Chaps (and gals),
I'm looking for some advice on a Skywalker x6 build. Let me explain...
Ok, so why an X6 in the first place? Well I'd like a FPV wing which I could take apart for travelling; after some research I narrowed down to either the X6 or the Zephyr Spade. The X6 was on sale last week at Hobbyking so I decided to give it a go :)
The expected performance I'm looking for is 5-7km range, 20-30 min flying time and enough power to throw it myself one-handed easily.
After some forum research (bignose13 build here plus RCGroups and FPVLab) and time on eCalc, I narrowed it down to a couple of options on which I'd appreciate your opinion and experience.
The basic build assumptions are: AUW of 2000g; Wing area of 60dm2 and a 4S battery with 5000 mAh. ESC will be either 60 or 70A.
So far my preferred Motor/ Prop combination options are:
- SK3 3548 840kv with either 11x7 or 10x6 props; eCalc calculates thrust-to-weight ratio of 1.41:1 and 1:1 respectively, with a 'flight time' of 7 and 11 minutes.
Or
- SK3 3542 800kv with either 11x7 or 10x6 props; eCalc calculates thrust-to-weight ratio of 1.24:1 and 0.88:1 respectively, with a 'flight time' of 8.5 and 12.7 minutes. This 800kv motor seems to be a popular choice on the forum builds.
I'm not entirely sure of what eCalc's definition of 'flight time' is; I've researched some setups where the calculated flight time was ~10min but the real flight time was ~30min.
So which combination do you think is better? Should I be looking at >1000kv motors? I could not get a >1000kv motor to perform significantly better on eCalc than the lower kv ones.
Am I missing something fundamental?
Cheers and thanks for your help,
Charles
first and foremost, eCalc cannot calculate flight times at all because there's no option to tell it what airframe you're using... there's more to it than just wing loading.
best guess is that it assumes an average current draw, where it guesses this figure from is a mystery lol
other than telling you to take what eCalc says with a pinch of salt, I can't really offer any other advice on your X6 build I'm afraid
I did however use a sk3 1200kv motor on 4S with a 9x6 prop with my old Go Discover... but that felt underpowered, I was limited with prop size. I'm not sure what the prop clearance is on the X6.
I know that on the Zephyr 2 builds they all pretty much use the OS1200kv motor with 10" prop on 4S.... but they're usually build for speed (but also capable of endurance/distance if treated nicely)
I dont pretend to have much knowlege on motors. Its a bit of a black art and ecalc is loved by some and hated by others. Lots of poeple seem to go on instinct and experience. What current and wattage was ecalc suggesting?
Assuming you're pulling perhaps 40A at full throttle- it probably guessed you would have burnt through your entire 5000mah in 7 mins.
You should be able to cruise a wing of that size and weight with 1/4 of that current- 10A (and quite possibly less)- which should give you 30 mins of flight time to drain the battery. Allowing a high take off current and some safety margin left in the battery- thats closer to 20 mins.
I think you need to ask yourself what you want to do with the wing. You have chosen low kv motors which generally are more efficient. But the low kv motor will make the wing less sporty. And if you're flying it alone- launching a wing with a 11" prop may be a bit of a risk or worry for you. Plus it's a little more likely to break on landing.
You could put a 2200kv screamer on there which would make it a hoot to fly- and wings generally suit this personality and flying style. But the X6 wing isn't really designed for super agile aerobatic stuff and bashing around. By the same token- a low KV motor around 800kv wont really suit the X6 either IMO. Much much larger planes suit the low kv motors- the x8 and skyhunter for example.
IMO go for a 1200-1800kv motor. Err on the lower side for longer flight times and higher side if you want to burn it around the place. Based on the sort of wattage my planes kick out and their ease of launching- something which kicks out around 500+ watts would be nice for a 2kg wing. I hate planes that are barely powered. I like to know i have lots of power in reserve if needed.
Something like this would be very nice
http://hobbyking.co.uk/hobbyking/store/__14342__NTM_Prop_Drive_Series_35_36A_1400Kv_550W.html (http://hobbyking.co.uk/hobbyking/store/__14342__NTM_Prop_Drive_Series_35_36A_1400Kv_550W.html)
On 4s you could run a 8" propellor and still get >600W. Launching would be a doddle, and safer, and you could probably cruise at under 10A which should give you a respectable flight time.
Quote from: BlueFlyer on July 24, 2015, 04:26:55 PM
I know that on the Zephyr 2 builds they all pretty much use the OS1200kv motor with 10" prop on 4S.... but they're usually build for speed (but also capable of endurance/distance if treated nicely)
I love this motor. It kicks out >1000W with a 10" prop. Lots of people use a 9x6 and its still mental. But as you said the Zeph is more an aerobatic wing and IMO the X6 is less suited to this type of flying.
The only reservation I had with my X6 is the battery choice, I seriously doubt you'll get a 5000 4s in there to balance without some serious surgery to the foam, I tried all different types of install but wouldn't balance with that battery
I just settled for a 4000mah 4s and balances nicely with the battery all the way back
Shame really as you can fit a double decker bus in the battery tray
I forget the motor I use but if you check my thread it's on there, It'll pull a wall down on the torque it has on a 10 inch carbon, also flys out of your hand with a gentle push, even easier with launch mode on the mfd ap
Hth
Simon
either this motor:
http://www.hobbyking.co.uk/hobbyking/store/__29572__Turnigy_D3542_5_1250KV_Brushless_Outrunner_Motor_UK_Warehouse_.html (http://www.hobbyking.co.uk/hobbyking/store/__29572__Turnigy_D3542_5_1250KV_Brushless_Outrunner_Motor_UK_Warehouse_.html)
or the 36mm version if you want to save a little weight. 9x6 folding graupner prop and it will do what you want. 70a esc on your 4s pack and it will cruise or go vertical and be easy to hand launch....
Quote from: bignose13 on July 24, 2015, 06:53:45 PM
The only reservation I had with my X6 is the battery choice, I seriously doubt you'll get a 5000 4s in there to balance without some serious surgery to the foam, I tried all different types of install but wouldn't balance with that battery
I just settled for a 4000mah 4s and balances nicely with the battery all the way back
Shame really as you can fit a double decker bus in the battery tray
I forget the motor I use but if you check my thread it's on there, It'll pull a wall down on the torque it has on a 10 inch carbon, also flys out of your hand with a gentle push, even easier with launch mode on the mfd ap
Hth
Simon
Interesting. Did you have much of the fpv gear behind the CG?
People seem to worry hugely about adding tail weight to wings. I think this is the OCD and purists im them. I have only ever managed to over load a wing once with weight and that took 3x 4000mah 4s batteries on a 60" with a few components killing the aero.
Every other wing of mine has loved a bit of extra weight.
The point im making is, if a 5000mah battery fitted- adding 50g of tail weight to get it to balance wouldnt concern me at all and would be a small price to pay for an extra 1000maH :)
But as you actually have the plane i will defer to your opinion :D It sounds like your motor is a damn good choice.
Blue, Billy, Simon, nowler,
Thanks for chiming in! Lots of food for thought...
Blue, how much did your Go Discover weight?
Billy, I get 35A / 480W with the SK3 3542 800kv (Simon/bignose13 motor) and 40A / 554W with the SK3 3548 840kv with a 11x7 prop at full throttle. Disclaimer: eCalc numbers. I'm looking for a wing to cruise around but not aerobatics but I'd love to do some 'mountain surfing' with it.
Just did a quick calculation with a SK3 3542 1250kv with a 9x6 prop and got ~50A / 660W at full throttle. Thrust-Weight: 1.31:1, 'flight time' of 5.5 min. hmmm sounds interesting!
Simon, the motor on your build is the SK3 3542 800kv, same as the Campilot build. I'm planning to carve the battery bay back an inch or so for additional CG running room. Did you do that yours?
nowler, thanks for the link. those specs look very similar to the Sk3 3542 I quoted above, just little lighter and lower max amps. I had a quick look at some Zephyr builds and a ~1300kv motor seems to be a popular and ritewing recommended choice. This guy (http://www.rcgroups.com/forums/showpost.php?p=29965167&postcount=76)used a OS Max 3820 1200kv, 10x6f, 4S 5000 mAh on a X6 and got ~28min flight time.
Thanks for the feedback guys... I have to say that right now I feel I'm moving towards a 1200ish kv option. I'll keep researching over the weekend.
Cheers!
Charles
Cant remember off hand, here's the build thread http://www.fpvhub.com/index.php/topic,21456.msg171405.html#msg171405 (http://www.fpvhub.com/index.php/topic,21456.msg171405.html#msg171405)
This plane is likely to be £3-400 by the time it's in the air. If in doubt buy a couple of motors- perhaps a 800kv and a 1200kv and try both and see which you prefer. The extra £15 for the second motor option isn't going to break the bank :)
Although it doesn't seem to have gained kmuch of a reputation on here- the happy flyers wwipe out motor was capable of running on 3s and 6s . As wings have such a wide speed envelope they are so diverse they are capable of slow cruising and mental speed- two battery options for the same motor (or indeed two motor options for the same battery) allows this dual personality to be really exploited :)
Yeah if the plane is in two halves then yeah I'd carve out a couple of inches behind the bay to get the battery further back
I didn't do that as I thought it was fine before building, bit of a school boy error
But if you can get the battery back further than say 3 inches you'll be onto a winner
i wouldnt read too much into the max amps and watts for the motor i reccomended. i run mine at almost double this a lot and as long as the esc is up to it and it's getting enough cooling, max amps and watts is almost irrelevant.....
Thanks guys,
I ended getting a SK3-3542 1250kv - the same one BlueFlyer had on his GoDiscover. The 800kv motors were out of stock but I'll get one of them when they pop back up. I'll be testing it with 9 and 10' props.
I'll leave the fuse glueing for last to make sure I can get the CG right with 1x or 2x 5000mAh batts.
Cheers!
Charles