T3 the Vertical Horizontal one

Rob_Lefebvre December 14, 2015 at 6:34am

Coby, not sure if you were looking for more details on my heli. This is a Protos 500 stretched to 465mm blades, so the rotor disk is about 1050mm. To those concerned about safety, I actually am going to try to assemble some junk parts I have into a minimum function chassis, and then fling a steak or chicken or something into the rotor. I'm very curious to see what happens too. My system operates with a greatly reduced rotor RPM, and the energy in the disk is probably less than 1/4 that of a standard helicopter of this size.

The empty weight of the frame is about 1680g, plus the 200g camera and batteries, it's about 3170g. The rotor disk is 0.86 m2.

By coincidence, I have a quadcopter that hovers for 45 minutes on the exact same batteries. It's empty weight is 1530g, and 15" props giving a cumulative disk area of 0.46m2. But note, the 45 minutes hovering is without the 200g camera, and it's not moving. I should put it up on the same mission and see how it does. I expect it will really start to suffer at speed. This machine is fairly well optimized with Hobbywing ESCs and KDE motors, and it's fairly lightly constructed (Tarot 650 quad frame). It folds up neatly, but takes up about the same amount of space as the helicopter does.

And this is the key differentiation here, and why I'm so bullish on helicopters for any application where you are required to actually *fly*. The helicopter required only about 25% more power to fly at 15 m/s than it did in a hover. And this helicopter is far from optimized. It is aerodynamically very dirty, I'm sure if it had a body, it could fly 20 m/s with the same power consumption. Also, mechanically, it's far from optimized, it uses a very draggy serpentine belt system and the motor is far too big. It's drawing 15A to hover on a motor specced at 60A continuous, so it's way down on the efficiency curve. I want to change the belt system and find a smaller motor.

Ah heck, I'm going to charge the batteries and go put it up, see what happens for comparison.

I did a bit of engineering work on the 18650 concept, and decided that they don't seem to be worth the effort and expense compared to the Multistar "10C" batteries (really, they are 2-5C, if you draw them at 10C, they puff). The thing about the 18650 Lion batteries, is that while they pack a lot of mAH into a given mass, they actually have a lower nominal operating voltage. About 3.4V/cell compared to 3.8V/cell for a LiPo. So when you actually calculate the Watt-Hours/KG, it's only about 20% higher than the 10C LiPos. Then when you consider how fragile the 18650's are, needing to be charged at only a 5-8 hour rate, and also factor in the cost, about 3-4 times that of the LiPos, it just doesn't seem worth it to me. They do make sense if you are trying to set a record, or if you just HAVE to have that extra flight time. But for most practical applications, it seems to make more sense to me to just use a good LiPo and return to change/charge more often. They are happy at a 1-hour charge rate, so you only need 2-4 sets to operate virtually non-stop. With the 18650's, you'd need 6-9 sets, to operate non-stop, so to equip a system for continuous operations, your battery cost could be 18 times higher than LiPo. Again, to gain only 20% longer flight time?

Furthermore, none of this seems to account for the nuance of the way the 18650's work. They have a much steeper discharge curve, starting full at 4.2V, but are intended to be taken down to about 2.4V, you have a 1.75 ratio of voltage from full to empty. Lipos are about 1.2. So when you consider the power system design, you need to plan for hovering thrust at 2.4V/cell, but then when fully charged at 4.2V, you will be throttled way back, operating at a low-efficiency point of the motors.

Coby December 12, 2015 at 9:03am

Rob,

Thanks for sharing details. For those who are wondering just how much more efficient a trad hell might be: We have a quad that is getting 45 minutes but that's mostly hover work. It also weighs 14 pounds and needs a 22,000 6s. Running 4 x 14in props for now but it's underpowered. Moving to three blade 15 and lower KV/bigger motors on the next build. Also keep in mind that we are sensitive to weight in our deign but it is built to be more of a farm implement than a potentially fragile ultra light build. I hope to have more detailed info in the next few months. Really want to see how far we can get for this T3.

R,
C

Rob_Lefebvre December 10, 2015 at 1:52pm

Benchmark set.

Today with my Protos 500, I flew for 48 minutes, and traveled 35km with a 200g payload. Resulted in light crash at the end as the battery dumped and it came down hard. Just broken landing gear luckily.

Rob_Lefebvre December 10, 2015 at 4:58am

I would like nothing more than to match airplane performance, with a helicopter capable of VTOL. ;) And this thing isn't even remotely optimized yet. Aerodynamically very dirty. Powertrain on this one is very inefficient. Just something I slapped together.

Actually, I would really like to get some 18650's. It can certainly take it. If I match the weight not the capacity, duration will go up over an hour. Could probably do 1 hour 15 minutes at speed. No multirotor can do that.

I've been holding off, unsure where to get good cells. Anybody know of a good source?

JB December 10, 2015 at 4:29am

Hey Rob

Good job! But for a fix wing pilot those figures are fairly normal ;-)

Have been using 4S 18650 packs for 18 months now. Only way to get good range really. As long you need more than 30 minutes endurance and don't have too much peak demand it's the only way to fly IMHO. I 3D printed some sleeves to make it easier to solder and hold them together. I can email you the file if you have access to a printer. Takes about 20min each to build with balance cables etc and then I just used some large heat shrink to seal it all up. Look out that you get original Panosonic cells, plenty of fakes around. Also don't forget to switch from lipo to lion on your charger. VTOL draw is a bit of challenge sometimes using those though. What battery are you currently using on your heli?

Rob_Lefebvre December 9, 2015 at 1:17pm

Ok, lets get this party started!

Took my small mapping helicopter up today, 200g payload. Flew for 32 minutes. Couple minutes of Loiter as I adjusted the mission a couple times. I managed 21.7 km. The heli has enough battery for at least 45 minutes at 15 m/s, maybe a little more. I only had to stop early to be home on time for my kids (need to time this better). Should be good for 30 km, I'll know for sure when I recharge the batteries.

I really need to get 18650's on this thing and it will be well over 1 hour easily.

JB December 7, 2015 at 7:36am

Stephen

I think you're doing it the right way round. In May I started with a hex then added a pusher prop then some wings too! ;-)

JB December 7, 2015 at 7:33am

Hey Rob you're exactly right of course. I only originally put it together as a joke for the photo, but the quadplane underneath is in fact one of our real challenge prototypes. It does actually fly vtol, but without the donut floaties, RC car and "flip flop". The flip flop will need to be better integrated, and the balls could go inside easily, but otherwise my originally "harebrained" idea does already work! We're still optimizing the speed to get the range from the batteries for the hour we have t the challenge, but it looks promising so far.

Nice set of very manly boots btw!

What do you think of the idea to feather the vtol into the wind btw?

T3

Stephen Zidek December 7, 2015 at 6:14am

Gonna try to do this one, a guy in my new lab is interested. We're thinking of tackling VTOL from the opposite direction. I think a lot start as airplanes then have 4 motors attached for hovering. We may try starting with a quad and attaching wings for lift in forward flight.

Rob_Lefebvre December 7, 2015 at 5:26am

JB, I thought that plane thing was a joke. Can that thing really fly for over an hour at 100 km/h with the FlipFlop on top and donuts on the wings?

My 500 Heli will do 45-60 minutes at 10-20 m/s with a 200g payload. 700 electric should be able to do over an hour at 20 m/s with about 2kg. I will also do a demo flight with the gasser, it's silly to exclude technology just because it's so far superior and it would dominate the competition. ;)

FYI, Ugg boots are really just fashion footwear used in the Autumn by city folk. I do have a set of -40C Sorels that I can probably use as target footwear with the bigger helis. Both boots.

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T3 the Vertical Horizontal one

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