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Old 01-31-2014, 12:57 AM   #1
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Default Computer Motor Performance Program Accuracy

There are many different computer programs out there that are useful for predicting how your power setup will perform.

One good one that I use a lot is www.motocalc.com. Problem is, these programs are only as accurate as the specifications that are provided by the motor manufacturer.

Case in point is my new Hyperion ZS3025-10 motor. Running this motor through motocalc showed results very close to the Hyperion 3025-10 motors published performance data.

Problem is, in the real world, the 3025-10 performance is far off from actual results. With the 12X6 prop recommended by Hyperion, the current and watts pulled is off by some 40%.

So, what to do???
I just ran some tests on this motor, with a 13X6.5 Prop, powered by a 5S1P A123 battery pack. The results were plugged into motocalc. The Hyperion motor specs were tweaked to match the actual performance data. Next, further tests were conducted with an 8X5 prop, and no prop. Results are attached.

The original Hyperion KV spec was 775KV. Tweaking that KV number to 640KV resulted in the motocalc predictions being within about 5% on the prop sizes tested.

So, if you have a no-name motor, or a motor whose specs are quite a bit off, just tweak the KV rating spec of the motor, and this will provide some guide on how different sized props will work. If you've got a motor mfg that does not provide the motor winging resistance, that can really provide problems with these computer programs.


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Old 01-31-2014, 08:58 AM   #2
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Just wondering how you arrived at a kv of 640? As you will know a rough way to find Kv is to run the motor with the prop off while recording input voltage and RPM. Divide RPM by voltage and you get an approximation of motor KV. Under load other variables come into it so you cant really take load RMP to estimate kv from.

Doing the kv calc with no prop, with your figures ( 11700PRM and 16.53V), yields 707Kv. Testing this way generally gives slight low Kv numbers because there is still some load on the motor, and Kv is for the theoretical 'no load' condition, so real kv might be closer to 750, so not far off Hyperion's stated figure.

Was motor calc using the actual measured winding resistance??
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Old 01-31-2014, 05:47 PM   #3
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Originally Posted by JetPlaneFlyer View Post
Just wondering how you arrived at a kv of 640? As you will know a rough way to find Kv is to run the motor with the prop off while recording input voltage and RPM. Divide RPM by voltage and you get an approximation of motor KV. Under load other variables come into it so you cant really take load RMP to estimate kv from.

Doing the kv calc with no prop, with your figures ( 11700PRM and 16.53V), yields 707Kv. Testing this way generally gives slight low Kv numbers because there is still some load on the motor, and Kv is for the theoretical 'no load' condition, so real kv might be closer to 750, so not far off Hyperion's stated figure.

Was motor calc using the actual measured winding resistance??
I just ran the three different loads on the motor, and adjusted the "KV" rating of the motor as required so the motocalc results matched what the actual measurements showed. Then the motor was saved in motocalc as a different name.

The important part of this thread is not so much how accurate motocalc is, or Hyperion (or any other motor mfg for that matter) is, but how to tweak what ever computer program you are using to match the real world for the motor being analyzed. Especially on some of those no-name el-cheapo motors with specifications that are not realistic.

For me, it showed that the proper propeller for MY model and the way I fly would be that APC-E 13X6.5, without having to go buy a whole bunch of props that may, or may not work out well.

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Old 02-03-2014, 03:18 AM   #4
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Whether or not the Motocalc results match reality, the real issue here is the Kv determination.... an intrinsic property of the motor which CANNOT be fudged. If no-load testing indicates 11700PRM and 16.53V, that provides a minimal value of 707Kv (actual Kv MUST be a bit higher since there is some load (friction etc) which MUST reduce the actual motor rpm). Suggesting that abitrarily deciding on 640Kv to resolve computational inaccuracies in MotoCalc predictions does resolve the issue.
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Old 02-03-2014, 05:33 AM   #5
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Originally Posted by Dr Kiwi View Post
Whether or not the Motocalc results match reality, the real issue here is the Kv determination.... an intrinsic property of the motor which CANNOT be fudged. If no-load testing indicates 11700PRM and 16.53V, that provides a minimal value of 707Kv (actual Kv MUST be a bit higher since there is some load (friction etc) which MUST reduce the actual motor rpm). Suggesting that abitrarily deciding on 640Kv to resolve computational inaccuracies in MotoCalc predictions does resolve the issue.
I wonder just how much the internal construction of these brushless motors affects how they operate under load, versus no load. Things like the magnetic gap between the magnets and stator, width of the "T" part of the stator, quality of the stator steel laminations, how thick the "I" part of the stator steel laminations is and so on.

Don't know if it can happen with our brushless motors, but if you magnetically saturate the "I" part of the stator steel laminations by severely overloading the motor, things will go south in a quick hurry. I suspect there are wattflyer readers that can respond to this issue.

One thing of note, the motors winding resistance. More and more brushless motor mfg's are not providing this information, and it has a definite effect on motor efficiency, and so on.

It's interesting. Motocalc and another very popular computer program were nearly identical on predictions of a large motor operations as reported in another wattflyer thread. But, at higher loads above safe limits, Motocalc suggested the motor would overheat very quickly, where the other motor calculator program did not.

Motocalc apparently also includes the weight of the motor itself in its calculations. Just take any motor, run the motocalc program, them change the motor weight to 50% of what it was, then run it again. Motocalc will definitely show a difference in performance, even though the KV rating, no load current, and winding resistance has not changed.

Bottom line, methinks all of these programs are only a guide to help decide if everything is safe to operate. And, after assembling the components, double checking results with a wattmeter is very wise. In my case with that Hyperion motor, a change was required to go to a 13X6.5 prop, versus Hyperions recommendation of a 12X6. At least for the model I've stuck that motor into.

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Old 02-03-2014, 05:50 AM   #6
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Denny - where did you get the motor data on the GS3025-10? The data sheet I found shows a kV of 705 and an Io of 1.38 and an Ir of 0.026 Ohm.

http://media.hyperion.hk/dn/gs/

I dont see any prop test data at the voltages your showing - only up to 3S.

http://media.hyperion.hk/dn/gs/GSpropdata.pdf

The values listed in MotoCalc can be edited by users and can sometimes be off significantly.


In my experience MotoCalc - and all of the other prediction programs Ive tried - are almost never all that close to reality. There are just too many variables.

As you said, the predictions can only be as good as the specs, but it goes beyond the motor specs.

For starters, the pitch on the props we use are often not whats on the label and results can vary from one "identical" prop to the next by a good bit.

Then motor kV can vary between "identical" motors. Ive measured as much as 10% difference on hi dollar, "name brand" motors and more than 50% on some of the cheaper motors back when I was beta testing.

Then there are esc variables like the forward resistance, how they do timing and sync etc.

Finally our batteries play a large roll in the predictions. The Ir of a pack has a lot to do with performance as Im sure you know. Going from a cheap or old pack to a newer hi performance pack can easily make a 30% difference in power output all by itself. Heck, just warming a pack up makes a big difference on some days - like today

That can all ad up to very very large differences between predicted values and actual results.

Ive played around a good bit with MotoCalc trying to tweek the predictions to match my test results. Its very rare that you can get ALL the parameters to agree - voltage, amps AND rpm. Ive had to adjust Ir on motors and batteries and esc, kV, Io etc. Just tweaking the kV has never worked too well for me.

I think I need a signature.
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Old 02-03-2014, 06:02 AM   #7
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Originally Posted by Larry3215 View Post
Denny - where did you get the motor data on the GS3025-10? The data sheet I found shows a kV of 705 and an Io of 1.38 and an Ir of 0.026 Ohm.

http://media.hyperion.hk/dn/gs/

I dont see any prop test data at the voltages your showing - only up to 3S.

http://media.hyperion.hk/dn/gs/GSpropdata.pdf

The values listed in MotoCalc can be edited by users and can sometimes be off significantly.


In my experience MotoCalc - and all of the other prediction programs Ive tried - are almost never all that close to reality. There are just too many variables.

As you said, the predictions can only be as good as the specs, but it goes beyond the motor specs.

For starters, the pitch on the props we use are often not whats on the label and results can vary from one "identical" prop to the next by a good bit.

Then motor kV can vary between "identical" motors. Ive measured as much as 10% difference on hi dollar, "name brand" motors and more than 50% on some of the cheaper motors back when I was beta testing.

Then there are esc variables like the forward resistance, how they do timing and sync etc.

Finally our batteries play a large roll in the predictions. The Ir of a pack has a lot to do with performance as Im sure you know. Going from a cheap or old pack to a newer hi performance pack can easily make a 30% difference in power output all by itself. Heck, just warming a pack up makes a big difference on some days - like today

That can all ad up to very very large differences between predicted values and actual results.

Ive played around a good bit with MotoCalc trying to tweek the predictions to match my test results. Its very rare that you can get ALL the parameters to agree - voltage, amps AND rpm. Ive had to adjust Ir on motors and batteries and esc, kV, Io etc. Just tweaking the kV has never worked too well for me.
Hi Larry
The motor I have is a Hyperion ZS3025B-10, not GS3025-10. It's a different wind.

http://media.hyperion.hk/dn/zs/zs30.htm Check the propeller data on this web page. Question, I could not find that APC 12X6SP prop. Have you heard of it

And, agreed: after running all the numbers on what ever calculator used, you still need do double check with an actual wattmeter with the battery/motor/propeller/ESC that is installed in the model.

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Old 02-03-2014, 07:29 AM   #8
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Sorry Denny! I am going blind too!

Never heard of an APC SP prop - Sport Prop?

I think I need a signature.
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Old 02-03-2014, 08:56 AM   #9
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SP is probably a typo of SF
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Old 02-03-2014, 04:50 PM   #10
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I hope not - the SF props are not rated for that kind of power. Thats also running at almost double the max rated rpm for a 12" SF prop!

I think I need a signature.
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Old 02-04-2014, 04:02 AM   #11
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12x6 Sport: http://www.apcprop.com/ProductDetail...ctCode=LP12060
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Old 02-04-2014, 05:56 AM   #12
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Originally Posted by Dr Kiwi View Post
Ah ha
Thanks for clarifying. It's appreciated.

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Old 02-04-2014, 06:05 AM   #13
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Originally Posted by Larry3215 View Post
In my experience MotoCalc - and all of the other prediction programs Ive tried - are almost never all that close to reality. There are just too many variables.

As you said, the predictions can only be as good as the specs, but it goes beyond the motor specs.

For starters, the pitch on the props we use are often not whats on the label and results can vary from one "identical" prop to the next by a good bit.

Then motor kV can vary between "identical" motors. Ive measured as much as 10% difference on hi dollar, "name brand" motors and more than 50% on some of the cheaper motors back when I was beta testing.

Then there are esc variables like the forward resistance, how they do timing and sync etc.

Ive played around a good bit with MotoCalc trying to tweek the predictions to match my test results. Its very rare that you can get ALL the parameters to agree - voltage, amps AND rpm. Ive had to adjust Ir on motors and batteries and esc, kV, Io etc. Just tweaking the kV has never worked too well for me.
[/SIZE]
Yeah, agreed: All though my two Hacker A50-12S motors turn identical RPM's on the same battery pack and same propeller.

As for accuracy, before retiring at work, we had an analog type high voltage breaker control that was specked at plus/minus 10% accuracy in trip values, over current timings, instant trip points and so on. And, it was a real to hold those tolerances over the full range of trip values, temperature (-40F to plus 140F) and a lot of other stuff.

Now we've got computerized controls accurate to plus/minus one percent. To do that requires 0.1% or better components in everything.

So here we are with our brushless motors, and the mfg tolerances they have. It's easy to count winding turns, but we've got variables in magnet strength, magnetic air gaps, and probably a lot of other stuff. Changing that magnet airgap has a very substantial effect on the motor. I've got several www.gobrushless.com motors with different air gaps that I wound some 10 years ago to prove the point.

Methinks that if the mfg actually tests their motors, and finds a real clinker in their production batch, they'd throw it out. But, perhaps some of those much lower cost mfg's ship everything they make. Who knows.

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