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less thrust now?

Old 10-14-2003, 12:06 AM
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slagburn
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Default less thrust now?

Well, I haven't flown the plane yet, but have noticed less thrust after putting a bigger motor on? I have a Slow Stick and put on the Great Planes kit with 3:1 gearbox and 400 motor. Rs380, that's 400, or Speed 400, right? I used the APC 11/7 prop. Before it had a stock GWS 300 motor/ gearbox w/ Uncle Mikey mod, advanced timing, GWS 12x6 prop. The battery and ESC are the same, Sanyo 8.4V 730 mAh, Zagi 20A speed control. Also battery life is down?
Maybe the motor just needs break-in.. I just want more power and climbout, and carrying capability.
Where did I go wrong? Prop, gearing, ?? I'm new at this and there's a lot more to electrics than it seems apparently...
Old 10-14-2003, 07:55 AM
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Matt Kirsch
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Default RE: less thrust now?

A bigger motor does not necessarily mean more thrust. Power is derived from a combination of battery size (number of cells), motor specifications, gearbox, and propeller. It's not a simple "bigger == more power" equation like in glow.

With electrics, if you change one piece of the equation, you affect all the other pieces of the equation. Small changes, like an inch either way in diameter or pitch on the propeller, the addition or deletion of a cell in the battery, a slightly hotter motor of the same type, normally don't require a total rethink of the power system. Major changes, like going from a Speed 300 to a Speed 400, require you to rework the entire power system. Otherwise, you're left with anemic performance, and damaged equipment (from a crash or overload).

What kind of RS380 motor is it? An RS380PH or an RS380SH?
Old 10-14-2003, 11:40 AM
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Default RE: less thrust now?

I don't recall and the motor is a few miles away as I type. The box says 7.2-8.4V motor. This is the kit: http://www.flyhobbies.com/greatplane...emt400gd31.htm
I bought this kit so I can put a brushless in the gearbox later and put it on any model, not necessarily the SS. It's calmed down today, maybe it will fly alright- but I'm not expecting any more than the Speed 300 from the bench run.
How can I straighten this out? I'm also looking at KAN's, LiPoly's etc but there's so much to know on this, even after hours of research it just gets deeper. What to do? Thanks..
Old 10-14-2003, 10:34 PM
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scudrunner77
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Default RE: less thrust now?

I am new to electrics too, but remembered see these charts at the bottom of this web page:

http://www.hobby-lobby.com/speed280.htm

There is a chart for direct drive and some gearbox setups...it has helped me understand a little more.
Old 10-14-2003, 11:06 PM
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Default RE: less thrust now?

Thanks for the reply. I was just digging around the archives and have found the solution, the 010 Astro Brushless setup in the 300 gearbox. I'm playing with a motor calculator to see if the 14x7 prop will work in the 6.xx gearing range.

Sheesh, so many extra parts around now! The 3.0 400 motor, gearbox and all the props I bought to match, a speed control that won't work with Li-Poly (just bought of course) regular and Uncle Mikey EPS300's with bent shafts, etc The hobby shop guys must chuckle when I come in.

Any tips on the care and feeding of brushless motors, break-in, cooling time etc?
Old 10-15-2003, 06:52 AM
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Default RE: less thrust now?

Spare parts means you haven't built enough planes yet! Get busy!

Brushless motors are essentially maintenance-free. No brushes to break in, and the only wear parts are the two bearings, which last practically forever under normal circumstances.

IF you're worried about the low-voltage cutoff and LiPolys, don't. You can land and test the voltage every few minutes for the first couple of flights, just to see exactly how long you can fly. Usually, you don't have enough power to fly the plane long before the batteries get into the danger zone.

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