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OtherHand
4th January 2016, 06:50 PM
When the Drak prototype was first unveiled for Kickstarter almost a year ago it was running a 4S motor. Later testing and tweaking by Ritewing changed their preferred power source to a 5S system, and that's the voltage of the custom motor Ritewing will be making available for the Drak.

For me, I'm really heavy into 4S systems and don't want to start collecting slightly oddball 5S batteries. Had I known 5S was going to end up as the preferred power source, I'd probably had serious second thoughts about ordering a Drak. As much as I'd like to get one of the custom Ritewing Drak motors, as far as I know they won't be making any available in 4S.

So I went off searching for what limited info is out there for powering Draks with a 4S motor. Since the data was scattered over a number of places I thought I'd combine it into a single post for anyone else looking to do a 4S system. The following is a collection of assorted data I've been able to find on the web. The first group are posts on the FPVLab in the Ritewing forum in the main Drak thread (http://fpvlab.com/forums/showthread.php?36231-Drak-60-quot-info-and-possible-kick-start-thread).

3-12-2015: By Ritewing, The Drak prototype used a 1200 KV 4S motor, probably the equivalent of a 2820 motor. It used an 11x7 prop, but Ritewing said 10x6 would be OK too.

4-3-2015: By Ritewing, For 4S the KV should be about 1200.

11-13&15-2015: By Ritewing, paraphrasing, 6S is good, 4S OK but 5S best in terms of power/efficiency. For 6S use about 740 KV, 5S about 950 KV and 4S 1100-1200 KV implied. Still seemed to use an 11 x 7 prop. A lot of good info in these two posts.

Other data sources:

2-14-2015: In the "aaron_gx Builds a RITEWING DRAK 60 (http://fpvlab.com/forums/showthread.php?37707-aaron_gx-Builds-a-RITEWING-DRAK-60-quot)" thread in the FPVLab "Pilot's Lab" forum is a build of a 4S Drak. Aaron seems to use a Ritewing 1300 KV 4S motor with an 11 x 7 prop. He described it as being a 2820 size and "..same size as a 3542 Turnigy motor, maybe slightly larger".

Stoneblue Airlines has flown and sells the Drak (http://www.stoneblueairlines.com/airplanes/airplanes/rite-wing/drak/ritewing-drak-60-wing-kit.html), and they seem to recommend a 4S setup. Their two recommended motors are either a Emax GT Series Motor 1090KV, or a Cobra Motor 1130KV. For a prop they recommend either a 10 x 7 or 11 x 7.

If anyone else has more info on using a 4S motor on a Drak, please add to this thread.

terbeaux
6th January 2016, 12:03 AM
I'll be sporting a Cobra 3515/14 950Kv with a APC 11x5.5 on 4S to start. Drak arrives tomorrow. I'll report back on performance after 1st flight.

OtherHand
18th January 2016, 08:46 PM
Although Ritewing has recommended using 1100 to 1200 KV motors if using 4S, I'm instead going with a 780KV motor turning an APC 11x7 prop. Here's why...

Since there haven't been any official figures published yet as to total wing area, I measured my own, including the eleverons and about 2.5 inches of the body closest to the wing where I assumed it would produce lift. I brought my dimensions into a CAD program and it calculated a total useful wing area of 744 square inches.

I'm planning on using my Drak as a slower flying Pixhawk mapping bird, maybe running under a Section 333 exemption, so a modest flying profile. Looking around at the few prototype Draks out there and what weights have been posted, I'm assuming an AUW for mine will be in the ballpark of 6.5 pounds (2950 grams).

This gives me a projected wing loading of around 0.14 oz/in^2 or 20.1 oz/ft^2

For gentle flying (no 3D!) I set my desired static thrust to 0.75 x AUW or 4.9 pounds (2222 grams)

All this stuff I put into Motorcalc and started doing sims. Initially I was using 1100 to 1200 KV motors, but the solutions had problems and cruise amps seemed high. So I let Motorcalc loose and it was coming back with desirable KVs in the mid-800 range with an 11 x 7 prop. Well, that was interesting.

I happened to have on hand a very nice, barely used Scorpion II 3020 780 KV motor from an earlier project. Would that work?

The motor is rated at 800 watts with 40 amps continuous. I plugged it into Motorcalc and it spit out a very nice solution using an 11x7 prop. It predicted a maximum current draw of 37 amps at static full throttle with 2360 grams of thrust. Top speed is predicted to be 50 mph (plenty fast for my purposes) with a most efficient cruise speed of 29 mph drawing only 4.9 amps (55% throttle). That all sounds pretty good, but how accurate is Motorcalc?

To find out I put the Scorpion motor on a test stand I have and ran it with an APC 11x7 prop on a fully charged 4S battery. At full throttle I measured a thrust of 2500 grams at 39 amps and 575 watts. That's pretty close.

Cutting the throttle back, at 5 amps I was still getting 586 grams of thrust statically. Motorcalc tells me I need to be generating 260 grams to keep the Drak flying at its calculated most efficient speed of 29 mph. What that static 586 grams will drop to when it's moving at 29 mph I don't know for sure. Motorcalc predicts the thrust at 29 mph to be 39% of the static thrust, and if so that would make my 29 mph 5 amp thrust about 230 grams. Again, in the ballpark.

Since I have the Scorpion motor already on hand, as well as a very fine Castle ICE 50 ESC, it makes sense to give them a try. The numbers look good.

I have run the numbers on an 11x8 prop and it also looks good, but the current increases a bit at full throttle and cruise, but top speed goes up to 55 mph. I may pick up an Aeronaut 11x8 folder and run that on my test stand.

JRTSuperfly
19th January 2016, 01:07 AM
Nice blog. I too was having this struggle. I was looking at cobra motors and could not find one that would give me 2700g thrust on 4s that would be efficient. In the end i opted to go for the ss motor and going to run 5s. I did find some cheeper 5s lipos at 10,000mah for 120ish. Granted its probably not a good lipo but i too am just looking to cruse so im not planning on pushing that battery either.

ritewing
19th January 2016, 01:31 AM
I worry more about altitude flying and launchin it on 4s with such a low kv.
Are you in colorado?
If so you mite have a bear of a time launching her with low kv on 4s.

The one nice thing about the 5s setup is it will fly out of your hand with ease like a rocket on a mission, then it can also cruise a sipping rate of 7 to 10 amps.
It also wont pull more than 60amps with the 11/7 on here will pulling strait up ver climbs.

Let us know what you find out, these are my concearns.

Although Ritewing has recommended using 1100 to 1200 KV motors if using 4S, I'm instead going with a 780KV motor turning an APC 11x7 prop. Here's why...

Since there haven't been any official figures published yet as to total wing area, I measured my own, including the eleverons and about 2.5 inches of the body closest to the wing where I assumed it would produce lift. I brought my dimensions into a CAD program and it calculated a total useful wing area of 744 square inches.

I'm planning on using my Drak as a slower flying Pixhawk mapping bird, maybe running under a Section 333 exemption, so a modest flying profile. Looking around at the few prototype Draks out there and what weights have been posted, I'm assuming an AUW for mine will be in the ballpark of 6.5 pounds (2950 grams).

This gives me a projected wing loading of around 0.14 oz/in^2 or 20.1 oz/ft^2

For gentle flying (no 3D!) I set my desired static thrust to 0.75 x AUW or 4.9 pounds (2222 grams)

All this stuff I put into Motorcalc and started doing sims. Initially I was using 1100 to 1200 KV motors, but the solutions had problems and cruise amps seemed high. So I let Motorcalc loose and it was coming back with desirable KVs in the mid-800 range with an 11 x 7 prop. Well, that was interesting.

I happened to have on hand a very nice, barely used Scorpion II 3020 780 KV motor from an earlier project. Would that work?

The motor is rated at 800 watts with 40 amps continuous. I plugged it into Motorcalc and it spit out a very nice solution using an 11x7 prop. It predicted a maximum current draw of 37 amps at static full throttle with 2360 grams of thrust. Top speed is predicted to be 50 mph (plenty fast for my purposes) with a most efficient cruise speed of 29 mph drawing only 4.9 amps (55% throttle). That all sounds pretty good, but how accurate is Motorcalc?

To find out I put the Scorpion motor on a test stand I have and ran it with an APC 11x7 prop on a fully charged 4S battery. At full throttle I measured a thrust of 2500 grams at 39 amps and 575 watts. That's pretty close.

Cutting the throttle back, at 5 amps I was still getting 586 grams of thrust statically. Motorcalc tells me I need to be generating 260 grams to keep the Drak flying at its calculated most efficient speed of 29 mph. What that static 586 grams will drop to when it's moving at 29 mph I don't know for sure. Motorcalc predicts the thrust at 29 mph to be 39% of the static thrust, and if so that would make my 29 mph 5 amp thrust about 230 grams. Again, in the ballpark.

Since I have the Scorpion motor already on hand, as well as a very fine Castle ICE 50 ESC, it makes sense to give them a try. The numbers look good.

I have run the numbers on an 11x8 prop and it also looks good, but the current increases a bit at full throttle and cruise, but top speed goes up to 55 mph. I may pick up an Aeronaut 11x8 folder and run that on my test stand.

OtherHand
19th January 2016, 01:43 AM
I worry more about altitude flying and launchin it on 4s with such a low kv.
Are you in colorado?
If so you mite have a bear of a time launching her with low kv on 4s.

The one nice thing about the 5s setup is it will fly out of your hand with ease like a rocket on a mission, then it can also cruise a sipping rate of 7 to 10 amps.
It also wont pull more than 60amps with the 11/7 on here will pulling strait up ver climbs.

Let us know what you find out, these are my concearns.

Thanks for the input Chris. I'm mostly around sea level or flying in the SoCal deserts, so probably no density altitude issues. I'll see how easy it is to launch and if it's a bear I might just switch to a bungee setup. 7 to 10 amps at cruise isn't bad, but if it really can get down to 5 amps, per Motorcalc, that would be really great. With a 10,000 MAH battery a 90 minute mapping mission should be possible.

OtherHand
31st January 2016, 04:53 PM
Looks like I've settled on a good prop combo for my 4S Scorpion II 3020 780 KV motor. I'll provide a brief summary of the data in case anyone else is thinking about using a motor around 800 KV with 4S. As long as the motor's wattage rating is above 700, it should be similar.

After doing a lot of work in MotorCalc I found six props that looked viable, three APCs and three Aeronaut folding props (I'm told the Aeronauts are very similar to Graupners and are nice stuff). I then tested these six on my static test stand with the Scorpion motor, running on a fresh 4S battery for each run.

The following is a condensed version of my data for each prop. All values are at wide open throttle. The first number is thrust in grams and the second number is the Amp draw.

APC 11 x 7E: 2,450 gms / 36 Amps

APC 11 x 11.5E: 2,330 gms / 30 Amps

APC 12 x 4.5 MRP: 2,900 gms / 40 Amps

Aeronaut CAM 11 x 8: 2,170 gms / 39 Amps

Aeronaut CAM 12.5 x 6: 2,850 gms / 41 Amps

Aeronaut CAM 13 x 6.5: 3,150 gms / 48 Amps

Since I'd slightly prefer a folder, I'm going with the Aeronaut 12.5 x 6 as it appear to provide essentially the same performance as the APC 12 x 4.5 MRP. Both are hitting about 40 Amps, which is my motor's max continuous rating. I am tempted to use the 13 x 6.5 folder but won't. Its top Amp draw exceeds my maximum of 40, but for quick bursts that wouldn't worry me much. Of greater concern is the ESC I have on hand and am planning to use, a Castle ICE 50, and I'm just too close to its 50 Amp limit.

So it's going to be an Aeronaut 12.5 x 6 folder. At full throttle it should be sufficient as my projected Drak AUW is 6.5 pounds (2,950 grams) so I'll have just a little short of 1:1 thrust to weight ratio. At 5 Amps I'm seeing it provide 670 grams of static thrust which is around what MotorCalc is telling me I'd need to push the Drak in most efficient cruise. So it appears to be on course for a 5 Amp or less cruise.

Scotttu
3rd February 2016, 01:41 AM
I'm going to give the SunnySky Angel 2820/1100kv a try with an 11x7.

ritewing
3rd February 2016, 01:50 AM
Be careful buddy from what I have seen it will most likely It will smoke that motor if you push it hard. 28 mm diam just doesn't have the tork for props over 10 inches, so amps go way up. Let us know how it goes .

OtherHand
3rd February 2016, 02:13 AM
I'm going to give the SunnySky Angel 2820/1100kv a try with an 11x7.

Per the prop data for that motor, aren't you going to be well over both the Amp and Watt limits?

ritewing
3rd February 2016, 02:26 AM
Thus the reason I went to 5s , a lower kv and a good size motor that will do the job with great power and efficiency .

DEMO7
3rd February 2016, 10:55 PM
Thanks for this information, I too have a lot of 4s batteries and didn't want to buy 5s. I wanted a 1100-1200kv 35 sized motor but couldn't find one with the specs I wanted. I ended up getting a Cobra 3520 980kv. The prop data looks pretty great with a 11x5.5" apc I'm new to this forum, can we post pics?

DEMO7
7th February 2016, 04:47 PM
Here is a rebroadcast of my maiden flight that was live streamed to youtube- Ill have a full edited video out soonhttps://www.youtube.com/watch?v=gQGOEYYSKVQ&feature=youtu.be

rayers1060
15th February 2016, 07:06 PM
When the Drak prototype was first unveiled for Kickstarter almost a year ago it was running a 4S motor. Later testing and tweaking by Ritewing changed their preferred power source to a 5S system, and that's the voltage of the custom motor Ritewing will be making available for the Drak.

For me, I'm really heavy into 4S systems and don't want to start collecting slightly oddball 5S batteries. Had I known 5S was going to end up as the preferred power source, I'd probably had serious second thoughts about ordering a Drak. As much as I'd like to get one of the custom Ritewing Drak motors, as far as I know they won't be making any available in 4S.

So I went off searching for what limited info is out there for powering Draks with a 4S motor. Since the data was scattered over a number of places I thought I'd combine it into a single post for anyone else looking to do a 4S system. The following is a collection of assorted data I've been able to find on the web. The first group are posts on the FPVLab in the Ritewing forum in the main Drak thread (http://fpvlab.com/forums/showthread.php?36231-Drak-60-quot-info-and-possible-kick-start-thread).

3-12-2015: By Ritewing, The Drak prototype used a 1200 KV 4S motor, probably the equivalent of a 2820 motor. It used an 11x7 prop, but Ritewing said 10x6 would be OK too.

4-3-2015: By Ritewing, For 4S the KV should be about 1200.

11-13&15-2015: By Ritewing, paraphrasing, 6S is good, 4S OK but 5S best in terms of power/efficiency. For 6S use about 740 KV, 5S about 950 KV and 4S 1100-1200 KV implied. Still seemed to use an 11 x 7 prop. A lot of good info in these two posts.

Other data sources:

2-14-2015: In the "aaron_gx Builds a RITEWING DRAK 60 (http://fpvlab.com/forums/showthread.php?37707-aaron_gx-Builds-a-RITEWING-DRAK-60-quot)" thread in the FPVLab "Pilot's Lab" forum is a build of a 4S Drak. Aaron seems to use a Ritewing 1300 KV 4S motor with an 11 x 7 prop. He described it as being a 2820 size and "..same size as a 3542 Turnigy motor, maybe slightly larger".

Stoneblue Airlines has flown and sells the Drak (http://www.stoneblueairlines.com/airplanes/airplanes/rite-wing/drak/ritewing-drak-60-wing-kit.html), and they seem to recommend a 4S setup. Their two recommended motors are either a Emax GT Series Motor 1090KV, or a Cobra Motor 1130KV. For a prop they recommend either a 10 x 7 or 11 x 7.

If anyone else has more info on using a 4S motor on a Drak, please add to this thread.


How has your experience been with the "Emax GT Series Motor 1090KV" motor? Any input would be welcome. My Drak is still a few weeks away before maiden. I currently have Emax 1090KV motor, Vector, Castle 75 Edge ESC. Will need a few more $$$ to complete this build. After reading this thread I might change motor/prop combo.

Cyprusflyer
30th March 2016, 10:18 AM
Interesting, I m also considering the Drak but will certainly will not consider the 5s nonsense, I would stay with 4s.
Looking at Scorpion motors, I would probably go with the 3026 - 890, 11x5.5 prop gives over 3kg thrust at just less that 70A.
A 10x7 would increase the speed a lot but drop the thrust, suppose the extra thrust is good for easy launches.

OtherHand
30th March 2016, 10:53 AM
Interesting, I m also considering the Drak but will certainly will not consider the 5s nonsense, I would stay with 4s.
Looking at Scorpion motors, I would probably go with the 3026 - 890, 11x5.5 prop gives over 3kg thrust at just less that 70A.
A 10x7 would increase the speed a lot but drop the thrust, suppose the extra thrust is good for easy launches.

The Scorpion motor you list would have been my first choice had I not had a 3020 780 KV already on hand.

ritewing
30th March 2016, 12:38 PM
Those motors should work fine. They will just be much harder to launch and takeoff. Even my motor on 4 cells should work better than those. They have lower kV and your prop has little bit lower pitch. This means your cruising speeds going to require higher amp draw and higher RPMs. My motor weighs about 200 grams and can fly on 4 cells. But we have found with the five cell that your cruise efficiency is much higher than about anything else we have found, we have also found it has very great takeoff capabilities. If you're putting a motor on the back of that that weighs much more than 200 grams you'll be countering that with weight on the nose. This will make your aircraft heavier, thus making your 4 cells combo have even more strain because you need more weight to counter it in the nose . When you look at your calculations you have to remember they are rated on wide open throttle numbers. We are flying at about 40% to 50% of that curve so the sweet spots we are finding are not something that is shown on a printed motor calculation. So all-in-all you'll have a little bit harder taking off and your flight times will probably be 1/3 - 40% less than ours. I've tried many 4-cell cell combinations and have yet to find anything that's closer to what I'm finding on 5.

Håvard Støre
30th March 2016, 02:05 PM
Just for the record... I use the SS with 5s, but I have spent some time looking at alternatives. Those who are interested in these things really need ecalc. Its not precise, but still..

As Chris has mentioned before back in the early parts of the Z3 thread, the two most important specs on a motor is KV and WEIGHT.
Max A, temperature, max watt etc are loosely made up by the manufacturer. Some specs are more daring and will give the impression of a motor that outperform a motor with more conservative MAX specs.

When choosing a motor for a plane like the Drak we want to be close to or slightly beyond the limits of the specs. Its not supposed to be run full speed on the bench for several minutes. When flying we get excellent cooling and lower amp draw.

Heres one motor that will give huge thrust and good speed on 4s and 10x6 prop... Efficiency is another matter:)
71459

ritewing
30th March 2016, 02:09 PM
Havard is on the money in his post.
My goal with my motor combo was to get the lightest most reliable most powerful setup that will cruise at the most efficient current draw I could possibly find. Trying to find all of these atributes in one motor is very challenging. It took me almost a year to find it.

Håvard Støre
30th March 2016, 02:21 PM
Heres another one:
71461

Håvard Støre
30th March 2016, 02:47 PM
Emax:
71463

Cyprusflyer
31st March 2016, 02:53 AM
Well, you almost have me sold, what puts me off is the lack of specs for the ritewing motor, are they available anywhere?
As an engineer they mean a lot to me and the only way to be subjective when comparing with E-Calc etc.

Håvard Støre
31st March 2016, 01:53 PM
Well, you almost have me sold, what puts me off is the lack of specs for the ritewing motor, are they available anywhere?
As an engineer they mean a lot to me and the only way to be subjective when comparing with E-Calc etc.
I bought mine directly from Chris.

It can also be ordered as a combo with esc. from RMRC:
http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=112_116_742&products_id=5126

I have looked at different motors at 4,5 and 6 cells in E-calc. I can't find any motor that can spin a 11/7 prop at the same speed at that low amp as the SS motor. Agree that it would be nice to see the numbers in Ecalc, but we can't.

OtherHand
31st March 2016, 04:07 PM
I have looked at different motors at 4,5 and 6 cells in E-calc. I can't find any motor that can spin a 11/7 prop at the same speed at that low amp as the SS motor. Agree that it would be nice to see the numbers in Ecalc, but we can't.

I'm curious how you know what amps the SS motor is using at which RPMs, and thus how it's better or worse than other motors? I'd be really interested in knowing if someone put one on a test stand and had some measured results. There have certainly been a lot of subjective statements on its behalf but if there has been any hard data posted then I'm sorry I missed it. I've been looking carefully at all the Drak Vector videos posted an the lowest cruise Amps I've seen displayed so far is around 12 amps. For my purposes I'd want to see about half that.

BTW, since you seem fairly adept at eCalc, I was wondering if it does motor analysis while an airplane is in flight? I've used eCalc for multis quite a bit, but never for fixed wing. I wasn't sure how accurate it would be, but I may have missed something. I've been modeling in Motorcalc which can give me the amps and efficiencies at all different flight speeds and throttle settings. I'd love to be able to put the data for the SS motor into it and see how it does analytically.

henkvdw
31st March 2016, 04:23 PM
For half of the 12A at cruise, 4S may not be your best option since the 12A is drawn at 5S. Probably worth looking at 6S to get your Amp draw down. That is if less Amps is all you're after.

Cyprusflyer
1st April 2016, 03:19 AM
For half of the 12A at cruise, 4S may not be your best option since the 12A is drawn at 5S. Probably worth looking at 6S to get your Amp draw down. That is if less Amps is all you're after.

Higher voltage will be a bit more efficient of course but dont forget that your battery weight goes proportionally as you increase cells.
Unless you drop the capacity of course, then you will end up with the same capacity in Watts which is what matters in measuring performance in terms of output and time. Chris has obviously experimented enough and found that 5s is good for the aircraft/motor combination without doubt.

Most of the specs concentrate of full power specs but for FPV and most other flying except speed runs we want something calmer and more efficient for duration at much lower throttle settings.

One more thing to look at is the ESC, for low throttle settings you want "active free wheeling" that uses FETs to switch the back emf to the battery rather than diodes that just heat up the ESC wasting power. From my helicopter flying I know that Kontronic does this but the Castle ESC's at the time did not.

Håvard Støre
1st April 2016, 06:24 PM
I'm curious how you know what amps the SS motor is using at which RPMs, and thus how it's better or worse than other motors? I'd be really interested in knowing if someone put one on a test stand and had some measured results. There have certainly been a lot of subjective statements on its behalf but if there has been any hard data posted then I'm sorry I missed it. I've been looking carefully at all the Drak Vector videos posted an the lowest cruise Amps I've seen displayed so far is around 12 amps. For my purposes I'd want to see about half that.

BTW, since you seem fairly adept at eCalc, I was wondering if it does motor analysis while an airplane is in flight? I've used eCalc for multis quite a bit, but never for fixed wing. I wasn't sure how accurate it would be, but I may have missed something. I've been modeling in Motorcalc which can give me the amps and efficiencies at all different flight speeds and throttle settings. I'd love to be able to put the data for the SS motor into it and see how it does analytically.
Sorry. I meant to compare the thrust and amp. I have not measured RPM. Thrust is about 3,9 kg at 60A. Take it with a grain of salt. I have not tested measured in any other way than holding the plane vertically and giving full throttle. I know the amp from my osd and the weight of my plane. So its all very rough.

About eCalc. and motors for that matter, I am far from any expert. Just find it useful instead of fumbling with the very little prop data thats available elsewhere. Unless someone actually puts the motor through its paces on a bench with all the bells and whistles we will never know more precisely. I could do it, but I would have to build a rig, learn more about it, and i am honestly not that curious about the exact result.

SecretSpy711
15th April 2016, 12:45 PM
Not to belittle Chris' work, but I don't really buy the 5S hype... I keep reading that it is a more efficient setup, and that may be true, but I've never seen hard numbers or a real comparison to back that up. I too am an engineer and using 3rd party information on faith without analysis or data to back it up is a huge no-no. Yes, higher voltage probably is more efficient in this case, but is it enough of a boost to justify buying > 6 new 5S packs (3 pairs, number required to charge & fly without much down time, ~$200+) when I'm heavily invested in 4S? I think for the majority of pilots, the efficiency difference is probably drowned out by other factors like flying style, being a lead-foot, not being smooth on the sticks, improper trim, build quality (i.e. looseness in aileron attachment or linkage train), protrusions (big CP antenna), etc.

If you are going for absolute efficiency, are a good enough pilot to take advantage of it, and have money burning a hole in your pocket, then go for the SS motor and 5S packs. Like many things in life (mountain bikes, camera gear, rifle scopes to name a few), there is a huge price jump to go from "above average / good enough for most people" to "top performance." You have to decide what is worth spending your money on.

I say all this because it looks like I may be inheriting one of the original Draks and will have to decide how to power it. FPV is not the only thing in my life.

OtherHand
15th April 2016, 01:42 PM
I tend to agree with you. I wouldn't call the 5S stuff hype, but it is Chris's opinion, one that's based on a lot of experience and his motor appears to be of very high quality. Still, he hasn't provided much in the way of hard numbers and has made performance statements that as an engineer I'm not exactly comfortable with.

The term "efficiency" can be somewhat slippery to pin down. Total flight time? At what speed? Minutes of flight per Watt? To say a certain battery/motor/prop combo is the most efficient without defining what efficiency is, isn't valid.

Of course in terms of improving electrical efficiency (reduction of power loss though heat) it's always better to run higher voltages and thus reduce currents. And maybe you can use a smaller, lighter ESC. But for the vast majority of people the difference in electrical power loss between 4S and 6S is very small compared to the typical amount of Watts they are burning while bombing though the sky. Now if you're trying to do an endurance crossing of the English Channel, then that's different.

To get the most amount of propeller thrust for the minimum amount of power you have to turn larger diameter props at slower speeds. This is widely understood in the multicopter world but seems to be less accepted with fixed wing designers. Of course you can get torque induced roll, but only at full throttle and you know when it's coming.

My thinking is that if someone is intending to hand launch a Drak they should strongly think about the SS 5S motor setup. From numbers posted by the first flyers, it appears the Drak stalls around 27 mph. There's no way someone is going to toss it horizontally like a normal foamy and get it to flying speed before it hits the ground. But the SS package provides well in excess of a 1:1 thrust:weight ratio (just how much more we don't know) which is enough thrust for it to launch vertically without ANY wing lift. The damn thing can more than hover! Now this is great for hand launching or 3D flying, but many would say it's way over powered for casual flying. for any sort of mapping bird, which is what it was pitched as way back in the Kickstarter days.

I'm only now just getting the last bugs out of my Drak to get it flying, so this is all my opinion. But I plan on doing a lot of measurements and will report what those are.

ritewing
15th April 2016, 02:14 PM
My Goal was to find the best motor for.

Easy takeoff by hand.
Very very efficient cruise amp draw.
Powerful enough to fly the plane heavy.
keeping motor as light as possible while having it modified to fit the needs precisely .

There are many motors out there.
During testing I ran 3s to 10s .
I did so many combinations your head will spin if you look at my piles of motors.

I went 5s not because it was easy, it just gave me the best results.

I have no problem you can choose what kv and size you want, I offer it because it was the best results I have found.

I do not do 10000 + $ orders of motors for no reason.

6s does ok, watt hour to watt hour used in all combos tried still does not get you the same as my motor. If you find a better combo, please let me know. I would use it!

4s was never close in efficiency.

I found a few motors on 4s too that fly the plane as well, they just do not fly very long.

Have fun and fly the Drak, its the most important thing.

SecretSpy711
15th April 2016, 04:14 PM
I believe you that you tested a bunch of motor & battery combos. What bothers me is that there is less info available for your motor than there is for most generic chinese motors. I mean, I assume it's a 5mm shaft, but I can't find anything about it. Also looks like it comes with a split-collar type prop adapter (which I hate). Or maybe it's integrated into the bell to save weight. I can't quite tell. These (and more importantly, performance numbers) are what I'm after.

So let's go through the process for picking a motor (this is mostly for people who don't know how -- it's not hard if you have a reference to something you want it to fly similar to.)

Since there's not much info on the SS motor, I have to make some assumptions. I suspect the basis for the SS motor is the Cobra 3515 950kv motor (http://innov8tivedesigns.com/parts/brushless-motors/cobra-c-3515-14-brushless-motor-kv-950). Comparing the two side by side you can see the similarities in design. It even has the same retainer collar that comes with Cobra's. The motor chart (http://www.rcdude.com/v/vspfiles/UserDownloads/Airplane-Motor-Chart.pdf) says there are no equivalents from other brands, either. The factory might have tweaked the kv or other parameters slightly. And yes Mr. Wayne, it comes in black.

So, assuming that's the basis, it lists the max continuous power as 810 watts on 5S. This is our target power number. Power is everything.

Now let's say we want an equivalent setup for 4S. Taking 950kv x 18.5v = 17575 RPM no-load speed. If we want to run a 4S setup using the same prop at the same RPMs, it's 17575 / 14.8v = 1187.5kv. So we're looking for a motor that has roughly the same max power, and is around 1100-1200 kv. Now look at the Cobra 2826 1130kv motor (http://innov8tivedesigns.com/parts/brushless-motors/cobra-c-2826-8-brushless-motor-kv-1130), the one that SBA recommends. Max continuous power on 4S is... guess what, 810 watts. They put some thought into their motor lineup. Bonus, it's even 7 grams lighter than the 5S cobra baseline, and if the 200g listed weight of the SS motor is true, then it's 29 g lighter than that.

Now on to the batteries. Again, power is everything. Let's say our baseline 5S setup uses 2x 4000mAh 5S (http://www.hobbyking.com/hobbyking/store/__16703__ZIPPY_Flightmax_4000mAh_5S1P_20C_US_Wareh ouse_.html) 20C packs. That's 2 x 4Ah x 18.5v = 148 Watt-hours. An equivalent 4S setup would be 148 Wh / 14.8v = 10Ah of battery, or two 5000mAh 4S (http://www.hobbyking.com/hobbyking/store/__8580__ZIPPY_Flightmax_5000mAh_4S1P_20C.html) 20C packs. Bonus again, the 4S packs are 39 g lighter (each). Maybe with all that weight we just saved, we could find some 5100 or 5200 packs for longer flight times to counteract the unknown efficiency loss we took in going to the 4S setup.

Props. One setup I know of uses a 11x8 prop. That's not listed in the Cobra motor charts so let's just pick an APC 10x7 for argument's sake. On our 5S baseline plane it pulls 49.96 amps. On the 4S plane we're building, it pulls 58.11 amps. At wide-open throttle (don't do this), the 5S setup will last (8Ah) / (49.96 A) x (60 min/hour) = 9.6 minutes. The 4S setup will last (10Ah) / (58.11 A) x (60 min/hour) = 10.3 minutes. Advantage, 4S ??? Maybe we don't need to find those 5100 packs after all.

The 5S setup does beat the 4S setup in one thing though, static thrust. 5S setup = 2672 g. 4S setup = 2574 g. 3.8% more than the 4S. The thrust efficiency is the same however, at 2.99 grams/Watt in both cases. I haven't even touched on the ESC... but if your eyes havent glazed over yet with all the numbers, may I suggest one with active freewheeling for greater efficiency? Again, I don't have any info on the SS ESC.

I realize this post might sound a bit condescending, but that wasn't my intention... It's just how it came out.

DEMO7
15th April 2016, 04:43 PM
Going from 4s to 5s was the best move I did for the drak. It went from dull to responsive and sporty which I like. Hit 102mph with a stiff tail wind the other day

ritewing
15th April 2016, 04:44 PM
I dont do for arguments sake, I only calc for a minimal baseline starting point.

My Prop adapter is awesome it is very true with very tight tolerances in comparison to others. It is very reliable and can be tightened many times with no issues.

I do tons of in flight and field testing, the only way to find the real sweet spots in my opinion.
The motor 2826 can not turn 11 props efficiently, we ran 28 series in the beginning on the smaller proto Draks.

This is why stone blue used them. They carried these in stock so it worked for them with other planes. After the inefficiency and heating issues of many 28 series motors I stepped the motor diam up and reworked the whole motor mount again. I even re modified the rear of the plane in cad to fit the new diameter and modified mount .

I will not play a full on numbers and calculation game here, I say knock yourself out.


No offense take so no worries there bro.
I am not a calkie ,it has never got me completely to the sweet spots.

Hmerly
15th April 2016, 04:47 PM
From my own testing, I've found Chris' combo to be an amazingly powerful setup that is also efficient. His SS drak motor let's me hand launch my heavy 9lbs plane with 10kmah 5s zippies easier than my old Z2 and z3 on the old 4s setups. The amount of thrust generated by the Drak combo allows me to barely throw the plane and have it fly out of my hand with no issues. With my z2 and z3 I'd have to really put force into the throw. Nothing empirical, but to me it's a huge difference in confidence when launching.

The ss drak motor is also pretty efficient. I coast along at 7-8 amps without losing speed. This plane will easily beat my old distance records (10+ miles) if I ever get the itch to do so.

DEMO7
15th April 2016, 04:51 PM
I should mention I was using a 980kv cobra motor

SecretSpy711
15th April 2016, 04:59 PM
Going from 4s to 5s was the best move I did for the drak. It went from dull to responsive and sporty which I like. Hit 102mph with a stiff tail wind the other day

The motor you originally picked (Cobra 3520 980kv) was meant for 5S, the kv is too low for 4S.

I just found your video for the SS motor, that helps. It does have some nice features and the prop adapter is nice.
https://www.youtube.com/watch?v=o6cviMnISNU (https://www.youtube.com/watch?v=o6cviMnISNU)

I have this motor on my SeaHunter, on 4S: Exceed RC Rocket 3520 1300kv. (http://www.hobbypartz.com/86mc303-3520-1300kv.html)
I think it would do well here. It's 15g heavier than the SS motor, but it will definitely turn an 11" prop on 4S.

ritewing
15th April 2016, 05:42 PM
Are you getting Justin's plane?

SecretSpy711
15th April 2016, 05:46 PM
Are you getting Justin's plane?

yes. He offered to sell me the electronics at a discount, but as I currently have a bench full of other projects I am trying to finish as well, I elected to just get the airframe for now and do some research into the power system. I'm not trying to be a pain, I swear.

ritewing
15th April 2016, 05:49 PM
I think he had a 3520 on his, it was the weight of your motor you are contemplating. I just sent him a new Drak kit with my motor, hopefully it does well up there, it should.
You will possibly be able to see numbers in flight side by side then.

SecretSpy711
15th April 2016, 05:54 PM
Ah, I didn't know you were sending him a motor too. That explains why he wanted to sell me the one in the proto Drak. I have nothing against a 5S power system... it's just a problem of batteries, and trying to be at least SOMEWHAT aware of money spent since my life is about to get more expensive very soon (baby on the way). Maybe by the time I finish my Nurf I will come around to buying new packs.

Håvard Støre
15th April 2016, 06:08 PM
Here is the cobra C2826/8 1130kv. It seems to be settling for a little less, but it is not bad:
71829

elmattbo
15th April 2016, 07:41 PM
I am such an outsider on this (don't own a drak) and a relative newbie compared to you fellas, but I think you are approaching the same problem from different starting points and there is merit in both solutions; so why should you agree if your incentives differ? Chris' motor/battery gives you absolute efficiency and power where's the alternative is maybe something that fits better if you already have 4s and don't want to invest more. You pays your money, you takes your choice...


Sent from my iPhone using Tapatalk

Hmerly
15th April 2016, 07:59 PM
Well, I have no problems with experimenting with different power systems. Differing from what the manufacturer recommends is a hallmark of most of us DIY FPV pilots. However, I am very hesitant to do this when its on a something expensive, like the foam on this plane. Certainly the most money I've ever spent on foam, not to mention all the electronics and parts and the time I've put into building this plane up. I didn't want to go with my usual 4s power plant and instead used Chris' motor and esc and have been very happy. Don't want to risk ruining something this expensive because I didn't want to spend a couple more hundreds on new batteries. Doesn't make sense to me as I've already spent 1k, what's another hundred or so.

henkvdw
15th April 2016, 08:31 PM
My 2C.
On a shoestring, Chris' method is the probably best you can get. Even a shipping rope size shoestring.
Had we Boeing and the likes' budget, we could get the numbers and mathematical models to predict accurately how these components will behave and combine.
Short of that, there is nothing that is going to beat Chris' experience, knowledge and feel for this aircraft and what it needs.
However, agreed that it would be nice to see some simple test data on that mountain of motors he tried on 3S, 4S, 5S and 6S.

epic4me
15th April 2016, 10:52 PM
My 2 proto Draks are 5s now, And also the new draks

Cyprusflyer
16th April 2016, 12:43 AM
Not to belittle Chris' work, but I don't really buy the 5S hype... I keep reading that it is a more efficient setup, and that may be true, but I've never seen hard numbers or a real comparison to back that up. I too am an engineer and using 3rd party information on faith without analysis or data to back it up is a huge no-no. Yes, higher voltage probably is more efficient in this case, but is it enough of a boost to justify buying > 6 new 5S packs (3 pairs, number required to charge & fly without much down time, ~$200+) when I'm heavily invested in 4S? I think for the majority of pilots, the efficiency difference is probably drowned out by other factors like flying style, being a lead-foot, not being smooth on the sticks, improper trim, build quality (i.e. looseness in aileron attachment or linkage train), protrusions (big CP antenna), etc.

If you are going for absolute efficiency, are a good enough pilot to take advantage of it, and have money burning a hole in your pocket, then go for the SS motor and 5S packs. Like many things in life (mountain bikes, camera gear, rifle scopes to name a few), there is a huge price jump to go from "above average / good enough for most people" to "top performance." You have to decide what is worth spending your money on.

I say all this because it looks like I may be inheriting one of the original Draks and will have to decide how to power it. FPV is not the only thing in my life.

Good post, agree totally, sticking with 4S and most likely get Chris's motor, cannot find how to buy just the motor, I have a spare Kontronic ESC that does the free-wheeling at lower than max throttle, and has the best BEC built in out there capable of powering 3D helicopters with really power hungry servos so rather use that!
I will try the recommended prop and another with more pitch or a 12" prop to make up the thrust and do some measurements, would like him to publish some specs, ie max watts for the motor although I know 80A x 5 x 4 = 1600 watts probably ok for a few seconds peak and work to that.

SecretSpy711
16th April 2016, 12:58 AM
Chris' motor on 4S will be a little underpowered, no?

Hmerly
16th April 2016, 02:33 AM
Yep, wouldn't recommend it. Its just making things more difficult for yourself, especially when launching.

epic4me
17th April 2016, 10:28 PM
4s was very good on the proto, but not on this