Motor/ESC matching

[Tim Kearsley]

Hi all,

I hope this isn't TOO daft a question - I'm still fairly raw in this exciting hobby!

I'm putting together a power train for a new EP model and have a general question about motors and ESCs.  Is it generally permissible to "mix and match" motors and ESCs from different manufacturers as long as the ESC is rated highly enough in terms of current capacity and (obviously) that a brushless motor is used with a brushless ESC?  I suppose really my question boils down to whether any ESC can be used with a given motor as long as current requirements are met?

Specifically, I've just ordered an EnErG C35-20 motor and SP50A ESC, but now find that the SP50A is fairly hard to come by at the moment and wondering what I could use as a replacement.

Thanks,

Tim.

[Tim Mackey]

Remember,   There are no daft questions...but the occasional daft answer appears

Basically YES. You can mix and match as you suggest, as a general guide, the best bet is to go for an ESC which  has a higher Amp rating than the maximum you are likely to use, which then provides a safety margin. The only downside is a small weight increase over its smaller brother......

For "valuable" or larger models, I tend to use the better brands such as JETI and for the foamie fun fly type stuff... most of the cheapos are fine these days.

BRC hobbies do some excellent value ESCs, as, of course, do other retailers

[Erfolg]

I agree with Timbo (you just have to), the controller needs to be at least the same rating as the motor max. As Timbo has said a (safety) margin is very desirable. I have seen the motors cut out (by the protection curcuit) where this general rule has not been followed, there has often been a lot of sratching of heads until the cause has been identified.

Unlike Timbo, my controllers are budget, using Robot birds "Budget" 3 off various ampages, "Pro-25", E-Sky and Tornado (overlander). For powered gliders, sport and scale these are fine. For 3D there lack of throttle sensativity (for hovering) etc. would be noticable. Tornado has one draw back, it really needs the Lipo to be fully charged each time you connect the battery, as it works out what has been connected.

Although you have not asked, I have now observed a large number of motors from budget to expensive. In my opinion they all seem to work well, as long as you do not push them to hard, expensive motors seem to be more tolerant (a more conservative rating perhaps). I have seen all types ruined by pushing realy hard, cooling realy becomes necessary under these circumstances. I use Tornado, HET, E-Max, Xtra, to date all work fine.

Erfolg 

[Tim Mackey]

Actually a very great percentage of ESCs have an auto detect function of the number and type of cells, and it is prudent to always assume this is so, ALL of my ESCs do, including the JETI's.

If a partially charged /discharged  pack is connected , and subsequently  identified incorrectly, the LVC  will operate incorrectly, and very possibly allow the pack to discharge below its safe minimum ( LiPos ). Having said that...it is bad practice to fly to LVC anyway, and one should stop flying as soon as a drop off in power is noticed. Then assuming your tr has one, set your countdown timer accordingly, and as soon as the timer beeps at you, LAND. Your packs will thank you for it with a longer life.

[Tim Kearsley]

Thank you very much chaps for answering my question.  I shall go ahead and purchase a suitable ESC then to go with the EnErG motor I've just bought.  I think a brushless controller rated at 50A should do the trick.

Many thanks again.

Cheers,

Tim.

[Tim Mackey]

Do you actually know how much current the motor AND PROP USED will be  pulling?

Unlike IC setups, electric power-trains are very critical about prop selection, as it this which pretty much decides entirely your current used.  

[Tim Kearsley]

Timbo, it's a good question.  The answer is no, I don't.  I'm basing my purchasing on the review of the Seagull Extra 300 which appeared in the last issue of RCM&E.  The reviewer recommended the EnErG C35-20 motor and the SP50A ESC.  I'm basing the spec. of a suitable ESC on the SP50A therefore.  I will use a similar prop as also recommended, which from memory was an 11 X 7.

As I'm still learning this game I'm playing very safe and going (literally) by the book at the moment!

Cheers,

Tim.

[Tim Mackey]

Although a little expensive, ( but getting more reasonable ) a "whattmeter" or similar cheaper version is a good investment for any flyer who is going to be using electric power in anything. This gives a real time accurate display of all 3 parameters Volts, Amps and Watts, ( a sum of Amps times Volts )

This is THE way to ensure your chosen prop motor battery combo is within limits..... 

[Erfolg]

A watt meter is essential.

Unless you know from the supporting documents, what the motor will draw with a specific propeller, measuring is not prudency, it is a necessity. As stated by Timbo

I have found that that there are differences from figures quoted for a one peice propeller and folderers etc. Sometimes suprisingly. Seems to depend not only on pitch and diameter, but also on the mass (radius of gyration etc).

I think the difference between the controllers that I generally purchase (and Timbos, I purchase mainly budget) is that you set the controller to the battery type and voltage, as part of the set up. If you then connect up something else, they all just sit there beeping. Failsafe.

The Tornado I have is different, you set nothing, it works out everything for itself. But there is a warning with the controller, the battery must be fully charged, or it may become confused and set itself incorrectly. "Plug and Play"

The only two expensive controllers I have are Kontronics. They are all right. For what I do, no better than the budgets.  

Regards

Erfolg

[Tom Mann]

Good thread y'all, thanks.

 I was sold a complete powertrain for my Century Swift electric, and I trust these guys.  However I noticed that the ESC they gave me is rated:

- higher than the battery  'continuous' rating in Amps

- lower than the battery 'max bursts' rating in amps

- also lower than the middle rating something like 'sustained' rating in Amps

Why do I not need an ESC that is rated higher than the max bursts and sustained?

Also what is with the '25C' rating on the battery alongside good old amps.  What does the C stand for??

 yours stupidly

tom

[Tim Kearsley]

Hi Tom,

The "C" rating is in essence a multiplier to give you a measure of the current that the battery can safely supply.  For example, if the battery is a 2000 mAh (milliAmp-hour), 20C rating, then it can safely supply 40 Amps (2 X 20).  If it was 25C rated then it could supply 50A.

Hope that helps.

Cheers,

Tim.

[Tim Mackey]

Tim ( great name by the way ) is spot on with his simple explanation of C rate.

The reason you were sold an ESC with the rating it has, was PROBABLY because as the shop knew what the likely current draw was on that particular setup, they decided that the ESC was within those tolerances, and probably helped tp get the package in budget as it were. Nothing wrong with that at all, but you should not try it in another setup without ensuring its capacity is up to it, and that really requires a wattmeter / clamp on ammeter. 

I think you had a chopper ( pauses to be slightly sick ) and therefore are limited as to changes that may cause problems, but if it were a proper flying machine, like say, a fixed wing aeroplane , then simply putting a prop on which was one size bigger could have disastrous consequences on the ESC

[Tom Mann]

Thanks Tims, that was spot on and, timbo, nearly funny .  Don't worry yourself about the size of my chopper too much... I only use it (and the 2 indoor choppers) to sate my stick twiddling needs given that my nearest F/W club is not near and requires knife-edge s-bends on finals.  But hey that's another rant.  I mean who needs flying fields anyway eh?  Much better to buy lots of models and spend quality time jut LOOKING at them.  grr.

 anyhoo, I think Timbo's final point about pitch change  is key here.  In the hover I'll be at similar pitch most of the time.  The only time I'd kick the amps up (if I've understood this and other reading) is if it was booted skwards on coarse pitch, and even then it would only be a short burst before the thing went out of sight.  All the same the ESC might cut out on the peak?  I must read the destructions, presumably the thing will say what peak, and peak duration it will put up with b4 throwing toys out of the pram (must practise that autorotate).

 I guess an analogy would be a variable pitch prop but few F/W modellers get that clever haha.

tom (so nearly in the 'tim' electric club, just one vowel)

[Tim Mackey]

LOL. Your right about the short burst of demand on the ESC in a high pitch fast ascent, but having said that, the shop, if they had done their homework right should have accounted for the max likely current draw. I imagine that you ESC is a dedicated chopper version without LVC feature, so it is unlikely to be the battery giving up the fight.

[Tom Mann]

OK LVC is low voltage cutoff.  I take it that is different to an over-current cuttoff (which may be 'uncontrolled' I guess as in it melts...) or maybe it is the same (vague recollection of volts and amps being inversely proportional)?

 Ref dedicated ESC, I don't think it is.  I'm running on an aux receiver pack, but still I would still like a LVC to protect the expensive lipo.  Actually scrub that comment:  £heli > £lipo!!!  Also was concerned that the ESC destructions told me to 'cut a wire' to disable BEC.  Sounds a bit severe....  Shirley there are non-BEC dedicated ESCs?

 I'm in the shop tonight, and equipped with this info I will be able to have a grown up conversation!  Thanks again Timbo.

 As you might have realised I'll keep asking things till you get bored of answering!

Ref Wattmeter... if it involves me getting up close and personal with 1m diameter of main rotor @ 2500RPM , I'll probably give it a miss.  Do you know of a heli-specific solution?  I can always stick this in the heli forum I suppose...I know how you feel about these technological marvels (sometimes I spend 10mins of quality time looking at swashplate linkage go up and down.  It is a thing of beauty.)

[Tim Mackey]

LOL. Yes I know what you mean about the "thing of beauty" comment - I was being slightly tongue in cheek about choppers - I do finf them fascinating contraptions.

Anyway.... the Qs.

No LVC is NOT the same as current overload cutoff. LVC monitors the pack VOLTAGE, which is inherently linked to current yes ( Ohms law - V=IXR ) and is designed to cut power to the motor if the voltage drops too low - this is soley to protect the battery, and stiop it getting so low as to either /both damage the battery or be incapable of supplying enough juice to the receiver and servos at all.... A VERY BAD THING

Now... with a chopper,sudden and complete cutoff of the votge to the motor is going to be pretty spectacular, ( except of course in "controlled" autorotaion manouveres) and for this reason ESCs designed for choppers ususally do not have an LVC feature. Many people confuse the BEC and the LVC and they are a bit like Paul Mc and Heather Mills -

They have NO RELATIONSHIP AT ALL !

The BEC merely taps off the main battery to supply the radio gear, and if using a seperate pack for this, then YES, you should snip off the RED wire from the ESC to receiver lead

( perhaps better to just remove the pin from  plug in case you want it back one day )

You MUST however leave the white and black / brown wires connected in order for the receiver to receive the throttle command signals from the ESC.  HTH

Not sure about heli specific whattmeters, best post in the eggbeater section

[Jacques]

try the Bantam Heli checkmaster: wattmeter, servo tester and rev counter all in one. J.