jeffeh

My Feedback: (13)

I am considering my first E-power project in a BIG way. I just purchased a 1/3 scale US Balsa Sopwith Pup that is about 95% ready to fly. I want to use a RimFire 50cc, GPMG4800 motor and use Lipo batterys. I am not new to RC, have been flying for over 35 years. I am reading everything I can about electric power. If you have any suggestions or tips to pass along, I am all ears.

speedy72vega

Hi Jeffeh, good luck with your project, I hope we get to see pics???????
As a general rule of thumb, you want around 100 watts/lb for trainer or slow flyer planes, 150 watts/lb for scale/sport flying, 200 watts/lb and up for speed/3D flying.
You will want to approximate the AUW weight of the plane, including batteries, and choose the motor from there. Once you have an idea of the motor and prop combo, you can then select the proper batteries for it. You want to make sure the discharge rate (15C, 20C, 25C, 30C, etc.) is right for your power requirements.
I don't know your level of experience with electric power, so i'll try to give a quick rundown. The MAh rating of the batteries tells you capacity, the cell count tells you the voltage of the pack (3.7v/cell for LiPo's), the discharge rate, or C rating, tells you the current, or amperage that pack can supply.
Let's look at a hypothetical example. Let's say you decide to run a 6S 5000ma 30C pack for your plane. 6S would be 22.2 volts, 5 amps (1000 ma = 1 amp, 5000ma = 5 amps). The 30C discharge rate means that pack is capable of delivering 150 amps constant. 10C means 10x the capacity- 10C X 5 amps = 50 amps, 20C X 5 amps = 100 amps, etc.
Knowing this, if your power system (motor/prop combo) is going to require 60 amps max static, you would be fine with a 20C pack. Your prop is ultimately going to determine your current draw. The motor's Kv rating tells you the rpm the motor will try to spin. Let's say your motor has a 350kv rating (Kv means rpm's per volt). That motor will try to spin 350 rpm's per volt supplied to the motor. If you're running 6S, or 22.2 volts, a 350Kv motor will try to spin at 7770 rpm's max. The lower Kv rating, the larger prop/higher pitch you can run, the higher the Kv rating, the smaller diameter/pitch prop you will want to run. The larger or higher pitch prop will require more current to turn, and you can burn up the ESC or batteries if overdrawn.
Hope this helps some, if you have any more questions, feel free to ask.

Walt Thyng

My Feedback: (9)

Jeffeh,

very good info in the above post. I would fine tune it just a bit. I am flying a VK Camel and it is very happy at 80 watts/lb. Also, since you are new, some of us old timers still prefer the 80% rule - never plan to use more than 80% of any given e-power value. Never discharge or charge at more than 80%; never plan on using more than 80% of capacity or getting more than 80% of the projected motor power. This comes from the early days of e-power, but due to widely varying quality of e-power components even today (especially Chinese stuff) it still works and avoid burnt out motors and ESCs and short life LiPos.
Walt

speedy72vega

I also should mention, please, PLEASE get a wattmeter. It will become your best friend if you decide to continue on with your venture into electric flight. Also, on battery discharging, Walt brought up a very good point. You never want to discharge a LiPo battery too far, it will ruin it. The general rule for most modern LiPo's is to never discharge below 3.3v/cell, and if you need to store them, make sure they're around 3.6-3.8v/cell.
I usually try to never discharge more than 70% of the capacity, but I recharge at a 2C charge rate. You can safely charge most modern LiPo's at 2C, some are even advertising a 5C charge rate, but I don't think I would try it myself. 1C is perfectly fine for pretty much any LiPo. It has been said that charging at higher rates will shorten the life of the pack, so you can decide what's best for you.

jeffeh

My Feedback: (13)

Speedy and Walt thanks a million for your input. I have not committed on any thing yet but with your inputs I am getting closer.

Thanks,

jeffeh

My Feedback: (13)

Ok guys, here is where I am at this time: HiMax HC6332-230 motor should be here today or tomorrow, 2 - 3300 MAh 30c batteries from HobbyKing are on order as well as a Wattmeter and Lipo charger. The one item yet to order is a speed control. Right now I am looking at a Phoenix 110HV controller. They are expensive! If you all have any suggestions let me know. I am having a problem finding a good controller that does not cost a lot. My math tells me I need a contorller that will handle 50 to 70 amps continuous with a burst capablity of around 100 amps.

Jeffeh

Walt Thyng

My Feedback: (9)

well,
you already ordered from HobbyKing/City; their Turnigy Plush controllers have been getting good ink. I also use the Great Planes Silver Series and program with the card (very, very easy).
Walt

speedy72vega

+1 on the GP/Electrifly Silver Series, very good, especially for the price. I have 3 different ones, never a problem whatsoever. I also have a couple of Turnigy Super Simple ESC's, haven't had a problem yet, but I don't think I would put one on a highly valued plane. I'm just overly suspicious that way I guess .

Walt Thyng

My Feedback: (9)

Speedy, I don't mean to hijack this thread, but I have two Super Simple 50 escx. I can get them to program, but not arm. any thoughts?
Walt

speedy72vega

Walt, I seem to remember reading on one of the HK forum threads about programming throttle travel for that problem. I don't remember the exact procedure, but it's there in their forum on the product documentation category I think. I will try to find it next time i'm on there and let you know. That's strange though, because I never had to do that with either of mine. I used the 50-60 SS on my Eratix, and the 40-50 I use for my motor test stand. Neither one of them had a problem arming. I'll research a bit............
Rob.

Walt Thyng

My Feedback: (9)

I'm leaving for an Old Farts' Flying Group coffee, but I'll re0check the HK forums when I get back. Any help would be much appreciated. The "Bush Discount" on my pension means I have to pinch on play money.
Walt

speedy72vega

Walt, here's a link to the programming manual, don't know if this will help. Also, i'm sure you probably know this but i'll mention it anyways. The 40-50 SS and 50-60 SS ESC's are Opto only, so you will need a separate Rx pack.
http://www.hobbycity.com/hobbycity/f...sts.asp?TID=21

jmohn

What will the finished weight be on the plane?

I have a 1/4 scale AZM D7 that's using an Eflite Power 160 with a 12S (2x6S 5000 mah packs) putting out 3000 watts using an 20-8 prop. It has lots of power and I can get flight times in excess of 12 minutes.


Jeff

speedy72vega

Jeff, I believe he said around 24 lbs, 3000 watts would be plenty. I think something with the power of either the Power 110 or Power 160 would be great on his plane.
Pics of your setup??

Walt Thyng

My Feedback: (9)

Speedy, i just went to the HK forum and discovered that you had responded to my June 09 post. I didn't have the "notify" button checked. That is one of the manuals that I have (both are the same). The question I have is how long did it take to "re-initialize"?
Since others are having realtively good luck with these, it has to be something I'm doing wrong, especially since neither of them works.
Walt (aka Revdoc)