tester423

hi -- I need some help/advice

I got a park flyer plane. Eflite cap 232 ep profile job. This is my first brushless experience. I think I may have it propped wrong. The E-flite set up calls for two ways -- sprt was I think a park 370 -- extreme was for a park 450. Both set-ups call for a 11x3.8 slow fly prop, so that is what got. I did not however go with the E-flite power system. I really did not want to put a ton of money in this unit so got the ebay Chineese special (tower pro). I really got this plane for the convience of the park flyer and just something to play with. I don't want it to go up in blaze of glory though.

I can compare what I am using to a park 450 set up. Since I don't know what I am doing I did alot of reading on here and found a great article in I think Model Airplane News about electric set up. I gathered the info I needed and was shooting in the 150-200 watt/lb range. The plane I have is supposed to be flight ready at 15-17 oz.

The E-flite 450 is ~890kv pulling 9-10 amps I think (going off of memory here). 3 cell li-po put it to ~100 watts. This set up is supposed to be extreme and used 11x3.8 prop.

What I have is an outrunner 1750 kv pulls 15 amps -- 18 amp esc -- 3cell li-po 1150 mah. discharge 15C -- 20C burst. So I have a battery that can discharge 17.25 amps -- ESC handles 18 Amps constant -- motor pulls 15 amps. So motor draw 15 AMP X 11.1 volts = 166.5 watts. Unless I did that wrong. I figure my numbers come out to be more powerfull that e-flite set up so it should swing the same prop no problem. I might be wrong here.

I installed the power system to check it out and all worked correctly. I ran the motor up and down at various speeds while just holding the plane. Seemed plenty powerfull to me. This lasted for maybe 45 sec to a min. Then I pulled it to 1/2 throttle and left it there for about 30 sec. From there I went to full throttle again and did not notice any real rpm gain. I decided to shut it off and check the battery temp and the ESC temp. Both were warm but not what I would call hot. Now I was told by a friend that li-po's don't really get hot after running them the way ni-cd or ni-mh do. I remember this from my touring car days. This is what lead to think I might have a problem. The heat and the lack of rpm gain from 1/2 to full throttle. the motor was only running for about a min and 30 sec. +/- and I had heat. I am thinking the prop is too big and causing the motor to draw excessive current. If I need to try other props that is no problem with me but I have no idea where to even start guessing on an electric.

So do you think I might have a problem or am I just over-reacting. I just do not want to learn the hard way by seeing the little plane go up in flames. Any insight you could give me would be great.

Thanks,
Richard

hobbydude214

My Feedback: (13)

it sounds like your motor is more along the lines of a 370 outrunner at that kv usually the larger outrunners run under 1000kv so if this is true you should be using a smaller prop 10x4.7 or 3.8 again im not exactly sure of what your motor is but thats the closest i can come up with. i had that problem before and just switched to a lower kv rated outrunner in the ultrafly series because of what i had on hand. This took care of the problem but you dont want to have to swap motors so try those props first.

tekajo

You should probably run a static test for a max of 30 seconds. It is easy to burn out motors and speed controls. Do not ask me how many. If you have a volt meter the best twelve dollars you can spend is on the fma web site. I bought the shunt that you plug in your volt meter to make a watt meter. No more guessing. Do your self a favor..... buy it.

tester423

I remember seeing a few smaller props at the LHS that said slow flyer -- Does that make a difference? I am pretty sure they had a 10x4 but I do not remember if that was one that said slow fly or not. I'll look tomorrow.

AJ1202

Just my 2 cents but if your running a 1750 KV and 3S 1150 I would not go with any thing larger than 7 or 8X4 prop even the 8 will be pushing things a bit, this is the same set up I use in a couple of my planes, A BP21 1750 KV and 3S 1350 batt, if I run a 8X4 my batt heats up a good bit more than I like, the plane you have descibed needs more like a 950 or 1050 max KV to use the larger prop for thrust. the higher KV is more for speed. I am currently running a 950 KV with the same 3S and a 12X6 and it is a good match, this set up is on my E-Flight Ultimate

tester423

FWIW -- I put a 10x3.8 slow fly prop on it and noting heated up. I did not fly it but just test ran it for a while. I held it and ran it through lots of rpm changes and full throttle several times for about 20 sec. burst. Seemed like it did fine to me. I ran till the ESC shut the motor down and checked the voltage on the battery. It was setting at 10.4 volts.

I have found that where I screwed up is in the KV rating. Aparently more is not always better. I think I understand better now. If I want to swing a bigger prop with low bite for that flippy dippy 3D stuff then the motor must turn slower to match that prop. How you tell exactly I have no idea but I'll get it eventually. I really like this electric stuff though. Just getting past all the figuring is the hard part.

I checked and the ebay listing compared this to a e-flite 370 outrunner. I looked at e-flite's specs on the motor. It was very close to my numbers and recommended a 9x6 to 10x4 prop. So that is what I went with.

thanks

j stumbler

A prop specifically labelled "slow fly" has a wider, fuller blade on the prop compared to a "sport" prop. The prop covers more surface area, so it moves more air, but at the same time, spins slower than a sport prop. Turning a slow fly prop also draws more power from the motor and the battery. If you put a 10x4.7 slow fly prop on a motor, and switch to a 10x4.7 sport prop, you should see a drop in amp draw with the sport prop. Like tekajo said, get yourself a watt meter. It's a necessary tool if you want to get the most out of your motors, esc's, and batteries.

On a different note, everyone has their opinion, but personally, I have had nothing but bad luck with the Chinese ebay stuff. I want a sweet deal, just like everyone else, but some things aren't worth it. After melting 2 Tower Pro esc's, I went back to old faithfull, Castle Creations. In my opinion, when it comes to r/c electronics, you get what you pay for. But that just one man's opinion.

Sorry for the mini soap-box moment there,
Al
[link=http://www.commonsenserc.com]www.CommonSenseRC.com[/link]

tester423

yeah well I figured I would try it. I did use the CC receiver though. At least i'll be able to fly it in if the motor quits right? I'm glad you chimed in AL I was looking for one of your posts last night but I could not remember you user name. I wanted you website link.

aeajr

My Feedback: (2)

Most motor mfg will provide recommendations as to what prop to use on their motor. You match the prop to the motor not the plane. Go back and see what the mfg recommends.

While the ESC and the battery might not be hot, how was the motor. You could be working within the range of the batery adn the ESC and be over stressing the motor.

Just guessing, but I would think you are still too big in that prop. Something 9 inches or less might still be in order. You could still be over working the battery pack or the motor.

Do you have a watt meter? Or do you have an amp meter that can measure 20 amps? If so, I would try to take a measurement remembering that you static measurements will be higher than what you will see in the air. Where glow planes are tuned by pitch and RPM, electric systems use the watt meter in place of the sound of the motor.

tester423

ok -- I solved this problem -- I put an eflite 400 outrunner on it. I have flown it twice and it worked great.

About the wattmeter or amp meter. If I can round one up. Where do you put it. I guess it would be a clip that goes around a wire like an automotive timing light has. If so where do you check the current? On one of the motor leads or the battery? I am lost here. Where is the meter on the FMA website?

aeajr

My Feedback: (2)

Most wattmeters go in line with the battery to measure volts and amps coming out of the battery. I understand there are clamp versions but I have not seen or used one.

I have the Watts-Up meter and it works well for me.