Unknown motor power.

[Bill McCreadie]

I've just opened the kit and out comes the electric motor & the ESC. Nowhere in the limited paperwork that appears next is there any indication of the motor size or power all it says (on the motor) is VMAX Brushless. Va 2410-12.

 

The esc is as follows :- VMX 18. Current 18A Max. and a vague recommendation for a 3s Lipo 11.1V.

Given the above info what size of battery do I need??

 

Another question that bothers me a bit (I'm new to electric flight though have flown powered models for years) if I just plug the Lipo battery in to the ESC will the motor just start running? or will it just sit there until the Rx is turned on with the BEC plugged into the throttle slot. The more I write the more springs to mind !! Should the BEC be routed through a switch harness to power the Rx on and off.

 

I must stop now and go and lie down in a darkened room!!

Bill

[David Ashby - Moderator]

Hi Bill

 

First question - what model is this going in?

 

OK, well the motor is of the smaller size, around 200-watt I would guess although you won't know till you run it up with a watt meter to get the specific output reading and this in turn will vary according to prop size.

 

The battery connects to the ESC yes and the ESC is instructed by the receiver into which the lead from the ESC plugs (usually channel 3).

 

There's no need to route the ESC through a switch harness I would say based on the motor size and the likely model size we're talking about here but...back to you...what's the model?

 

 

[ken anderson.]

hello bill...please take care with you equipment that has you baffled.....if you arm the motor and aren't aware of the fact..at the least you'll get a 'nip' on the finger's and at the Worst a severe Cut.....req a visit to the local A and E...small ic motors stop...electric motors dont....

 

ken anderson ne...1.

[Bill McCreadie]

Sorry I should have said, the model is the Vmar P51 Mustang.

After a lot of hunting on the net I have found that the motor is 150 Watt.

 

Can I make sure I'm clear on switching the system on, all is plugged in and the receiver is live, will the motor start?or will nothing happen until I power up the Tx and it sends a signal to the throttle control?

 

The Rx is only accessible with the wing removed so I would have thought that a switch isolating the BEC would have been a good idea.

 

As I have said before I'm very new to electric flight and have never even seen a watt meter, besides until I know what power of battery to safely fit I couldn't run it up to measure the wattage.

 

One more thing (I bet everyone says that!) the prop supplied is a 10x4.7 peach coloured slow fly model and looks a bit wimpy for a Mustang. Is there an equivalent 3 or 4 blade prop and spinner which would make it look just a little more like the real thing??

Bill

[David Ashby - Moderator]

OK Bill, I know the model you mean. NIgel Hawes reviewed it in Sept 2009 in the mag so if you have a copy then that's worth a read.

 

Sounds like you have the power system designed for the model so use that initially. Fly it with the two-blader, a 3-4 blader will be less efficient although you could perhaps look at the GWS props once you've established what the model will do with the power system supplied. Changing props around really calls for the use of a watt meter to remove the guess work.

 

The motor shouldn't start when every thing is switched on but restrain the model and do it all outside just to be on the safe side. You don't need a switch to isolate the BEC with such a small model (and power system) like that. Nothing should happen until you advance the throttle.

 

Nigel used a 3S 1800mAh pack.

[Hamish]

Like IC Bill the first thing you switch on is the Tx and not as it would appear the Rx. Ensure the throttle is at zero. You should hear a number of beeps as the ESC goes through its initiating procedure. You should now be able to run motor with fingers well clear.

 

You really need a Watt meter to determine what power is being used in order you do not burnout/destroy motor, ESC and battery

 

Edited By Hamish on 14/04/2011 18:11:28

[Bill McCreadie]

Thank you for your patience. There is just one more thing(see- I told you!) The battery pack quoted is a 3S 1800mAh isn't there another number and letter needed ie 20C or 40C or some such??

Bill.

[Bill McCreadie]

And another thing (once more!!) As soon as the BEC is plugged into the Rx, which has to happen before the wing goes on, means that the Rx is always on before the Tx -- doesn't it??

Mind you I can always switch on the Tx and throttle down before upending the model, plugging in the Rx and fitting the wing.

I'll need to go back to my darkend room!!

Bill.

[Hamish]

If you have 20C it means your 1800mA battery will give 36Amps which should be OK for your motor. 40C would mean 72Amps.

 

For safety reasons the Tx should always be switched on first, irrespective of your wing fitting.

[Bob Cotsford]

You switch the receiver on by plugging the battery into the esc lead, the esc-receiver lead stays plugged in permanently.

So switch on trannie and check the throttle is low, then plug in the flight battery to the esc which powers up the Rx, at this point the model is 'live'

[Bill McCreadie]

Aren't there caveats concerning battery power in Amps not being too much for the ESC? Mine says 18A max so what should the battery be?

 

There is no flight battery as the ESC has a BEC connection so that means that the Rx is on all the time unless the Lipo is removed for charging, or the wing removed and the BEC unplugged. (Unless it goes through a switch harness.)

I'm sorry to appear to go on and on but please bear with me -- I'll get it eventually!

Bill.

[Hamish]

The size of the battery does not matter provided it is bigger than the current required, The ESC must be greater than the current required by the motor. The larger the capacity of the battery means the longer you can fly, however there is a weight penalty.

 

Unplugging the BEC from the Rx only removes power from the Rx and the ESC/BEC will still draw power. At the end of a flight it is normal practise to disconnect the Lipo.

 

Lipos should always be removed from the model when being charged. It is possible for a Lipo to go on fire and then if in the model you would have a serious problem.

[David Ashby - Moderator]

Well the guideline is say 20-30% safety margin Bill. So if you're pulling say 40 amps then you'll fit a 60amp ESC. There are exceptions though and many RTF models and power system packages leave little headroom if any.

 

If your ESC is 18 amps and say you have a 20c 1800mAg 3S li-po then the li-po will be good for around 36amps. Most li-pos are 20c+ these days so that won't be your worry. It's more likely to be the ESC but it's all guesswork unless you put a wattmeter across the system to see what's really happening.

 

I sincerely hope the RX is on all the time when it's in the air but you'll only put the li-po in the model and connect it up when you fly so what's the worry?

 

Never store li-pos in models, always remove them after every flight. The moment you disconnect the battery (li-po) the model won't be live which is what you want. Just leave the lead that goes from the ESC to the RX in place all the time, don't fiddle with it or remove it. Just put the battery in the model, connect it up to power up the system and then unplug it and remove it after every flight.

 

One thing you can do when setting up a model is to either ....

 

1. remove the prop so you can safely adjust servos etc. without the risk of the prop turning...or......

 

2. Use a normal RX batt temporarily while setting up the model (adjusting rates etc.)

 

 

 

[Bill McCreadie]

OK then given all the info in my original post concerning motor power (150watts) the ESC 18A max and a suggested 3s 11.1V Lipo can you suggest which battery power I need to handle the motor current and not overpower the ESC. or am I just proving that I still don't really get it?

Bill

[Hamish]

As David has said an 1800mA Lipo was used in the review.

 

The battery will not overpower the ESC provided it is a 3S or 11.1 volts battery. The greater the capacity of the battery, say 2300mA, means you can fly longer but it is heavier and bigger.

[Bill McCreadie]

I think its starting to dawn at last except for one thing(and again!!) Lipo batteries are listed as e.g. '3s 1800mAh 11.1V 20C' or some other C number. Does this not matter when attached to an 18amp ESC.

Bill

Edited By Bill McCreadie on 14/04/2011 21:17:52

[Pete B]

A 3s 1800 Mah or 2200 Mah, rated at 20C or 25C, will be more than adequate, Bill.

 

The propellor will dictate the power needed by the system, so stay with the 10 x 4.5 or a 10 x 5. If you put a 3-blade, or larger 2-blade on, it will require more power to turn it.

 

Simplifying the figures, you have an 11V battery to operate a 150W motor. If you divide 150W/11V, you get 13.6Amps. That means the 18A ESC supplied is well within limits.

 

Now, let's say the battery is 2000Mah, which is 2.0 Ah. 1C is 2A, so a 20C-rated 2A battery can discharge at 20 x 2, which is 40A. As above, provided you keep the prop to about the same, you'll be drawing about 13A.

 

There is no point in spending big money on 30 or 40C rated batteries for this sort of usage. I run some of my largest models on 20C rated batteries, and provided the current draw is within their C rating, there is no problem.

 

Hope this helps,

 

Pete

Edited By Pete B on 14/04/2011 21:20:23

[Bill McCreadie]

Thank you Pete. An island of clarity in my fogbound brain.

Bill

[Pete B]

By way of example, GC offer (and have in stock!) this 1800 Li-Po in their economy range. It seems to be getting good reports. If you want to spend a little more, they also have this 2300 Li-Po, which may be more useful for later models.

 

Don't worry about the 5C, that just means that it can be charged more quickly than the other pack. If you want that explained further, just ask

 

Pete

 

 

 

[Bill McCreadie]

Thanks Pete B very useful info. Just one more thing (!!!) My nice new battery arrives I unpack it and admire its sleek good looks then what do I do?

Is it charged? Is there a bit of paper with hints and tips on how to look after it? Not likely!! So how do you recommend I treat my new arrival??

Bill.

[Hamish]

Hopefully Bill you will have a charger. I use this one GT Power and in addtion a 12 volt supply, which can be a car battery. I charge my new lipos for the first few charges at 1C, which would be 1.8A or less for a 1800mA Lipo. You will also need to ensure the battery has the same connection as your ESC and charger. I have standardised on deans type connector but there are others.

 

Edit 

 

I have used the 1800   Loong Max and have been delighted with there performance as they appear to go on forever.  I consider I have had the equivalent of at least three galllons of glow fuel out of them and they still go on and on.

Edited By Hamish on 14/04/2011 22:35:58

[birdy]

Hi Bill,

 

First thing you should do is check that there is no postal damage (eg dents in the battery or it is "puffed up"). After that I would check that it is above the minimum safe voltage (thats 9 volts for a 3 cell lipo) - this could be done with something like this , or if the main power lead has a compatible connector then most chargers will tell you.

Often however you will find that the battery has the wrong connector - I use deans connectors, but lots of people like 4mm bullet connectors or even "ec3" connectors. Sometimes batteries come with no connectors at all. In this case you need to solder on the connectors you want to use, but make sure that you don't short the battery whilst doing this - strip the insulation from one wire, solder it and insulate it before stripping the insulation from the next.

After that I tend to balance charge it (although you should really do this every time you charge you lipos anyway). Once thats done, I put it in a safe place - away from small metal objects and leave it there till I need it. Incidentally it is better to store lipos in a place at room temperature - they don't like getting to cold.

[Bill McCreadie]

Hi Birdy, by balance charge do you mean plug the battery into the charger using the small white plug?

Bill

[birdy]

Your charger should have a main power lead and a place for the small white plug. You should be plugging both leads in if you can. So yes, small white plug.

[Bill McCreadie]

Gentlemen.

Thank you for enlightening my darkness. I think I've got it now.

My new battery arrived this morning. Now I have to start soldering Deans plugs to everything!! Wish me luck.

Bill.