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oracle_9
10-08-2006, 06:14 AM
Hi,

I am not sure exactly how to put my question, but I'll start out by saying what application it's for and the plane. I will be building a fairly new design called "Guppy" electric sailplane. It requires a speed 400 6V motor direct drive with a 6x3 folder prop. For competition flying, I am limited to 1 or 2 minutes motor run to get as high as possible before turning it off when time elapsed. I guess I should add for competition thermal I will use 8 cells 750 nihms (rated 20A max discharge), and for just casual thermal to use 7 cell CBP 1150.

Specs:
60" span
316 sq.in. area
Estimated AUW to be 15-17oz.
(I am aiming towards 15.5oz for competition, and around 16.9oz for casual thermal)
Airfoil is some thin flat bottom, eppler.

I see there are many Speed 400's out there, are any particularly better than the others? By this I am not sure how to put it, maybe by torque? or efficiency? or overal performace? or they practically the same, and only the price differs?

Currently, I am leaning toward a Graupner Speed 400 + Graupner 6x3 folder package.

Any input will be appreciated. Thanks.

Sky Sharkster
10-08-2006, 06:49 AM
Hello Oracle, most of the Speed 400's I've seen are re-labeled Mabuchi 370's. Hobby Lobby sells them in 4.8Volt, 6.0Volt and 7.2Volt. Most flyers use the 6.0Volt, this seem to be the best compromise between performance and life expectancy. Some LMR pilots use the 4.8Volt motors but there the life expectancy is measured in minutes. The "Rocket" motors seem a bit faster also. I've seen (but never used) a "long can" 400 and I'm told the Zagi motors run a bit faster. They may have the timing reset for the prop rotation, this will increase RPM slightly.
I don't think there's a "better" 400 than the ones Hobby Lobby and other major distributors sell, but there are worse ones! The $2.00 motors you'll see occasionally are likely "off brand" or "seconds". Not even worth the price, usually!
If you get a 400 from a reputable vendor, that's a good start. From there, I'd suggest you re-time it for the direct drive application, a good water break-in and careful oiling. Balance your props. Use a quality ESC and don't even let dirt get near the motor. Record the performance (Wattmeter and Tachometer) when it's new and as soon as it starts to decline, replace it. At $10.00 a copy, why settle for less-than-optimum performance?
There's also a very good article on the Charles River site by Mark Drela on re-configuring the CAM 6 x 3 folder for more performance and less amp draw. http://www.charlesriverrc.org/articles/allegrolite2m/prop_mod.pdf
Here's info on the water break-in;
http://www.wattflyer.com/forums/showthread.php?t=5788&page=2
LMR is not always decided by the best climbing model but it doesn't hurt! Your glider sounds like it should do well, so give it every advantage in the power department and find the good air!
Thermals!
Ron

oracle_9
10-08-2006, 03:52 PM
Thank you for the information. It was very helpful.

CHELLIE
10-08-2006, 08:21 PM
Hi, are you limited to brush motors only, If not, use a brushless motor, they are much lighter and much more powerful, they will get you plane up in a big hurry, where a brush motor will struggle and get hot, lots of good brushless motors on e bay at great prices too :) Chellie.

oracle_9
10-08-2006, 08:39 PM
The event has two categories. One of which I mentioned is a brushed speed 400 motor, with 1 to 2 minute motor run. And the other category is brushless . I currently have one 1 brushless plane called the Windex 1200C by Nick Ziroli, using lipos. But I thought that why sit around for one category to finish, if I can fly a brushed plane too. :)

Btw, if I use lipos on the brushed or brushless there is a minimum wing loading of I think 8oz/sq.ft or something like that. So thats why I gonna use those 750 nimhs...and their cheaper too :)

CHELLIE
10-08-2006, 09:00 PM
ok cool, I was just wondering if you were limited to a brush motor only, I have switched to brushless motors and what a differance, more power :)
E flight park 400 is a nice brushless motor its a 4200 kv , I saw it on ebay for 49.99 item number http://cgi.ebay.com/Eflite-Park-400-Brushless-Motor-4200KV-for-Mini-Funtana_W0QQitemZ120013393614QQihZ002QQcategoryZ34 055QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

Have fun, and always, Burn up the Sky :) Chellie