ESC upgrade

[doctormike]

I am not really clear on what happens with replacing an ESC with a higher amp ESC, while using the same size battery. Does it give more power with less time? Would someone enlighten me, please? Doc

[fhhuber]

All else being equal... just upgrading the ESC will have no noticeable effect.

Rare that all else is equal unless you are replacing with an ESC from the same series with the same firmware. But even with that, there may not be enough difference to measure.

Castle recently had a firmware upgrade for the Thunderbird series that has the potential to make a difference in some applications...

[OV10]

I am not really clear on what happens with replacing an ESC with a higher amp ESC, while using the same size battery. Does it give more power with less time? Would someone enlighten me, please? Doc

Hello Doc,
There are basically three reason for upgrading the ESC to a higher amperage.
If you change out a motor to one that has higher amp demands like say bumping up the Kv's when used with the existing battery S(voltage) rating or you bump up the battery S rating with the existing motor(that is if it is rated for such) or a combination of the both of these. The third reason is changes in prop diameter and pitch. Anytime that changes are done to the stock power system it is a very prudent practice to measure what the wattage demands are on the modified system. Too many pilots out there mess around doing this with out really confirming what they have done to the electrical sciences and then are baffled why their bird burned up because of an inadequate ESC for the changes they did. A $35 power meter is an inexpensive investment to this hobby. This is a tool in my arsenal that is used all the time.
http://www.motionrc.com/gt-power-130...ower-analyzer/

Best regards,

[doctormike]

Thanks, guys! Doc

[Konrad]

Since it has been mentioned I'll try to show the relationship of power to the propeller’s variables.
Static Power in simple terms is: P= K x P x D(4th) x RPM(3rd)

“K" is a constant that address things like air density, prop shape and airfoil. For our toys it can vary from about 1.11 for APC props to 1.31 for props with blades that look like Master Airscrew or Top Flite. For thin carbon blades 1.18 works well.

But what I want you to notice is that the ‘Pitch' of the prop is linear and has least effect on the power absorption. ‘ RPM' is a cubic function, so small changes in RPM has a huge impact on power. This is why the ‘kv’ of a motor has a huge effect on the performance. Then there is the ‘Diameter’, its impact on power is to the fourth power.

I can’t stress this enough. If changing any component in a power system you need an amp meter!

Now to the question of changing only the ESC to one rated at a higher value. One needs to think of the whole power system as a voltage divider network.
https://en.wikipedia.org/wiki/Voltage_divider

The total resistance of the power circuit controls the current draw. This current times the voltage drop across the motor defines the power available to the motor/prop.

Anything you can do to lower the resistance of the power circuit will result in more current being allowed to flow. This is why we use as short a set of wires as practical, use high quality connectors, and high ‘C’ rated batteries. All these things lowers the resistance in the power circuit. This has the dual benefit of allowing more current to flow and allows more voltage to reach the motor. More voltage and more current equals more power.

When looking at your power system think of the total resistance as two components the motor is one and all the other resistant sources as the other. The total voltage will drop across these two resistance sources in direct proportion to their resistance value.

To answer the question of what impact changing the ESC will make, the answer depends. With motors that have a high internal resistance (low kv) the effect at the motor and in fact the whole system will be negligible.

But if using a low resistant (high kv) motor just about any change in the resistance of the whole power circuit will have a noticeable effect.

To help one get a visceral understanding of this I recommend that one play with one of the emulators, like E-Calc. Notice how the resistance changes as you swap out components.
http://www.castlecreations.com/suppo...alculator.html

For a good understanding of how the power systems in our toys react I like to recommend Robert J. Boucher’s little pamphlet “The Electric Motor Handbook” . Bob holds patent’s on electric flight. He also was the founder of Astro Flight inc.

The short answer is yes upgrading the ESC will result in more power, this is assuming the resistance of the ESC is lowered, and in many applications the effect is noticeable. For example in EF-1 racing the rules say to use a 60 amp ESC minimum. Most of us are using 80 to 120 amp ESC as there is a noticeable improvement in the power to the prop. The reason we all don’t use the 120 amp esc is that they are heavier and as a result have a drag penalty. So as with everything there has to be a balance reached. Does the added power over come the added drag. The guy that figures that out is usually found on the winners podium!

As to run time if using the same amount of power the run times will actually increase as less energy is lost to heat in those other resistant loads other than the motor. But in practice as you probably wont pull back the power to the same level as the old ESC the run times will go down, but your power went up.

I really wish MotionRC would publish the engineering spec’s of the products they sell. Data like this is very helpful in keeping guys from burning up equipment.
http://www.castlecreations.com/products/phoenix-45.html
http://www.neumotors.com/NeuMotors/FAI_Motors.html

All the best,
Konrad

[doctormike]

Thanks, Konrad! I am sure there was a noticable improvement in speed when I upgraded the ESC in my E-Flite p-51. One of the club guys insisted it would not improve speed or power, that the increase in speed was just wishful thinking! Doc

[Konrad]

As you have witnessed it is very real!

Now you can direct him as to the whys. More voltage is reaching the motor as shown by the voltage divider. And as voltage defines the rpm on an electric motor, that means that there is a higher pitch speed and more power. Now assuming that there is enough thrust (AT SPEED) this pitch speed will result in the aircraft going faster.

Please note I said "at speed" as 'static thrust' really is next to worthless in our application as we have to fly at some velocity per the lift equation.

A problem with a lot of "Club guys" is that they think that the battery voltage is what reaches the motor. In a perfect world that would be true. But reality has a nasty habit of raising its ugly head.

Isn't math just wonderful!

All the best,
Konrad

[Grossman56]

Hey Konrad, great information! I wonder if you ever considered starting a thread focusing on the technical details as I for one have found it a challenge to understand.
I for one would like to see that and it would be great to have a thread where it was all together as regards the ESC/prop/and motor.

Good on you Buddy!

Grossman56

[fhhuber]

There's even more ...

Dynam Me-262. OEM ESCs (60 amp 6S rated), 1100 watts

Replace with old firmware version Castle Thunderbird 54 ESCs (54 amp 3S / 15 v rated... actually tested and they are fine on 4S)... 1200 watts
Upgrade to the new firmware... 1400 watts (on a very tired LiPo).

Just having more efficient software in the ESC can make a noticeable difference.

[doctormike]

Konrad!!! You big egghead. You are appreciated!!!!!! Doc

[Konrad]

I've actually been told to try to dumb down my posts as some folks think I'm trying to be condescending when I actually answer a question with supporting arguments and links. I'm willing to help anybody that asks and encourage folks to keep asking until they have an understanding of the subject at hand. But because of some precious snow flakes the management has asked that I not attack the subject with too much zeal.

So until we get clear guidance as to what the management wants from the forum for detailed technical discussions I'll have to respectfully decline.
Now this should not deter others who are a bit more understanding of folks feelings from tackling the subjects. (yes, I'm pissed at the management of Hobby Squawk)

So to start it might be helpful to others to understand where your issues are. Is it with Ohms law, how a voltage divider works, or how the prop works? These are all legitimate issues than need to be understood to, in my opinion, gain the most from this fine hobby while not letting out the magic smoke!:s

Sorry I can't help,

Konrad

[Konrad]

Konrad!!! You are appreciated!!!!!! Doc

Thanks, but not by the management!

[doctormike]

You make me want to be a smarter man! Doc

[boomer108]

Hey Konrad!

I must admit that when I read some of your first posts I thought you were a little condescending, but I came to realize that you were just on a higher level of understanding than I was when it came to engineering and electronics. That being said I do appreciate your trying to help people to understand and to get to the root of their problems. Thanks.

Roy B.

[Grossman56]

Hey Konrad, what I need to know, or would like to know, is how I can work these calculators.

http://personal.osi.hu/fuzesisz/strc_eng/index.htm

They ask for all sorts of info that totally befuddle me.
Here's what I've considered...
I have a 50A ESC and I want to mate it to a 3536 1250kv motor, how do I fill in the calculator so that I know what type of prop would be appropriate?
an 11x5.5 two bladed prop is what the RocHobby MSX is using albeit with a 40A ESC. Is there a three blade prop I could use?
I'm hoping to put the rig in my Pandora, but don't want to burn out the ESC.

Grossman56

[Konrad]

You make me want to be a smarter man! Doc

Thanks!

I assume that we all strive to be wiser today than we were yesterday. And to that goal I put fellowship as a secondary endeavor.

All the best,
Konrad

[Konrad]

Hey Konrad!

I must admit that when I read some of your first posts I thought you were a little condescending, but I came to realize that you were just on a higher level of understanding than I was when it came to engineering and electronics. That being said I do appreciate your trying to help people to understand and to get to the root of their problems. Thanks.

Roy B.

I'm at a loss to this.
I've never said or called anyone a fool or an idiot, well not here in public.:rolleyes: When it comes to a level of understanding I try to set some background that we can all work from. I don't want to be too basic as I've been told that is condescending. I also don't want to loose the 'masses' with too much maths. So I choose a level that I think is appropriate. If I'm snowballing somebody I expect then to stand up for themselves and say; hey I don't understand "X" can you go over that.

I'm sorry to say I'm not clairvoyant, so like with all communication it takes a dialog between people to have true communication. If I want a condescending dialog all I have to do is have a meeting with management, any management! I don't seek it here on the forums as I'm well aware that there many who are far more versed than I on any number of subjects.

All the best,
Konrad

[fhhuber]

Sometimes a simplified answer is enough.

When it isn't, the person who asked the question is the one that should say they need more.

It is widely believed that the Bernouli description of lift explains it all, even though that is just a part of what is going on. This is because that is the explanation given in most introductory texts. Even though the Bernouli equations are intended for used in a closed loop PIPE system, not open air over a wing...
But it explains enough that people understand that when airflow over the wing is disrupted (stall) the airplane tends to fall out of the sky.

[fhhuber]

Hey Konrad, what I need to know, or would like to know, is how I can work these calculators.

http://personal.osi.hu/fuzesisz/strc_eng/index.htm

They ask for all sorts of info that totally befuddle me.
Here's what I've considered...
I have a 50A ESC and I want to mate it to a 3536 1250kv motor, how do I fill in the calculator so that I know what type of prop would be appropriate?
an 11x5.5 two bladed prop is what the RocHobby MSX is using albeit with a 40A ESC. Is there a three blade prop I could use?
I'm hoping to put the rig in my Pandora, but don't want to burn out the ESC.

Grossman56

The calculator you linked isn't going to give the answer to your question without a series of "educated guess" inputs.

the answer is::: Yes, there is a 3-blade prop you could use. There is always a 3 bladed prop you could use.

The basic rule of thumb for moving from 2 blades to 3+ blades is: Reduce by 1 inch pitch or 1 inch diameter for each added blade.

The assumptions in the rule of thumb:
You are using a .40 glow engine spinning a top Flite 10X6 (White nylon, manufactured in the 1970's for blade shape and stiffness) at 10,000 rpm and you want to keep spinning 10,000 rpm. The final prop will be as close to the same blade type (material and pattern) as the original as is possible.

Change ANYTHING and the rule starts to break down...

Its a useful guide in helping experiment with the fewest props possible even with the flaws in the "rule". Its goal is keeping the same load on the motor/engine.

***********************

Lets look at your linked calculator and your info given:

You don't supply ALL of the info needed to input the "best guess" numbers for making the calculator help you select the prop. We need the cell count of your battery.
Assuming 3S, we have:
(Assuming 3S because the 3720 series motors I have use 4S but have significantly lower kV than yours but use the same prop size)

11.1 v nominal * 1250kv = 13875 rpm (appx) that the motor is TRYING to spin the prop.
Using nominal instead of full pack voltage will be closer to actual at full charge than at near end of charge.

Use the APC standard prop... its a glow prop, but they don't offer the E series, which is more efficient. But its easier to find a glow 3-blade than an E style 3-blade.

The calculator is assuming sea level. Use 68F for general purposes.
Sea level 60 F 14.696 psia (sea level in good weather) is considered "Standard temperature and pressure"
Use higher temperature to simulate higher elevation. (less dense air)

Hit "Calculate"
The program fills the rest of the boxes...
The ONLY box we care about is... Required Power: 1.139 kw = 1139 watts

1139W/11.1v = 102.6 amp... (I have good reason to think there's a problem with an assumption somewhere... or the calculator is really bad)

Now.. change the diameter and pitch to a 3-blade we know can be found: 10X6. Calculate. Result: 1.187 kw = 1187 watts

1187W/11.1v = 106.9 amp...

Pretty close to the original... I'd try that.

But there are a lot of assumptions going on... and some educated guessing... and I would bet a calculator error... and so you should still do a wattmeter check. I'd also do a tachometer check to see if that motor is labeled the correct kv.

(or check that you listed the correct prop)
Turnigy 3536/6 1250kv says use a smaller prop and don't exceed 500 watts

[Konrad]

Sometimes a simplified answer is enough.

...

Sometimes, but rarely!
I often write my "books" to clear up what I see as misleading or easily misunderstood responses or conclusions. If the OP doesn't have enough background he often doesn't know to ask for follow up questions. So no, for the most part I don't like simple answer, giving them or receiving them.

It is widely believed that the Bernouli description of lift explains it all, even though that is just a part of what is going on...
But it explains enough that people understand that when airflow over the wing is disrupted (stall) the airplane tends to fall out of the sky.

MUST RESIST...resistance is futile.
************************************************** **

I too gave that calculator a glancing look and came to the same conclusion. That with what we are given it is not the proper tool. Now I haven't worked with it.

All the best,

Konrad