Little Screamer and E-flite brushless ESC
 

OK guys, I need help here. I’m pretty new to EP and am having a little trouble with a new motor. I bought one of Hobby Lobby’s new “Little Screamers” motors, the Purple Peril. It’s the second one shown on [link=http://www.hobby-lobby.com/littlescreamers.htm]this page[/link].

I’m attempting to run it with an [link=http://www.horizonhobby.com/Products/Default.aspx?ProdID=EFLA311B]E-flite 20 amp brushless speed controller[/link] and having some trouble. The motor powers up and will slowly advance to full throttle with an 8 x 4 prop. If I try to advance the throttle faster than a 4 or 5 second transit time, the motor starts stuttering and almost sounds like grinding gears or something similar (it’s not a geared motor or connected to a gearbox). When I do manage to get it up to full throttle, my WattsUp reports a load of about 20 amps and output around 200 watts. The prop is a lightweight, flexible unit that came off another brushless I have. I don’t know much more about it.

This is all on a 3S 1150 maH lipo rated at 15C. I know this exceeds the amp draw of the battery and is right on the border for the speed controller, but this battery and prop is just what I had laying around and was only installed for test purposes. I was only expecting to see around 16 amps and 165 watts, as noted on HL’s web page. Anyway, what worries me the most is that the motor got pretty hot after several seconds of full throttle operation. I’m talking about less than 10 seconds or so. It was not so hot that I couldn’t hold it, but it was approaching that point. I suspect it’s not at all normal for the engine to get this hot, but have no idea how to troubleshoot this setup.

I would very much appreciate any guidance or suggestions you may have.

RE: Little Screamer and E-flite brushless ESC
 

Hi Erik-

Not all props of the same size are created equal. One manufacturer's 8x4 may draw more current than the same size prop from a different manufacturer. If you can, try a couple of other 8x4 props.

You definitely do not want to let the motor overheat. Even if you don't melt the insulation, overheating can permanently weaken the magnets, requiring that they be replaced.

- Jeff

RE: Little Screamer and E-flite brushless ESC
 

Jeff,

I surmised that heat was bad. :) I can only hope the few seconds of exposure to heat didn't do any damage. The prop I used is the ony E prop I have in that size. It's a no name black plastic, very bendy prop from a prepackaged "bargain" motor/esc combo I had laying around. I do have an APC 8 x 4 glow prop but the hub is so large, it will not sit properly on the prop saver hub of the new motor. It seems reasonable to conclude that the effective load of my cheapy prop is less than that of a good APC E series prop, which leads me to think that, if anything, my measured results should have been on the low side of 16 amps and 165 watts and not the high side. Regardless of the suitability of the prop, the god-awful noise the motor is making is what worries me the most. Any ideas what might be causing that?

RE: Little Screamer and E-flite brushless ESC
 

Hi Erik-

I've heard nasty sounds when a motor is being over-propped, which is why I suggested trying a different prop. I still think that's a good idea. Maybe also try a slightly smaller prop, such as a GWS 7x3.5HD.

Without at least trying a couple of different props, you don't have much data with which to analyze what's happening.

May we presume that the motor sounds OK when you run it without a prop?

- Jeff

RE: Little Screamer and E-flite brushless ESC
 

Wow, it never even occured to me to run it without a prop! I guess we can blame that on my glow history. :-) I will make it by the LHS today and see if I can scrounge a smaller prop, such as the GWS 7x3.5HD you suggested and see what happens. I'll also try it without the prop and see if the noise is still present. Thanks for your help, Jeff.

RE: Little Screamer and E-flite brushless ESC
 

Erik-

Just run it without a prop long enough to see if the noise is present. The idea is to find out if the noise is due to a defect in the motor or due to a prop issue.

Get a GWS 8x4 prop as well. That no-name black prop may be losing its shape at high RPM, and you might find that a higher quality prop will actually draw less current. Not that GWS props are the pinnacle of propellor design.

At any rate, props are cheap, so it's well worth it to experiment a little.

- Jeff

RE: Little Screamer and E-flite brushless ESC
 

Thanks Jeff. It looks like my run to the LHS will have to wait until tomorrow, but I'll be sure and report back with my findings.


Erik

RE: Little Screamer and E-flite brushless ESC
 

Your flexible black prop is probably a slow flyer type, and that will draw a lot more amps than an APC E will. Your 200W through a 25g motor under static conditions is a recipe for melt down in a few seconds. These hot new LS motors can't cope with more than a few seconds WOT on the bench at these high amp draws - though apparently they are okay in the air. I think any 8x4 on the PP at 3s is on the ragged edge. A 7x5 APC E is a bit safer, and a 7x3.5 GWS HD or a 6x5.5 APC E is far more prudent.

RE: Little Screamer and E-flite brushless ESC
 

Doc,

THANK YOU so much for the education. This is exactly the kind of info I was looking for. I'll ditch the floppy black prop and go for one of the one you and Jeff recommended. Today I'll make it a point to hit the LHS and stock up.

Thanks again for helping out a rookie. :)

Erik

RE: Little Screamer and E-flite brushless ESC
 

Jeff and Doc,

I managed to find a 7x5 APC E prop. I know it's not exactly what either of you recommended, but it's close and it's all they had. I first ran the motor without a prop and it's smooth as silk, which is a relief because it means the motor itself is fine. I next tried it with the APC prop and was clearly able to see that it was not sitting on the prop saver hub properly and after just a second or two, was wobbling around and creating the same horrible noise. Now that I know what I'm looking for, it's easy to spot the problem: the prop is not mounted properly. I am CLEARLY missing something here. The motor instructions have absolutely no information about how to mount the prop and I imagine they assume some minimal level of knowledge, which I simply don't have. Here is a pic of the motor hub:

http://i57.photobucket.com/albums/g2...y/RC/motor.jpg

And here is a pic of the prop hub, along with a couple of spacers:

http://i57.photobucket.com/albums/g2...vy/RC/prop.jpg

I've never used one of these "prop saver" hubs before but have seen them in use. Is it as simple as wrapping a rubber band back and forth across the prop hub and around the two screw heads on either side of the shaft? Frankly, I'd prefer to see a threaded shaft and nut like all my glow engines, but if this is the way it's done in the E-world so be it. I just need some guidance on how to get the prop centered and secured on the darn hub. I really feel stupid having to ask such simple questions and I appreciate you guys taking the time to school a noob.

Thanks!

RE: Little Screamer and E-flite brushless ESC
 

Can anyone here lend some guidance on this issue?

Thanks!

RE: Little Screamer and E-flite brushless ESC
 

The prop saver on the little screemer fits a GWS 8X4HD perfectly, and fits nothing else very well. When using a slow flight APC prop you need to get a prop adaptor and mount it on the shaft. A prop adaptor is an aluminum threaded piece with slices on the end that fit to the motor. As you tighten the prop it squezes down on the shaft. Graupner makes a bunch of them. There is just enough shaft sticking out for this to work. (Most of the time I used a prop adaptor).

Larry

RE: Little Screamer and E-flite brushless ESC
 

Larry,

Thank you very much for this valuable piece of info! I'm off in search of a suitable prop adapter. I'm guessing I just need to measure the diameter of the existing shaft, right? Are there any other details I will need to get the right size?

Erik