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NiMh to LiPo upgrade

Old 03-07-2005, 01:51 AM
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rahtware
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Default NiMh to LiPo upgrade

Hi all

A couple of years ago I scratch built a 199g (7oz.) 1/8-scale copy of a southern California ultralight. The original plans for a 1/4-scale model of the “Desert Duster” were published in the now defunct Model Builder magazine. This is my third model of this plane. The first was a .15 (nitro) powered 1/4 scale, the 2nd was a rubber powered peanut scale, and now the 1/8 scale E-powered.

The E-powered version gave mixed results due to the NiMh battery. I used a 7 cell 300mah NiMh to power the GWS motor. On a hot day the plane flew great giving almost 15 min flights at 3/4 power. But, on a cold day (even with the battery fresh off the charger) the plane might not get off the ground. So I hung it in the rafters of the garage.

Well, today I made the switch to LiPo power. I picked up an 860mah, 2 cell Thunder Power battery and a Castle Creations Pixie-7p ESC. The weights aren’t that much different, I saved 1g on the Pixie over the GFS 12 that it replaced. The 300mah/8.4V NiMh battery weighed 55g, where as the 860mah/7.4 LiPo weighs 47g for a savings of 8g and a potential tripling of it’s flight time.

I hope to fly it Friday morning, will post how it does.
Old 03-07-2005, 01:58 AM
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rahtware
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Default RE: NiMh to LiPo upgrade

Here are some pics of the original installation. The NiMh is hiding under the JR RX.
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Old 03-07-2005, 02:09 AM
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Default RE: NiMh to LiPo upgrade

Here are comparison pics of the components that I exchanged. The Pixie is the small ESC.
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Old 03-07-2005, 02:15 AM
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rahtware
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Default RE: NiMh to LiPo upgrade

And here are a couple of pics of the(almost) completed reinstallation. The LiPo is just a tad wider (but still fits in the tray) and much shorter than the NiMh.

I can’t wait to see how it does!!!
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Old 03-07-2005, 06:46 AM
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Woody 51
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Default RE: NiMh to LiPo upgrade

Don;t forget to make sure that you have a charger that can handle Lipo's Larry. One that can do NiMH and NiCAD only, won't be suitable.
Old 03-07-2005, 11:46 AM
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rahtware
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Default RE: NiMh to LiPo upgrade

Woody 51

Thanks for the input. I have a Triton that has a LiPo function... But even with that I was a bit nervous during the first cycle due to all of the warning notices (5) that came with the Battery.
Old 03-07-2005, 09:49 PM
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Default RE: NiMh to LiPo upgrade

Thought I should show a couple of pics of the DD in flight.
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Old 03-08-2005, 05:22 AM
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Woody 51
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Default RE: NiMh to LiPo upgrade

I know what you mean. I have an APACHE Charger to go with my collection of POLYQUEST Lipo's. Then I realised that I really needed one that could do all types of cells and packs as I was also starting to build a collection of other brands, without the seperate charge jack that is peculiar to POLYQUESTS.

So I purchased a PLATINUM EX unit. It does the lot, from Lipo's to Wet Cell Auto Batteries.

When I finally figure it all out, the whistles, bells and buzzers I mean, I should also be able to become a Philadelphia Lawyer!!!
Old 03-08-2005, 12:41 PM
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Default RE: NiMh to LiPo upgrade

When I finally figure it all out, the whistles, bells and buzzers I mean, I should also be able to become a Philadelphia Lawyer!!!
So true...

"So... did it fly?" You ask. YES IT DID!!! Man do I love LiPos and am kicking myself for not making the conversion sooner.

The notes:

Charged the battery a day before flying, took it out on a cold morning (both I couldn't do with the NiMhs), pointed it down the road and advanced the throttle.

Before I get into the results I feel I should list some specifications... Plane's weight is now less than 6 3/4 oz. (191g). True wing area (not counting the cabin top) is 6.5" X 30" or 1.35 sq ft. This works out to just over 5 oz per sq ft wing loading. This number drops even farther when I include the giant flying-stab. Power is a GWS IPS DX2 with an 8.43 prop.

As I advanced the throttle I applied a touch of rudder and elevator and she lifted off into a gentle climb out. In the air I had to keep bumping in positive elevator so I tried to set the trim but it kept wanting to nose down... Oh, new battery, new CG! I dropped the power and brought her in for an acceptable landing considering I haven't flown in over a year.

Plan to move the battery and try again after a Drs. appointment I have this AM.

Let me say it again... Man do I love LiPos!!!

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