Fan type/ size question

[Babylon5]

Hi Edmond, We may disagree in many things. Have you try the Tahmazo EDF fan?

Pertaining to the Tahmazo EDF my stand is still the same

1) Higher KV motor of the same class same EDF being equal =more static thrust less efficient
2) Lower KV motor of the same class same EDF being equal =lesser static thrust more efficient
( note base on 3S Lipo setup)


Moreover the Tahmazo thrust data are given by the manufacturer.
The data speak for themselves.

I don't wish to go into an endless debate till we turn blue.

You yourself said is the law of diminishing return so am curious which portion of my statement is blind????


Cheers

[bigfilsing]

Yes babylon of course i'm interested in the 720 gram setup

I think we also have to remember that thrust and efficiency are not linear progressions so quoting max amp/thrust data and sub dividing them to get the average is mathmatically correct, but doesn't take the other factors into account.

I'm also experiencing something which i can only guess is blade stall in the fan. There's only so much thrust to be had from a certain diameter/blade count/pitch . The point where more RPM's actually gives less thrust
All interesting stuff...all input appreciated

Cheers

PS i've got a wierd vibration problem in my edf. from 60% to 75% throttle it vibrates like hell but above or below it's smooth. I've tried a couple of different fans and prop adapters but still stays. So that leaves the motor (new) and fan housing .....any ideas???

[edmond22]

Hi Edmond, We may disagree in many things. Have you try the Tahmazo EDF fan?

Pertaining to the Tahmazo EDF my stand is still the same

1) Higher KV motor of the same class same EDF being equal =more static thrust less efficient
2) Lower KV motor of the same class same EDF being equal =lesser static thrust more efficient
( note base on 3S Lipo setup)


Moreover the Tahmazo thrust data are given by the manufacturer.
The data speak for themselves.

I don't wish to go into an endless debate till we turn blue.

You yourself said is the law of diminishing return so am curious which portion of my statement is blind????


Cheers

Check your first post. You recommended general 3kv over 4kv and did not specify a brand motor. That is general blind science. I gave you a motocalc example of a 3kv vs 4kv motor combo which is the same mega brand of which the 4kv motor can be flown at less throttle and gave almost the exact same efficiency as the 3kv at 100% throttle. It is only when I probed further that you start digging for data to support your findings.

Based on your general statement, I have already given you the examples and asked you a very simple question. Why limit yourself to a motor combo choice which you recommended when you can have the option to run another combo just slightly higher kv to have both speed and efficiency? All you need to do is use your throttle and fly the way you like it. It is ok to say you preferred it that way, but it is not ok to claim better efficiency. Debunked already.

It is no longer a debate if you haven't noticed already.

Your findings:
1) Higher KV motor of the same class same EDF being equal =more static thrust less efficient
2) Lower KV motor of the same class same EDF being equal =lesser static thrust more efficient

I never tried a Tahmazo fan, but I can tell you quite confidently that if you use option 1 and throttle down, it would have very close efficiency as that of option 2. The efficiency you are talking about cease to really mean anything to decided between the 2, you might as well pick the higher power one as long as it is within spec, just like the link you gave recommending the use of 4200 kv motor.

on the other hand, you also said

On the other hand I have come across other twin set up(not a Tahmazo fan) on 3s 2200mah lipo drawing a mere 25amp capable of hauling a 720grams aircraft with good vertical performance.

11.1v X 25 = 277.5 watt. That means 174.5 watts per pound. That falls between 150w/lb for Fair EDF performance and 200w/lb for Good EDF performance. That is a better measure, not "good vertical performance". I dun even dare to say good vertical performance despite getting 320w/lb performance and being categorized as "Extreme EDF performance" for the HET F20....

Do you get the picture? When you want to share an opinion like a good business deal, try to measure it using a standard measure if possible. I have been using 50% discount method to align your claims to real life these days.

[bigfilsing]

Hdt Hst

Well while hunting down some info i found this from a German site.
The factory has 2 types of fan . HDT and HST ( respectively high dynamic thrust and high static thrust)
The picture shows their testbed for their new HST fan ..lots of blades

I wonder how much this baby will cost ...better start saving

[edmond22]

Hey Bigfilsing,

I too get the problem when I use 2w20 with Minifan 480. It is from 50% - 75% throttle range too. I fooled with timing and switching freq to lessen the symptom but it is still there. Interestingly, I switched to HET 6904 and all is fine.

[bigfilsing]

Well at least i'm not alone Edmund

WHats a HET 6904. Sorry if it's a dumb question! i'm trying to catch up on this stuff!

Cheers

[edmond22]

It is another equivalent of mini 480 fan type by HET brand.



See http://www.rc-warbirds.com/index.php/cPath/69_89 For range of fans

I normally get my stuff from them, they have the bungee stuff, necessary electronics and also a good selection of EDF kits locally.

[Babylon5]

If you read properly, I wasn't recommending that setup to him, I am telling you that blindly recommending 3kv motor in favour of 4kv quoting better efficiency is plain wrong. The way to do it is ask yourself what watt per pound range you want to achieve, you then work backward from there and THAT IS exactly what I recommended to Bigfilsing and he did find it useful. If you read carefully again, you would have noticed I offered a setup that is completely within his constraints.

I have given you the example of why your logic doesn't make any sense (can't be any subtle anymore cos you asked for it) and you are clearly unable to answer. I am not against you recommending advice and such, but you must learn to accept that people can tell bad advice from good ones and they CAN tell. Deal with it.

On the honest side, I am pretty sick of it time and time again how you similarly try to advocate cutting 6 blades to 3 blades and claim better efficiency. So before you talk about using 3kv motor instead of 4kv for better efficiency, learn to throttle down first and see if it makes any diff.

I dun want to start with your "good vertical performance" really. It took you long enough time to phrase it that way and not incur some of the member's wrath here on the claim to unlimited.

Hi Edmond in my post #2 I mention that the Tahmazo comes with a 3.7KV Reno motor There are link to the product as well in my post. Did you actually go to the link or am I missing something ....so in which area I did not mentioned this motor.



I also mention that the LHS can change the motor ( they are only two types the 3.7Kv or the 4KV).
Where did I miss up mentioning the motor .
Did you go the LHS and check up with regard to the motor or the fan ? I bet you didn't. Am I right.


How on earth can you expect our friend to get good performance out with the wemotec fan base on the 3s 2200mah mentioned in thread#1? Also brand of Lipo mention in post #1 also unknown.
Don't get me wrong , Wemotec Fan are really great but they need a matching motors and a suitable LIPO setup .


Cheers

[edmond22]

Hi Edmond in my post #2 I mention that the Tahmazo comes with a 3.7KV Reno motor There are link to the product as well in my post. Did you actually go to the link or am I missing something ....so in which area I did not mentioned this motor.



I also mention that the LHS can change the motor ( they are only two types the 3.7Kv or the 4KV).
Where did I miss up mentioning the motor .
Did you go the LHS and check up with regard to the motor or the fan ? I bet you didn't. Am I right.


How on earth can you expect our friend to get good performance out with the wemotec fan base on the 3s 2200mah mentioned in thread#1? Also brand of Lipo mention in post #1 also unknown.
Don't get me wrong , Wemotec Fan are really great but they need a matching motors and a suitable LIPO setup .


Cheers

You start by saying "Hi a twin 55-60mm size will give you a good thrust."

Then you have 2 links there showing the same product twice, I get the impression you are saying any 55-60mm fan is good and you merely offered 2 links. Then you proceed to say 3.7kv and blah blah blah, no brand or name of motor except of the brief mention of Reno. I am sorry I do not know them at all BUT granted that even if I am on the same page with you on the Tamazo brand, you still dun get it that if you throttle down a little, you might just be able to achieve the same efficiency as the 3.7 kv motor. All this efficiency talk of yours would not have held any water. SO PLEASE ANSWER THIS: WHY PICK THE 3.7kv that gives you efficiency only when you CAN ACTUALLY TAKE THE 4.2kv and get both efficiency and speed? I am already saying you are reinventing the wheel with that theory of yours and you still dun get it? If it is within spec, less than theadstarter's 35 amp constraints, recommended by the same link you gave, WHY WHY give the impression that 4.2 kv is not efficient when they actually ARE!.... Jesus....

and I suggest you read again below before I think you are blind:

"For 500-650 gram AUW, I like GWS edf55mm with Himax 2025 4200 motor, this mate with 25 amp esc will give you about close to 250watts which is over the 175w limit for that motor, so be careful with newer high discharge batts.

For 1kg - 1.3kg AUW, I like HET 6904 fan or Wemotec minifan 480 with HET 2w20 on 4s or 2w23 on 5s. The 2w20 combo on 4s will give you about 40ish amp draw with about 500++ watt power. The motor is capable of 700 watt. I am currently pushing the motor further with 5s and my latest results tells me I am getting about 850-900 watts on about 50amp draw."

LIKE I was trying to say.

I AM REALLY OK with you giving recommendation and all. I just think you needed to focus a tiny bit more on using a stand measure so that people can understand you better.

You post a example before saying this guy in RCgroups reached 100mph on a mere amp draw of 30 something, can;t recall the exact numbers.... but I corrected you to say if you use the watt per pound guide, he actually falls under "250w/lb for Great EDF performance" category, completely opposite of the impression you try to give mere 30 amp draw, remember?

Now you come with this "good vertical performance" on mere 25 amp draw when it is actually only 174.5 watts per pound. That falls between 150w/lb for Fair EDF performance and 200w/lb for Good EDF performance.

I am sorry if I am a bit hard on ya, but you have a history of advocating stuff on science that is plain wrong.

AND dun forget how you use to say 4200 kv motor is too hot and will melt the EDF fan when a youtube video link is always around to show you it works without issue. I can't help but feel that you will pull whatever crazy science to support your notion of 3.7kv just because you felt like it. This is consistent with your multiple threads here and RCgroups (suspect you only) on blade cutting for again better speed, thrust and efficiency.

[bigfilsing]

Me again more questions.

Whats the best way to measure static thrust ?

Is there a "set way" of doing it

Here's what i'm thinking of doing ( from the bottom up)
Digital scale then a piece of blue foam 400 x 400 mm, then the EDF unit with a 100 mm gap between EDF outlet and blue foam.

I'm not expecting any "true" readings but what some comparison data for later.

Cheers

[edmond22]

Me again more questions.

Whats the best way to measure static thrust ?

Is there a "set way" of doing it

Here's what i'm thinking of doing ( from the bottom up)
Digital scale then a piece of blue foam 400 x 400 mm, then the EDF unit with a 100 mm gap between EDF outlet and blue foam.

I'm not expecting any "true" readings but what some comparison data for later.

Cheers

Think you will prob need to construct a rig that sits on the weight scale. Zero the bugger, mount the edf on and orientate it down. I toyed with the idea alot but never got down to doing it.


I actually want to let this go but.....
Anyway, taking Babylon5's calculations of efficiency. I refer to the following sources:
http://www.okmodel.co.jp/shincyaku/Ductedfan-motor.htm (3.7kv)
http://www.tahmazo.com/products/catalogue/75/161 (4.2kv)

I use the figure from the those 2 sources, I get the following results using his method of calculations.

Tahmazo 3.7Kv motor 55EDF=480gram/ 18amp=26.66grams per amp
Tahmazo 4.2KV motor 55EDF=520/20 =26grams per amp.

So babylon5, you either want to tell OK model or Tahmazo to revise their figures because they are not giving your theory the much needed selling angle. Who will bother with 2% efficiency difference?

If you want to drill further, look below:

32000rpm/18amp = 1777.77 rpm per amp
37000rpm/20amp = 1850 rpm per amp

from here, it is worth noting that the additional KV actually churn out more RPM but it is not translated to what? Static thrust, still the ongoing blind measurement of static thrust only. What if the fan is stalled? What if the additional efficiency of more RPM is only useful at flying speed?

[bigfilsing]

You mean like this



This is the 69 mm Tahmazo fan with the Tahmazo 282534DF motor ( 3400 kv)
Theorectical thrust 1150 grams but thats on 4S 3000mah so i think with 3S 2200 i'll get 450 to 550 maybe. I'm still waiting for my lipo to charge

I'm trying another 68mm ( from Jet hobby) on a GS motor tomorrow. Borrowed from a mate.

We shall see

Cheers

[bigfilsing]

Edmond . Do you have any tips for balacing fans. i've got a magnet balancer but still can't seem to get them right

Do you use the tape or CA method ??

Cheers

[edmond22]

Edmond . Do you have any tips for balacing fans. i've got a magnet balancer but still can't seem to get them right

Do you use the tape or CA method ??

Cheers

Tape is a lot quicker and most importantly reversible. CA is a bit messy. I tried both before. Just make sure the tape stay on.

Another thing I noted is that I never needed balancing with wemotec or HET fans, they are great as they come (maybe luck).

[bigfilsing]

Edmond....Thanks for the prompt response.

I guess that explains the additional cost of the "branded" fans !

I have the tahmazo EDF 69 (21 bucks)and it vibrates like hell ( very similar to the 68mm from Jet hobby( 18 bucks)) I'm not complaining. At these prices it's good for experimentation but am still a bit miffed with the Tahmazo as i expected a bit more. I've written to them to ask how to improve or get them dynamically balanced ( i'm not holding my breath waiting for a response thou. )

Test data to come