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more speed!

Old 02-22-2009, 09:40 AM
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racerxwest
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Default more speed!

I have a thunder tiger ripper obl 2928 outrunner;25 amp speed controler,11.1 volt lipo battery;9x7.5 prop in a 30 oz airplane.What motor do I go to for more speed? Has to be no more than 28 mm in diameter. Thanks for the help.
Old 02-22-2009, 10:37 AM
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Walt Thyng
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Default RE: more speed!

rxw,
you can get more speed in three ways.

1) increase the amp flow i.e. more pitch on the prop

2) add a cell: more volts = more rpm

3) get a higher Kv motor = more rpm/volt

Nos 1 &2 assume both the motor and controller can handle the changes.
Walt
Old 02-22-2009, 10:38 AM
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Dr Kiwi
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Default RE: more speed!

A 72g Suppo 2217K-6 (1500Kv) on 3s with a 7x7 APC Sport prop will get you 26.7oz thrust @ 87mph from 21.2A/227W. If you run it on 4s with a 6x5.5 APC E you get 28.0oz @ 96mph from 20.9A/303W.
Old 02-22-2009, 10:48 AM
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Walt Thyng
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Default RE: more speed!

doc,
you always have great technical details and specific info!
Walt
Old 02-22-2009, 12:48 PM
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racerxwest
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Default RE: more speed!

New to electric. Seams when you go up in kv,s the prop also gets bigger. I am stuch with a 9 or 10 inch prop. Dr. Kiwi what brand and were do get a 72g Suppo 2217 k-6? Again thanks for the help.
Old 02-22-2009, 01:20 PM
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Walt Thyng
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Default RE: more speed!

RXW,
actually, in general (hard and fast rules are always dangerous in e-power), the greater the Kv the smaller the prop FOR A GIVEN MOTOR SERIES. There are some other factors that have to be taken into consideration such as magnet size (length), number of poles, and number of winds(turns).

If you're stuck with a given prop (why?), it get a bit more complicated.
Walt
Old 02-22-2009, 01:25 PM
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racerxwest
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Default RE: more speed!

I am stuck with the 10 inch dia for ground clearance. I have tried different props, pich and diameter with no basic increase in speed and after flying the lipo battery in just barely warm.
Old 02-22-2009, 07:29 PM
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Dr Kiwi
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Default RE: more speed!

If you use a smaller high pitched prop it may spin faster than your 9" prop did... thus speed may well increase. Obviously if you motor is not "hot" enough to drive that small prop to high rpm, you'll need higher voltage or a higher Kv motor.

Suppo motors are available from www.lightflightrc.com and www.graysonhobby.com

Heck, I just realized that your motor is only 910Kv (or maybe even 750Kv)... no wonder you can't get much speed - at 11v the most you'll be getting with 910Kv and a big prop is probably 7000rpm and perhaps 40-50mph. Shove that 1500Kv Suppo in the nose and you'll get 13000rpm with the 7x7... you'll have more speed (86mph) than you know what to do with! I'd like to say use an 8x8, but that would be more than the Suppo 2217K/6 motor can cope with.

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