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Old Dec 10, 2004, 07:40 PM
npm
Registered User
Portland OR
Joined Jan 2003
86 Posts
Not to worry ChuckD. Here's the formula:

Power = current X voltage

Power is measured in Watts
Current is measured in Amps
And of course votage is measured in volts

If you know any two of the three you can figure the third.

Also keep in mind

Voltage = current X resistance

Resistance is measured in ohms

It's been about 25 years since my last physics class so if this isn't right, please somebody set me straight.

npm
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Old Dec 10, 2004, 07:41 PM
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Lol

I love parkzone.


espicaly there Stryker.












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Old Dec 10, 2004, 07:59 PM
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NPM,

Thanks a bunch...so my Mega CAN handle the power with a gearbox and prop! Now I am in business...

Again, for your help, I thank you; no end!


Spence....if it flies, I will buy one....


--Chuck
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Old Dec 10, 2004, 09:02 PM
Counter agent of B.S.
United States, IN
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Quote:
Originally Posted by ChuckD
So that is how much it can take? 480 watts? Is that correct (sorry for the 'needing to have it beaten across my forehead' approach)...but I am still new to all of this.

My best,

--C
Watts = Volts x Amps

A fully charged 4S1P LiPo pack will have a reading of 16.8 volts fresh off the charger (a bit less a few minutes later). Sooo, take 16.8(volts) x 25(amps)=420 watts.

But why the sudden interest in watts? Mega's specs & LiPo specs deal only in amps & volts.

Best you get an Astro Flight Watt-Meter & CHECK your setup for yourself!

Jim
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Old Dec 11, 2004, 12:55 AM
If it floats....sail it!
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Elk Grove, CA
Joined Sep 2002
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Quote:
Originally Posted by a1pcfixer

But why the sudden interest in watts? Mega's specs & LiPo specs deal only in amps & volts.

Best you get an Astro Flight Watt-Meter & CHECK your setup for yourself!

Jim

npm:
As a former HS Physics teacher, I can confirm you are correct!

fixer:
The reason Chuck is interested in watts is that is really what matters in working with motors. In fact, it is really the energy lost to heat that matters, since that is what heats up the motor and too much heat will either demagnetize the permanent magnets or melt the insulation on the windings, shorting it out. Programs like MotoCalc come in handy when selecting the correct propeller since they can show the watts lost to heat. The programs get you close, but real world testing (via current and voltage meters or an integrated meter like the Astro Whattmeter) is necessary, particularly if you are using expensive and current sensitive lipo packs.

The motor manufacturers give the limits in interesting ways; they specify the voltage limit since that is proportional to the rpm and if the motor spins too fast it will throw a magnet damaging the motor; then they specify the current limit since the wire is a fixed diameter and if you try to run more current through the wire it will heat up and melt the insulation, and then assuming you are running less than the max voltage and max current, they tell you the max wattage because that is all the heat the motor can dissipate (you check your own current x voltage).

These are all just approximations anyway. Depending upon how much air flow you have over the motor, and the ambient air temperature, you can push the motor past the specs without any trouble. The Stryker flown on a 50F day is great with motor out in the open and lots of cold air flowing over it. Put the same motor inside a Tiger Moth 400 with a fully enclosed cowl and you will cook it.

FoamCrusher
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Old Dec 11, 2004, 01:05 AM
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Joined Dec 2003
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ChuckD

Remember, when it comes to wives (who we love very much), its much easier to get forgiveness than permission especially when it comes to R/C planes.

I was LOL at your earlier description of talking about justifying the expense of the hobby to your wife.

Rgds,

Mike
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Old Dec 11, 2004, 06:17 AM
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Thanks Jim, and again, Foam...

Although becoming an avid pilot over the past few months, there are always the questions that humble me.

My concerns with WATTS are driven simply from a guy who does not know better; and after three decades of 'just trying it' and then leaving 'it' in a box after I screwed it up...I now ask the proverbial experts before I jump.
With age comes wisdom; and mine is the wisdom of inquiry...don't try to do plumbing, dont try to fix a microwave, and for the love of my mother...DONT HOOK UP A 4s LIPO to a 300 dollar power system and then toss it into the air if all you are going to do is make a flying ball of fiery styrofoam.

(hey, it only took 30 years, right?)

I still slip sometimes, though...like buying the wring gearbox for a mega motor...(see my post in 'power systems')

Thanks for being my mentaurs in this new hobby...and I will have MORE questions. I do have a MEDUSA power meter...bet have not assembled all of the equipment yet...motocalc says my setup is good....I just want a 'human' opinion before I jump.

...gotta go get my parachute!

Thanks a million,

Chuck
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Old Dec 11, 2004, 07:01 AM
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Quote:
Originally Posted by FoamCrusher
fixer:
The reason Chuck is interested in watts is that is really what matters in working with motors.
FoamCrusher
I'll grant you that watts is a part of the entire equation, but overall has little value to us in these particular situations. Both mfg's of these brushless motors & LiPo's are primarily concerned with MAX amp draw. The brushless motor's rating include cell count based on 1.2volt NiCd/NiMh style batteries, for voltage limitations.
Nice to know the wattage information, but we only need concern ourselves with amps & volts.

Jim
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Old Dec 11, 2004, 07:14 AM
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Quote:
Originally Posted by ChuckD
Thanks Jim, and again, Foam...

My concerns with WATTS are driven simply from a guy who does not know better; and after three decades of 'just trying it' and then leaving 'it' in a box after I screwed it up...I now ask the proverbial experts before I jump.

(hey, it only took 30 years, right?)

Chuck

Hey, we're ALL still learning, if not you're dead.

I've been checking my F-27 Styker brushless/LiPo setup for flight enduance times. WOT for most of a flight & I get around 9 minutes. Conservative flying, some motor off/gliding, and I've gone 16 minutes.

That's with a Mega 16/15/4, CC-25, Kokam 2000/15C-3S1P, and MAS 6X4 prop.


Quote:
Originally Posted by ChuckD
Thanks for being my mentaurs in this new hobby...and I will have MORE questions. I do have a MEDUSA power meter...bet have not assembled all of the equipment yet...

Thanks a million,

Chuck
Hmmmm, haven't yet heard anything about a Medusa power meter. Is that the one like AF's Super Whattmeter, but can connect to your PC?

Jim
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Old Dec 11, 2004, 07:17 AM
Counter agent of B.S.
United States, IN
Joined Aug 2003
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All,

Looking to order another Mega brushless motor & a Berg receiver for my second F-27 Stryker.

Where online, did you get yours?

Prices?

Does anyone carry both items?

Jim
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Old Dec 11, 2004, 09:27 AM
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...I put all my stuff together from LHS, Hobby-Lobby (motor), and Bishop Power Products (ESC)....

--C
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Old Dec 11, 2004, 09:43 AM
If it floats....sail it!
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Elk Grove, CA
Joined Sep 2002
4,191 Posts
Quote:
Originally Posted by ChuckD
...I put all my stuff together from LHS, Hobby-Lobby (motor), and Bishop Power Products (ESC)....

--C
AirCraft World in Japan - quick shipping (only $2.50 world wide) and no sales tax. I get items here on the left coast within 5 days.

When looking for the best deal, the added tax and shipping make a difference when the total of all of the items starts getting up there. I can usually get another item for what I save buying from Dave.

Bishop PP, eDogFight, and e-Flightline are my other favorite places, but the CA sales tax is a price killer for me on big purchases.
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Old Dec 11, 2004, 11:22 AM
"Marcy" VF-A
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Marysville, WA
Joined Jul 2004
193 Posts
I just saw an ad in the for sale section here. Hobbys and beyond are running specials until the end of the year. I haven't dealt with them yet, but may place an order. "combo deal= Mega 16/15/4 and CC Phoenix 25 =$135.00 " They are offering free shipping too. Best price I've seen yet.
Tim
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Old Dec 11, 2004, 12:58 PM
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Quote:
Originally Posted by FoamCrusher
AirCraft World in Japan - quick shipping (only $2.50 world wide) and no sales tax. I get items here on the left coast within 5 days.

Well, I just made my first order from them. Getting a Berg 4*DSPII MICRO STAMP Rx 72Mhz with FREE CRYSTAL, 2 micro servo's, a Mega 16/25/3, and connectors.

This being the weekend, I'll fathom a guess at sometime around Dec 21-23rd to get to me in N.W. Ind.

Thanks ALL for your input on dealers!

Aircraft World
Just had everything I needed!!!


Jim
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Old Dec 11, 2004, 04:23 PM
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Quote:
Originally Posted by wekenav8r
I just saw an ad in the for sale section here. Hobbys and beyond are running specials until the end of the year. I haven't dealt with them yet, but may place an order. "combo deal= Mega 16/15/4 and CC Phoenix 25 =$135.00 " They are offering free shipping too. Best price I've seen yet.
Tim
check out
www.b-p-p.com
http://rctoys.com/parts.php
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