.

I cannot see the need for lipos for brushless motors ,they seemto go very well with nihms, and they are very easy to charge.

The Turnigy motor will take 18 v so 12v is ok, depending on the improvement ,I may use two 7.2v in series

Down to the lake next Sunday morning depending on the weed, I shall give a full report afterwards

Onward and upward

Thanks everybody for all your assistance

[Dave MilbournParticipant @davemilbourn48782]

Yep – the speed will be 12/7.2 [or 1.66] times that originally obtained. The nice thing about brushless motors is that the maths is so easy – you know just what you're gonna get!

There are certain types of racing models which use geared-down glowplug motors. These motors are invariably fitted with tuned exhausts and can exceed 30,000RPM – hence gearing them down if only to prevent cavitation rapidly eating away the very expensive props they use! Have a shufti around Prestwich Models' website and you'll find all manner of such treats. Be prepared to have your eyes widened by the cost of some of the items…

LiPo batteries have had a bad press, largely through the ignorance and recklessness of certain people who have mishandled them. They have a 50% better capacity/weight ratio than NiMH cells and can handle much higher discharge currents. In a big model like the 1/8 Huntsman the difference in weight doesn't matter anything like as much as in its half-size version (See MB Jan/Feb 2016). They were adopted by model aircraft and helicopter fliers as the best source of power for their brushless motors and, almost inevitably, the word went round that you can't run brushless motors from anything except LiPo cells. Untrue. Neither are they difficult to charge as long as you have the correct equipment and you take reasonable care – which applies to charging any type of battery anyway. The downside with them is that even with the best charging and discharging regime you'll only get about 100 usable cycles from a pack whereas that figure can easily be exceeded tenfold by NiMH cells. They are also less tolerant of physical abuse.

If you need to draw very high currents and /or weight is critical then LiPos are a no-brainer, but if you are happy to run a moderately "cool" motor/prop/battery setup then there's no reason why you shouldn't use NiMH cells. In those circumstances they have everything to recommend them – not least their long-term cost-effectiveness.

Dave M

[BRYAN ASTONParticipant @bryanaston57723]

Greetings all

Connected two 7.2v c nihm packs in series and connected to esc of brushless motor ,it lit up but would not fully light up, it did not make the usual noises, motor would not run, reconnected the 12 v battery ,it ran perfectly, tried the 14.4 setup again , nothing, connected a meter to 14.4 v setup it showed .14.4 volts,any ideas? Perhaps the esc can take 12v max. Life is a continuous battle against ever increasing odds.

Bryan

[Dave MilbournParticipant @davemilbourn48782]

Bryan

I've just checked the full specs of the speed controller and found to my surprise that that it is limited to 3S LiPo packs (11.1v). **LINK** That would be fine when you are running a 12v NiMH or two 7.2v packs in parallel – but not in series (14.4v). It looks as if you will have to stick to the 12v NiMH. Investing in a 3S LiPo would not improve the performance over the former. Ironically the 50A Hawk ESC, which was the other option, will handle up to 6S LiPo's…

I guess we both should have checked in a little more depth. Sorry, Bryan.

Dave M

[BRYAN ASTONParticipant @bryanaston57723]

Dave

We have all been on a learning curve,I will try the boat this Sunday with a 12v batt. If the performance is disappointing ,I have a 3200 kv inrunner that I will install, you don't have to run it flat out all the time, but it is nice to have an occasional blast.

I think the subject of this thread has been interesting and educational to many readers including me , eventually most boats will be powered by brushless motors.

I will let you know how it runs next week ,no need for apologies

Onwards and upwards

Bryan

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