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@Stefan_Go
You have a lot of rubbers (too much is also a problem), but you need dampers (something like earplugs). Also the weak point is your gimbal, namely the servo, here (between servo and servo-arm) you should add some foam to prevent the servo-arm to move and vibrate freely. best regards Ferdinand |
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@EOD:
Before I went with the long arms, I tried really a lot with vibration dampening, namely different foams and rubber-foam combinations. You can see some remainder of this at the camera also. The only thing I didn't try was Moongel and Kyosho Zeal because I couldn't find any dealer in Europe who has it and buying it from the US was too expensive - $30 shipping for a $10 sheet of Zeal... With the current setup, I had the best results. The rubber posts are relatively hard and the balls under the APM relatively soft but squeezed by the rubber band. With the 800kV/10x4.5 drive train, I had X and Y vibrations around +/-0,5 and Z vibrations around -11/-9. With the big props I have X/Y around +/-5 and Z around -16/-4 which is enormous. But when the copter flies, you can see that it's no "vibrations" anymore but real shaking, as if it was overtuned, but it isn't. If I tune it down, it becomes sluggish but the vibes are still there. The servo arm doesn't move at all on itself. I tried 4 or 5 different servos before I found one that has absolutely no play. It just twitches a bit here and there but that's not because of play but either the RX or the servo electronics. |
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I finally found a way to way to benchtest thrust of the 4822-390kV 22-poles motors with a 18 5.5 props and got a little confused.
I used a wooden holder placed against a kitchen scale. Granted, the error introduced with this set up is probably not minimal, but at this point I wanted to get some approx. thrust and amperage to have a vague idea on the amount of arms/motors I may need (4 or 6) in a future configuration under 3s and 4s. I was expecting 3s to be more efficient but maybe with not enough thrust for my intended applications. Against my theory, I found that 4s was more efficient. Is my theory wrong, or how this could be explained? This is what I measured: ----------3s-----4s ---------------------------- 1A:----95g---115g 2A:--165g---195g 3A:--215g---260g 4A:--265g---320g 5A:--305g---360g 6A:--345g---405g 7A:--385g---455g 8A:--415g---490g 9A:--450g---530g 10A:475g---570g As it can be seen, 4s consistently more efficient than 3s. How could it be? |
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Power (watts) = current (A) x voltage (V) |
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and also, 4S battery is 33% heavier than 3S with same mAh in it.
which raises watts needed for hover. in this topic's setup(360KV, 17''), 4S performs better because it enables you to discharge it completely for hover (to a safe level for cells ofcourse), 3S during flight at some point drops below volts needed to hover(roughly, KV x V = RPM, as voltage drops - motor spins slower) and some energy remains in battery, but you can't use it for flying. Tom http://www.tinyurl.com/drtomyubito |
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Last edited by Dr.Tom; Nov 06, 2013 at 01:54 PM.
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Last edited by blimppilot@ph; Nov 06, 2013 at 01:58 PM.
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Yea, like many have already mentioned, you have to make that comparison table using W.
You table in W is this: Watt----3s----4s 11.7----95---- 15.6--------115 23.4----165---- 31.2--------195 35.1----215---- 46.8----265----260 58.5----305---- 62.4--------320 70.2----345---- 78--------360 81.9----385---- 93.6----415----405 105.3----450---- 109.2--------455 117----475---- 124.8--------490 140.4--------530 156--------570 If you chart it and you will see the 2 lines goes almost overlapping each others. |
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Yes, 3s @ 4A gives me similar thrust and same wattage as 4s @ 3A But why do I care about wattage if what I want is to spend 3400mAh to lift X grams for the longest time? This is the table again removing 150g for 3s and 200g for 4s -------3s1p---4s1p ---------------------------- 3A:---65g----60g 4A:--115g---120g 5A:--155g---160g 6A:--195g---205g 7A:--235g---255g 8A:--265g---290g 9A:--300g---330g 10A:325g---370g 4s will still lift more grams than 3s for the same mAh (or last longer for the same amount of grams) I can go further and remove 150g for the ESC/motor/prop -------3s1p---4s1p ---------------------------- 5A:-----5g----10g 6A:---45g----55g 7A:--185g---105g 8A:--115g---140g 9A:--150g---180g 10A:175g---220g |
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Last edited by AGS2; Nov 06, 2013 at 03:49 PM.
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but in real life and batteries ON BOARD make a difference. you must take into account that each mAh from 4S comes with about 33% added weight. because it needs 1 cell more in air, if you don't want that weight penalty, you must lift off with smaller 4S batetry, with less mAh than 3S (but same weight as 3S) some HK samples: 3s 5000mAh 443g https://www.hobbyking.com/hobbyking/...arch=5000%203s 4s 5000mAh 578g https://www.hobbyking.com/hobbyking/s...5000%204s%2040 so, same multi(props/motors/frame) CAN'T use SAME watts for hover if weight is not the same. bottom line is: you state that 4S is more efficient for your setup, that is in the spirit of this topic maybe with some other prop/motor combo, 3 or 5S would be more efficient than 4s |
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Last edited by Dr.Tom; Nov 06, 2013 at 03:33 PM.
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So take a good look at the profile of the prop tip an see if they are the same on both sides. |
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What matters is power, that is VxA ... not just A ... you did not measure the voltage, so we can just assume that on 4S you have 4/3 more voltage. So let's take this line: 5A:--305g---360g At 5A, 305g on 3S ... once going to 4S, I would expect that for have the same g/w relation, the thrust should have been above 400g .. being 360 ... it is way less efficient in g/q Other example 3A:--215g---260g 4A:--265g---320g 3A x 4S = 4A x 3S ... same watts So ... with 3S set up, you get 265g, vs 260 ... a little advantage for 3S In general lower S is always give better efficiency, but it also limit the max power that can be delivered ... These conclusion we got already from other test data done in the past and published here |
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When you removed the 4s weight you automagically made the frame 50g lighter by keeping the same thrust for both. Off course you will fly longer if you can take 50g more battery at the same AUW, doesn't matter whether you take it in the form of a 4S or a 50g heavier 3S (a clear example why Watts and not Amperes are used to compare batteries). Lets assume 350g AUW, 200g battery: Battery power (Wh) is = density * weight ... so it doesn't matter what config you take (3S or 4S), the Power in Wh is the same for the same weight. At 350g thrust you need (approximately): - 67,5W to hover with 3S - 72W to hover with 4S Since the Wh are the same flight time will be 6,6% more with 3S at same AUW. Now it's true that you get more total thrust at 4S, thus making the hover point at higher throttle % at same auw with 3S. But that means that you're actually not utilizing the full motor power at 3S and should increase prop size (hence this thread). Bottom line - if you're limited by propeller size, 3S will still give you more (hover) flight time at same AUW at the sacrifice of agility and power. |
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Last edited by TheJams; Nov 07, 2013 at 03:58 AM.
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Thank for your patience guys, I understand that if what it counts is watts, then 3s is more efficient. And I know I am wrong somewhere, that Work/Watts is what it should matter, but I cannot see why. Simple example: 1s Panasonic 50g battery gives 3400mAh 2s Panasonic 100g batteries give 3400mAh 3s Panasonic 150g batteries give 3400mAh 4s Panasonic 200g batteries give 3400mAh Let's imagine an hypothetical motor with similar characteristics (4s lifting a little more under the same current than 3s) 3s @3.4A lifts 300g (Nett 150g after accounting for the battery weight) 4s @3.4A lifts 400g (Nett 200g after accounting for the battery weight) 4s will lift 400g (200g) for 1h ideally (or 45 mins in reality) 3s will lift 300g (150g) for 1h. 4s will lift 300g (150g) for >1h So yes, at 4s there will be more wattage, more work, more load, more rpm... but also either more lift of more flight time for the same lift, since the batteries are rated for mAh and not for Wh. What am I overlooking? |
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Last edited by AGS2; Nov 07, 2013 at 06:03 AM.
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