I guess the CF tubes from Hobbyking are pultruded and finished off with a nice weave on the surface...I can tell cause the inside of the tube looks like the pultruded rods I use for winged planes...I'll have to find a good source of 16mm aluminium tubing if I'm to use those stiffer props.
Trouble with APC 13X6.5
- Thread starter iconflyer
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I haven't used them simply because I wouldn't try. In terms of manufacturer-supplied usage guidelines, it's one of the few existing examples in this sector so to ignore it is, IMO, just...well...dumb ;-) Another example of "I've seen a guy on YouTube doing it so it must be okay"? ;-)
On a very low kV pancake type motor you might scrape in under that RPM limit but, since there are alternatives, why bother with the risk? I'm a firm believer in wood props - right material for the job - and JXF/Xoar cover the requirement reasonably well on these larger sizes.
On a very low kV pancake type motor you might scrape in under that RPM limit but, since there are alternatives, why bother with the risk? I'm a firm believer in wood props - right material for the job - and JXF/Xoar cover the requirement reasonably well on these larger sizes.
I totally agree...I didn't want to ignore it and that's why I'm experimenting 
I will definitely try the JXF props, just need to fix the torsion stress issue by either replacing the arms or figuring out a better way to mount the motors. Have you tried the CF props from himodel?
I will definitely try the JXF props, just need to fix the torsion stress issue by either replacing the arms or figuring out a better way to mount the motors. Have you tried the CF props from himodel?
KopterX
Member
I would not underestimate the APC SFs. The reason why even Droidworx suggest these props for heavy lifters is very simple. This props are elastic and bent in the turbulence, absorbing the shock. Use them at the right speed and size this props are doing a very good job, better then using a wood or carbon prop. The cons are: noisy and impossible to balance. If the noise is not an issue and if you are able to change ball bearings on motors, then, this props are perfect for aerial cinematography in combination with the right airframe.
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Very interesting...so you say "able to change ball bearings" because basically their elasticity together with the fact they can't be properly balanced means faster wear on bearings? I guess the SF 14" are an ok match for the 2814/22 motors I have for a maximum AUW of about 5KG on a hexacopter... would you agree?
KopterX
Member
Yes, that's the reason for changing the ball bearings, sorry if i was cryptic about it
I would say 14" props on 2814/22 is not a good match, too big. Props too big will cause 2 main problems:
1. power needed to spin them is bigger> higher current > warm motors and ESCs and will dry your lipo faster.
2. bigger prop will induce a lot more vibration in week booms. You need a very good designed airframe.
So, i would suggest to try APC 12"x3,8SF. It will lift easy your hexa on 2814/22.
A word on wood and carbon propellers, these propellers are awesome, but not perfect for aerial cinematography. You can use them better for aerobatics and FPV speed machines where you don't care about vibrations. When you talked about vibration i assumed you built for aerial cinematography.
I would say 14" props on 2814/22 is not a good match, too big. Props too big will cause 2 main problems:
1. power needed to spin them is bigger> higher current > warm motors and ESCs and will dry your lipo faster.
2. bigger prop will induce a lot more vibration in week booms. You need a very good designed airframe.
So, i would suggest to try APC 12"x3,8SF. It will lift easy your hexa on 2814/22.
A word on wood and carbon propellers, these propellers are awesome, but not perfect for aerial cinematography. You can use them better for aerobatics and FPV speed machines where you don't care about vibrations. When you talked about vibration i assumed you built for aerial cinematography.
Thanks for the feedback...only problem with 12X3.8 props is that they are not sufficient to lift my overweight hexa...on ecalc it's showing that I have to give about 85% throttle to hover the 5KG setup... I learned this the hard way when my DJI WKM tried to stablize my 5200grams copter(including DSRL and AV200 mount) and ended up flipping after rocketing up briefly. On the 14" I was drawing about 9amps of power per motor but the motors were really hot when it landed which is a bit strange because that's about 50% of the motor capacity. And you're absolutely correct...I built this hexa for aerial cinematography so stability, reliability, and flight time is my main concern. I typically use 7d, GH2 or nex5n for my work...the GH2 and nex5n are fine on my mini x8 copter and the hexa is more for independent camera operation setup for the AV200 and obviously bigger payload of camera.
KopterX
Member
Hmm, i don't think rocketing up and flipping had anything to do with propellers size, it sound more like setting the IMU 180 degrees in wrong direction. The 14" APC SFs are definitely to big for 2814/22, that's why the motors went hot. Indeed 9 Amps are half the current load for 2814/22. How did you measured the Amps?
KopterX - "cryptic" is the not exactly the word I was thinking - more like "self-contradictory" ;-)
You say APC SF props are "impossible to balance", to the extent that you need to change the bearings in your motors regularly due to the increased wear. So you're saying they vibrate badly. But then you say that wood and carbon props are okay to use when "you don't care about vibrations". So you're saying that they vibrate badly too.
On the subject of the APC SF RPM limit: their thinness/flexibility is the very reason for the low RPM limit (compared to the stiffer/thicker) APC E props. Spin them too fast and the blade will try to flatten itself, exerting a torsional force at the root where it joins the hub, together with the centripetal force trying to pull the blade away from the hub. Add some vibration from the motor and a constant change in these forces due to acceleration/deceleration and you have a high potential for blade failure.
You say APC SF props are "impossible to balance", to the extent that you need to change the bearings in your motors regularly due to the increased wear. So you're saying they vibrate badly. But then you say that wood and carbon props are okay to use when "you don't care about vibrations". So you're saying that they vibrate badly too.
On the subject of the APC SF RPM limit: their thinness/flexibility is the very reason for the low RPM limit (compared to the stiffer/thicker) APC E props. Spin them too fast and the blade will try to flatten itself, exerting a torsional force at the root where it joins the hub, together with the centripetal force trying to pull the blade away from the hub. Add some vibration from the motor and a constant change in these forces due to acceleration/deceleration and you have a high potential for blade failure.
well I flew it for a couple of minutes before adding my 7d and the moment i tried to take off with the 7d onboard and in atti mode and reached mid point throttle everything went wrong. After replacing the broken arms, I was measuring the current draw from the battery after connecting only one of two 5000mah batteries using my quanum telemtry kit...the amp reading on the battery that was connected was about 54-56 amps...that is with the 14x4.7 props...the motors were hot but I could touch them for about 10 seconds without getting burnt which i assume means that they were in the 60 degrees C range....not ideal but I guess within operating range. Again ecalc estimation shows 85% throttle for this weight so I just assumed that the WKM was not able to balance properly with the <20% range and behaved erratically. i see alot of AP companies lifting 7D and 5D on hexas with AV200s , 2814s, and 12" SFs...but I assume the flight times are no longer than 5minutes...which is fine but not safe. On ecal the recommended 13x6.5 props also exceed the current limit of this motor and don't provide as much thrust..but they keep breaking my booms!
I'm going to buy a few T-Rex 500 alu tail booms from a local hobby shop and give the 13X6.5's another try, if they work I'll get a few of the wooden props and test with those...like I said other than flight time and stability, safety is a big concern because I can't afford to have the copter drop from 50m with an expensive camera...not to mention the USD 1200 camera mount! i just would like to know how the AP companies out there are using 12" SF and lifting the AV200 and 7d/5d cameras...hexaprod.com is an example...according to the droidworx website they are using an ADHL-6 frame with AV200 and 12" props...the picture on their website look more like 13x6.5.
KopterX
Member
Jes1111, you are right, but there are a few different kinds of vibration induced by props.
The vibration caused by unbalanced prop are higher on the equatorial plane of the prop, making the bearings to wear faster. This vibration have high frequency equivalent with the rpm of engine and usually are noticed on the footage as blurry image. However APC SFs are much lighter compared with wood props, so is not is so important to be perfectly balanced, (which is almoust impossible with SF). If the frame have some decent anti-vibration feature, this micro vibration will be damped.
But, I was talking about large vibration caused by blade hiting turbulence. A flexible blade will do better than a rigid one in this situation, by bending and absorbing the shock and attenuate this kind of vibration
On the APC SF rpm limit. I had the same concern until I did stress tests with APC SFs, up to 25k rpm, mounted on a biax, after arguing with a colleague who did 5 holes in the hub section trying to balance them. I wanted to demonstrate him that the prop will break in the hub section and his wrong making holes. The prop hold and i loosed the bet. If you have an old APC SF try to break it with your bear hands on the hub section and you will see how hard they are. I'm supposing your are not Chuck Norris ;-)
The vibration caused by unbalanced prop are higher on the equatorial plane of the prop, making the bearings to wear faster. This vibration have high frequency equivalent with the rpm of engine and usually are noticed on the footage as blurry image. However APC SFs are much lighter compared with wood props, so is not is so important to be perfectly balanced, (which is almoust impossible with SF). If the frame have some decent anti-vibration feature, this micro vibration will be damped.
But, I was talking about large vibration caused by blade hiting turbulence. A flexible blade will do better than a rigid one in this situation, by bending and absorbing the shock and attenuate this kind of vibration
On the APC SF rpm limit. I had the same concern until I did stress tests with APC SFs, up to 25k rpm, mounted on a biax, after arguing with a colleague who did 5 holes in the hub section trying to balance them. I wanted to demonstrate him that the prop will break in the hub section and his wrong making holes. The prop hold and i loosed the bet. If you have an old APC SF try to break it with your bear hands on the hub section and you will see how hard they are. I'm supposing your are not Chuck Norris ;-)
yeah, i read other posts that seem to support the same experience...most people are using them way above their limits..not saying it's a good thing...just stating the facts.
I have all three kinds of props and so far I have success with the SF...at least they don't shatter my booms for weights lower than 4200g I'll use the 12"...when I need to go higher i'll use the 14"...again my tests with the 5KG setup seem to be identical to the ecalc data...about 9amps which is well within the amp limit of this motor...no idea why they seem too hot to me though.
KopterX, when will you have some tech specs on your frames? I just subscribed to your site, the design seems very interesting...is that a 7D on your test video? What was your AUW? motors/props? props look like SFs as well.
I have all three kinds of props and so far I have success with the SF...at least they don't shatter my booms
for weights lower than 4200g I'll use the 12"...when I need to go higher i'll use the 14"...again my tests with the 5KG setup seem to be identical to the ecalc data...about 9amps which is well within the amp limit of this motor...no idea why they seem too hot to me though.KopterX, when will you have some tech specs on your frames? I just subscribed to your site, the design seems very interesting...is that a 7D on your test video? What was your AUW? motors/props? props look like SFs as well.
Okay, I see where you're coming from. But, on the flip-side, APC is very specific on their website about the RPM limit and the dangers of exceeding it. So I remain unconvinced by your argument.Just a thought - in the development of your (very interesting) craft, which came first: your choice of SF props or the "anti-vibe" grommets on the motor mounts?
KopterX
Member
Iconflyer,
AUW on that test is 6200g but that configuration lifts 8000g when i put the camera stabilization and the second LIPO. Engine are KW4 Pro with 12x3.6 APC SFs. Camera is 7D. The airframe is still under development. You will get a email when the final specs will be released.
AUW on that test is 6200g but that configuration lifts 8000g when i put the camera stabilization and the second LIPO. Engine are KW4 Pro with 12x3.6 APC SFs. Camera is 7D. The airframe is still under development. You will get a email when the final specs will be released.
KopterX
Member
Just a thought - in the development of your (very interesting) craft, which came first: your choice of SF props or the "anti-vibe" grommets on the motor mounts?
Jes1111, thanks for watching
The anti-grommets and gel dumpers idea came after i have seen a gel dumper pad on a snare drum. The grommets are there for the radial vibration of props. The SF prop came after reading a university study about prop elasticity role on multirotor designs.
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