Skyjib 8 Heavy Lifter Build


Lanzar

Lanzar

Member
to carry a RED on a MK is just about the same as driving a new ferrari on offroad. 1 small mistake and it is gonne. I wish more ppl would try to understand this are not toys and that if u drop it someone could get dead. My advice is start small and learn with progress.
Red gets droped at least 1x per month cause ppl hire guys who never took one for a ride and then they spread bad word in the name of multirotot world.
 

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R_Lefebvre

Arducopter Developer
What did that guy do? Just CFIT?

That has been my whole plan from the beginning, to design based on enough power/weight to enable a motor loss. I play with Ecalc, do an 8 motor setup, look at the %throttle for hover, and then take the setup and reduce it to 6 motors, which is what happens if you lose a motor. You still need to have less that 80% throttle to hover like this to have any chance of staying in the air when a motor goes.
 

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silastyler

Member
jes1111 said:
Good idea on the soldered wiring, although you should never need to go thicker on a wire than what's already provided - i.e. if the batt has 10AWG then there's little/no advantage in using 8AWG between it and the next junction point. Same with the ESCs - match the gauge of the fly-leads they come with and you'll be good. Don't forget that 300A of DC will produce some wicked EMI so twist the pos/neg pairs together right the way through the system.

One neat trick I learned for making soldered junctions is to use small lengths of thin brass tubing. Squash it into an oval in a vice and you have a perfect receptacle to poke the (pre-tinned) wires in from both sides then fill with solder. You need a big-*** soldering iron, of course. The other trick is to use individual strands of copper (pulled from a length of multistrand) to "bind" the pre-tinned ends together so they're held while you solder them all together.

For connectors I just can't bring myself to trust hobby-grade stuff - I've gone with Anderson connectors - crimped ('cos that's actually better than soldering). They make 'em in all sizes and the ratings are meaningful (and actually very conservative). So they're bulky, sure, but peace of mind is more valuable than some otherwise unoccupied space. I've actually gone with multiple 5000mAh packs just to spread the total draw across more connectors (I'm using the "45Amp" Anderson's).
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I'm really glad you mentioned the Anderson connectors, I was looking for something with a little more heft than the hobby-grade stuff out there. And the real world ratings are a blessing. Thanks for that. Your suggestions about bundling for the loom are awesome, I've seen video of guys wrapping bare wire, but the copper tube idea is fantastic. What a great suggestion!
 

J

jes1111

Active Member
R_Lefebvre said:
What did that guy do? Just CFIT?
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Makes a case for pilot certification, doesn't it? Not sure who was more stupid - the pilot for taking the gig without enough hours on the sticks, or the DOP for hiring that idiot without taking references ;)
R_Lefebvre said:
That has been my whole plan from the beginning, to design based on enough power/weight to enable a motor loss. I play with Ecalc, do an 8 motor setup, look at the %throttle for hover, and then take the setup and reduce it to 6 motors, which is what happens if you lose a motor. You still need to have less that 80% throttle to hover like this to have any chance of staying in the air when a motor goes.
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Why 6?


I see this as a three-stage plan:
1. Design for redundancy
2. Design/build for reliability, including the de-rating of critical components referred to above
3. Rigorous pre-flight checks and planned replacement of critical components.
 

S

silastyler

Member
jes1111 said:
KoolKiwiKat is proposing some interesting components and this is a fundamental decision that every heavy-lifter must make: "lightweight sports car" with potential fragility or "over-powered tank" withbullet proof performance. Lotus vs Mercedes, if you like. With any electrical/electronic system, the closer you run to its rated capacity the higher your risk of failure will be. It's the same with mechanical systems - lighter equals more fragile. The gap between these two approaches can be closed (to some extent) with "money". So its one of those "pick any two" choices: lightweight, reliable, cheap.


Personally, to fly a RED, I'd go with the OP's approach - over-specify everything. Efficiency/flight times are much less important than reliability - long flight times are not needed, absolute reliability is.
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This really is the seminal issue here for those of us building for professional use. I'm a cinematographer, and this is a platform for aerials, and as such needs to be reliable and safe. I am in total agreement with all the calls for redundancy, but I also completely agree with jess111 that by over-specifying the power train I end up with a system that runs cooler for lower current draws. I'm talking about lifting a camera package that will come in around 15-17lbs. Body, battery, lens, Focus motor, HD Transmitter (or downconverter box and SD transmitter). On average we're talking about more than 20K worth of gear just hanging from the gimbal.

As far as the motors go, the only commercial builder I've been in contact with is Al at Hoverfly, and those are the motors he puts in his heavy lifters. They may not be the end-all solution, but the footage I've seen online that I really admire has been shot from platforms with this configuration of motors, and an ESC based power train, and that is why I am trying to vet them. I'm not interested in being able to whip around with this multirotor, my experience with technocranes and cable cam work is that graceful fluid movements produce the best results, for both platform and the operator. And yes, longer flight times are a non-issue. I'd be perfectly happy with 5-6 minutes per pair of 5S batts.

Vortex :
And as far as 5s vs. 6s on the Axis, I can always change the batteries later if I'm not satisfied. Al at Hoverfly recommended the 5S 11,000, and since this is my first bird and his track record includes 2 years of building experience I dont intend to take that advice lightly. I've heard the same thing you have about the AXi's wanting 6S to meet their potential, but I will take someone's real-world experience over a datasheet.

koolkiwikat:
Thanks so much for all your helpful comments, You've made so many good points that I'm not sure where to start. eCalc is a little mystifying to me when I plug in the numbers I have, so I'm not sure how to proceed in terms of determining how much throttle I need to keep my bird in the air after a motor failure. Could you go into a little more detail if you have a moment?

you given me a lot to think about. The only portion of your first post I would take issue with the suggestion to use DJI. A buddy of mine just had an AD-8 built with Axi 2826 motors chinese ESCs flashed to work with the Wookong-M, and when he took it out for its first flight and put it in Attihold it flipped over and crashed. Just because they are large companies and popular doesnt mean their products are reliable. Hoverfly doesnt have a crash record that I can find, and their customer service is excellent, and that is why I chose them. That, and they are made here in the US.

This thread has already proved to be an amazing source of info, thank you all for your replies!!
 

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silastyler

Member
jes1111 said:
I see this as a three-stage plan:
1. Design for redundancy
2. Design/build for reliability, including the de-rating of critical components referred to above
3. Rigorous pre-flight checks and planned replacement of critical components.
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I am in total agreement. Is there anyone out there that has worked out an approach for critical component replacement schedules?
 

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silastyler

Member
R_Lefebvre said:
What did that guy do? Just CFIT?

That has been my whole plan from the beginning, to design based on enough power/weight to enable a motor loss. I play with Ecalc, do an 8 motor setup, look at the %throttle for hover, and then take the setup and reduce it to 6 motors, which is what happens if you lose a motor. You still need to have less that 80% throttle to hover like this to have any chance of staying in the air when a motor goes.
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Are you taking away two motors for dual redundancy? eCalc says I need 71% to hover with 8, 77% to hover with 7, and 84% to hover with 6. I dont know if I've put in the information correctly, but if I can still maintain a hover with 6 even for 20 seconds safely, I can definitely descend under control at the same rating no? I mean if I lose even one motor at all I'm going to be instantly headed for that spot I designed at takeoff as a safe crash/hot landing spot. What am I missing?
 

J

jes1111

Active Member
Do a screen-grab of your eCalc setup and post it - unfortunately the linking doesn't work.

71% throttle to hover sounds worrying - you should be aiming for 50%. Don't forget that you need headroom on throttle for the FC to control the craft - i.e. if your throttle is already at 71% to hover, you lose a motor so that goes to 77%, leaving only the last 23% for the FC to use to correct using that corner. If the FC demands more than that 23% to correct against a wind gust then the motor "tops out" - and you flip :( Factor in the +/-15% accuracy that eCalc admits and you're playing in dangerous territory.
 

Photronix

Photronix

Pilot
The ship Silas is building is basically our Erista Aerial system with a few details I'll keep secret. I can tell you that it can fly a Red Epic at 50% throttle with lots of power for quick pull ups. This is an AUW of 36lbs or 16.2 kg. And is is very smooth and solid in the air using our HoverflyPRO/GPS combination.
 

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silastyler

Member
Photronix said:
The ship Silas is building is basically our Erista Aerial system with a few details I'll keep secret. I can tell you that it can fly a Red Epic at 50% throttle with lots of power for quick pull ups. This is an AUW of 36lbs or 16.2 kg. And is is very smooth and solid in the air using our HoverflyPRO/GPS combination.
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Thank you for chiming in Photronix, it's great to hear this list of components is not far off the mark, regardless of what ecalc says! What prop size/pitch are you using if you don't mind?
 

Lanzar

Lanzar

Member
For axi 4120 i would suggest 6s as a must.Our 5s test were not even close to 6s. but it depends on configuration and props. For 4kg payload those axi are way too heavy. And dont wory about motor failure, motors are the last thing that will die on you. Esc, battery and electronics will die before, pilot is the number 1 killer of mrotors.
 



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silastyler

Member
Lanzar said:
For axi 4120 i would suggest 6s as a must.Our 5s test were not even close to 6s. but it depends on configuration and props. For 4kg payload those axi are way too heavy. And dont wory about motor failure, motors are the last thing that will die on you. Esc, battery and electronics will die before, pilot is the number 1 killer of mrotors.
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I'm not sure where the 4kg payload number is coming from Lanzar, my payload will be closer to double that. What prop motor configuration would you suggest using 6s then?
 


Vortex

Vortex

Member
Lanzar said:
For axi 4120 i would suggest 6s as a must.Our 5s test were not even close to 6s. but it depends on configuration and props. For 4kg payload those axi are way too heavy. And dont wory about motor failure, motors are the last thing that will die on you. Esc, battery and electronics will die before, pilot is the number 1 killer of mrotors.
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Interesting......Isn't that what I said and was brushed off......
silastyler said:
What prop motor configuration would you suggest using 6s then?
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Your AXI 4120/20 are a good choice on 6S with Xoar 15x5
 

Lanzar

Lanzar

Member
mitmit said:
Lanzar, what fc would you suggest to carry red, if not mk, btw? wookong? ;)
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Depends on person. We dont have any experience with hooverfly (have 2 boards in shop but no time to test) we basically fly Mk and we are testing dji also a lot.
 


S

silastyler

Member
Vortex said:
Interesting......Isn't that what I said and was brushed off......



Your AXI 4120/20 are a good choice on 6S with Xoar 15x5
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Vortex, I didn't mean to make it seem like I brushed off your OP. between you and Lanzar there is obviously a strong feeling that 6s is a better fit for the motors in question. I may just have to test both configurations in order to understand the difference and to see the results first hand. I do have a set of 15x5 props, so I guess I'm covered if I go 6s instead. The only component I haven't purchased yet is the batteries, so this discussion has given me pause. I would just love a more detailed explanation of the differences (pros/cons) between a 5s and 6s system. Will one result in longer flight time at the expense of thrust?

Cheers
 

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