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Feb 03, 2011, 12:52 PM
Mayday! Mayday!
jpt1205's Avatar
My question is why do most of these UM's use brushed motors instead of direct-drive BL motors like the UM Beast? Is it more economical to use brushed, geared-down (or up, depending on your perspective) motors at this size or is it a physics thing?
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Feb 03, 2011, 12:54 PM
Flash, AAAAAAAAAAAHhhhhhhhhh
flashkick's Avatar
its more efficient battery wise and its cheaper.
Feb 03, 2011, 12:59 PM
Power Wheels Guru
UNGN's Avatar
Quote:
Originally Posted by jpt1205
My question is why do most of these UM's use brushed motors instead of direct-drive BL motors like the UM Beast? Is it more economical to use brushed, geared-down (or up, depending on your perspective) motors at this size or is it a physics thing?
It's physics.

Small motors can make a lot of RPM, but very little torque, just like in a car.

So they make Horsepower at high RPM and gear them down to spin a larger prop.

A DD prop would have to be 2" to run the same amps as a gearboxed motor running a 5" prop.

The 5" prop is going to move air much more efficiently than a fast spinning 2" prop, so it makes more thrust... and even if the 2" prop made more thrust, it would look pretty stupid on a warbird.

The Beast uses 2S (high volts keeps the amps down for the same power output) which gets away from the simple/cheap/light nature of 1S.
Feb 03, 2011, 01:00 PM
Registered User
Cheaper I understand, but I thought BL was supposed to be more efficient?

Edit: I see the above post, disregard this one!!
Feb 03, 2011, 01:00 PM
Aerobatics?
Britnkurt's Avatar
Anyone know the release date? I was about to pull the trigger on a UM P-51, this one definitly will be my next if the RD isnt next year :P
Feb 03, 2011, 01:01 PM
Mayday! Mayday!
jpt1205's Avatar
Quote:
Originally Posted by akwardflyer
its more efficient battery wise and its cheaper.
Is that only because of the scale of UM's? Otherwise, why the migration in the Parkflyer scale and above to Brushless motors??

Edit: Nevermind--I saw the answer (man, there are alot of messages crossing in cyberspace!!)
Feb 03, 2011, 01:10 PM
Mayday! Mayday!
jpt1205's Avatar
Quote:
Originally Posted by UNGN
It's physics.

Small motors can make a lot of RPM, but very little torque, just like in a car.

So they make Horsepower at high RPM and gear them down to spin a larger prop.

A DD prop would have to be 2" to run the same amps as a gearboxed motor running a 5" prop.

The 5" prop is going to move air much more efficiently than a fast spinning 2" prop, so it makes more thrust... and even if the 2" prop made more thrust, it would look pretty stupid on a warbird.

The Beast uses 2S (high volts keeps the amps down for the same power output) which gets away from the simple/cheap/light nature of 1S.
Great explanation! Many thanks--that helps a lot. I really like to understand the inner workings of these models--I'm geeky like that (no offense to anyone resembling that remark)
Feb 03, 2011, 01:53 PM
Registered User
Quote:
Originally Posted by Dora Nine
Or just do what I did..I had a pretty good feeling something was coming soon, and I sold off a couple of my UM's.
Yeah...TO ME! And I'm havin' a ball flying new (to me ) planes RIGHT NOW! HAHAHA. I'd be having even more fun if it weren't for all this blasted snow. Had to put on snow shoes just to get out into the flying field. Definitely perfecting my hand-catch tecnique!

LaneVT
Feb 03, 2011, 01:59 PM
"Aircraftus Fragmentum"
kydawg1's Avatar
Just awesome........very cool little bird.
Feb 03, 2011, 02:01 PM
Registered User
Hello Ungn.
I have to do some balancing too most of my GWS props, before i have, some more exact
result. I have done the test without ESCs, only batterys. I want to see the amp too, but
i do not know, how to use my multimeter for this. The Bravo SX with a Sukhoi prop 130x70 and HY 240 mAh or the Eflight 500 mAh, give at the first 30 sek 75/78 gram of thrust,
then falling to 66/68 the next several min.,but no ESC. With the 5043 it is 2 or 3 gram less. Motor warm up a little.
John
Feb 03, 2011, 02:20 PM
Power Wheels Guru
UNGN's Avatar
Quote:
Originally Posted by johnkielsen
Hello Ungn.
I have to do some balancing too most of my GWS props, before i have, some more exact
result. I have done the test without ESCs, only batterys. I want to see the amp too, but
i do not know, how to use my multimeter for this. The Bravo SX with a Sukhoi prop 130x70 and HY 240 mAh or the Eflight 500 mAh, give at the first 30 sek 75/78 gram of thrust,
then falling to 66/68 the next several min.,but no ESC. With the 5043 it is 2 or 3 gram less. Motor warm up a little.
John
I can't wait until the SX motors are readily available with 9T pinions. Those thrust numbers sound very impressive.
Feb 03, 2011, 03:14 PM
Registered User
I forgot to tell you, I use a gearbox from a Extra 330, with ball bearings, this gearbox is easy to mod, just remove the brass and put in the 4x1,5 ball bearings. Remember there is some loss in the ESC, and I don`t now any brush ESC with a very low resistance, like YGE 4s or others brush less ESC. Can anyone tell me how to use a multimeter to see the amp draw. Itīs easy to changes the 9 t cog, if you have a puller, it is a press fit to the SX motor. I see others do with reamers and so, no needs.
John
Feb 03, 2011, 03:21 PM
the Ford man
ford f47's Avatar
well I love it!!!and I will defenitly be pre ordering this airplane



ford f47
Feb 03, 2011, 03:35 PM
Registered User
Quote:
Originally Posted by Britnkurt
Anyone know the release date? I was about to pull the trigger on a UM P-51, this one definitly will be my next if the RD isnt next year :P
this site say end of this month


http://www.rcpitstop.co.uk/parkzone-...380-2057-p.asp
Feb 03, 2011, 03:38 PM
Mayday! Mayday!
jpt1205's Avatar
Quote:
Originally Posted by Britnkurt
Anyone know the release date? I was about to pull the trigger on a UM P-51, this one definitly will be my next if the RD isnt next year :P
US side is early March according to HH.


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