SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Oct 11, 2012, 12:12 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,047 Posts
Of course you can 'reverse engineer' those numbers to get SOMETHING from them.. Just not a lot.
And as mentioned, some cases - such as those ones - will then give a somewhat clear(er) indication of the system, but only because it was a low power one (which means numbers are more at one end of possible scales anyway). More typical ones will give no more than a quite grey area of possible result.
eg When Vm is more within the 'grey' range of somewhere between a great battery and a poor one.... you can't pinpoint what truly caused what then.
But if you had ALL the info..... plain as day, it is there... and no 'reverse engineering' even required.
So I wonder what numbers set is the more sensible and useful one to use?? 4 numbers... or ALL the numbers? (as a standard)


If you world continued to do things 'as they always have been done', we would still be in the stone-age!! LOL
PeterVRC is online now Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: FPV - what NOT to buy !!!
Reply With Quote
Sign up now
to remove ads between posts
Old Oct 11, 2012, 12:29 AM
Extreme CNC Alloy EDF
Extreme_RC's Avatar
Australia
Joined Mar 2006
11,590 Posts
Quote:
Originally Posted by anlucas View Post
Just quoting results in a format that others have decided upon a long time before I ever decided to get involved in electric RC models....I 'd be happy to adapt to whatever format the mass wants...
Its a hard one to answer as there have been many variations over the past couple of years in here. When I started recording EDF data back in 2005 for my own interest I was taking snap shots of amps, watts, volts, (rpm once I got a hyperion meter) and I was taking these figures after the system had been running for a little while, maybe 20 seconds or more.

I continue to record data after a settle period so that the battery voltage stabilises, to me this was the most useful measurement, peaks are not much use, sustained flight readings are.

Recently peak thrust numbers have been used to exaggerate how good a particular fan/setup is, marketing spin that really doesnt have much value in the real world. I see little point in claiming for instance 2.95kg thrust from your fan peak, when it actually sits around 2.6kg stabilised 30 seconds into the run.

I believe figures taken after 20+ seconds of continuous WOT running are worthwhile figures, they show us how much the battery voltage has dropped under the load which gives a good indication of whether the load is too much for the battery being used, and they show us a fairly stable rpm and thrust reading if the equipment is on hand to record it.

Even 5 years ago companies like Hyperion were talking about battery voltages and what was considered a reasonable drop under load, from memory 3.5v per cell was considered the minimum you wanted to see for long term pack life, I am sure they based this on the cell structure at the time and how hot it got if pushed harder. The Koreans were also the leaders in lipo technology at the time, chinese cells could not compete.

These days we are dealing with a vast range of battery quality, from premium grade 1 cells to the really cheap lipos, so there is much more to quantify when testing stuff whether it be hobbyist or commercial based testing. Some of the cheap lipos will put out just as much power as a premium pack when brand new, this does not last however, cycle life is a lot harder to graph as it requires someone to actually do it over a period of time. I have done it a couple of times comparing other packs to my own and its tedious, obviously the results are not something I would talk about on a forum as it would be seen as bias. It has proven to be extremely interesting however!


As I have posted many times in the past, it would be nice to see a standard method of testing and recording that is along the lines of:
Use an inlet lip if the fan has no radius on the intake.
Run the fan up to WOT.
Let it run for 20 seconds.
Record volts, amps, watts, rpm and thrust from the meters while its running.
And to make it more complete, post up these figures along with the battery size and rating.
Extreme_RC is offline Find More Posts by Extreme_RC
Reply With Quote
Old Oct 11, 2012, 12:45 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,047 Posts
Amen....
Marketing hype... yep. But also just the carried on pattern of 'post just this bit'. (seemingly because "that is what everyone has always just done").
And almost no one ever questions the shortfalls of that manner! "Lets just keep doing it this way...."

Maybe the first people to post full info felt a bit ashamed of the 'lower' numbers that the useful ones added up to. LOL (Not really)
PeterVRC is online now Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: FPV - what NOT to buy !!!
Reply With Quote
Old Oct 11, 2012, 12:47 AM
Registered User
anlucas's Avatar
Greece, Attica, Athens
Joined May 2011
3,367 Posts
Quote:
Originally Posted by Extreme_RC View Post
I believe figures taken after 20+ seconds of continuous WOT running are worthwhile figures, they show us how much the battery voltage has dropped under the load which gives a good indication of whether the load is too much for the battery being used, and they show us a fairly stable rpm and thrust reading if the equipment is on hand to record it.
I also record these figures for future reference and my own understanding of the expected performance.

To me, the main valuable bits of data are:

Volts minimum or volts under full load (Is this battery going to cut it? Maybe the load is too much?)
Amps during first 20 secs while running (Can the motor take it or is it likely that I will have to deal with a deadstick sooner rather than later)
Motor temps after run if amps are within reason(Is this thing going to cook?)
Thrust after the first 20-30secs(Will this thing accelaratey my plane the way I want after it takes off?)

The above help me understand what sort of performance I should expect to get in the air.

Unfortunately I don't have the time to fully clarify my thought processes in these pages due to other priorities (Very demanding job,, Wife, Kids, building and flying models....)
anlucas is online now Find More Posts by anlucas
Reply With Quote
Old Oct 11, 2012, 12:51 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,047 Posts
hehe
PeterVRC is online now Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: FPV - what NOT to buy !!!
Reply With Quote
Old Oct 11, 2012, 12:59 AM
Extreme CNC Alloy EDF
Extreme_RC's Avatar
Australia
Joined Mar 2006
11,590 Posts
Quote:
Originally Posted by PeterVRC View Post
Amen....
Marketing hype... yep. But also just the carried on pattern of 'post just this bit'. (seemingly because "that is what everyone has always just done").
Actually this was done I believe more because of the huge amp draws that came along with the figures...I still see peak thrust numbers being quoted on websites and by other vendors but the amps and watts are strangely missing from these quotes...
Extreme_RC is offline Find More Posts by Extreme_RC
Reply With Quote
Old Oct 11, 2012, 06:12 AM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
13,604 Posts
Quote:
Originally Posted by PeterVRC View Post
Of course you can 'reverse engineer' those numbers to get SOMETHING from them.. Just not a lot.
And as mentioned, some cases - such as those ones - will then give a somewhat clear(er) indication of the system, but only because it was a low power one (which means numbers are more at one end of possible scales anyway). More typical ones will give no more than a quite grey area of possible result.
eg When Vm is more within the 'grey' range of somewhere between a great battery and a poor one.... you can't pinpoint what truly caused what then.
But if you had ALL the info..... plain as day, it is there... and no 'reverse engineering' even required.
So I wonder what numbers set is the more sensible and useful one to use?? 4 numbers... or ALL the numbers? (as a standard)


If you world continued to do things 'as they always have been done', we would still be in the stone-age!! LOL
The snapshot numbers tell some of the taleand like you guys say it needs some clarification. The rpm is a definite clarifier as it tells the tale of how the motor is dealing with the load, if the vilts are X and the motor Kv is Y and it should be at least 80% efficient under load then the answer is Z, lower rpm with a higher amp draw indicates the motor wont cut the cheese and better rpm and lower amp draw then the motor is in its design range. The difficult thing is the average guy who wants to participate likely wont have the tools to gather this sort of information easily.
Maybe one thing you guys can do is generate a list of suitable tools that wont break the bank for those that want to and can gear up.
For me I can see by the calculated numbers that the amp draw should be a defined ammount so seeing grossly higher amp draw tells me I picked the wrong motor.

Cheers,
Eric B.
AirX is offline Find More Posts by AirX
Reply With Quote
Old Oct 11, 2012, 07:44 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,047 Posts
For a start everyone should have one of these:
http://www.hobbyking.com/hobbyking/s..._Analyzer.html

And plugs/leads made up so they can use it across all their aircraft/setups.
I use XT150 connectors to the unit, as you want to start with the largest connectors you need, and then "work down" the sizes in your adaptors. Same adaptor steps for both ends.
eg XT150 to XT60 or XT150 to HXT4mm etc
That allows you to have adaptors made up for all your connector types, and the XT150 end is a 'zero impedance' to current flow (more or less).

This meter will give you real time Volts, Amps, Power, plus records Vm, Ap, Wp
It also records capacity that has flowed through (mA) and time.

You are still better off to VIDEO its display as you test, so you can go over all the numbers later on your PC, and get to see what truly happened across the time period.
PeterVRC is online now Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: FPV - what NOT to buy !!!
Reply With Quote
Old Oct 11, 2012, 07:46 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,047 Posts
This is a handy item to have too:

A digital infrared thermometer. It can record a value, or just keep running real time.
Good for motor temp checking, and a small use for battery temp (but battery you can tell by hand if it is amiss!).

http://www.hobbyking.com/hobbyking/s...0Celsius_.html
PeterVRC is online now Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: FPV - what NOT to buy !!!
Reply With Quote
Old Oct 11, 2012, 07:50 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,047 Posts
And this:

http://www.hobbyking.com/hobbyking/s...L_motors_.html

A KV and RPM meter that runs off the brushless motor phase, thus gives quite accurate RPM readout. It can also do KV ratings accurately for that same reason (calculating off the power source and the motor phase).

Just for people's info.... the number of poles set for most meters is "HALF of the real poles". So a 6 pole motor you set "3".
To find the number of poles a motor has you just need to count the MAGNETS in it - somewhat easy with outrunners, somewhat hard with inrunners. Nicer if you have the motor specs (valid ones!) from somewhere. (maunufacturer?)
PeterVRC is online now Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: FPV - what NOT to buy !!!
Reply With Quote
Old Oct 11, 2012, 07:54 AM
Registered User
Australia, VIC, Melbourne
Joined Nov 2006
11,047 Posts
And this:

http://www.hobbyking.com/hobbyking/s...to_select.html

A servo tester. This allows you to control the ESC without an RX/TX. Though in some cases using a TX that has 'test modes', or delay timers, can allow you to run a motor up, and down, to a pattern - useful for balancing in some methods.
But a servo tester is useful to activate retracts... test servos (of course).... so it is very useful for a fair number of reasons.

Pretty much a 'must have'. Which the Power Meter is also.
PeterVRC is online now Find More Posts by PeterVRC
RCG Plus Member
Latest blog entry: FPV - what NOT to buy !!!
Reply With Quote
Old Oct 11, 2012, 08:50 AM
Registered User
WhalleyB0Y's Avatar
Canada, BC, Surrey
Joined Jul 2011
893 Posts
It seems to me that even after you get readings for rpm, amps and watts etc you are still left wondering how much thrust you are actually getting. Wouldn't comparing your thrust to the watts produced the only true way of measuring the aircraft's muscle? Resistance in leads, connectors and IR losses of batteries can fool the meter into building watts that aren't really being used in actual thrust output.
I have all the tools except for the thrust meter and next time I am at the hardware store I will look for some nice drawer slides as to make a nice thrust test setup.
WhalleyB0Y is offline Find More Posts by WhalleyB0Y
Reply With Quote
Old Oct 11, 2012, 09:09 AM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
13,604 Posts
Thrust is a function of velocity, the fan is basically a positive displacement pump so if rpm increases in a bench test the load/thrust increases. Only burried in poor designed ducting will this not happen. Even if the inlet ring is left off the rpms and thrust will rise and fall together.
The CS70 is loaded up with so much pitch the motor becomes critical, if it cant make enough torque it wont have good performance at higher voltages.

Cheers,
Eric B.
AirX is offline Find More Posts by AirX
Reply With Quote
Old Oct 11, 2012, 12:47 PM
Diverted by planks
tracknoob's Avatar
South Florida
Joined Dec 2010
5,077 Posts
Quote:
Originally Posted by AirX View Post
I and a lot of others are getting tired of it.
Has it occured to you that this is just a hobby? Many people are not looking to gather information that is correct to an engineer or for someone with an engineering background. What we need to do is to educate without being overbearing.
FWIW, I'm an engineer and engineering manager with multiple university degrees, and 33 years experience, and trust me, it's not just laymen on the forum that rapidly get their fill of certain poster's bloviations.


The forum's Ignore feature works a treat:




tracknoob is offline Find More Posts by tracknoob
Last edited by tracknoob; Oct 11, 2012 at 01:16 PM.
Reply With Quote
Old Oct 11, 2012, 01:07 PM
chuck
santa barbara, CA
Joined May 2009
4,145 Posts
guys, i need some opinions on this question;

is it viable to think that i could run this fan in the 800 watt range and expect to get similar performance to a 5 or 6 blade fan running in the 600watt range?

i am looking for sound improvement and noise reduction at similar thrust and eflux speeds and trying to judge about how many watts it costs.

thanks , chuck.
chas650r is online now Find More Posts by chas650r
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
New Product Change Sun 12 blade 90mm Flip Flop Electric Ducted Fan Jet Talk 7081 Jul 28, 2014 08:25 AM
New Product Change Sun 120mm and new 10 blade 70mm fans Flip Flop Electric Ducted Fan Jet Talk 131 Apr 27, 2012 07:07 PM
Sold Change Sun electric retracts Flip Flop Aircraft - Electric - Jets (FS/W) 3 May 23, 2011 06:20 AM
Sold Change Sun Electronic retracts w/Lander struts hole digger Aircraft - Electric - Jets (FS/W) 2 May 06, 2011 01:27 PM
Sold Change Sun Electric retracts NIB 75.00 jzuniga Aircraft - Electric - Jets (FS/W) 2 Sep 03, 2010 09:36 AM