Sky Sharkster

Hello PaperAirplane,
Kyleservicetech + Mred are correct, brands like Hacker, AXI, NEU, Plettenberg, Actro Kohler, AstroFlight are seldom discounted. These are top name brands and they sell for what they are worth, in my opinion.
But you can get reasonable prices and performance from mid-range motors. E-Flite, Scorpion, Himax and a few others are within most budgets and will serve you well as "Sport" motors.
It also depends of the level of performance you need; Hacker makes FAI Competition motors and less-expensive sport motors. AXI has the top "Gold" series and a less-costly "Silver" series.
Shop around online and buy from reputable dealers and shops. You will find as many opinions as there are flyers, but most agree, you get what you pay for!
Ron

PaperAirplane

do you think this motor would work with a 25 oz trainer?
http://www.hobbypartz.com/alpha-480-...ess-motor.html

Sky Sharkster

Hello PaperAirplane,
If the manufacturer's specs are to be believed, it should be more than enough power. It's listed as 910Kv, (up to) 250 watts, 20a Constant, 25a burst, 3.9 ounces weight. That's about twice as heavy as a typical "400" outrunner and the 4mm shaft indicate it's a a hefty motor.
But I'm not familiar with that brand or any of the others HobbyPartz sells. The Alpha brand look like knock-off's of Atlas, which in turn are Asian knock-off's of AXI. This doesn't necessarily mean they're bad.
And the Elite brand look like re-badged E-Flite motors, but much cheaper.
I'd be interested in hearing from anyone who's tested these motors. Without first-hand results to go by, I'd say try it, but don't be suprised (or disappointed) if it's not all it claims.
JMO,
Ron

mred

That looks just like the motors that Nitro Planes sells and from what I hear, they are pretty good motors, but I have never had one or seen one in use. I have just read about them and they sound pretty good for a cheaper motor. Nitro Planes can't seem to keep them in stock very long, so they are selling pretty good. If it will perform according to specks, it should haul that plane around plenty good. You may want to fly at reduced throttle if it will put out that much power, but other then that it sounds like a good motor.

Ed

PaperAirplane

Thanks guys.
Even Though it is a bit too much power I'd rather have to much than too little. I think if i used a 9x5 prop it would maybe draw a bit less than 250 watts. What do you think?

And yeah, I probably wouldnt fly on full throttle for anything besides takeoffs.

Ill tell you guys how it all turns out if i remember.

Last, where is the best place to buy relatively inexpensive batteries? (Lipo or NiMH)

PA

gittarpikk

Last, where is the best place to buy relatively inexpensive batteries? (Lipo or NiMH)

http://hobbyking.com/hobbycity/store...2&ParentCat=85

I have bought many lipos fronm here...Rhino seems to be extremely durable and forgiving...and always meets/exceeds the expectation..

Have never bought a bad battery from HK (Rhino, non name, Turnigy etc)...but always figure your shipping as it is somewhat high. I always pay for the somewhat quicker postage as I get it as quick as other suppliers...Make SURE everything is in stock at time of order..or it WILL hold up your (whole) order indefinately. Carefully read that sentence...ask me how I know....

PaperAirplane

Thanks.

If the battery discharge rate is 40C and it is 1850mAH does that mean that it would give off 74000 mAH for 1.5 minutes?
I dont think i am understanding the concept of discharge rates correctly.

mred

The 40C is the amount that the battery is able to put out without burning it up. In this case it's 74 amps. You multiply 40 times 1.85A in this case and that gives you the amps you can pull at max constant without burning up a battery. You had better have VERY good cooling to pull that kind of current though. I wouldn't put that kind of draw on any battery if you want it to last any time. That is simply the max you can draw from it. Most batteries are 25C and 30C, although they are coming out with new batteries every month. Most of the batteries you will find at Hobby City are 25C and 30C. I like the FLightmax or Zippy batteries the best, but there are others that are just as good.

Under the listing for each item is the in stock amount. MAKE SURE IT IS + and not -, or you will be waiting for you order until the out of stock items comes in, which could be awhile. I have seen them come in weekly and some monthly, but depending on what you order, it could take 2 or 3 months to get one. Each -number is an order, not how many are on back order and some of those guys are dealers ordering quite a few, so you could have to wait for quite a while for them to get to you. The best way is to put your E-Mail address on that part and they will tell you when it is in so you can order it then. Also, sign up on the site and get a discount. The more you buy, the bigger the discount to some extent. On some items you may save very little and on others you may save half the price. It just depends on what you are ordering. If you have any more questions fire away.

Ed

PaperAirplane

Thanks a billion and one.
I will have another question or two soon.

PA
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PaperAirplane

Got one.

If the battery mAH is smaller than the batteries mAh (say by 100 mAH) it wont work, correct?
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Experienced Pile it

Thanks again, Sky Sharkster.
We'll see if it works at the bottom of this post.

Mred.
-----------
"Also, sign up on the site and get a discount. The more you buy, the bigger the discount to some extent."
-----------

I did the sign up thing but see no changes in the prices of what is in my cart. My order is a little less than 100 bucks. Too small of an order? or maybe it won't show the discounts until I go to checkout?

I shaved a few things off the order to keep the weight under 1 kilo. It's 999 grams If this order goes well I might order again later after the re-up their supply of a few items.

mred

Make sure you are signed in when you buy something. You have to sign in every time you go to their site. Also, if this is your first order, you may not get much of a discount, but after you order a couple of times you get a nice discount. The more often you order, the more your discount will be. I am at Platinum right now and I think that is the max discount, but you have to order a few times to get that. It's not the size of your order, it's how many time you order from them. You should see the discount listed in the price for the item before you even buy it. If this is your first order, you may not see a discount yet.


"If the battery mAH is smaller than the batteries mAh (say by 100 mAH) it wont work, correct?"

I'm not sure what you are saying here, but if the motor draws more then the battery is able to put out, then you are going to see a BIG voltage drop and the motor will not run at it's best. If your motor pulls 20 amps, then you are going to need something like a 2200MAh battery around a 20C or better to get any run time out of it. It you try to put a 1500MAh 10C battery in there, then you are not going to run very good. The motor is going to try and pull more out of the battery then it is able to give. The battery willl get hot and burn up pretty fast simply because it is not able to put out that kind of amperage at a constant rate. Take the current you are looking to run at, then take a battery that has a C rating that will put out about double that and you should be able to get some decent flight time out of it and not run the battery to hard. For a 20 amp motor, you should run around a 2200MAh 20C battery at least. That will give you 5 to 10 minuets run time depending on how you work the throttle. The bigger the MAh rating on the battery, the longer you can fly. The higher the C rating, the more current you can pull out of the same size battery. Changing props will change the current that the motor pulls too, so you need to take it as a system and not just a single item. If you don't have a watt meter yet, you better get one. Otherwise you will not know what is going on with the motor and battery. For a 20A motor, I would say use at least a 25A ESC. I like to use 30A's on mine, but that's just me. Give yourself some head room and what ever you do, don't every try and run an ESC at a lower throttle setting to try and keep it under what the motor is pulling so you can use a smaller ESC. It doesn't work that way and you will burn up the ESC pretty fast. You will be lucky to get one flight out of it like that and you may not get even that. I hope this answers your question, but if not, try again. I couldn't understand quite what you were trying to ask for your question about the battery and a battery.

Ed

PaperAirplane

I meant to say "If the battery mAH is smaller than the motor's mAh (say by 100 mAH) it wont work, correct?"
But you pretty much anwered my question completely:-).

The weight of the battery gets kind of high after 2000 MAh, and that is the only problem.

Thanks again
Pa

kyleservicetech

Just a note here about Amps, Ma, and Mah.
Amps is the current being pulled out of your power source, in this case the battery, and sent to your load, in this case the motor. Typical values of the Amps being pulled in our electric models range from a few amperes to over 100 Amperes on some of those multi Kilowatt models. As a comparison, the starter in your auto pulls currents on the order of 140 Amps or higher, depending on if you've got a big V8 (gas hog?) or a little 4 cylinder engine. Ma is the amps divided by 1000, or Milliamperes.

Mah is defined as milliamperes multiplied by hours, therefore Mah for Milliampere Hours. So when you see a battery is rated for 2000 Mah, it will put out 2000 Milliamperes (Or 2 Amps) for one hour. Or 4 Amps for 1/2 hour, 8 Amps for 1/4 hour, and so on.

Now, if you rate that 2 Amp Hour battery in minutes, you have a battery that will put out 2 Amps multiplied by 60 (minutes) or 120 Ampere Minutes. If you divide that 120 Amp Minutes by 3 minutes, you have 120 Amp Minutes/3 Minutes (the minutes drop out) and you will be pulling 40 amperes. (Assuming your Lipo is rated for 40 Amps!)

And, if you've got a 4 cell Lipo, thats about 3.7 volts per cell or 4 times 3.7 or 14.8 Volts. Multiply that times 2 Amps, you get 14.8 multiplied by 2 or 29.6 watt hours. (Or 29.6 multiplied by 60 minutes or 1776 watt minutes.) Now, if you discharge your battery pack in 5 minutes, divide 1776 (watt minutes) by 5 minutes and you can pull about 350 watts out of your pack, assuming the battery pack is capable of putting out 20 Amps.

Note the terms on these numbers. 1776 watt minutes divided by 5 minutes equals 355 watts. The minutes drop out of the equation leaving the answer in watts. (1776 watt minutes/5 minutes)

As long as you include the definition on what you are working with such as Amp Hours, Mah (Milliampere Hours), minutes and so forth, and include them in your number crunching, it might help to figure out just what is going on with these Mah, Ma, Amps, Volts and all sorts of stuff.

Speaking of definitions, say you fly your model for 5 minutes, and take 1.6 Amp Hours out of your battery. That 1.6 Ah (Ampere Hours) is 1.6 times 60 minutes or 96 Ampere Minutes. So, if you flew for 5 minutes, you have 96 Ampere Minutes/5 Minutes or 19.2 Amperes. Again, the minutes fall out. So your AVERAGE current for that 5 minute flight is 19.2 Amperes. Interesting.

The worst part of all of this, is it will make perfect sense to your 5th Grader.

PaperAirplane

So mah isnt the same as amps? I thought that a 2200 mah battery would give you 2.2 amps. I dont think i am understanding how to find the amp rating from the mah.

Thanks for all the help.

By the way, what would the be the least expeensive watt meter you could find that would actually work decently?

PA

mred

Your right. 2200ma is 2.2 amps. Current rated in small amounts such as .1 amp is normally written as 100ma. It is nothing more then another way to write it, so ma is the number to the right of the point and amps is the number to the left of the point. Combine them together and you get 2200ma or 2.2 amps.

Ed

PaperAirplane

I was wondering about MAH. the H threw me off a bit.

mred

You can use a smaller battery if you want to as long as it is able to put out the amps that the motor requires. The problem comes in with flying time. The smaller the battery the less flying time you get. You could more then likely get away with a 2000mah battery and get some flying time if you don't fly at full throttle all the time. You may not even need full throttle to take off. I have a couple of planes that take off fine at half throttle and fly at less. What you want is the biggest battery that you can get in the plane and still fly it OK without overloading it to get the most flying time out of it. A 26oz trainer would more then likely fly fine with a 1500mah to 1800mah battery if you go easy on the throttle. The battery I used was just an example to explain things. I didn't mean that you had to use a 2200mah battery. Just make sure the battery can handle the amps your motor needs to pull.

Ed

PaperAirplane

Yeah, definetely.
I just dont understand the difference between mah and ma, besides the fact that one has the hours part to it.

I also found a 197 gram 2200mah 11.1v battery that should power my 175watt motor.

mred

ma is nothing more then a way to write a number. Normally a number such as .01a is written as 10ma. It's just a different way to write it. MAh is how many amps the battery will put out for 1 hour. If you have a 2200mah battery, then it will put out 2.2A for 1 hour. Read this answer just above for a good explanation of what a battery will do and how long it will last.

"kyleservicetech" Post 114

You can find the time your battery will allow you to fly so you know when to land. It's better to know when the battery will go to low and land a little early then to fly to cutoff. If you do fly to cutoff, then bring the throttle stick all the way back and then go to about half throttle or less. That may give you enough time to land it using the motor rather then just landing it any old place it happens to be. Normally I fly a new setup for about 4 min and then land. I change the battery to find out how much I used and then I know for sure how long I can fly before cutoff. I like to land after using about 80% of the capacity. That way the battery will last longer. So with a 2200mah battery I normally don't go past 1800ma back into the battery when I charge it.

Ed

PaperAirplane

I think i figured it out.

Does mah mean the average amount of continnuos ma a battery will give off in an hour? And is this where the motor comes in? As i understand it, the battery can give off any amount of ma but the more ma the faster your battery will run out. SO if the motor requires 2 amps out of a 1amp per hour battery, the motor will only be able to run for 1/2 hour before the battery runs out.

I am not sure if this is correct, but I am working my way through figuring this out:-)
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Experienced Pile it

"You can find the time your battery will allow you to fly so you know when to land. It's better to know when the battery will go to low and land a little early then to fly to cutoff. If you do fly to cutoff, then bring the throttle stick all the way back and then go to about half throttle or less. That may give you enough time to land it using the motor rather then just landing it any old place it happens to be. Normally I fly a new setup for about 4 min and then land. I change the battery to find out how much I used and then I know for sure how long I can fly before cutoff. I like to land after using about 80% of the capacity. That way the battery will last longer. So with a 2200mah battery I normally don't go past 1800ma back into the battery when I charge it."

Awe, c'mon. Where's you sense of adventure?

Dead stick landings are the easiest. Doesn't matter your attitude, elevation or airspeed - it's all down hill from there.

kyleservicetech

You've got it! ma (milliamperes) is the current (Think gallons per hour in your car) in the circuit between your battery and motor. And Mah or milliampere hours (Think driving for 3 1/2 hours in your car) is how long you left that current flowing out of your battery. So, if you pull 2.5 Amperes or 2500 Milliamperes out of your battery for 5 hours, that will be 12.5 Ampere Hours, or 12500 Mah or Milliampere Hours. Same as driving your car that "Pulls 2.5 Gallons per hour" out of your gas tank and driving it for 5 hours. That would be 2.5 gallons per hour times 5 hours, or 12.5 gallons of gasoline. (So your gas tank's capacity in gallons is comparable to Milliampere Hours, or Ampere Hours in your battery.) Something else is involved here, that is the batteries voltage. That's covered in another thread on how your radio works, a thread listed below.

(Yep, Amperes, or Milliamperes is defined as the flow of electricity, in electrons per second or some such crazy thing.)

Note that the common automotive lead acid battery is rated in Ah, or Ampere Hours. Typical deep cycle battery used for charging our model's batteries range from 60 Ampere Hours to the 120 Ampere Hours for the batteries I use. (Big electric fork lift batteries can run over 1000 Ampere Hours, and weigh in at several tons)

As an example, imagine placing a dead short on your battery for one tenth of a second. You will get a LOT of current, plus smoke, and maybe destroy your Lipo in the process. But since the current was on for such a short time, the Mah, or Milliampere HOURS would be very low. In this case, the Mah or Milliampere Hours would be the current multiplied by the time. Or 1/10 second, (you got to convert seconds to hours). That would be, if you run the numbers, 1/36000 of an hour. (1/10 of 3600 seconds in an hour.)

So even if you pull 100 Amps for 1/10 of a second through your shorted (and newly damaged) battery, the total ampere hours would be 100 Amperes times 1/36000 Hours, or 0.0027 Amp HOURS. (And to be metric, multiply 0.0027 Ah times 1000 to convert to Mah, that would be 2.7 Mah for that 100 Amp short for 1/10 of a second.

So, you can have very high currents out of a battery, and still have very low Mah involved because of a very short time. Weird huh? And, on the other hand, you can have very low currents out of a battery, and have very high Mah. Think of a wall clock that runs on a AA Alkaline cell, that will run for a year or more on a 1500 Milliampere Hour battery.

Even stranger, just how much Power is your shorted Lipo putting out?? Well, it's going to be that 100 Amps multiplied by the voltage across your load. Your load is a short circuit (zero ohms), so the output POWER will be virtually zero, since 100 Amps times zero Volts = Zero. Where is that battery power going??? Your battery is getting hot very quickly. Yep, that's where it went. That power is heating up the battery itself, and will very quickly destroy it or set fire to it.

So, if you severely overload your Lipo or other type battery pack by placing to high of a current demand on your battery, that battery is going to overheat, and overheating Lipo batteries will lead to another discussion.

Take a look at my posting on how your radios work per below:
http://www.wattflyer.com/forums/showthread.php?t=45173

The first part of this 35 page PDF article deals with the batteries we use with our model airplanes. It covers all this stuff. Might be helpful.

Take a look at another posting on electrifying models of the four stroke 70 size engine size per below:
http://www.wattflyer.com/forums/showthread.php?t=45222

That series covers more of this battery thing.

Have a good one!

mred

I have a great sense of adventure, but I also don't like landing my plane in a field of corn that is 7' high and then trying to find it. Or how about the other end of our field that is full of trees. Yea, I have a great sense of adventure, just don't like looking for 5 hours to find a plane only to find it 100' up a tree when I can fly it back to the field using the motor and land someplace that is more reasonable. Also, on some planes that don't glide very will with power off, it is much easier to land them under some power rather then none at all. I know you were just joking around and I don't mind, but it is much easier to land with some power then none at all. A new guy may not know to use the throttle to get power back if not told how to do it.

Ed

kyleservicetech

That brings back memories. I once had a small Enya 09 powered model airplane in the 1960's, tried to land it ON PURPOSE in a corn field :o Radio was a "Galloping Ghost" system I'd made out of an old Citizenship radio system.

Not the brightest stunt in the world, that corn did a real number on the airplane, poked all sorts of holes in it.

It can be rather hard on those Lipo and A123 cells to run the battery pack down to where the ESC powers down. You run the risk of allowing one or more cells to drop below the dreaded 3.0 Volt minimum allowable voltage on those Lipo batteries. And, potentially causing permanent damage to them.