Over Propping - It Works For Me

[Futura57]

On my Top Quark own design prototype I'm using a DYS D2826 2200KV out-runner with a 7x4 APC propeller. It was the only suitable motor 'in-the-ballpark' I had to hand. Ditto the propeller. After looking at the motor specification table (below) I figured the combination on 3S would be fine. Of the 4 different KV options I was happy to have the highest power output motor of the bunch. The model weights 695g all-up and has a low wing loading of 14oz. / sq. ft. It's also quite slippery through the air.

 

I'm always sceptical of specifications so, after the usual initial calibration of my ESC / Tx throttle range, I put my Watt Meter into action. It was obvious from the outset that the 7x4 propeller was going to overload the motor as regards the stated 342 max wattage. Different sources state the max current to be 32 and 34 Amps. Again, easily exceeded.

 

My solution to my problem was simple. I dialled down my high throttle movement on my Tx to around 75%. This gave a sustained peak current and wattage on a fresh 3S Lipo of around 30A and 340 Watts, respectively. Perfectly within limits (if they are accurate). Since this was a static test I would expect slightly lower figures in flight as the propeller unloads. With good cooling through the entire fuselage I installed a 30 Amp ESC I had available. I would not be flying around on full throttle for more than 10 second bursts anyway. The lightweight motor, good max power output and adequately light ESC were perfect for the model. It climbs like a rat up a drainpipe and I get a comfortable 6 minutes flight time with a 1300 mAh Lipo. With 50+ flights under her belt, what's not to like!

 

So why was it over-propped? The attached specification table appears to show two propeller sizes for each KV option. The first for 2S and a second one for 3S. Have I misread the 2200KV entry? Is the 7x3/7x4 recommendation the wrong way around? The other KV prop sizes show a smaller (second) propeller for 3S, which I would expect.

 

I could try a 2826 1400KV motor with the 7x4 propeller, though I expect to be disappointed by the lower performance. Or just get a 7x3 propeller and try it. My model is by no means a hot rod, but a moderate turn of speed and good vertical performance, as well as a fair duration, is what I want. I suppose I could go up to a 2834 1600 KV motor with the 7x4 propeller. But my restricted high throttle setup does the business and works for me. The only downside I can see is remembering to reset my Tx high throttle movement to 100% if ever I need to recalibrate the ESC /Tx throttle range. Then set it to 75% again.

 

I get it that by sticking with a recommended propeller you shouldn't over load a motor on full throttle. But, with all other things being equal, why shouldn't a higher KV option with a Tx restricted high throttle range not give equal or better performace?

 

What would you do? Your thoughts please?

 

 

 

[MattyB]

1 hour ago, Futura57 said:

I get it that by sticking with a recommended propeller you shouldn't over load a motor on full throttle. But, with all other things being equal, why shouldn't a higher KV option with a Tx restricted high throttle range not give equal or better performace?

 

What would you do? Your thoughts please?

 

This has been discussed in multiple threads down the years, here's a couple. Personally I don't do it, but I admit the the odds are probably relatively low that you will have an ESC failure because of this unless you are operating the powertrain at the new limited "full throttle" for extended periods without modulation...

 

 

 

[Mike T]

I'm more inclined to suspect the 2S prop size quoted.  Given the 'spread' quoted for the other winds, I suspect that the 6-turn 342W motor should be turning a 6 x 4 on 3S.

[Jake Bullit]

Cut the prop down?

[Don Fry]

36 minutes ago, Mike T said:

I'm more inclined to suspect the 2S prop size quoted.  Given the 'spread' quoted for the other winds, I suspect that the 6-turn 342W motor should be turning a 6 x 4 on 3S.

I’ve got one of those motors, came with a HK foam flying wing, 3s, 6x4 prop. Ballistic, exceeded the structural integrity of the airframe.

I’m thinking of sticking it in a Hanky Planky Foamy Woamy. I think it would melt on a 7x4

[Don Fry]

4 minutes ago, Don Fry said:

I’ve got one of those motors, came with a HK foam flying wing, 3s, 6x4 prop. Ballistic, exceeded the structural integrity of the airframe.

I’m thinking of sticking it in a Hanky Planky Foamy Woamy. I think it would melt on a 7x4

Sorry, nagging thought, I’m wrong, just checked it, and it’s got a 7x4 prop, so it is a goer on a 7x4. Sorry about the duff gen

[Don Fry]

Right, I’m right sorry, busy, over tasking the remaining  brain cell.

 

I have gone into my bag of spare motors. The motor 2826  6 turn,  2200 kv, as sold by HH has a 6x 4 prop fitted. But I was running it on 3 s, 100% movement on the stick. 
Still going into the Hanky Planky, assuming I remember to fit the wing in front of the tail plane.

[Frank Skilbeck]

If you've got a current sensor you could use telemetry to alert you when you approaching the max current limit.

[Futura57]

First off, my apologies that this topic has been done to death before. I did try a search on "over prop" and could not find what I was looking for.

 

It would seem that limiting the high throttle movement is a viable tactical solution, but probably not the best idea longer term. If I'm going to publish a plan then I suppose I should get the recommended power train spot on so that no magic smoke escapes 🤣.

 

I received a cheapie Chinese  DYS 2826 1400KV motor in the post today. Before swapping it in I shall hunt down a 6x4 prop or cut down my 7x4 prop and see how the model performs.

[Futura57]

Just tried my Top Quark model with a 6x4 APC propeller at my local club field. Throttle range was reset to 100% all round and recalibrated the ESC. Full throttle now gives circa 25 Amp and 280 Watts which results in no significant reduction in performance or change in duration. I will be happy specifying a 6x4 prop and 30 Amp ESC on my plan. Thanks for all your suggestions.

[Mike T]

Always nice when contributions are acknowledged, however modest.

[gangster]

This issue has gone round and round with regards calibrating the esc to 100% and then limit the max throttle throw to say 75% to reduce max speed. Is there someone out there who can give a definitive answer and not just a guess.

one school of thought is that it is bad for the esc, Why would it be so, an esc surely works by switching not voltage drop.

The second school of thought, which is the one I subscribe to, is that this is perfectly fine as it is no different to flying with the stick 3/4 up.

Please only answer this if you really know and can supply a technical reason rather than repeating an old wives tale as we so often see on social media

[Philip Lewis 3]

Because technically the esc is working hardest at part throttle switching the voltage on and off, at full throttle it just lets it straight through but is still switching the fields, however, who flies around at full throttle anyway whatever the endpoint is set at?

 

In my opinion it's fine, it's simply doing what it was designed to do and all of my planes are on a reduced throttle because the motors as stock have a surplus of power, been like that for 3 years now and not had an ESC failure, the ESC though would run a little warmer because of the increased workload. 

[PatMc]

4 hours ago, gangster said:

This issue has gone round and round with regards calibrating the esc to 100% and then limit the max throttle throw to say 75% to reduce max speed. Is there someone out there who can give a definitive answer and not just a guess.

 

I don't know if this only applies to some older type's but not all ESC's need to be calibrated to recognise the Tx throttle limits. I have some old Jeti ESC's that state "The position of full throttle will be adjusted automatically" - i.e. once the initialisation beeps are complete each time the ESC is powered up. 

[PatMc]

5 hours ago, gangster said:

 

one school of thought is that it is bad for the esc, Why would it be so, an esc surely works by switching not voltage drop.

 

 

The ESC overheating due to extended periods of part throttle may only have been a problem with older versions in pre lipo days when full or near full throttle was needed for most of a flight. But most flight times were usually much shorter due to limited battery capacity so any such problem were rarely encountered by most of us.  I certainly never experienced it. 

First (& only) time I heard of the problem was watching Brian Collins & Nigel Hawes on TV preparing for, then flying the first electric model aeroplane across the Channel.

IIRC they unexpectedly burnt out an ESC at low throttle during the preparations but the manufacturer later supplied them with a modified version that could withstand extended part throttle settings.

[Futura57]

6 hours ago, gangster said:

The second school of thought, which is the one I subscribe to, is that this is perfectly fine as it is no different to flying with the stick 3/4 up.

 

I gotta say, I'm with gangster on this. As long as the motor and ESC are within max limits I see no problem.

 

In my particular case, I want to publish a plan with a recommended power setup. It might be controversial (and perhaps confusing or even dangerous) specifying a D2826 2200KV outrunner with 7x4 prop and 75% high throttle, versus just a 6x4 prop. The thing is, I can get the very last ounce of performance (340W) from my motor using the larger prop and dialing down the high throttle until my Watt meter tells me I'm good. Changing prop diameter and pitch is a coarser/discreet adjustment which won't always get me to the max limit. In my example only 280W with the 6x4 prop. Of course I could try a 6x5, but you get my point.

 

I appreciate the technical input guys. For the purposes of my plan I will stick to convention. For my own setups I will take it to the max 😀

Edited September 15, 2023 by Futura57

[Don Fry]

Bottom line, how many nights sleep will you lose, you have burnt out/ caused an earlier failure of, a small speed controller, or a small motor. Answers on a pin head please. 

[gangster]

2 hours ago, PatMc said:

I don't know if this only applies to some older type's but not all ESC's need to be calibrated to recognise the Tx throttle limits. I have some old Jeti ESC's that state "The position of full throttle will be adjusted automatically" - i.e. once the initialisation beeps are complete each time the ESC is powered up. 

Interesting point I have never come across such an esc. I am struggling to get my head round how that would work as it would never know what full open stick looks like on start up . It would however defeat limiting the throw

[PatMc]

3 hours ago, gangster said:

Interesting point I have never come across such an esc. I am struggling to get my head round how that would work as it would never know what full open stick looks like on start up . It would however defeat limiting the throw

The same way that a servo know the stick limits ?

[PatMc]

3 hours ago, Futura57 said:

I gotta say, I'm with gangster on this. As long as the motor and ESC are within max limits I see no problem.

 

In my particular case, I want to publish a plan with a recommended power setup. It might be controversial (and perhaps confusing or even dangerous) specifying a D2826 2200KV outrunner with 7x4 prop and 75% high throttle, versus just a 6x4 prop. The thing is, I can get the very last ounce of performance (340W) from my motor using the larger prop and dialing down the high throttle until my Watt meter tells me I'm good. Changing prop diameter and pitch is a coarser/discreet adjustment which won't always get me to the max limit. In my example only 280W with the 6x4 prop. Of course I could try a 6x5, but you get my point.

 

I appreciate the technical input guys. For the purposes of my plan I will stick to convention. For my own setups I will take it to the max 😀

The motor data chart is missing the most important parameter, namely the max current.

There is no such thing as a max power figure unless the applied voltage is given. i.e. the max power using a 3s battery is 50% higher than it would be using a 2s battery.

 

BTW the way our wattmeters are connected means that you can't measure the watts unless you have the throttle fully open. Which means that the 340W you measured is higher than the true figure by the fraction of throttle that's applied. If the throttle is 75% then the power taken is 255W.. 

 

 

[gangster]

10 hours ago, PatMc said:

The motor data chart is missing the most important parameter, namely the max current.

There is no such thing as a max power figure unless the applied voltage is given. i.e. the max power using a 3s battery is 50% higher than it would be using a 2s battery.

 

BTW the way our wattmeters are connected means that you can't measure the watts unless you have the throttle fully open. Which means that the 340W you measured is higher than the true figure by the fraction of throttle that's applied. If the throttle is 75% then the power taken is 255W.. 

 

 

Yes Surely the max current has got to be the most significant factor. Without that you have nowhere to start.

[Martin Harris - Moderator]

Perhaps another way of looking at the lack of electrical current information is that the voltage is specified within the limits of 2-3 lipo cells so by not exceeding the wattage, the current will be limited to a safe value?

 

For example, a motor rated at 370W would have a nominal worst case current flow of 50A using a 2S pack
(I=P/V….370/7.4) but using the same current with a 3S pack would exceed the power rating of the motor (by 50% i.e. 550W).

[PatMc]

That would mean that the power of all motors are being restricted to 2/3 of there potential. 

In fact there is no reason that more than 3 cells could be used so long as the max current is not exceeded & a practical size prop can be used.

Edited September 16, 2023 by PatMc

[Futura57]

In my original post...

 

Different sources state the max current to be 32 and 34 Amps.

 

My max power readings have always been in the context of reaching the max rated current.

 

I sure do hope my Watt meter, which also shows current and voltage, is giving an accurate reading.

Edited September 16, 2023 by Futura57

[PatMc]

56 minutes ago, Futura57 said:

In my original post...

 

Different sources state the max current to be 32 and 34 Amps.

 

My max power readings have always been in the context of reaching the max rated current.

 

I sure do hope my Watt meter, which also shows current and voltage, is giving an accurate reading.

Can you give a link to the max current for the other Kv rated motors in the table please ? 

 

The true power readings can only be taken at max throttle, if you have restricted the throttle to when max rated current is reached the power reading is not true, it's too high.

 

I don't doubt your wattmeter's accuracy in the manner it's designed to be used. However none of our wattmeters are able to measure the power input to the motor except at full throttle.

This is because they measure the voltage at the ingoing battery side of the ESC which is not the RMS voltage that's being supplied to the motor via the 3 wire outgoing side except at full throttle. The current measurement is accurate as it's common at both sides. The wattmeter derives the wattage by multipling the voltage & current readings it detects.