Servers by jDrones

Skywalker X8 Quadplane Build 4

(darrell) #11

Yes, you are right. It’s not a requirement to have a power module for the battery used on the vertical motors. I’ve never actually referred to info it provides in flight. With vertical flight I know the time the battery will last from test flights and that it is good for two take off and landings, if they are quick. My goal with quadplanes is to get up in the air for transition to forward flight quickly and to land quickly. The less time in hover mode the better as far as I’m concerned.

I have the power module connected because I’m doing comparisons of different motors and I like to check the logs for current draw and voltage drop of the batteries. The more data the better.

(Anthony) #12

Currently, we are using the same setup and only have a power brick on the forward motor.

However, I am seriously considering installing a second power brick on the multi rotor part. It will give the following advantages:

  1. monitoring the health and condition of the multi rotor battery.

  2. have a secondary power to the pixhawk for redundancy.

I just recently learned the Cube doesn’t have redundancy from the servo rail which resulted in a serious crash. So to use the multirotor part to give redundancy would be a very good solution.

(Tony Atma) #13

Hello Darrell, I have built three Vtol using different airframe, and I am curious about two important issues:

  1. Why you change from 6S to 4s? As we understand that using 6S will lower the current which is good for the battery.This is more relevant because your AUW is 5-7 kg. It needs very big current during take off -hover-landing. Any special reason you change to 4S ??
  2. You also change the vertical motor to be very small for 5-7 kg Vtol. Do you think if we use 15" prop. may cause too much drag???

Regarding the power system, I agree with you to use two power system. My Vtol also use two power modules, while the second power module connected to ADC 3.3 v on Pixhawk. So we can activate the second power (Batt2. on mission planner).

(Anthony) #14

Hi Darrell,

Can you share your PID settings for this build? I am in the process of building one as well and it would be nice to have a starting point.

(darrell) #15

The purpose of this build was to experiment with smaller motors spinning faster and using smaller props. The Sunnysky motors also are lighter and cost less than the T-Motors I was using. The motors are why I changed to 4S as that’s what they require. I also wanted the flexibility in configuring the power to come from combined batteries or keeping them separate for vertical and forward so it’s nice to have it all 4S. A large part of my reason for doing this test was watching how the commercial version of this build was coming along. We were building more or less at the same time and I noticed the DeltaQuad went slightly different directions. The DeltaQuad really impresses me and they seem to have come up with a very good design. I don’t think you will have issues with 15" props. I was using 14" with the slower T-Motors running on 6S and that worked just fine.

(Tony Atma) #16

Hi Darrell thank you for your information. Have you got conclusion which one is more efficient between 4S and 6S for this 5-7 kg Auw Uav?? I am also impressed with the Delta quad system, especially how they can achieve 3 hours flight time with 6 kg Auw? I really eager to know what size of props. do they use for forward motor and for the quad. Also what kv motors do they use for forward anf also for the quad.
By the way, you mention that in Cruise mode (Fbwb) the current is below 10A using 14x8 prop. could you share what is the ground speed (based on Gps) is this 4S or 6S configuration? I suggest you try also 13x10 prop. for forward motor to make it more efficient. Do you use airspeed?

(darrell) #17

I fly large multirotors so when I started this project I built the vertical side as I would with that type of airframe. Specifically, slower KV T-Motors with large props using 6S batteries. That worked quite well. But watching the DeltaQuad made me wonder why they went a different direction as it’s obviously very well engineered.

Now that I have tried smaller faster motors with smaller props I think I’ll continue with them. The reason is that this is not a multirotor and the vertical side is designed to get you in the air and to land, not to fly around like a multirotor. I’m now using Sunnysky 3120 1100Kv motors with 13" props running off 4S battery. This saves a bit of weight and the motors cost less but it does require wiring that can handle the high current. Hovering requires 60 amps and it can peak to 90 amps.

The airspeed was 17m/s when drawing less than 10Amps during cruise using 4S battery. I do use an airspeed sensor. I’m using a fairly large forward motor, HobbyKing SK3 4240 740Kv.

Thanks for the tip about the forward prop. I’ll definitely give that a try.

(Tony Atma) #18

Hi Darrel, Thank you for your sharing, what is your gps ground speed when your airspeed sensor is 17 m/s ? I also use many Sunnysky motors, as they have good products. But I am curious that you use SK3 (HobbyKing/Turnigy) motor for forward motor. Do you think that motor is better than the Sunnysky motor ?

(darrell) #19

The ground speed would depend on how much wind there is as the plane is flying by airspeed. I only use the HobbyKing motor because they are easy to source in Australia.

(Tony Atma) #20

You are right. So basically Q_Assist only refer to airspeed sensor. But the problem (at least me) is some times it is not easy to have good quality of the AS. Any suggestion what is good /reliable airspeed sensor? Any link of vendor would be great. Tks. Darrell.

(darrell) #21

I believe the airspeed comes in an analog and digital version. Just make sure it’s the digital version. I usually get them online from eBay, GoodLuckBuy or HobbyKing Airspeed Sensor etc. They don’t seem to have a brand name, just generic devices. When using an Air Speed sensor it’s critical to do a ‘preflight calibration’ each time you fly with your hand cupping over the air speed sensor but not touching it.

Using an airspeed sensor on a quadplane does create an issue of how to place it given you don’t want the vertical props to influence it. I had the following Airspeed Sensor Mount 3D printed for my build.

(lior) #22

Hi, i have to say i’m really impressed with your work!
I have the X8 equipped with:

  • scorpion 4020 540KV main motor
  • APC 16X8 propeller
  • scorpion commander 110A ESC
  • PIxhawk 4 with ArduPilot 3.9.8
  • DragonLink V3 data link
  • Mauch 100A current sensor

I’m now working on making my X8 VTOL myself using your post and there are a lot of questions regarding your built that might help me go through this process. sorry in advance for that mass of questions:

  1. Why did you use both Mauch and the HobbyKing sensor? to measure the seperated power system currents?
  2. why did you choose these specific motors for the VTOL?
  3. Why did you make the wing extension 180mm and not less or more?
  4. are the VTOL bars 980 mm each? Why this specific length and not more or less?
  5. Did you change anything with the original carbon bars for the wings?
  6. What is the wing extension made of?
  7. I didn’t fully understand the way you implemented the aluminum reinforcement for the carbon bars?
  8. What is 12X12 (Aluminum inserts)
  9. How much weight did the VTOL system added to the complete plane?
  10. What is the original X8’s stall speed (without the VTOL system)?
  11. How did you plug the VTOL to wing and the VTOL to fuselage interfaces (to the original plastic hooks?)?
  12. Is the air speed sensor crucial? what contribution does it have?

Thanks in advance!
Any tips and help will be appreciated!

(darrell) #23
  1. I use two power boards to measure the vertical motors and forward motors separately. HK sensor is rated to 60Amp only so I use it for the forward motor. The Mauch is rated to 100Amp so I use it for the vertical motors, which hover at 60A but can peak to 90A.

  2. On this build I choose these motors to see if I could get smaller 4S motors with higher Kv to work as used in the commercial version of the plane, DeltQuad which is a very impressive build. I normally use 6S slower T-Motor with large props and was very curious why the DeltaQuad used smaller motors with smaller props spinning faster and using higher current 4S voltage. This configuration appears a bit lighter but honestly, I don’t see much difference and I am having a heck of a time getting the smaller motor setup tuned properly.

  3. I made the extensions a bit larger to accommodate larger props. But even with the smaller props I like them as it adds more wing area/lift. I was hoping the extra lift would give me better flight times and a lower stall speed. I do mapping and it’s important to fly slowly to allow the camera to keep up.

  4. Yes the motor bars are 980 mm each. The length is to accommodate the prop size, especially keeping the forward motor away from vertical motors.

5/6/7. Yes. I actually use two 500mm CF 15x15 square tubes. I join them by inserting a 230mm 12x12mm aluminum square bar in to the CF bars. The trick to getting the 12x12 tube in to the 15x15 is to shave the corners of the 12x12 a little bit. Then it will slide right in. The reason I do this is that I drill 10mm holes in the CF tube to slide the spars through which is a huge bite out of the tube and will weaken it. But with the 12x12 tube inside it’s extremely strong even when drilled though. I’ve tried just attaching the 15x15 to the spar but you don’t get nearly as stiff of a build. The goal here is to limit wing twist which is a serious issue with quadplanes.

The wing extension is cut by a local foam company on a CNC cutter. I took the wing joiner from the Skywalker to them and asked them to use it as a guide for the wing shape. They use a type of foam which is similar to EPO but a bit denser. But you could use just about any foam and then wrap it.

  1. The wing extensions with SunnySky motors come in at 880 grams each.

  2. The stall speed of an X8 is about 14m/s

  3. I use the standard Skywalker wing joiners to connect the wing extensions to the fuselage and wing. You can find them on eBay for cheap. Make sure you sand the plastic and the foam before gluing them to give the glue a better grip.

  4. The plane will fly fine without an air speed sensor. The advantage of an airspeed sensor is you will get longer flights in wind with one and better stall detection on turns. But I fly without one all the time and it works just fine.

(lior) #24

wow, i appreciate your detailed response so much!
If i may ask several questions regarding your answers:

  1. “I am having a heck of a time getting the smaller motor setup tuned properly.”
    what does the tuning process include?
  2. “12x12 tube in to the 15x15”
    this means the thikness of the carbon bars are 3mm?
  3. Are there any pictures of the carbon to aluminium mechanizm? it’ll help me understand it better.
  4. “The wing extension is cut by a local foam company on a CNC cutter.”
    do you have the model file of the shape cutted by CNC?
  5. how does the air speed sensor help getting longer flights?

and again, thanks a lot!

(darrell) #25
  1. That’s difficult to answer. Please read the section on tuning in the quadplane doco. It should take off fine with defaults but I’d recommend you do an autotune with the wings off. I have just finished another build today and I’ll be doing some tuning next week. I was thinking about doing a video of the process so that will probably be of interest.

  2. Well, more like 2.5mm but it varies. Anyway, you will find that the 12mm fits very nicely in 15mm square tubes.

  3. Have a look at this photo. The top bar shows the internal black aluminum bar sticking out of the right 500mm CF tube. It has about 120mm inside the tube and another 120mm sticking out of the tube which will end up inside the left 500mm CF tube. I get this section of aluminum tube from HobbyKing. Make sure you use a drill press to drill through the CF and aluminum tubes as it’s critical that they are perfectly vertical and centered. That photo actually shows 12mm spars going through the tube but the correct size is 10mm which is the size of the spars that come with the Skywalker. You will need to buy a longer rear spar for the build to accommodate the wider wing span.

  4. I don’t have the file but they said they would give it to me. I’ll give them a ring and see if I can get it. They charged me over $400 for the time it took to create it so if I can get it that would save your a lot of time/money.

  5. Well, Ardupilot does have some sophisticated way of calculating air speed without a sensor but that’s over my head. My understanding is that if you are flying in to wind and not using an airspeed sensor the plane will be flying faster than it needs to as it will be calculating speed by ground speed. Basically an airspeed sensor just adds accuracy to the flight and that will give you slightly better flight times. Hopefully someone with a better understanding of it will give a better explanation.

(Tony Atma) #26

Hello Darrell,
Just to update recent discussions, last time you mentioned that the Current consumed during Cruising of the X8 is about 10A right? Is it based on 4S battery? If it is 4S that means the power is about 148 watts right? Is this best so far, or can you get better/lower power (more efficient) during latest test? I think 148 watts during cruising at 17 m/s is good, however I try to do testing for a better efficiency (needs more time). I have checked again, and found that the Delta Quad also have similar power consumption during cruising, about 150watts. Did you use the SK3 (HobbyKing/Turnigy) motor 500Kv or SunnySky as forward motor during that time??Regards,

(darrell) #27

I’m using a HobbyKing SK3 4240-720 for forward motor. From what I’ve seen it would be quite difficult to get a 6.5kg plane with this size wing area to cruise at less than 10 amp current. I get about an hour of flight which gives it about 60kms of flight. How far do you want to go?

(Tony Atma) #28

Just to confirm again, this is based on 4S battery right? Which means about 148 watts? Are you using 14x8 propeller right? Is it from Apc or other brand? I believe propeller size and brand is one key point to get high efficiency.

(darrell) #29

4S battery and 14x8 prop. I don’t know the brand of the prop. I think it’s from HobbyKing. Cheers.

(darrell) #30

I just checked my plane and the forward prop is actually a 14x7 not 14x8 as stated above. I’m tuning a new plane tomorrow and I have a 14x8 prop on it. I’m not sure if I’ll have time to do forward flight with it but if I do, I’ll let you know the results with the 14x8 prop as I suspect they will be better. I’ve also calibrated my current sensor so the results should be more accurate than before.