Espritmodel.com Telemetry Radio
Reply
Thread Tools
Old Feb 21, 2012, 07:55 AM
Registered User
tim.fuggdesign's Avatar
Bristol UK
Joined Aug 2010
172 Posts
I sent them an email about this as well but I'm not expecting much in a way of a result, they did say that iit might be an idea to wait for the next batch to arrive but having already spent 26 on motors that dont suit my needs I'm reluctent to spend another 13 in the hope that this one will be labelled correctly.
tim.fuggdesign is offline Find More Posts by tim.fuggdesign
Reply With Quote
Sign up now
to remove ads between posts
Old Feb 21, 2012, 07:58 AM
Registered User
Snoggle's Avatar
Deutschland, NDS, Oldenburg (Oldenburg)
Joined Aug 2011
572 Posts
yes thats exactly what i think... and in my case its not just 13 but ~18 pound because of european shipping... if i knew that the motor i received is mislabled and the one i will be getting is right i might do it... but take another leap in the dark? no way! with the money i have spent then i could have bought some higher quality motor right away...

but maybe if there are enough customers with this problem that report back they may do something about it!
Snoggle is offline Find More Posts by Snoggle
Reply With Quote
Old Feb 21, 2012, 08:05 AM
Registered User
tim.fuggdesign's Avatar
Bristol UK
Joined Aug 2010
172 Posts
lets hope so, it might be an idea to leave a review on the GC website listing your results, it might encourage others to post there results and lend a bit of weight to our argument.
tim.fuggdesign is offline Find More Posts by tim.fuggdesign
Reply With Quote
Old Feb 21, 2012, 08:09 AM
Registered User
Snoggle's Avatar
Deutschland, NDS, Oldenburg (Oldenburg)
Joined Aug 2011
572 Posts
i will do so later, i am just waiting for a final result from giantcod about the support ticket i opened...
Snoggle is offline Find More Posts by Snoggle
Reply With Quote
Old Feb 21, 2012, 08:34 AM
NaN
Andy2No's Avatar
Manchester, UK
Joined Nov 2005
3,724 Posts
There's a section of the Giantcod forum specifically for motor test results, meant as a resource for people wanting to buy motors:

http://www.giantcod.co.uk/forum/viewforum.php?f=24

It would be good to post your data there - feel free to add my spreadsheet of your results, Snoggle. You might want to post about it somewhere that is more likely to get noticed too.

FYI, response from the staff or Rob, the owner, via the forum is very unlikely these days. You're more likely to get responses from other customers though. I find the forum email notifications don't work any more - at least not for me - so you'll probably have to check for replies the old fashioned way.

Many of the motors I've tested don't meet the quoted specs. Keda have been better than most, apart from having a strange definition of Rm (or possibly just guessing the figures). It might be worth contacting Keda directly. Maybe they still care about their reputation.
Andy2No is online now Find More Posts by Andy2No
Reply With Quote
Old Feb 21, 2012, 08:39 AM
Registered User
Snoggle's Avatar
Deutschland, NDS, Oldenburg (Oldenburg)
Joined Aug 2011
572 Posts
i got a reply on my ticket from rob this morning, i wrote an answer to that right away. you are right about the forum, but i guess there are not that much people looking in there.

contacting keda might be an option, but then again if they want me to send the motor in and i will have to pay for the shipment myself, than that will be already more than i actually paid for the whole motor. lets see what will happen... i will for sure report on what i did and with what result here...
Snoggle is offline Find More Posts by Snoggle
Reply With Quote
Old Feb 21, 2012, 09:53 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,644 Posts
Beyond the possibility of a simple labeling error there is also the possibility that the turn counts in the windings have changed. And also, the Kv that results from a given turn count is also affected by the magnets, the gap between the stator hammerheads, and even factors as subtle as the number of crossing turns in the wind. So any number of things can change the Kv.

And then the process of measuring the Kv can vary from one manufacturer to another and again with the type and quality the instrumentation and even who is running the tests.

On the motor rewinding forums we tend to use the simpler methods for measuring the Kv (no load RPM / no load voltage) and to not take the results too seriously as far as accuracy and repeatibility. We sometimes call it a "raw Kv" to point that it is sort of approximate or not accurate to industry standards. A "raw" Kv will generally be a little higher than a Kv taken in the industry.

A variation of one turn on a motor can change the resulting Kv by 50-60 RPM or more, even up into area 100 RPM or more. And any winding errors like arms with miscounted turns will cause further variation.

The process of winding a motor to the Kv that works best with one prop is once of the incentives of motor rewinding. We always feel that we can get it perfect with a small adjustment on the next rewind if this one is not that way.

Jack
jackerbes is offline Find More Posts by jackerbes
RCG Plus Member
Old Feb 21, 2012, 02:27 PM
Registered User
Snoggle's Avatar
Deutschland, NDS, Oldenburg (Oldenburg)
Joined Aug 2011
572 Posts
you are absolutely right and i am used to variance of +/-10% from the kv a motor is rated to the "raw kv" which i measure at home, but in this case it is 20% lower than it is rated at, and that is simply too much of a manufacturing aberrance!
Snoggle is offline Find More Posts by Snoggle
Reply With Quote
Old Feb 21, 2012, 03:26 PM
Registered User
Snoggle's Avatar
Deutschland, NDS, Oldenburg (Oldenburg)
Joined Aug 2011
572 Posts
Here is the Mail i just sent to KDModel (the manufacturer of the Keda motors)

Quote:
Dear Sir or Madam,

i recently purchased one of the brushless motors ThumRun TR 2834/04 from Giantcod.co.uk in Great Britain.

I have a problem with the motor however and i am not sure if this is a general problem or i might have received a mislabled or faulty motor.

As per the technical specs and the label on the motor, this motor is rated at 2650 KV. I choose that motor specifically because i wanted a motor with about that KV and the size/weight of the 2834 series.

But my bench tests at home using high quality measuring equipment showed that the actual KV of the motor i received is not 2650 but more like 2100-2150 KV. The tests were repeated with different lipo batteries and different escs but the rpm readings form the no load test runs were all about the same and resulted in a calculated kv of around 2100-2150.

So my question is, is a 20% difference to the rated KV normal/acceptable? I know there are differenced due to variance in manufacturing the motors and the quality of the turns, but imho 20% difference seem a bit too much.

With the KV the motor actually has it is pretty useless to me, so i am a bit disappointed and want to know if other customers experienced similar issues and what i can do about this.

Yours sincerly,


XXX

i will keep you guys up to date if i receive any answer from them!
Snoggle is offline Find More Posts by Snoggle
Reply With Quote
Old Feb 21, 2012, 06:41 PM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,197 Posts
On the motor rewinding forums we tend to use the simpler methods for measuring the Kv (no load RPM / no load voltage) and to not take the results too seriously as far as accuracy and repeatibility. We sometimes call it a "raw Kv" to point that it is sort of approximate or not accurate to industry standards. A "raw" Kv will generally be a little higher than a Kv taken in the industry.

My experience is that "calculated Kv" derived by using programs like DriveCalc or MotoCalc.. is always higher than "raw Kv" [RPM/V].... one can never hope that a motor will be absolutely frictionless and 100% efficient... the measured RPM at a certain voltage has GOT to be lower than the theoretical possible (which is what I assume DriveCalc and MotoCalc are computing).
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Old Feb 23, 2012, 07:28 AM
Registered User
tim.fuggdesign's Avatar
Bristol UK
Joined Aug 2010
172 Posts
Well hers the reply I got from Rob at giant cod:

Hi Tim,
I would order a different type of motor if you and others aren't happy with the results.
Regards,
Rob.

Hmm, not really sure what to make of that.
tim.fuggdesign is offline Find More Posts by tim.fuggdesign
Reply With Quote
Old Feb 23, 2012, 09:16 AM
Registered User
Snoggle's Avatar
Deutschland, NDS, Oldenburg (Oldenburg)
Joined Aug 2011
572 Posts
very good idea, but as long as i do not know if this is an issue with my motor or the kv on all those motors differs that much from what they are rated at bying a different motor would just be buying a pig in a poke...
Snoggle is offline Find More Posts by Snoggle
Reply With Quote
Old Feb 27, 2012, 01:45 PM
Specialist in Crashing
UK, Loughborough
Joined Jan 2004
1,106 Posts
I am after a motor for a ~450g parkflyer as a first aileron trainer. I have read through this thread and would I be correct in saying a Keda TR2830/14 ~1620kv motor would be a good choice when running on 2s? If so what sort of prop would I be looking at, something like an 8x6E?

Or am I better to go for a different make motor?
saitrix is offline Find More Posts by saitrix
Reply With Quote
Old Feb 27, 2012, 03:20 PM
Registered User
Snoggle's Avatar
Deutschland, NDS, Oldenburg (Oldenburg)
Joined Aug 2011
572 Posts
do you already have the batteries? if so, the 2830/14 would be fine with 8x6 on 2s, if you need a little more thrust you could also go for a 9x6 without problems.

if you don't have the batteries yet i would go for a 3s setup though, 3s seems a lot more versatile to me... and its more effecient as well, especially on that particular motor. with the 2s setups you will only get ETA in the 6x% region, with a 3s setup and a 7x4 prop you get an efficiency of almost 75%.
Snoggle is offline Find More Posts by Snoggle
Reply With Quote
Old Feb 27, 2012, 03:52 PM
Specialist in Crashing
UK, Loughborough
Joined Jan 2004
1,106 Posts
Yeah the reason for a 2s setup is due to the abundance of 2s Gens Ace 1300mah packs I have! I don't mind taking a little hit to the eta if it means I don't need to get loads of new batteries. Will probably give both 8x6 and 9x6's a go. Are the APC E series props the one to go for?
saitrix is offline Find More Posts by saitrix
Reply With Quote
Reply


Thread Tools