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Post by Silverback on Mar 9, 2011 22:42:35 GMT 1
So I'm finding a lot of discussion for stock LP cub props, but a lot of that is also around how far can you push it and not burn out the stock electronics.
Well, I started with burnt out electronics and have a new 20A brushed ESC, DX6i... and am not worried about burning them out (for that matter, I've got a brushless motor coming, I don't know that I'm _that_ worried about burning out the original motor, don't want to do it unnecessary but I'm not going to cry if it goes).
Secondly, I don't really care much about top speed, I'm adding flaps, flaperons, and may play with slats/vortex generators/more wing area. It's got big tires on it and want bush plane type performance.
Any recommendations on prop (brand/style/size)? I'm almost tempted to try something in the 11x4.7 or 5.5 range (Not really sure that I have the ground clearance to not break one), or maybe even a 3 blade, 10x5 or something
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Post by flydiver on Mar 9, 2011 22:49:31 GMT 1
You'll fry the ESC now. 20A is not sufficient to push the envelope very far.
FWIW I'd check the LVC of that ESC carefully. VERY FEW brushed ESC are lipo friendly. Easy to ruin your lipo too.
Make sure you read up on Spectrum Brown Out and the need for a UBEC if you are going to do all that experimentation. Plenty of discussion in the group-I ain't about to rewrite it all.
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Post by Silverback on Mar 9, 2011 23:08:33 GMT 1
Fry a 20A? Really? I've done some searching here and a few other forums most people were listing some pretty low watt numbers even with big props, like all below 100 (with 10.8V coming out of a LiPo that should be less then 10A). I'm seeing way below that with the stock 9x8 that came with my SC.
Are you suggesting that the motor will play nice at MUCH higher loads? I expected that the limit would be not that much higher, I thought I remembered seeing some posts that the stock motor will burn itself out quickly with an 11x7 prop with amp draws in the low teens....
I'm using a Turnigy 20amp ESC, jumpered for LiPo, which has a 5V BEC and shouldn't brown out on the spektrum AR6100e that I'm using (not supposed to be a problem unless power drops below 3.5V)
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Post by flydiver on Mar 10, 2011 0:04:25 GMT 1
The old stock 10x8 pushes 18-19A with the stock lipo (not a high output lipo). supercubclub.proboards.com/index.cgi?action=display&board=batt&thread=1831&page=1Put a larger prop and a better/larger lipo on there and you can easily push over 20A. It's nice to have a 20% buffer on the top end for the ESC. Do you trust Chinese specs? I don't. That's the problem with the stock system. There is no overhead anymore. Brown out could be problem with the multiple servos you are planning adding [I'm adding flaps, flaperons], especially with low efficiency, high draw servos like HXT 900 or digitals. |
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Post by Silverback on Mar 12, 2011 0:25:48 GMT 1
hehe, you wouldn't expect Chinese amps to be smaller than American ones, would you?
huh, again, I'm not sure I'm worried about burning it out (I might even have a bigger ESC around to try if I was/if I did, and heck, I have a brushless motor coming that I'll eventually convert to).
None of this is at all dealing with the question though, what is the best prop for the kind of flight characteristics I'm hoping for? I wonder if a 10x8 might be too much pitch speed for what I want, again, don't know for sure an 11 will clear (I am running slightly over 2.75" tires for that tundra tire look), so I'm even debating a 3 blade (though a it scared to try it from all the negative stories on the forums)
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Post by john66 on Mar 12, 2011 12:14:06 GMT 1
hehe, you wouldn't expect Chinese amps to be smaller than American ones, would you? Not at all suprised! After all, living here in the UK, we are used to hearing how much bigger and better all things American are, mostly from Americans!  ;D John |
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Post by flydiver on Mar 12, 2011 17:37:48 GMT 1
Me thinks you would really like a wattmeter. Perfect for this kind of investigation. Otherwise you are relying on feedback from folks that have good intentions but may not have any real idea of what they are doing.
Over propping is certainly common. It may or may not get you extra performance. What is will get you is extra heat. Where a particular power package lets out the smoke is highly dependent on the weakest link, the QA of the individual components, the plane load put one the package (weight, drag, speed), and the flying style of the pilot. One guy may get away with [power pack A] but that doesn't mean another one will.
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Post by cubcruncher on Mar 12, 2011 19:48:33 GMT 1
Just to Add my two pence, flydivers right, whats the motor your going to receive in the post? I have just put in my cub an 1100kv turnigy clone with a 9-6 prop, minimum for this is 25 amp, for safety a thirty is better, in fact I have a 40 amp esc as I'm going to switch out the motor for a 1700kv in the future, which I already have, this will pull 32-33 amps max with a slightly smaller prop, I will check it out with a watt meter when the time comes. Lads,... what does a Cub look like in the sky when its on fire?  ?  If you fly conservatively you should be alright but usually the bigger the prop the more amps you pull so be careful not all advice is correct, the problem with electrics there are so many variables, A slightly bigger battery than stock is a good idea for a first upgrade! |
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Post by flydiver on Mar 12, 2011 20:21:28 GMT 1
in fact I have a 40 amp esc as I'm going to switch out the motor for a 1700kv in the future, which I already have, this will pull 32-33 amps max with a slightly smaller prop, I will check it out with a watt meter when the time comes. Slightly smaller? 1700KV is pretty high KV on 3S. My stryker motor (on a Funjet) is 1900KV and I use a 6x4 prop on it. Cub is pretty draggy for those kinds of prop speeds. Not sure this is an optimal power plant for the Cub. That kind of KV is a good for 2S or very high speed 4/5/6S applications I have some small motors wound that way for 2S/3D. |
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Post by cubcruncher on Mar 12, 2011 22:21:04 GMT 1
It was worth a try, so whats the max size we can safely get away with on the cub? I'm no expert, like I said so many variables in flight electronics still trying to get my head round it all!
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Post by flydiver on Mar 13, 2011 1:06:46 GMT 1
Don't understand the question.
Max size on what, motor size, prop size for the motor, or prop size for the Cub?
You prop for the motor. You motor-size for the plane.
So I was referring to props for a 1700KV motor, not knowing if it's a little bitty motor or a brute.
A similar sized plane the Multiplex Minimag comes stock with a direct drive 400 brushed motor and 5x5 prop-same exact power system as the Easy Star. It's pathetic on the MM and OK on the ES.
So, lots of guys upgrade to brushless. The brushed is an inrunner type and putting an outrunner in there is entirely possible but not a drop in. Since the MM is often used as an aileron trainer (I jumped from the Cub to the MM) many people are intimidated by that conversion. Multiplex sell an inrunner direct drive
Himax 2815-2000 Brushless Motor. That's 2000KV. They use the same 5x5 prop. Folks love it compared to the crappy brushed setup. So it works. It's not as effective as a lower KV motor of similar power turning a 9x6 prop but if you don't know....you don't know.
Note-just got done fixing the wiring on my buddy's MM. He put an outrunner in. Wires come out the front of the motor (reversed shaft) and need to be routed under the spinning can. Wires came unglued from the floor and the can chewed them up. That's part of the problem with these kinds of upgraded.
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Post by cubcruncher on Mar 13, 2011 1:14:10 GMT 1
Sorry flydiver, I meant the size of motor on the cub, whats the optimal, not too powerful not too mundane?
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Post by flydiver on Mar 13, 2011 2:13:14 GMT 1
No clear answer.
For power, ~ 15-20A the stock being more like 10-13A.
But, for weight and CG it helps to go larger since the stock power is pretty heavy out on the end of the nose. Those motors if fully powered are a handful.
Too much power can cause it's own set of problems. I have an old Aerobird-brushed 400 as described above: ~6A max. I upgraded my Funjet and took the Stryker motor I have in there and put it in the Aerobird. Exact same size and weight-simple re-fit with a MUCH larger ESC. Now it's in the low 20A range.
The thing is no longer mild mannered. It's a handful. It GOES almost as well as my Funjet but was never designed to handle that kind of speed. It's a bit erratic. I can't actually say it flies better so much as way differently.
You can under prop. Often you gain some efficiency at the expense of some performance. This is not always a bad trade-off.
Good looking Cub.
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Post by cubcruncher on Mar 13, 2011 12:47:47 GMT 1
the post of the pics of my cub I posted here I have moved to : Plane building and Reviews with a better explanation of what I did.
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Post by Silverback on Mar 25, 2011 17:43:10 GMT 1
So, no one is even going to attempt to answer my actual question? I mean there isn't even any discussion about a prop on a stock motor at all here, much less what the stock motor/gearbox will work with well in the SC.
I don't know what it has to do with this question, but you asked, I won a 2830 1000kv brushless + 40A ESC for $.99 on ebay (Slightly smaller and lighter than a lot of people go with, but still should be more power than the stock motor) , but I'd like to see what the stock motor will do before trying that...
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;D
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