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Old Oct 10, 2012, 12:46 PM
buyer of the farm
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Originally Posted by Eli Lipschitz View Post
Here are the specifics: it is a waste of time because you will spend lots of your free time playing with it when it is not very helpful. Like I mentioned, using a watt meter and extra propellers is perfectly correct. Propellers are cheap-most planes only have 2 or 5 possible propellers anyway, given that model plane propellers are manufactured in standard sizes. (11x8, 12x6, 12x8 - not 11.7x8, 11.9x5.5, et.)

I recommend this setup to everyone. A thrust stand and a watt meter-pick your desired pitch speed, and then use the prop with that speed and the greatest thrust-watt.
Non-responsive. Try again. I said that manufacturer and model number are more important than diameter and pitch. Your turn. Danger: next I trot out actual data. Would you believe that a 12x6 prop can draw fewer amps than an 11x4.7? The water could get very deep if you wish to continue with your incorrect line of reasoning.
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Old Oct 10, 2012, 12:58 PM
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Originally Posted by Rockin Robbins View Post
Non-responsive. Try again. I said that manufacturer and model number are more important than diameter and pitch. Your turn. Danger: next I trot out actual data. Would you believe that a 12x6 prop can draw fewer amps than an 11x4.7? The water could get very deep if you wish to continue with your incorrect line of reasoning.
I guess you just refuse to read what I wrote. Nothing will be more accurate than testing your props in person-even if your calculator is more accurate. There are also lots of motors (thousands) available, so your calculator most like won't have individual motors listed.

Test different propellers with a thrust stand and a watt meter. Use the one with the highest thrust and lowest power ratio. If you are calculating pitch speed too, then just pick the highest thrust-power with your pitch speed.
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Old Oct 10, 2012, 02:06 PM
buyer of the farm
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Okay let's go one question at a time. First question:
Quote:
Are you claiming that a normal hobbyist can duplicate the quality and skill of a Dr Kiwi and be willing to pay many times the cost of the models he flies to obtain information that has already been bought and paid for?
Simple question. How much money is worth spending for test equipment that is nowhere near as good as Dr Kiwi's? How good are you at performing these tests and obtaining valid results, compared to Dr. Kiwi? Are you going to purchase a hundred dollars worth of random props for your testing and toss $96 of them so you can do the testing yourself? As a practical matter, what is the problem with benefiting from more qualified testing by people who have thousands of dollars invested in their equipment?

I say learning from others' experience is the key to progressing faster in the hobby. It makes no sense to reinvent the wheel at great expense, especially when it takes a long time to reinvent it and your wheel won't be as good as existing wheels.

You have been entirely non-responsive on this issue.
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Old Oct 10, 2012, 02:14 PM
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I have a watt meter on the way, is there a post on the forums showing a guy how to setup and use the watt meter,or does it come with anything (yea right lol) like a manual to show a new guy to watt meters how to test different motors and props ?
If not for this forum,there is no telling how many esc,s motors and whole planes i would have ruined lol
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Old Oct 10, 2012, 03:18 PM
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RR, don't waste your time with Eli. Just.... don't.

Quote:
I have a watt meter on the way, is there a post on the forums showing a guy how to setup and use the watt meter,or does it come with anything (yea right lol) like a manual to show a new guy to watt meters how to test different motors and props ?
Wattmeters are fairly intuitive beasts. You plug them in between your battery and your load and then watch (and maybe record) the numbers on the screen. They actually have a whole lot of uses in this DC-oriented hobby besides power system testing, though. I bought mine specifically to test motor and prop combos, but it's a really handy little tool for general electrical stuff like measuring servo/LED current draws or getting quick voltage readings off lipos.
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Old Oct 10, 2012, 03:35 PM
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RR, don't waste your time with Eli. Just.... don't.



Wattmeters are fairly intuitive beasts. You plug them in between your battery and your load and then watch (and maybe record) the numbers on the screen. They actually have a whole lot of uses in this DC-oriented hobby besides power system testing, though. I bought mine specifically to test motor and prop combos, but it's a really handy little tool for general electrical stuff like measuring servo/LED current draws or getting quick voltage readings off lipos.
What is the problem mate? To be clear, RR is talking to someone else, not me. But in case you noticed that-I have a great post, and great info. Just measure thrust and watts. Calculators are nice, but nothing will be better than actually testing it yourself. What's wrong with this? RR is entitled to his opinion, but I think it's clear my info is good. This doesn't make anyone wrong, it's just something I hope people can make use out of.
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Old Oct 10, 2012, 03:39 PM
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Originally Posted by Rockin Robbins View Post
Okay let's go one question at a time. First question:


Simple question. How much money is worth spending for test equipment that is nowhere near as good as Dr Kiwi's? How good are you at performing these tests and obtaining valid results, compared to Dr. Kiwi? Are you going to purchase a hundred dollars worth of random props for your testing and toss $96 of them so you can do the testing yourself? As a practical matter, what is the problem with benefiting from more qualified testing by people who have thousands of dollars invested in their equipment?

I say learning from others' experience is the key to progressing faster in the hobby. It makes no sense to reinvent the wheel at great expense, especially when it takes a long time to reinvent it and your wheel won't be as good as existing wheels.

You have been entirely non-responsive on this issue.
Hi, just to be clear that is not me you are quoting. But I'd like to add, that motor/prop combos only have a few possible prop combinations. My Slow Stick is not going to have a prop smaller than 9" and not bigger than 13"-this is probably 5 or 9 possible prop combinations. Propellers are dirt cheap, and a watt meter is only $20. A scale/thrust stand is another $20. These are both things you should have (and need for high performance models) anyways, so you are not spending anything close to "hundreds of dollars".

The answer is yes, your own tests will be way more accurate than any Dr. Kiwi man on the internet. It is really simple. Measure your thrust, and compare it to your wattage. If you have pitch speed in mind, just calculate it yourself and then pick the best pitch speed and thrust-watt prop. It's as simple as apple pie.
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Old Oct 10, 2012, 04:15 PM
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What is the problem mate? To be clear, RR is talking to someone else, not me.
You're not even making sense here. I mean, this is grade-A nonsense.

Quote:
he answer is yes, your own tests will be way more accurate than any Dr. Kiwi man on the internet. It is really simple. Measure your thrust, and compare it to your wattage. If you have pitch speed in mind, just calculate it yourself and then pick the best pitch speed and thrust-watt prop. It's as simple as apple pie.
Simple, yes, but terrible advice in more ways than I feel need to be explained.
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Old Oct 10, 2012, 04:29 PM
buyer of the farm
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I'll let the issue lie. Nothing to be gained here. I appreciate the fact that Dr Kiwi and others have spent thousands of dollars and many years building up for us a database of real and reliable test numbers for a tremendous variety of RC power system components and programs with substance like Drive Calculator and MotoCalc can use this actual testing data to predict performance of an unbuilt system with great accuracy.

It's obvious that there are too many props available to be able to buy the gamut and test them. Let's take Eli's Slow Stick and grant him his restrictions of 9" to 13" diameters. Let's ask Drive Calculator which props fit in this range: it finds 33 9" and 9.5" props, 37 10" props, 21 11" props, 20 12" props and 20 13" props. Now at 50 apiece that's 131 props times 50. Only $65.00 worth of props for testing. What? It's more like $4.00 apiece? Still cheap, eh? Need I publish the list?

<irony>Oops, guess he was right. There ARE only 5 to 9 different props (plus 122) to test and it's cheap as beans. Hate it when I'm wrong. Okay, just buy the props and test 'em. It's cheap. I stand corrected.</irony>
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Old Oct 10, 2012, 06:56 PM
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Originally Posted by C₄H₁₀ View Post
RR, don't waste your time with Eli. Just.... don't.



Wattmeters are fairly intuitive beasts. You plug them in between your battery and your load and then watch (and maybe record) the numbers on the screen. They actually have a whole lot of uses in this DC-oriented hobby besides power system testing, though. I bought mine specifically to test motor and prop combos, but it's a really handy little tool for general electrical stuff like measuring servo/LED current draws or getting quick voltage readings off lipos.
Ok so if i want to test a prop/motor combo, i plug watt meter into battery and then plug motor into it on other end ? what about the esc ?
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Old Oct 10, 2012, 07:15 PM
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Nope. You plug the wattmeter in between the battery and ESC. The load in this case is the motor AND the ESC, because you need the ESC to drive the motor. The ESC itself doesn't affect the numbers enough to matter.
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Old Oct 10, 2012, 07:26 PM
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Originally Posted by C₄H₁₀ View Post
Nope. You plug the wattmeter in between the battery and ESC. The load in this case is the motor AND the ESC, because you need the ESC to drive the motor. The ESC itself doesn't affect the numbers enough to matter.
thank you !
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Old Oct 10, 2012, 08:17 PM
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Originally Posted by Rockin Robbins View Post
I'll let the issue lie. Nothing to be gained here. I appreciate the fact that Dr Kiwi and others have spent thousands of dollars and many years building up for us a database of real and reliable test numbers for a tremendous variety of RC power system components and programs with substance like Drive Calculator and MotoCalc can use this actual testing data to predict performance of an unbuilt system with great accuracy.

It's obvious that there are too many props available to be able to buy the gamut and test them. Let's take Eli's Slow Stick and grant him his restrictions of 9" to 13" diameters. Let's ask Drive Calculator which props fit in this range: it finds 33 9" and 9.5" props, 37 10" props, 21 11" props, 20 12" props and 20 13" props. Now at 50 apiece that's 131 props times 50. Only $65.00 worth of props for testing. What? It's more like $4.00 apiece? Still cheap, eh? Need I publish the list?

<irony>Oops, guess he was right. There ARE only 5 to 9 different props (plus 122) to test and it's cheap as beans. Hate it when I'm wrong. Okay, just buy the props and test 'em. It's cheap. I stand corrected.</irony>
For a Slow Stick, one will only be using 5 or 9 propellers. This is not rocket science, just models/toys. A propeller is a propeller. You are only going to save up to 25 % about.

I'm very confused why some really think it's a bad idea to test this stuff yourself. I didn't say Dr. Kiwi is bad, just that it is probably a waste of time because you'll spend lots of time having fun on it instead of using it. I know, because I've done that before.
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Old Oct 10, 2012, 08:20 PM
buyer of the farm
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Originally Posted by Eli Lipschitz View Post
For a Slow Stick, one will only be using 5 or 9 propellers. This is not rocket science, just models/toys. A propeller is a propeller. You are only going to save up to 25 % about.

I'm very confused why some really think it's a bad idea to test this stuff yourself. I didn't say Dr. Kiwi is bad, just that it is probably a waste of time because you'll spend lots of time having fun on it instead of using it. I know, because I've done that before.
I just proved that within your restricted idea of what's appropriate for a Slow Stick there are 131 propellers to choose from. How do you get from there to 5 to 9? Where do you obtain your 25%. You're a mile off, by the way, and I have the research to prove it.
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Old Oct 10, 2012, 08:54 PM
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For a Slow Stick, one will only be using 5 or 9 propellers. This is not rocket science, just models/toys. A propeller is a propeller. You are only going to save up to 25 % about.
I'm still unclear by exactly what you mean by "using 5 or 9 propellers". Is this supposed to be a range of between 5 and 9 different props?

... And save 25% of what?

Quote:
I'm very confused why some really think it's a bad idea to test this stuff yourself.
Testing one's own props is a good idea. The only bad ideas here are the testing criteria you've laid out. Thrust per amp? That's like choosing a new car based solely on its power-to-weight ratio without considering any other factors (fuel efficiency, safety ratings, options, price, type of vehicle etc.).

If I chose every prop based on its ratio of static thrust to current consumption, I'd end up with a lot of planes that flat-out don't fly. You mention considering pitchspeed as a sort of offhanded remark while attaching vitrually no significance to it.

Quote:
I didn't say Dr. Kiwi is bad, just that it is probably a waste of time because you'll spend lots of time having fun on it instead of using it. I know, because I've done that before.
Phil's test data collection is solid gold. Anyone who says it's anything else is either blindly ignorant or is fooling themselves. The difference between his collected data and the multitude of calculators out there is... REAL-WORLD TEST DATA. It's actual empirical information taken straight from his test stand regarding a staggering number of motors and props, each at a wide range of voltage inputs.
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