Work and Efficiency of P4 motors

[amstar]

I did some calculations (just for fun) to see the motor efficiency of our P4 motors in real life. The data is from a 62030 ft run that I did yesterday obtained directly from the .dat file in the P4.

I flew the P4 at a constant 33.6mph or 15m/s and for their given power of 800kV and stock weight of 1380gms (with battery and props) that seems to the ideal speed.

 

[With The Birds]

How did you arrive at 100% efficiency (obviously this isn’t possible)? I’m not sure what you are demonstrating with respect to efficiency in your analysis, this simply shows power motor power consumption for one flight.

Interesting exercise though.

800kv does not denote the power of the motor, it is simply a standard applied to brushless motors being RPM/V.

 

[amstar]

Watt-sec/distance (actual data on board) gives you the energy consumption. 1/energy consumption is the efficiency. Watt-sec/velocity (another data recorded on board) is a surrogate for efficiency too. I know 100% efficiency is impossible but that how the data plots.
It just happened that I was flying at 33.6mph. The data would be quite different at other velocities.
We may at least conclude what the optimal velocity for a stock P4 should approx be.

 

[With The Birds]

If your intent is to ascertain optimum speed to achieve maximum flight distance from a given battery consumption the range threads demonstrate this, it is just slightly less than your speed for this flight.

Energy consumption would be watt sec * time. I don’t understand how 1/energy consumption gives you efficiency? Efficiency with respect to this exercise is seemingly how far you fly for a given mah consumed at one constant speed compared to another (comparative rather than absolute). You might do the same exercise for max flight time, in which case you will find the speed would be closer to hover (least efficient) but significantly less than that to arrive at maximum distance.

 

[Geoff G]

I didn't realise that you could get data like that out of the machine! What does the horizontal axis represent please? Time, distance or samples.

 

[BudWalker]

I didn't realise that you could get data like that out of the machine! What does the horizontal axis represent please? Time, distance or samples.

The horizontal axis in @amstar 's plot are the row number in the Excel spreadsheet. But, the data is uniformly sampled ( 30HZ is the default) so, in effect, the horizontal axis represents time.

That Excel spreadsheet was created by using DatCon to convert the .DAT to a .csv. The .csv has two coulms, flightTime and offsetTime, that are expressed in seconds which could have been used for the horizontal axis. You can also use CsvView to view the contents of the .DAT.

To see the motor power calcs you'll need to select them; with DatCon the use Categories option in the menu bar, and with CsvView use the DatCon Fields option in the menu bare.

I did some calculations (just for fun) to see the motor efficiency of our P4 motors in real life. The data is from a 62030 ft run that I did yesterday obtained directly from the .dat file in the P4.
.......

These data aren't in the .DAT but are computed by DatCon from data that does occur in the .DAT. The info at

V3 .CSV column descriptions

specifies which fields are derived.

 

[ftttu]

This the first time I've seen anything "hard" about optimum speed for distance runs. Before this, I flew at 28-29 mph which others found was optimum through trial and error.

My batteries are too old to get any good distance now, but I will try 33 mph when I do to see if I get better results. Again 158' more and I would have broken 5 miles on my longest, so I plan on breaking that in the future.

 

[sar104]

If your intent is to ascertain optimum speed to achieve maximum flight distance from a given battery consumption the range threads demonstrate this, it is just slightly less than your speed for this flight.

Energy consumption would be watt sec * time. I don’t understand how 1/energy consumption gives you efficiency? Efficiency with respect to this exercise is seemingly how far you fly for a given mah consumed at one constant speed compared to another (comparative rather than absolute). You might do the same exercise for max flight time, in which case you will find the speed would be closer to hover (least efficient) but significantly less than that to arrive at maximum distance.

Agreed - not all of that makes sense. However, note that power x time (Watt seconds) is energy (Joules). The product of Watt seconds and time has no physical meaning. Energy per unit distance is effectively the UAV equivalent of mpg. The inverse of that is clearly distance per unit energy, which is definitely not a fractional efficiency since fractional efficiency is, by definition, a normalized quantity. Interesting exercise though.

 

[amstar]

The horizontal axis in @amstar 's plot are the row number in the Excel spreadsheet. But, the data is uniformly sampled ( 30HZ is the default) so, in effect, the horizontal axis represents time.

That Excel spreadsheet was created by using DatCon to convert the .DAT to a .csv. The .csv has two coulms, flightTime and offsetTime, that are expressed in seconds which could have been used for the horizontal axis. You can also use CsvView to view the contents of the .DAT.

To see the motor power calcs you'll need to select them; with DatCon the use Categories option in the menu bar, and with CsvView use the DatCon Fields option in the menu bare.

These data aren't in the .DAT but are computed by DatCon from data that does occur in the .DAT. The info at

V3 .CSV column descriptions

specifies which fields are derived.

Yes, l should have referenced Budwalker as being the creator of DatCon. Great work!

 

[amstar]

Agreed - not all of that makes sense. However, note that power x time (Watt seconds) is energy (Joules). The product of Watt seconds and time has no physical meaning. Energy per unit distance is effectively the UAV equivalent of mpg. The inverse of that is clearly distance per unit energy, which is definitely not a fractional efficiency since fractional efficiency is, by definition, a normalized quantity. Interesting exercise though.

I’m not clear what both of you are saying here. Wattsecs is Joules or energy. Energy per unit distance is energy consumed. Inverse of that is efficiency.

 

[With The Birds]

Agreed - not all of that makes sense. However, note that power x time (Watt seconds) is energy (Joules). The product of Watt seconds and time has no physical meaning. Energy per unit distance is effectively the UAV equivalent of mpg. The inverse of that is clearly distance per unit energy, which is definitely not a fractional efficiency since fractional efficiency is, by definition, a normalized quantity. Interesting exercise though.

That’s where I got to- we need to compare the phantom mpg for different constant speed runs to get anything useful here

 

[amstar]

That’s where I got to- we need to compare the phantom mpg for different constant speed runs to get anything useful here

Already been done, 33.6mph is the most efficient.

 

[sar104]

I’m not clear what both of you are saying here. Wattsecs is Joules or energy.

Agreed.

Energy per unit distance is energy consumed.

No. Energy consumed and energy are dimensionally identical with units of energy (J). Energy per unit distance has units of J/m, and is an energy consumption rate.

Inverse of that is efficiency.

No. Inverse of that is obviously distance per unit energy, with units of m/J. Energy efficiency is a measure of actual energy used divided by theoretical minimum energy required. It is dimensionless.

 

[With The Birds]

Already been done, 33.6mph is the most efficient.

Most efficient in what respect? Just under that will give you greatest range for a given energy consumption while significantly slower will give you longest flight time.

 

[Dragonfly Joe]

This entire thread has given me a headache. I never think about these factors when flying. Guess it's true-- ignorance is bliss.

 

[amstar]

Agreed.



No. Energy consumed and energy are dimensionally identical with units of energy (J). Energy per unit distance has units of J/m, and is an energy consumption rate.



No. Inverse of that is obviously distance per unit energy, with units of m/J. Energy efficiency is a measure of actual energy used divided by theoretical minimum energy required. It is dimensionless.

I’m not sure we are on the same page here.

Motor efficiency is defined as
η = 0.7457 x hp x Load Pi
Where:
η = Efficiency as operated in %
Load = Output power as a % of rated power

It can also be stated as the ration of mechanical energy out to the electrical energy in. the rest being unused losses as heat etc.
All of these require complex calc of power/energy in vs out.
Similarly, The energy efficiency in transport, is the useful travelled distance of a given load; divided by the total energy put into the transport propulsion means. The energy input might be rendered in several different types depending on the type propulsion like electrical energy. The inverse of the energy efficiency in transport, is the energy consumption in transport or vice versa.
Here we have measured data of energy consumption provided to us by the machine and hence it makes for an interesting exercise.

 

[Geoff G]

The horizontal axis in @amstar 's plot are the row number in the Excel spreadsheet. But, the data is uniformly sampled ( 30HZ is the default) so, in effect, the horizontal axis represents time.

Thanks very much for the explanation and additional info.

Moving away from the various definitions of motor efficiency for a moment (which sound more like motor power factor expressions!), it strikes me that, by recording the individual motor currents on a regular basis and, in a normalised way, it may be possible to predict impending motor (and esc) problems. Can you acccess any temperature data with Datcon?

With zero redundancy in the power chain of these quadcopters, that would be very useful!

 

[BudWalker]

....
Can you access any temperature data with Datcon?

With zero redundancy in the power chain of these quadcopters, that would be very useful!

There is temperature data on a per motor basis (Motor:EscTemp:<motor>). But, it can't be the temp of the motor because each motor only has three wires and those are used to power the motor. So the assumption is that it has to be a temp sensor in the ESC circuitry.

 

[sar104]

I’m not sure we are on the same page here.

Motor efficiency is defined as
η = 0.7457 x hp x Load Pi
Where:
η = Efficiency as operated in %
Load = Output power as a % of rated power

Sure - there you have defined an efficiency as the ratio of a realized quantity to a theoretical quantity, so that is consistent.

It can also be stated as the ration of mechanical energy out to the electrical energy in. the rest being unused losses as heat etc.

Agreed - that is a definition of thermodynamic efficiency for an electric motor.

All of these require complex calc of power/energy in vs out.

Yes.

Similarly, The energy efficiency in transport, is the useful travelled distance of a given load; divided by the total energy put into the transport propulsion means. The energy input might be rendered in several different types depending on the type propulsion like electrical energy.

No - that's not similar at all. That's simply a rate of consumption of energy per unit distance. It's not dimensionless and it's not a measure of efficiency, not least because it has no theoretical limit with which to normalize.

The inverse of the energy efficiency in transport, is the energy consumption in transport or vice versa.

Your line of argument appears to have become circular at this point. If you define energy consumption not as energy, but as rate of energy consumption per unit distance, and you arbitrarily define energy efficiency as the inverse of that then yes - that statement is correct in isolation. But it's a misuse of the thermodynamic concept of efficiency.[/QUOTE]

Here we have measured data of energy consumption provided to us by the machine and hence it makes for an interesting exercise.

That I agree with - the data and analysis are interesting - just not, as @With The Birds pointed out, a quantity that should legitimately be called efficiency.

 

[amstar]

Sure - there you have defined an efficiency as the ratio of a realized quantity to a theoretical quantity, so that is consistent.



Agreed - that is a definition of thermodynamic efficiency for an electric motor.



Yes.



No - that's not similar at all. That's simply a rate of consumption of energy per unit distance. It's not dimensionless and it's not a measure of efficiency, not least because it has no theoretical limit with which to normalize.



Your line of argument appears to have become circular at this point. If you define energy consumption not as energy, but as rate of energy consumption per unit distance, and you arbitrarily define energy efficiency as the inverse of that then yes - that statement is correct in isolation. But it's a misuse of the thermodynamic concept of efficiency.

That I agree with - the data and analysis are interesting - just not, as @With The Birds pointed out, a quantity that should legitimately be called efficiency.[/QUOTE]

Let’s go easy on the spin here and not make this into a frat spat.
The only thing to be amazed here is the data stored from each, mind you each, flight on this machine.