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Old 03-26-2011, 12:25 PM   #1
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Default How accurate is MotoCalc?

I'm just returning to model flight after many years away. I'm looking at changing out the motor and batteries on my old Katana Mini (that i haven't flow in years). I read up on what people have used historically in this model, with most going for a Hacker A30 28S, while others suggest the Park 480 1020Kv. I have looked at both with MotoCalc and actually neither are advised and in fact the Park 480 910Kv seems to take top honours. My question is does this seem right? should i buy based on this? and.. are these motors still current or have they been superseded by more modern equivalents?

Thanks in advance.
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Old 03-26-2011, 12:52 PM   #2
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Old 03-26-2011, 02:36 PM   #3
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The serious 3D guys seem to be using motors which consume 280W-300W... I saw mention of a Scorpion SII 3008-1090 with an 11x7 on 3s... a Park 480 (really a 200W-220W motor) might fly it okay, but you probably need more punch for unlimited 3D.
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Old 03-26-2011, 05:41 PM   #4
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Originally Posted by ikarus_dm View Post
I'm just returning to model flight after many years away. I'm looking at changing out the motor and batteries on my old Katana Mini (that i haven't flow in years). I read up on what people have used historically in this model, with most going for a Hacker A30 28S, while others suggest the Park 480 1020Kv. I have looked at both with MotoCalc and actually neither are advised and in fact the Park 480 910Kv seems to take top honours. My question is does this seem right? should i buy based on this? and.. are these motors still current or have they been superseded by more modern equivalents?

Thanks in advance.
I've been using motocalc now for about 4 years.

With my Hacker motors, motocalc is within 10% or so of predicted current, voltage, watts, and RPM.

Problem is, many of those "Less expensive" motors have specifications that are not even close to actual values. And more than a few of these motors don't even give the motors winding resistance, an important number for motocalc to use for its predictions.

I even ran across a name brand of motor that had a published KV rating that was off by some 25%.

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Old 03-26-2011, 07:09 PM   #5
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Originally Posted by Dr Kiwi View Post
The serious 3D guys seem to be using motors which consume 280W-300W... I saw mention of a Scorpion SII 3008-1090 with an 11x7 on 3s... a Park 480 (really a 200W-220W motor) might fly it okay, but you probably need more punch for unlimited 3D.
I'll look into this motor, it's not one i've heard of before but that's the sort of feedback i was hoping for, I've been away from this for a while. The park 480 documents at providing nearer 250W but I don't know how accurate this is. Motocalc shows it at 241W for the 910kV (and 287W for the 1020kV - although it warns about the 1020 running very hot).
I'll take a closer look at the Scorpion - thanks for the feedback

Originally Posted by kyleservicetech View Post
I've been using motocalc now for about 4 years.

With my Hacker motors, motocalc is within 10% or so of predicted current, voltage, watts, and RPM.

Problem is, many of those "Less expensive" motors have specifications that are not even close to actual values. And more than a few of these motors don't even give the motors winding resistance, an important number for motocalc to use for its predictions.

I even ran across a name brand of motor that had a published KV rating that was off by some 25%.
This is great feedback too, thank you. I checked all the specs for both the park 480 1020kV and the park 480 910kV, both were correct according to manufacturers data. I guess what it comes down to then really isn't "is motocalc accurate?", but more like "are motor manufacturers honest with their spec"?

Thanks again guys, getting a bit of a feel for this now
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Old 03-26-2011, 10:02 PM   #6
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Originally Posted by ikarus_dm View Post
I'm just returning to model flight after many years away. I'm looking at changing out the motor and batteries on my old Katana Mini (that i haven't flow in years). I read up on what people have used historically in this model, with most going for a Hacker A30 28S, while others suggest the Park 480 1020Kv. I have looked at both with MotoCalc and actually neither are advised and in fact the Park 480 910Kv seems to take top honours. My question is does this seem right? should i buy based on this? and.. are these motors still current or have they been superseded by more modern equivalents?

Thanks in advance.
I can relate my path with Motocalc. I started with the download to try it out. For a few weeks I was disappointed at the results I was getting. I read the tutorial and e-mailed Steve Vorkonetter (stefanv.com) for a little help. Both helped tremendously...Steve was very responsive.
The quality of the output is directly proportional to the quality of your inputs, so be careful and give yourself sanity checks when adding information.
I like it and use it regularly for system building and experiment with different setups prior to my building.
Best advice I can give you is try it (and there are others) until you find one that you have a high confidence level for.
I think it is a great tool for this hobby.

Happy flying!

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Old 03-27-2011, 12:20 AM   #7
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The prop constants are always a question mark as is the battery pack resistance. It is a valuable prediction tool as are other programs and is good for making comparisons.
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Old 03-27-2011, 12:55 AM   #8
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Originally Posted by ikarus_dm View Post
This is great feedback too, thank you. I checked all the specs for both the park 480 1020kV and the park 480 910kV, both were correct according to manufacturers data. I guess what it comes down to then really isn't "is motocalc accurate?", but more like "are motor manufacturers honest with their spec"?

Thanks again guys, getting a bit of a feel for this now
Yup, the motor in question, the mfg KV data was off by 25%. (One of those inexpensive imports)

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Old 03-27-2011, 01:50 AM   #9
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Ive been using MotoCalc for several years as well.

I like it and use it regularly for predicting what a new setup MIGHT perform like, more or less, maybe, aproximately

In general, Ive found it does best with hi quality, name brand gear - motors, batteries, esc's, props. Like others have said - garbage in = garbage out as far as specs.

On top of that, its generally closer when predicting INrunner performance and not as good for OUTrunners.

I get the best results if I have some known data for a particular motor esc combo.

I use geared inrunners a lot and in many cases the same motor can be used with a number of different sized packs and props and planes just by changing the gear ratio.

For example, I have used the same motor direct drive in one plane on 5S with a small prop, direct drive on 3S with a larger prop, and geared on 8S with a much larger prop and geared on 5S and 3S with huge props. Geared inrunners are far more flexible and can be used in a much wider range of applications than any outrunner - but thats beside the point

I started using MotorCalc early on and found its predicted values for my first setup with this motor were off about 15-20%. I tried a few different props and packs and played with the values in Motocalc and gradually got the predicted results to match the "real" values somewhat closer.

I finally decided it was never going to be "perfect" and started using it as a general guide to 'differences' more than an absolute predictor. In other words - how many more amps will you draw going from an 11" prop to a 12" prop or from 3S to 4S or from 1000kV to 1200kV? Its pretty good at that sort of thing as long as you dont push toooo far in the range.

Once motor calc decides a motor is outside its efficiency range the results tend to get further off.

I guess the bottom line is - dont use it to make purchace decisions until you have used it a lot and then only for hi quality gear. Id go by the mfg or user recommendations and then AFTER you have the motor AND a watt meter, you can start to see how its numbers vary from reality and make intelligent adjustments from there.

I think I need a signature.
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Old 03-27-2011, 02:05 AM   #10
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Originally Posted by Larry3215 View Post
Id go by the mfg or user recommendations and then AFTER you have the motor AND a watt meter, you can start to see how its numbers vary from reality and make intelligent adjustments from there.
Nice thing about motocalc, if you've found its predictions are off by 5 or 10%, just save the motor characteristics under a different name, and tweek the KV rating (and battery resistance) until it matches what your motor/battery pack does. Works every time!

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Old 03-27-2011, 10:27 AM   #11
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Interesting reading!

I have about 3 or 4 different brushless powered models now all running different outrunners / inrunners / ESC's etc. Im quite inspired now rig up a test bench and run the motors up under different configs and log some data. I was already thinking of re-using the electrics out of an old model and buying something new, i think this just might be the ticket to helping select the right model.

Thanks a lot guys, very helpful
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Old 03-27-2011, 06:11 PM   #12
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Originally Posted by ikarus_dm View Post
Interesting reading!

I have about 3 or 4 different brushless powered models now all running different outrunners / inrunners / ESC's etc. Im quite inspired now rig up a test bench and run the motors up under different configs and log some data. I was already thinking of re-using the electrics out of an old model and buying something new, i think this just might be the ticket to helping select the right model.

Thanks a lot guys, very helpful
Would this help you?

http://www.rcgroups.com/forums/showt...t=thrust+stand
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Old 03-27-2011, 06:17 PM   #13
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Originally Posted by Dr Kiwi View Post
After looking at this thrust stand, I'm looking at testing my Hacker A60-16M 2400 watt motor with 19X12 APC-E prop.

For safety reasons, guess I'll just tie a spring scale to the tail of the model airplane and power it up.

At any rate, someday I'm going to build one of those for my smaller motors.

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Old 03-27-2011, 06:19 PM   #14
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Originally Posted by ikarus_dm View Post
Interesting reading!

I have about 3 or 4 different brushless powered models now all running different outrunners / inrunners / ESC's etc. Im quite inspired now rig up a test bench and run the motors up under different configs and log some data. I was already thinking of re-using the electrics out of an old model and buying something new, i think this just might be the ticket to helping select the right model.

Thanks a lot guys, very helpful
Take a look at www.motocalc.com, perhaps you might be lucky, and find some of your older motors listed under motocalc's built in library of motor specifications.

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Old 03-27-2011, 10:10 PM   #15
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I started using Motocalc in 2004, and stopped using it around 2006 because the data it gave me was not accurate or precise.

I built my own thrust stand and torque bench and started collecting my own data, so that I know FOR SURE what I'm putting on my aircraft before I put it in the air.

Motocalc is okay when you're first starting out -- but when you've been in the hobby for a few years, you really need to start testing your power systems yourself so that you fully understand what's happening. At that point, you should have a good idea of what all the numbers really mean, and have the ability to do the work yourself.

Just my two cents.

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Old 03-27-2011, 10:57 PM   #16
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Originally Posted by Lieutenant Loughead View Post
I started using Motocalc in 2004, and stopped using it around 2006 because the data it gave me was not accurate or precise.

I built my own thrust stand and torque bench and started collecting my own data, so that I know FOR SURE what I'm putting on my aircraft before I put it in the air.

Motocalc is okay when you're first starting out -- but when you've been in the hobby for a few years, you really need to start testing your power systems yourself so that you fully understand what's happening. At that point, you should have a good idea of what all the numbers really mean, and have the ability to do the work yourself.

Just my two cents.
Don't know if motocalc is more accurate now in 2011. But anyhow, nice thing about all this electric power stuff, with the modern brushless motors and high powered batteries, given a reasonable, proper power system, just about any electric powered model will fly . And once you've got the model put together, it's still a good idea to test and verify with a wattmeter to make certain to not overload anything. Or, "underload" the motor, making the model fly underpowered.

One reason I like those Hacker motors, motocalc is very close on RPM, voltage and current, given the Hacker motor specifications. Not always true on some of those other motors.

As for me, one good guide is rate of climb of your model, and from what I've been able to determine with one of those "How high is it?" gadgets, motocalc is in the ballpark.

But, if you're into hovering and so on, exact measurements would be critical.

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Old 03-28-2011, 02:10 AM   #17
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Don't get me wrong -- I still check motocalc every once in a while, and I still don't trust the results.

For example, ALTITUDE makes a big difference in amp draw of a power system. Cox/Estes is located in Penrose, Colorado and does all their power system testing at altitude -- as a result, their recorded amp draws are very low. When someone buys one of their RTF airplanes and flys it at sea level, they will find a much higher amp draw. (When I interviewed with Cox/Estes a few years ago, I brought up this issue -- but they didn't seem to understand the situation.)

In any event, ALTITUDE is not something that you can enter into Motocalc. That can make all the difference right there.

I don't know -- I just don't trust Motocalc at all. I urge anyone reading this to actually TEST a power system at your own home, and compare your results against Motocalc -- I think you will find there is a rather large gap in the results.

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Old 03-28-2011, 02:29 AM   #18
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Originally Posted by Lieutenant Loughead View Post
In any event, ALTITUDE is not something that you can enter into Motocalc. That can make all the difference right there.

I don't know -- I just don't trust Motocalc at all. I urge anyone reading this to actually TEST a power system at your own home, and compare your results against Motocalc -- I think you will find there is a rather large gap in the results.
Don't know how accurate it is, but my copy of motocalc (version 8.07) under options allows you to enter your elevation, air pressure and temperature.

As for testing, agreed, you absolutely must verify motocalc results with an actual wattmeter. Some time ago, I ran a name brand motor into motocalc, suggested proper prop size. When he actually ran the motor, current was only 50% of motocalc predictions. Not enough power to get the model off of the ground. When I asked him to re-run with a tiny "no load" prop, the motor's published specified KV rating was way the heck off. Not even close.

He had to go from a 6S2P A123 pack to an 8S2P A123 pack to get the RPM and power level he was after.

Ref:
http://www.wattflyer.com/forums/showthread.php?t=44686

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Old 03-28-2011, 03:15 AM   #19
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I tend to use MotoCalc for a quick check, and DriveCalc for a better look! I've entered a heck of a lot of data into DriveCalc, so I like to imagine that its results are closer to reality! For motors (at least for the ones I've contributed) the Kv's used in the calculations are derived from real world testing (no matter how much they differ from manufacturer's/distributor's figures). Certainly for props... the constants (based on real data) are available for a very wide selection of props... on an individual basis. For Motocalc every single APC E prop (within a certain P/D ratio) is given the same constants..... that surely can't be so.
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