Brushless motors

[Dave MilbournParticipant @davemilbourn48782]

Aw shucks, m'duck – I'm all embarrassed now! Paul F will say that any retainer has to come out of Colin's budget and Colin is currently away, spending that budget in Greece….. Oy veh – great will be my reward in another place.

Bryan – you're more than welcome and I'm pleased that we all managed to get you there. I hope the new gear in the Huntsman solves that issue as well but if I were you I'd leave the set-up in this brushed-motor model well alone. It ain't broke so it don't need fixing.

For those still scratching their heads and wondering how/why it worked, the power wires between the ESC and the motor have a rapidly pulsing current along them. As every schoolboy should know, this will create a magnetic field around them. In other words they are a perfect generator of RF interference. Keeping them short reduces the length of this "aerial" and by twisting them together you break down this electromagnetic field. I'm sure Professor Google can explain further if you've an afternoon to waste. The more fiscally cautious among us will also point out that they should also be kept short because, at around a quid for a metre of 14AWG, silicon cable isn't to be wasted! By "short" I would suggest not longer than six inches (150mm).

So now you know.

Dave M

[Malcolm FraryParticipant @malcolmfrary95515]

The twisting causes the magnetic fields to be equal and opposite and, beyond the immediate space that they take up, cancel each other out. The constant change of direction helps break up the direction of the field as well, so all good. Not a complete substitute for capacitors, but every little helps. Sometimes, twisting the servo/esc to RX lead can help by reducing the chance of them picking up stray signals, but that might be getting desperate.

Dave regards 6" as short, but could be bragging. Perhaps he could ask Colin to send one of those postcards from Greece depicting Priapus? Out of the allowed budget, obviously.

[Dave MilbournParticipant @davemilbourn48782]

Malcolm

Behave yourself.

Dave

[Charles OatesParticipant @charlesoates31738]

Earlier today I was looking through a 1969 RCM&e magazine for info on a project, the instructions for an early receiver included twisting the wires together. I always used to think it was just for tidyness, now I know better. Thanks guys, proof that I'm not too old to learn, well, not quite!!!!

Chas.

[Charles OatesParticipant @charlesoates31738]

Dave, surely it's fair to say that less than 6 inches ( of wire) will reduce the chances of interference?

OK, I'll shut up now.

[Colin BishopModerator @colinbishop34627]

Yes, they have those devices on sale here. They come in different colours, presumably to deal with different levels of interference but I can confirm they are all six inches long. Mrs B would prefer me to buy a mug instead….

Colin

[Dave MilbournParticipant @davemilbourn48782]

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Malcolm Frary on 05/06/2016 22:15:20:

The twisting causes the magnetic fields to be equal and opposite and, beyond the immediate space that they take up, cancel each other out. The constant change of direction helps break up the direction of the field as well, so all good. Not a complete substitute for capacitors, but every little helps. Sometimes, twisting the servo/esc to RX lead can help by reducing the chance of them picking up stray signals, but that might be getting desperate.

………

 

Anyone using network cables will soon find out that Cat5, or the telephone standard CW1308 cable, is what they call a 'twisted pair', for exactly this reason. It is of interest to consider the history, which stretches right back to the first telephones.

The very first phone had no problems with inter cable interference, but as soon as they put two different telephone cables together it was noticed that cross-talk occurred, and the practice of running telephone cables next to power cables also caused heavy interference. During the 1880s/90s a lot of work was done on the problem, leading to a much better knowledge of the effects of capacitance and induction on transmission circuits. A lot of the clever gubbins you find in modern cabling, including twisted pairs, were developed between this period and the 1930s, when high-frequency co-axial cables were developed, just in time for television!

Nowadays, of course, we think about fibre optics when we want to send a high-frequency signal down a wire…

 

Edited By Dodgy Geezer on 06/06/2016 11:02:45

[BRYAN ASTONParticipant @bryanaston57723]

To all

Everything is now working perfectly, I would like to thank all who helped me solve my problem, I hope all the discussion on this thread helped others with perhaps a similar problem .

Thank you

Bryan

[BRYAN ASTONParticipant @bryanaston57723]

Greetings all

It's me again, I installed a 50a 22.5 v brushless esc in the Huntsman , the motor is rated to18 v, connected a12v nihm battery ,switched on the transmitter turned the power on, beeps from the esc and the motor sprung into life, success , worked perfectly forwards and backwards, when I stopped it with the trans. It refused to start again it juas twitched then it beeped and then it started again and ran perfectly for some time including forward and reverse, then it would not start and just twitched, it beeped again and ran perfectly and then stopped and then repeated the problem.

I had the same problem when I first fitted the Etronix setup in the Sea Commander took it back to the dealer and he said the battery was not fully charged , but it was but he seemed to cure the problem after topping up the battery. The 12v battery tried in the Huntsman was fully charged and so was a Fully charged 7.2v nihm .

Any ideas?

Yours in anticipation Bryan

[Dave MilbournParticipant @davemilbourn48782]

It does sound like a battery issue. Do the speed controller or the motor also have a minimum working voltage? Have you tried connecting your two 7.2v packs in series to give 14.4v? How does that work?

DM

[BRYAN ASTONParticipant @bryanaston57723]

Dave

Thanks for your reply, I will recharge the batteries tomorrow an see what happens . I refitted the original low max .voltage esc and the problem disappeared .

Watch this space, all will be resolved eventually.

Again thanks

[BRYAN ASTONParticipant @bryanaston57723]

Dave

recharged the 12v battery pack and the motor ran perfectly ,no problems, also connected two 7.2 packs in series, no problems, so it would seem that the dealer was correct and the battery was low, how I don't know

I don't know if I have asked you before but what is the discharge rate of a not connected fully charged c pack over two days?

Thank you for your help

Bryan

[Dave MilbournParticipant @davemilbourn48782]

Bryan

A little thought just occurred. If the ESC has a low-voltage cut-off then check that it's set correctly for a 10-cell NiMH pack. If it's set too high then your pack may be tripping it accidentally. There may also be a lazy cell in the pack which is dropping well below its nominal 1.2v under load. You can check that only by applying a digital voltmeter across each cell in turn with the pack running a load.

No-one said this was going to be easy, but I admire your resolve. I can think of at least one person who wouldn't have got past Hiccup #1.

Dave M

[Dave MilbournParticipant @davemilbourn48782]

Bryan

Didn't see your last post as it arrived about the same time as I hit the Send key on mine. On self-discharge of NiMH cells, see this from Wickipedia (which is about as succinct as I could find):

The self-discharge rate varies greatly with temperature, where lower storage temperature leads to slower discharge rate and longer battery life. The self-discharge is 5–20% on the first day and stabilizes around 0.5–4% per day at room temperature. But at 45 °C it is approximately three times as high^.

Also don't forget that a fully-charged NiMH cell peaks out at over 1.5v, so that 20% discharge value only brings it down to its nominal voltage of 1.2v where it will stay for 90% of its capacity before it goes into a steeper decline. The minimum voltage you should let any NiMH cell get to is 1.0v.

All of this assumes that all the cells in the pack are in good condition. If there's one rogue cell then it will screw up all those figures because the good cells will discharge into the bad one and flatten the pack a lot faster. More recent technology has resulted in low self-discharge cells like Sanyo Eneloop, which can retain 85% of their charge for a year.

From a practical point of view, for main power packs I would recommend a full charge at no more than the C rate on the evening before you go sailing. If you slow-charge at C/10 then you can leave the pack on charge almost indefinitely. The C rate is the battery's capacity less the H i.e. a 2500maH capacity pack has a C rate of 2500ma (or 2.5A).

Kevin – Please note that this applies to Nickel Metal Hydride cells only. NiCADs and LiPos have their own quirks!

Dave M

[harry smith 1Participant @harrysmith1]

Hi All

I use the same Dave charge rate for my Lipo batteries, but, with the balance lead connected as well.

I have had a battery come up on the charger as voltage too low.

The charger would not start charging.

I disconnected the balance lead and restarted the charger.

Run the charger for about 30 seconds, turned off the charger, reconnected the balance lead and it was all back to normal .

The problem was because I did not connect the low voltage when I used the battery!!!!

SENIOR'S MOMENT!!!!!!!!!

MY MICK STEAK!!!!!

Harry Smith

[BRYAN ASTONParticipant @bryanaston57723]

Dave

Thank you for the info on the batteries question, perhaps I should charge them and store them in the fridge, I don't think that she who must be obeyed would be very happy.

The Huntsman runs no problem in the garage / workshop wether or not it runs ok on the pond time will tell.

Fitted a spare brushless in my MTB tried it today on the lake ,I couldn't control it , it looped the loop,,literally ,some of superstructure fell off and eventually drifted to the bank, I am not going to try that again.

When I got home I took the brushless out and fitted a spare Johnston .700 series motor in the boat, I'll try that.

Onward and upward

Bryan

[BRYAN ASTONParticipant @bryanaston57723]

Dave

I am beginning to think brushless motors are more trouble than they are worth, the brushless setup in the Sea Commander has ran perfectly for weeks, it's performance is more than satisfactory, last Sunday at the pond/lake it suddenly stopped in the middle of the pond , after being pushed back to the side by a yacht !! nothing would get it running again ,changed the batteries , checked all joints , no joy.

I have never had any trouble with brushed motors, any old motor ,any handy speed controller,connect battery and away you go, no problem, this is progress ??

I have two battery powered vacuum cleaners in the house, obviously running on brushless motors on 15 v battery, no problems , turn them on they work perfectly, when the battery runs out just plug them in and recharge them , my point is why do I get problems in the boats, what the hell am I doing wrong

Regards

Bryan

[Dave MilbournParticipant @davemilbourn48782]

If I knew the answer I would pass it on, Bryan. I've been running them for two years and had no problems at all – nothing. Stopping suddenly can be down to a flat battery, failsafe triggering (lack of range), ESC deciding the current or temperature are too high as well as the obvious stuff like failing joints.

Can you try the ESC and radio with a different brushless motor, just to see if they operate it OK? If they do then the clear implication is that the motor itself has failed. My solution to any problem like this is to swap things around and see if I can isolate the problem down to one unit. I then swear violently at it in a Geordie accent – for some strange reason this often has the desired effect! If not then it makes me feel better!

At least these items are not as fearfully expensive as they might be were they to come through the usual manufacturer to wholesaler to exporter to importer to main agent to retailer chain. The Brexit vote will have an adverse effect on the prices though, because the Chinese insist on being paid in USD. £1 = $1.328 today. That's 15c down from January. We were warned…

DM

[BRYAN ASTONParticipant @bryanaston57723]

Greetings all

Would it be okay to use a 12v nihm battery to power a brushless esc that is rated at a max voltage of 10.8 volts or am I pushing my luck

Bryan

[Dave MilbournParticipant @davemilbourn48782]

"Okay" – No. Fully charged the voltage can be around 18v.

"Pushing my luck" – Yes. See above, unless the price is silly or you already have one that you're prepared to sacrifice.

My opinion only. Suit yourself.

Dave M

[BRYAN ASTONParticipant @bryanaston57723]

Greetings all

Simple question, does anyone know of a 60amp auto setup brushless esc , forwards and reverse, in other words plug and play? I am getting near to giving up on brushless motors, life is too short

Bryan

[BRYAN ASTONParticipant @bryanaston57723]

Greetings all

I omitted to say , and runs on over 14.4 volts,

Bryan

[harry smith 1Participant @harrysmith1]

Hi Bryan

What brand of auto ESC is it???

I can help with the Hobbyking ones, or see my setup in Sea Hornet 2015.

The only change I do is the cutoff voltage for 3S and 4S Lipo batteries.

Harry

[Paul FreshneyParticipant @paulfreshney24971]

Bryan

Re: 60 amp brushless esc.

Try Cornwall Models:

Hawk 60 amp brushless forwards and reverse esc and rated for LiPo 2 to 6 cells – £55.

They also do a 75 amp and 100 amp version.

I have had no problems whatsoever with this brand of brushless esc which are in 3 of my models.

They are not true 'plug & play' but can be easily set-up following the included instructions or using the optional programmer device.

Paul Freshney

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