Mike Connor

My Feedback: (5)

All my parts were in and I was getting excited about testing the system. About two minutes into the first static run I bumped the throttle up and about 50,000 rpm the motor mechanically let go. I hope this was a defect problem and not a sign of what happens to electrics like cp talks about. Anyway, the maiden will be delayed.

Final RTF weight is 2 lbs 9.5 oz - That may increase to 2 lbs 11 oz if I have to go to different motor.
Prop pitch speed is 219 mph with just over 2 to 1 thrust ratio. at 52,000 rpm.
Keep in mind the 4S 4000mAh battery would actually power an entire house with AC running (for a couple of minutes).

dhal22

i think our Sooners season went poof also. at least you have a good backup.[X(]

combatpigg

My Feedback: (3)

Mike, you're supposed to run 'em rich for a little bit before you floor it.

So...does this mean you need to adjust your throttle travel to whatever they say the limit is?

ChrisAttebery

My Feedback: (15)

NOOOOOO

That's a good way to smoke an ESC. You have to swap the prop until you get under the limits.

Mike Connor

My Feedback: (5)

I started with a 4.1x 4.1 that should draw 60 amps at 52,000 rpm. Way under the 4.5x 4.1 I intend to run.
I had an amp meter connected and I did not get close to the limits of the 100 amp ESC. I think the motor was defective as I was only at full throttle for 1 second when it went.

Edit - The 4250 Kv motor is rated for 52,000 rpm, 50 amps/500 watts continuous.

Mike Connor

My Feedback: (5)

You adjust the prop size to make it "richer". not the throttle travel.

lfinney

My Feedback: (44)

BTW we have a club member here who reworks his turnigy motors, he upgrades the bearings, he coats the windings with special epoxy for windings, then after all this he balances rotor, and has now started using same epoxy to glue in between magnets, he had a prop break and had a out of balance prop run, the magnets came loose[:@], now the magnets aint going anywhere, FWIW

soarrich

My Feedback: (98)

Bigger or smaller?

What happen to the motor? Did it physically come apart?

freakingfast

My Feedback: (3)

I've seen a 65 hp Industrial brushless servo over speed, the term grenade is pretty close. The engineers [sm=bananahead.gif]used the wrong controller (speed control).

Crazy4Flight

My Feedback: (540)

poof ???

the wimpy version of BANG !!!

MJD

My Feedback: (1)

No kidding! At least the Lipo's could have grenaded. It just ain't the same without an explosive mixture of some kind.

Kidding.. mondo power electrics are okay I guess.

Hope you make it work Mike! My electric Demon is coming, but the motor system will not set any world records.

MJD

Mike Connor

My Feedback: (5)

The motor did not come apart but whatever is attached to the shaft broke loose and sent out a spark with a small jerk. It was not as eventful as the sound of the 50,000 rpm prop (in the house). I think it is louder then a glow.

The motor tries to reach a rpm equal to the Kv x the volts. In my case it would be 4250 kv x 14.8 volts for 62,900 rpm. The prop load will not let it get there completly but it tries. The bigger the prop the harder it tries and that requires more amps. So you can have a poof from too many amps or a poof from an over speed caused by too many volts and a light load.

I wanted a 2800 Kv motor but it was out of stock everywhere and they talked me into the 4250 Kv. I may have exceeded the rpm limit of the motor. It will be interesting to see how they respond to my situation since they recommended it. Unless they insist it is ok and send me another motor, I will try a lower Kv motor next time. BTW, the motor cost $55, one of the cheapest components I bought.

Mike Connor

My Feedback: (5)

It has been a learning experience with a moderate amount of frustration. Soldering 10 AWG wire with the wrong iron has been the hardest thing so far. If I figure out a good combination, there are two Demons in line for extreme electric power.

iron eagel

Smaller in diameter or pitch, or both if you really need to drop it down.
Running the motor with less load reduces the current drain, but...
When you are not loading the motor down with the prop the rpm's tend to climb...

Like everything else in aviation it is all about trade offs.

iron eagel

Mike,
Looks like you used a shoe horn to get it all in there, with that battery.
Nice job on the soldering, the connectors look good.
Normally you will get a bit of a peak in current as you approach max throttle, what I have seen is a spike of 3-4% max.
Usually it has been the case when I blow a motor electrically, the has been a lot of heat and smoke involved.
Like I said before it sounds like you may have thrown a magnet, or had a bearing failure...

I agree with you that a 2500-4000 kv motor may be better but as you said try to find one...

Mike Connor

My Feedback: (5)

It all fits real nice and close with routing the wires the only pain.
The more I think about it I am thinking about ordering the new Arc 28-58-1 3180 Kv motor that is rated at 1 Kw+ continuous. Is is 11mm longer and weighs 1.5 oz more with a price tag of $89. But looking at the calculator the #'s look good even when staying well under the power limits. It is in stock and my RTF weight would only go up to 2 lbs 11 oz.

iron eagel

Well a kilowatt is a lot closer to what your application calls for...
The numbers look pretty good as far as the calculator goes.
I do not know what the max current and voltage spec is for the motor, like I really pay a lot of attention to that anyhow.
If I did, I would not be running a motor rated at 3O amps continuous at 11.1 volts, at 35 amps 18.5 volts (right now it has about an hours flight time on it spinning a 10X6 3 blade MAS).

z06kal

A 4.1 x 4.1 is too small for your wing. You are not getting nearly enough thrust to even approach pitch speed. Your wattage would be much better spent on a bigger prop. I'd say something like a 5x5 or the sizes between 5x5 and 6x6. Just FYI, we use a 5x5 prop on a much much slicker f5D airframe at 1400 watts to crack 200mph and even that is still behind pitch speed.

Oh yeah and your 4S 4000 pack will not run a house with the a/c. A typical 4 ton a/c uses about 5kw when powerd up. Pulls like 25-30 amps at 220v a/c. That is JUST THE AC. a typical house will use like 3-4kw when all powered up (not including ac). Even if your pack could burst 60c or 240 amps (for just a few seconds with heavy voltage sag) that is only about 3kw. So I suppose not including a/c you could stretch it if you were pulling 60c from the pack (full charge to full discharge in 1 minute).

iron eagel

I tried to put this amount of power levels into perspective for Mike by telling him that up until the late 70's the typical service installed in a house was rated at 100 amps. I was just trying to explain to him the type of current involved not the output over time. True the maximum power the typical 100 amp home service provides 22 KWhours (lots of juice), but 1 to 1.5 kilowatts in an airplane is pretty darn potent. I do not know his background in electricity, or his understanding of it, and was trying to point out the dangers of working with high power systems because of safety concerns, as well as the fact that you are still dealing with a lot of energy both potential and kinetic.
The example I used was geared more to point out the instantaneous power levels he was working with, not power vs time.

Mike Connor

My Feedback: (5)

Thanks for your input. It looks like a 5" prop or bigger is in my future. You may have a much much slicker airframe but I have a much much lighter wing loading. So what do you think happened to my motor? over speed form the voltage/Kv combination? I did mention pitch speed but do not actually hope to achieve 200+ at this time. Vne may be 150 mph or less on this scratch built 2.2% thick wing. We will see. This is my first venture into electrics so your thoughts on my thoughts are welcome. I obviously did not make a good choice the first time around. [:@]

Yes, my battery would not power your big house but maybe my little house.

Mike Connor

My Feedback: (5)

I know where the light switch is.

Mike Connor

My Feedback: (5)

Not because of frontal area.

iron eagel

I think the 150 figure is no problem...
Maybe even a bit better than that is not out of the question. Should be interesting to see what it does in the air.

Mike,
I was thinking about your run/test time, here are a few tips...
First of all don't ever go full power on the first few runs let everything wear in a bit sometimes the bearings are a bit stiff and need time to loosen up. Also it will give you a better idea of any heat issues before they get to a point that become a failure, this is a good point to have one of those no touch temperature probes ($39 home depot) point push a button you get a temperature reading, sometimes you can not feel where or what is getting too hot. These thing are point and shoot the one I have has a laser aiming guide so you know where you are looking (such as the coils). When I run a motor on the ground I limit the runs to about a minute and a half to two minutes maximum, because I don't like them to run too long without a lot of air blowing through the motor. After each run I write down the data an let the motor and equipment cool down for about 15 minutes, I usually swap in a fresh battery as well. When I start the next run I quickly push it up to what I know was a good run then creep up slowly from that value til I encounter over current or start to get signs of heating. You are probably aware that they rate the continuous power, much lower than the burst power (typically burst power is for a maximum of 60 seconds), now with a lot of cooling this can at times be stretched a bit, but you are in the danger zone. Now I have exceeded that time limit on the order of two or three tomes longer, and have gotten away with it, not that I am recommending it.

Mike Connor

My Feedback: (5)

Thanks for the information Paul. I actually think the speed will be good and the airframe will stay together but time will tell. I am putting ear plugs in the next time I run high rpm for any length of time. I sent an email to the folks I bought it from and to Lightflightrc to get there thoughts and to see if they are going to do anything for me. I did tell then exactly what I was going to do when they recommended the motor.

iron eagel

I told you that theses small motors set up this way make quite the noise...
I wasn't kidding about Darth Vader's Tie fighter, wait til you get it in the air, there is nothing like the sound of a prop spinning at high rpm with no exhaust noise.
But I still like the sound of an engine spinning one up as well, this is just a bit different, and as the battery technology improves it may become even more commonplace.
No greenhouse gasses with these, or emission control, I heard something about they wanted to put catalytic converters on lawnmowers now, you know sooner or later they will be coming after our little two strokes.
Their motor spec says 35,000 rpm max, I doubt that this will be covered under warranty, who knows.
The only ones I know for sure that off the shelf can spin up in that range are the Neu's which are rated at 60,000 rpm.
But sometimes you get one here and there that holds together way beyond its specified range.
Yours made it real close before it broke, at least now you have an idea if how hard you can push them...