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Electra power

Old 07-04-2008, 10:35 PM
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Samson4721
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Default Electra power

I have an old electra I am re building. I want something light to carry this plane up, in hopes of retaining good floating. What would be needed?

would this work? http://www3.towerhobbies.com/cgi-bin...?&I=LXWK48&P=7
Old 07-04-2008, 11:44 PM
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Default RE: Electra power

No it won't. It's way down on power compared to what you need. It's an old school brushed motor and it won't provide anywhere near what you need for the Electra

However the good news is that you can get a brushless setup that'll easily carry up the Electra for cheap these days. It'll have better performance than the old setup and weigh about 1/4 to 1/3 the weight of the old motor and nicad battery pack.

Something like LINK REMOVED folder from 2 lipos or a 9x5 folder on 3 lipos will pull the Electra up strongly. You want to prop it to pull around 15 to 18 amps and it'll climb like a homesick angel. Run it with a 30 amp speed control. They need to be rated higher so it makes up for the lack of airflow around the speed control to cool it.

Another option that may do the job is LINK REMOVED. But in a way I hesitate to suggest this combo since while it'll have enough power to fly the Electra the prop shaft is a rather thin and weak setup. But if you were to adapt a shaft saver to it you could fly the model with this motor and a regular prop and if it drags a prop blade on the landing the saver should let the prop swivel and save both the shaft and the prop. But I'd be sure to get some spare Orings for the saver and a few spare shafts and props since this method may not prove too robust. And if you dork the plane then the motor shaft will bend right now and possibly it'll even distort and bust the motor case. Like I said, it is attractive from the price standpoint but it's really not a robust motor for this use.

If you haven't learned about brushless then all of this may seem like black magic. The key is the Kv value and the current that a given prop pulls that determines if the motor will do the job with the right size prop and survive the ordeal. Higher Kv values are geared to small props and speed flying or for using with gear drives. Lower Kv values are intended for direct drive at lower RPM's with bigger props. Basically the lower Kv value motors are like the old style can motors WITH a gear box while the high value Kv motors are like running direct drive on the old motors. It's just that it's all integrated into the motor winding arrangement now. The size of the can which used to be so important is now not really an indicator of much within a range of similar looking items.

Lipos will require a special charger and some minor safety procedures as pertains to storage, transport, charging and general use. The big issue is that they are a little bit physically fragile so if you crash and damage a battery you need to carefully discharge it away from anything flamable and then take it to a battery place for proper disposal. But they are worth it as they have some amazing energy desities. Another option is the fairly new A123 cells.
Old 07-05-2008, 10:08 AM
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Samson4721
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Default RE: Electra power

Thanks for the info. The links you posted are not working for me.
Old 07-05-2008, 10:00 PM
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Default RE: Electra power

OK, I found out that the firm I linked to has some sort of lame clickback deal in place so it produces a bazillion hits on our site spaming their site. Just do a google for hobby city and then look up the motors KD 36-28S and under the combo deals look up for the TowerPro BM2408-21T / 18A BEC / 1047 Prop Combo deal.

Lets try another outfit...RC Hot Deals. I've dealt with them twice now and they are great in the mail order department.

http://www.rchotdeals.com/Products/r...orsandESC.html

Go down the list of combos here to the A2217K-9 T item. This motor with a 10x5 folder looks like a winner when running on 3 lipo cells for what you want. Don't worry about suggested weights listed there. Those figures are for smaller power models intended for more aerobatic flying. But for best performance I would strive to keep the weight of your Electra down to the lower 30's. The motor and pack will help. THe motor and ESC will be around 3 oz and a 3 cell 1300mah pack is another 4 oz. So all in all your entire motor, ESC and battery is going to be about the same weight as what the Electra originally used for a battery pack only. The other 4 oz of original motor isn't even going to be there. So with a setup like this you're ahead by 4 to 5 oz before you even start. Because the motor is lighter it would be nice to really watch your wood in the tail surfaces. If in doubt buy some lighter stock and replace the stock stuff. Also I'd suggest some lighter covering film such as some of the parkflyer films. A few grams saved in the tail means a few ounces saved in the nose. It's a HUGE payback. No point in using a nice light motor and battery combo if you end up replacing the saved weight with lead.

I've got one of the motors in the 2217 series and they are a nice solid motor with a heavier than normal shaft size for this size of motor. That should hopefully result in less bent shafts. In fact when I think about it I'd recomend you don't go for that BM2408 motor just due to the shaft which WILL bend like overdone pasta.
Old 07-06-2008, 07:47 AM
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Default RE: Electra power

very good points. Thank you a lot for the info. I have been trying to keep weight down on the tail while repairing.

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