Motor shut down

[barryorbik]

One thing I forgot to mention in my last post were the power connectors need to be suitably rated to carry the increased current when using a lower cell count, plus the C rating of the pack will need to be higher too to be able to provide the required power.

Ian, I thought it was only a typo as the rest made sense.

Barry

[coolice]

I know I'm right actually. Many on line motor specifications showing the same thing (example quoted below). The reason you use less amps is that (with nothing else changed) the RPM on 4S will be 2/3rd of the RPM on 6S. Power required to drive a rotor is to the cube of RPM. 2/3rd ^3 = 0.3.. So this means that to spin a rotor at '4S RPM' takes only approx 30% of the power of '6S RPM' (which is why low headspeed helis fly much longer). Yes, you need more pitch to hover but I'm assuming here the total maximum pitch is unchanged (i said it's assumed nothing else changes when you swap batteries).

Here's a Scorpion motor data chart. If you check the current draw with the same prop current goes UP when you increase voltage. For example when fitted with an APC 10x5E prop powered with a 4S (14.8V) battery it puls 33.48A. The exact same motor and exact same prop when powered with a 5S battery (18.8V) pulls 44.57A.. these are not my figures, it's are Scorpions official data and the same trend goes for all of their motor testing and also every other manufacturer who has published data. A heli is no different, a heli rotor is basically just a large propeller.

I'd love to debate further but if you want to please start a new thread because I dont want to de-rail this one...

FWIW the current rating of the BEC will be higher at lower input voltage (not lower as mentioned previously). This is because the at lower input voltage the BEC has less work to do in order to reduce voltage to your output voltage value (i.e. input and output are closer). You can see this trend very clearly in Castles published data here: CC BEC PRO 20A MAX OUTPUT, 12S (50.4 VOLTS) MAX INPUT SWITCHING REGULATOR

For example of the Castle BEC Pro:

2S-4S: 15A
5S-6S: 13A
7S-8S: 11A
9S-10S: 9A
11S-12S: 8A

Morning.

Wow, is it April fools day already :-)

Ok, so the new ploy is to use static thrust tests of a fixed pitch propeller and compare them to the flight loads of a variable pitch rotor blade setup (propeller again to keep it simple) that not only provides a helicopters lift but also pitches and de-pitches with cyclic inputs, thus putting even more load on the electric motor driving the blades (propeller)?!

Granted the chart makes for good reading, but as with helicopter electronic choice to work effectively for the given application, if you look at the data you will see "right sized", "can't be used", "can be used with limited throttle" and "too small for good performance".
Looking at the various values and going by experience in fixed wing to, you choose the right diameter prop and pitch to suit your motor/ESC combination to get the best performance, without over-stressing the motor/ESC.
Much like the gear ratios in our helicopters is matched to the motor Kv rating, battery cell count and choosen ESC rating, to work as efficiently as possible.

In fact, going back over your response, this line has clearly highlighted the above need to choose your power system components correctly;

"For example when fitted with an APC 10x5E prop powered with a 4S (14.8V) battery it puls 33.48A. The exact same motor and exact same prop when powered with a 5S battery (18.8V) pulls 44.57A.. "

You've just highlighted the need to match components, as you just wouldn't run a 5s pack on the same setup as what works well on a 4s pack. Well you might, but it won't last long, as the conditions have changed and so does the amp draw as you've pointed out.
So you would change the setup to keep maximum thrust, but with as low an amp draw as possible. So this brings us back to your helicopters choice of motor Kv, combined with input power source voltage and gear ratio choice once more. So as t okeeps things cool and running efficiently.

Basically you can't really compare a fixed wing propeller to a helicopters rotor blades/head, it just doesn't work the same and/or give the same responses. It will give you an indication yes, as the chart does which you've linked to, but just highlights the to need to match each component in the power system chain to one another.

Low head speed heli's do not fly longer due to the lower amp draw, as we all know if pushed hard they will pull more amps.
No, the reason they fly longer is that they are lighter, thus the disk loading is reduced which in turn means less amp draw to fly casually as the model is more floaty. However, do a full pitch climb out on this type of machine running a 6s and then fit a 12s pack and do the same and you will see a sharp increase in amp draw when using 6s.
Why do you think 550's fly with 100amp+ ESC's and 700's can get away with 120amps+? simple logic here. I'll admit once again 6s to 12s is a much bigger change, but it paints a picture.

CC BEC PRO, good point but wrong I think. Someone more indepth with their electronic design would be able to clarify this better, but I'm 99% confident I can explain the figures.
I think you'll find that the BEC actually has to work harder reducing the higher input current, say 10S (40.2 volts) down to a more radio friendly <8 volts. Thus it's capability to do this 30+ volt drop compromises the BEC's output capability due to heat build up, it will have to switch a lot faster to reduce a higher voltage than that of a lower one going into it.

You can't get away from the simple maths, no matter how much you try to, higher voltage in means greater efficiency overall and in our helicopters any advantage is a handy thing to have.

Please do start another topic if you feel you need to, it will be good banter once more. But you've tried to prove a theory in a topic that is discussing amp draw and misleadings need to be addressed I feel, as I think you might be over-looking the basic principles of how a helicopter works.

Ian Contessa

[coolice]

One thing I forgot to mention in my last post were the power connectors need to be suitably rated to carry the increased current when using a lower cell count, plus the C rating of the pack will need to be higher too to be able to provide the required power.

Ian, I thought it was only a typo as the rest made sense.

Barry

Hey Barry.

Yes, thanks mate. In the need to be accurate and on the small screen, it's easy to make a mistake. My last post has been amended 5 times and I am on my PC.

It's a good topic and perhaps I am derailing the main topic a bit, but it will make good reading for the new blood coming in.

Ian

[atomiccomp]

This an an excellent thread, entertaining and informative

Keep up the good work guys.

[Grumpy]

I dont want to get into a pi$$ing contest but lets just say that if over current of the ESC is the cause then the ESC would get very hot. So go fly the heli and check the ESC after flight, if it's so hot that it's uncomfortable to touch then ESC over current probably is an issue.. If not then it's almost certainly not.


PS.. Ian, the figures I presented for the BEC rating were not my figures, they were Castle Creations.. I think they should know what they are talking about better than you or I.. no?

[kenny d]

( I dont want to get into a pi$$ing contest )

If it’s a pi$$ing contest then I might have a chance of winning this one lol

[coolice]

PS.. Ian, the figures I presented for the BEC rating were not my figures, they were Castle Creations.. I think they should know what they are talking about better than you or I.. no?

Afternoon.

Please don't misunderstand me, I am not debating Castles Creations knowledge at all. As like you say, the values are there for all to read following their extensive testing of various fixed pitch aeroplane propellers. The latter provided to help their customers choose the right motor/ESC/prop combination, so they have no problems in their models during use.

However, what I am questioning is your linking between Castles Creations motor/ESC/prop testing data that is for a fixed wing setup, as being applicable to the environment which is that of an RC Helicopter. The latter as we know, behaves much more differently than a fixed wing models propeller, due to the much greater role a rotor head/disk plays in a helicopters flight overall. Specifically providing both lift and direction control.

Also, I base my responses on actual real world experiences of helicopters which I may have experienced in my many years of flying. Combined with perhaps what I have read on forums and hear from others in conversations with them.

I'm not interested in pi$$ing contests, but what I do still strive for in my responses within forum topics, is clear and accurate advice to provide the best help to those asking for it.
I don't do this to win any contest, I'm here for the passion I have for the hobby still and for what I feel I can give back to keep it moving forward by helping others based on what I have learnt and used to great effect over the years.

Ian Contessa

[Grumpy]

Afternoon.

Please don't misunderstand me, I am not debating Castles Creations knowledge at all. As like you say, the values are there for all to read following their extensive testing of various fixed pitch aeroplane propellers. The latter provided to help their customers choose the right motor/ESC/prop combination, so they have no problems in their models during use.

I was referring to the BEC figures, props etc are irrelevant to a BEC. The Castle data clearly show that a BEC can deliver higher currents when operated on a low voltage supply vs. a high voltage supply. Here's the link again: http://www.castlecreations.com/en/cc...ro-010-0004-01

This data means that failure of the BEC due to using a 4S rather than 6S battery is not valid, if anything the BEC will perform better with 4S supply than it does with 6S supply.

[Mike Sanders]

If it’s a pi$$ing contest then I might have a chance of winning this one lol

No chance. Wait until you get to my age. All activity has to be planned around the need for a wee wee.

[Grumpy]

No chance. Wait until you get to my age. All activity has to be planned around the need for a wee wee.

I'm getting that way myself. At least being a man 'the world is your toilet'

[Grumpy]

Ian,

here's a video by Chris Reibert you might want to consider on the subject of 6S vs 12 current draw. In the video Chris flies his Logo 700 on a single 6S 5000mAh battery rather than his usual 12S 5000mAh setup. If current draw was higher then obviously his flights would be shorter but as Chris explains in the video this isn't what happens. In fact his flights on a single 6S 5000mAh are TWICE AS LONG as his flights on 12S 5000mAh. Obviously if the battery mAh is the same then to fly twice as long the current must be half as much, that's simple maths.

(PS.... sure the 700-800g saved will help with flight time but it doesnt explain why it would be doubled)

here we go:

Of course the downside is you end up WAY down on power.

[coolice]

I was referring to the BEC figures, props etc are irrelevant to a BEC. The Castle data clearly show that a BEC can deliver higher currents when operated on a low voltage supply vs. a high voltage supply. Here's the link again: CC BEC PRO 20A MAX OUTPUT, 12S (50.4 VOLTS) MAX INPUT SWITCHING REGULATOR

This data means that failure of the BEC due to using a 4S rather than 6S battery is not valid, if anything the BEC will perform better with 4S supply than it does with 6S supply.

Hey.

Ah sorry, mistakenly thought about the wrong information.

I may eat humble pie here but, we've established the CC BEC PRO's current capability drops with higher input voltages.
This is due to the higher voltage going in requiring the switching circuit to work harder, dropping the BEC output to servo friendly values, thus it gives out less amps.
Googling this throws up lots of evidence that switch mode BEC's do this.
So from my side, I'm half right and half wrong on what causes it.

Now onto the ESC in this topic, does it get effected by a change from 6s to 4's cell count?
Seems most ESC's have a window in which the current capability stays the same, but changes above a certain point. The CC BEC PRO does by a full 2 amps, so does the Align also, or as it is supplied to work in a 6s environment does it not?

Hmm, I'm still on the fence thinking it's still input voltage related. But can't tell without testing to prove in which area of the ESC the blame may lay for the problem.

Ian Contessa

[Mike Sanders]

a BEC can deliver higher currents when operated on a low voltage supply vs. a high voltage supply.

That may be right but when you look at what is required, watts, then, usually, it seems to me, more will be produced by the higher voltage set up,even if the current may be lower.

[coolice]

Ian,

here's a video by Chris Reibert you might want to consider on the subject of 6S vs 12 current draw. In the video Chris flies his Logo 700 on a single 6S 5000mAh battery rather than his usual 12S 5000mAh setup. If current draw was higher then obviously his flights would be shorter but as Chris explains in the video this isn't what happens. In fact his flights on a single 6S 5000mAh are TWICE AS LONG as his flights on 12S 5000mAh. Obviously if the battery mAh is the same then to fly twice as long the current must be half as much, that's simple maths.

(PS.... sure the 700-800g saved will help with flight time but it doesnt explain why it would be doubled)

here we go:

Of course the downside is you end up WAY down on power.

Hey.

And I thought we were getting somewhere.

Good video, but he answers the reason why for you "collective management".
He also goes on to say for sport flying or just pottering around then the 6s is great.
He's doing a lot of forward flight in that video to, so you gain even more benefit from transational lift as the rotor disk acts as a lifting wing. Again conserving power.

Low head speed combined with the lower weight, more forward flight and less spirited flying = longer flight time.
Try to fly hard 3D like you can with a 12s pack, but on 6S as in the video and current draw will go up.

It's all relative, that model on 6S can't be thrown about or mistreated like it can when powered by 12s. So you adjust your flight style to suit thus conserve energy as a result.

If I don't fly 3D with my 700E or 550E, but fly F3C style manoeuvres, I can get more flight time. If I do more tic-toc practice in a flight I use up more power and my timer needs reducing, as I've been demanding more power in the pitch pumping.
My car is the same, if I don't keep it on boost I use less fuel and travel further before I have to fill up.

I can hold my hands up over the BEC debate, but not on the 6s Vs 12 flight time comparison, as you cannot fly exactly the same and adjust your flight style to suit.

Ian Contessa

[coolice]

That may be right but when you look at what is required, watts, then, usually, it seems to me, more will be produced by the higher voltage set up,even if the current may be lower.

Hey Buddy.

Sadly on the BEC's it turned out true of the switch mode type which mostly used now and I hold my hands up to Grumpy for bringing that to my attention.

This goes against what you think, but is due to how the higher voltage is reduced down to what is needed I think. Thus compromising the overall capabilities.

I was trying to find out the true specs of the Scott Gray Reactor HVX as it was a beast and could use 3s to output 9 volts to the servos. So I was keen to see if there was mention of the amp differences when running from a 2s to 3s pack, but can't find any tech specs.

Another consideration is the BEC's output voltage and it's effects on the system. Give a servo 5 volts and it'll desire more amps, but give its 6 volts and the amps it needs to do the same task will reduce.

Ian