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View Full Version : Just when you think you had a plan....


Mike Freas
01-09-2006, 04:47 AM
Ok all you e-flight experts lend me some advise/encouragement. My STM project is quickly coming to an end and I'm only missing one thing to get the bird in the air, the battery. Now I have been on a mission to find the least expensive way to power my bird without buying stuff that will take a dump in a few months. I got an AXI 4120-18 so I know that is bullet proof. My first problem may be my ESC. I bought a diamond (premier) 50A controller for 79.00. I just couldn't see spending twice that for a Jetti or Castle Creations controller. One thing that really got me was that Dymond advertised a cheaper ESC that was 5 cell compatible but the one I got is only good to 4 cells. While I was at the field this weekend one of the guys that has a bunch of e-flight birds uses dymond packs but says the ESC's are crap and burn out quickly. Well I guess I will have to wait and see about that. Now I was planning on getting a TrueR/C 4S2P 8000 mah pack for about 137 bucks with deans connector. I was under the assumption that these were 7C discharge packs but the site was updated (they sold out of these) and they are only 5C rated. So now I'm worried about having enough power and I may want to go with a 4S3P 12000 set up. I'm not looking for speed or 25C discharge performance here. I simply want a pack that will last a long time, pull my bird with power to spare and give me some good flight time without costing 500 bucks. So I guess I'm looking for some encouragement that my set-up will work without the "you get what you pay for" comments.

slipstick
01-09-2006, 10:11 AM
I apologise, my eyesight really isn't good enough to read that tiny font you're using, but I can't see anywhere where you say what current you need from your batteries.

Steve

Mike Freas
01-09-2006, 07:38 PM
I'm not trying to be smart with the font size and bold. I simply can't figure the thing out. I have a 50A controller and the 4S2P pack from TrueR/C is rated at 48A continous. So to answer your question I guess 48A.

Mike Freas
01-09-2006, 07:44 PM
So if a 4S2P pack is rated at 48A continous then a 4S3P pack would be good for 72A correct? I may have to upgrade my controller.

slipstick
01-10-2006, 10:36 AM
Yes a 4S3P would be rated at 72A but you are not obliged to use all of it. Indeed batteries are much happier if you don't use them right up to the maximum possible current. Also the 4120 will not take that much current.

The current is actually controlled by the motor and prop that you're using. IMO the 4120/18 is best used with 5 or 6 cells and with the current kept down to about 40A so you might be a bit down on power with only 4 cells.

I'm sure someone will be able to help with the best vendor for your battery. I'm in the wrong part of the world to help much.

Steve

Mike Freas
01-10-2006, 04:41 PM
Seems everyone has different ideas about what pack configuration will work with the STM. Mike from HL said they fly it on a 4120/18 and a 3S pack while others are using a 6S pack. I may have to pay more and go down to Dymond and get a pack from them. I'm still confused.

Jeremy Z
01-11-2006, 02:24 AM
Acronym Translation Please: What's an STM? It must be big...

Mike Freas
01-11-2006, 02:54 AM
Senior Telemaster

95" span and about 10 lbs

Matt Kirsch
01-11-2006, 03:28 AM
Mike,

No need to be confused. Think of Volts like cubic inches in an engine. More Volts, more power.

The Senior Telemaster is a plane that doesn't need a lot of power to fly. Hobby Lobby's conversion just shows you how little the plane needs to fly well (3S LiPoly). Others have more "Tim 'The Toolman' Taylor" tastes, and power their STMs with higher-voltage packs and bigger motors to handle the power. STMs on 5 or 6 LiPoly cells have a signifigant payload capacity, or can climb almost vertically with an empty cargo bay.

It's all a matter of personal taste. With what you have, I would go with a 4S or 5S LiPoly pack, and a 14x10 or 13x10 prop, respectively. You won't be disappointed. The plane is going to be absolutely overpowered.

I set up a STM for a gentleman in my club here a couple years ago. I think we went with a 4130/16 and 20 NiCd cells. He put floats on it and flies it in the field across from his house all winter long (he lives in the boonies). From all accounts, it's a monster even though it weighs 12+ pounds.