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Old May 20, 2016, 03:20 PM
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Sebart AngelS 30E - 3S or 4S - vibration problems - harmonics

I tried flying this model with more or less the stock setup and was underwhelmed by the flight durations .

So I decided to go up to 4S, the motor (Turnigy SK3 3548 840kv) was rated for it and I'd already employed an overspec ESC in a Turnigy Plush 60amp. It was not successful for long because the airframe developed severe vibration problems. All would seem perfect with the motor and prop spooling up to about 70% with barely a tremor then suddenly after that all hell would break loose, enough to damage the F1 firewall on one occasion.

Failed solutions:
Using a smaller prop made NO difference, I even tried a balanced 12x6.
Tried three different motors, 840, 840, & 800kv.
Tried a different ESC.
Tried a different prop adapter.
Perfectly balanced the Spinner.
Tried a different spinner
Tried without any spinner.

After making no progress resolving the vibration after hours balancing everything to perfection. I Sherlock-Holmes'd it to the rpm, reasoning that a 840kv motor on 3S gives c.10080 rpm while on 4S it would give 13440 rpm. So I am currently hopeful that my problems are resolved by using the TX to limit the throttle curve to 70%.

I get the impression that some people have gotten away with what I tried and will be wondering what all the fuss is about, I don't blame them.

Possibly I have just been unlucky enough to get a 'funny' airframe.

Toying with the idea of installing an SK3 4250 500kv... if I can get it to fit.

If anyone can suggest anything that I haven't thought of I would be most grateful.
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Old May 20, 2016, 09:16 PM
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What prop brand/size/type are you running? Are those calculated theoretical RPM figuress or real world measured RPM?

If that's an APC e-prop or similar then you are exceeding the safe operating RPM even on a 12" prop by about 1400 RPM. My guess is that your prop blades are flapping and causing the extreme vibration... If you insist on 4S you should probably get a glow engine prop which a 12" could safely handle ~16,000 RPM, 13" ~ 14,600 (see APC's website, their glow props handle RPM up to 190,000 divided by prop diameter).

There is no advantage running 4S if you limit it to the RPM that you would get on 3S, all the extra voltage is wasted and you pay a weight penalty.
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Old May 21, 2016, 12:04 AM
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I think ChillPhatcatis right. Ive seen many people comment on having problems with Sebart 30E series aircraft when trying to go from 3S to 4S batteries. Stick with a 3S system and look for other options to increase duration.

What batteries are you using?
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Old May 21, 2016, 04:49 AM
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I would also suggest you try another manufacturers motor and ESC. If the motor is out of balance it will cause vibrations or if the timing of the ESC is out it will cause vibrations. I use balanced APC 12 X 6 props on my Extreme Flight and Sebart planes without problem on 4S but I rarely ever go full throttle. Vibrations can be difficult to find.
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Old May 21, 2016, 05:47 AM
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I missed the first comment you made too, why not increase the capacity of your pack instead? That's usually what most people do first when hunting for duration. Increase capacity by 33% rather than voltage.
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Old May 21, 2016, 07:37 AM
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Quote:
Originally Posted by Watdazit View Post
I would also suggest you try another manufacturers motor and ESC. If the motor is out of balance it will cause vibrations or if the timing of the ESC is out it will cause vibrations. I use balanced APC 12 X 6 props on my Extreme Flight and Sebart planes without problem on 4S but I rarely ever go full throttle. Vibrations can be difficult to find.
He mentioned trying three different motors and a different ESC in his first post, but no mention of what manufacturers they came from.

Interesting problem.
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Old May 21, 2016, 12:35 PM
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All three motors were Turnigy SK3, 2 were 3548 @ 840kv and the other was 3542 @ 800kv.
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Old May 21, 2016, 09:15 PM
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But why are you increasing voltage to increase duration?
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Old May 22, 2016, 02:38 AM
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If you have a look at Sebastiano's models he designs them pretty close to their practical power limits. As ChillPhatCat suggests you are upping the power by around 33%. I have not tried the Angel but I've had several of the Sukhois including both 30s and 50s and frankly they do not like being over powered.

Modellers tend to ignore airframes but in full size aircraft there are recognised limitations and without serious modification upping the power without thought usually end in disaster.

You mention being "underwhelmed" by flight duration in your first statement so ANY change of the sort you suggested actually draws more current and therefore shortens the flight time. If you are seeking longer duration you actually need either greater battery capacity (easy) or move to lower power so that you are drawing less current and hence more economy.

Forgive me but you appear to have taken a strange direction.
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Old May 22, 2016, 02:56 AM
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The Angel 30E is NOT the Stev 30E

Quote:
Originally Posted by David Hipperson View Post
If you have a look at Sebastiano's models he designs them pretty close to their practical power limits. As ChillPhatCat suggests you are upping the power by around 33%. I have not tried the Angel but I've had several of the Sukhois including both 30s and 50s and frankly they do not like being over powered.

Modellers tend to ignore airframes but in full size aircraft there are recognised limitations and without serious modification upping the power without thought usually end in disaster.

You mention being "underwhelmed" by flight duration in your first statement so ANY change of the sort you suggested actually draws more current and therefore shortens the flight time. If you are seeking longer duration you actually need either greater battery capacity (easy) or move to lower power so that you are drawing less current and hence more economy.

Forgive me but you appear to have taken a strange direction.
Hi David, we meet again, I put a 4S system into my Stev, very much against your advice if memory serves, and I'm not criticising, but the aeroplane flew wonderfully on 4S and I had no problems of any kind. Clearly, it was a foolish assumption to think that I could get away with the same 'nonsense' with the Angel. It would seem that the airframe is just NOT rigid enough.

However, even going back to 3S (2x3S 2200mah in parallel) the Turnigy SK3 3548 840kv weighing only 30g more than the Hacker and 40kv more causes a severe vibration cascade in the top 30% of rpms, this with a 14x8 APC prop. Personally I have never experienced anything like it before and I have balanced everything with the precision of a Swiss watchmaker.

However... again, I seem to have found a fix, I'll flight test it later today, with a Graupner 3 blade 12 x 8. This runs on 3S to 100% with barely a tremor.
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Old May 22, 2016, 01:38 PM
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Back from flying... the solution of Turnigy SK3 3548 840 kv turning a 12x8 3 bladed prop seems to be working BUT there is some concern that the motor is running too hot. I plan to properly check the amps being drawn. This may be because the prop is a Graupner for glo engines, so a bit beefy. I easily got 9+ minutes flying with reasonable vertical ability: not outstanding though.
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Old May 22, 2016, 05:19 PM
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Dear Richard,
Ah well, as you say, back again. Hi!

Because of my situation and occasional idiocy I've flown a fair number of varying models. Not all have pleased me. As you'll gather I do like Sebart models regardless of some of the (in my opinion) flaws. It may sound odd but I still have my Stev as a sort of casual "toss in the car" flier despite being sold as a trainer.

However, back to the issue. Too many of the built up models as opposed to foamies are constructed slightly too light. It is a fine balance for the designer/manufacturer I admit but some border on fragile with no real need. We have plenty of power and capacity available to us and I'd suggest that perhaps 50 grams of extra weight in the structure would be unlikely to cause a problem.

A couple of years ago I flew a CAP 232 which from the designer had been constructed very lightly. So much so that the whole nose including, motor, ESC, cowl and ply structure fell off in flight and no, it was powered by the manufacturer's recommendation. Surprisingly enough there was not too much damage so (unusual for me) I took some time to repair it and re-design the whole front end. Weight went up by about 60 grams but the model flew perfectly and I continued to use it before selling it off and I think the guy is still flying it.

My point is that a combination of lack of forethought by the maker and, perhaps, too much hole cutting with the laser cutter can leave you with the occasional problem. In your case vibration. I can't remember exactly our last conversation but a review I did on a Sebart Shark had the motor mount develop a "buzz" in flight, motor cut, plane landed safely but on inspection the mount had pulled away. These things do happen.
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Old May 24, 2016, 06:23 AM
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Amps and Temperature Test:
Sebart Angel 30E, Turnigy SK3 3548 840kv on a Zippy 3S 2200mah turning a Graupner 12x8 3 blade Glow Prop.
The amps peaked at 50 then falling to 48 at full throttle. Tried to emulate a normal run with the motor throttling from 60% to 100%.
The motor casing temperature rose to 61C in the minute after the test ended but was only 58C at engine cut-off, presumably from the effects of air cooling. I gather that 80C is when BAD things start to happen.

I have therefore somewhat enlarged the holes in the cowl to increase and improve air-flow.
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Old May 24, 2016, 08:03 AM
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Static testing is the worst you can throw at any setup... your inflight current draw will be lower than what you see in static testing. 80C may not kill your electronics but it's uncomfortably warm... most damage occurs above 90 or 100C. That glow prop you are running will have a significantly higher RPM tolerance, so no surprise there.

What is the C rating on your 2200 mAh pack? That's a significant current draw on a 3S 2200 mAh pack... I'd say you want to be running 40C at minimum... And anything under 30C and you would be absolutely pushing it to the limit... and that results in voltage sag, power loss, and short battery life.
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Old May 25, 2016, 02:59 AM
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ChillPhatCat... I looked into this properly, and I hadn't previously understood it, thinking the C WAS the amps. My two weakest matched pairs are 25-50C, the other three pairs are significantly higher. Presumably a parallel pair of 25C lipos giving a total capacity of 4.4ah gives a potential continuous amp availability of 25x4.4=110amps.
However, I do have some 4500mah lipos winging their way from HK. They are also, due to me not properly thinking it over, 25-50C discharge... but, as I now understand the maths they should be fine. We'll see.
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Last edited by Richard Haynes; May 25, 2016 at 03:01 AM. Reason: typo
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