Help Choosing Hexa Power System

[Borneoben]

Hi Guys

As some of you will know i am working on a new design for a APV rig and would like some help and advice choosing the correct power system for it.
Details on my airframe and camera mount can be found HERE

I have be pointed towards the very nice eCalc Multirotor calulator but embarresingly i am having trouble interpreting wat it tells me.

A few pointers would be great.

Please see screen shot of my current settings that look promising to me.

What i dont understand fully is what is included in each section and what it all means.

My airframe should weigh close to 2.8Kgs including the flight batteries
Does the box where you enter xcopter weight take into consideration teh batteries or is it just the airframe inc motors and props?

When my APV rig is fully loaded with Camera mount and DSLR it will weigh a TOTAL of 4.4Kgs
which means to me that the payload i need is 1.6KG.

I can see that from my Hexa settings the RCT 3536 910kv motor with 11x4.7 prop draws 26.5 amps peak per motor and hovers at 5.2 amps per motor

This particular set up gives me 10.8 minutes of Hover time and allows me to lift an additonal payload of 2.6Kg

Have i understood this correctly?

What i dont understand is that if i changeteh prop to a 12x4.7 i get longer flight times and i can lift almost another KG of payload.

Am i understanding this right?

Another thing i dont understand is that if i add 2 more motors and change it into an Octo
I get slightly longer flight times and i can lift yet another KG of payload!!

I think i am reading the information wrongly.

Any help and advice would be greatly appreciated.

Thanks

Ben

 

[jes1111]

I always set the weight in the top line to "without Drive" and enter only the weight of the frame, gimbal, camera, landing gear, electronics, etc., i.e. leave out the weight of the motors, batteries and ESCs. That way you can vary the batteries, motors (type and/or number), props, etc. and see the exact result. A couple of other things:
- set the Field Elevation to your actual height above sea level - makes a big difference.
- set battery charge state to "full"
- set "Motor Cooling" (at the bottom) to "excellent" (they are sitting in their own prop wash)

Calculating backwards from your 4.4kg AUW, subtracting the weight of the batteries, ESCs and motors as entered, that means your figure for the top line is 2600g (although that doesn't seem to concur with your other weight estimate). The result of setting it that way is attached. Notice that the AUW in the bottom line is showing ~4400g.

The important figures you're now looking at are the "Throttle (linear)" (shows your throttle setting at hove, should be around 50%), and Flight Time Hover. Plus, of course, nothing should turn red.

Those RCTime motors are obviously a good choice 11x4.7 props. At max throttle they will be pulling 424W, leaving a comfortable margin to their 470W max rating. They won't be so happy with 12x4.7, however - that exceeds their capacity.

6.58 minutes is not terrific for hover time. You can go 4S3P and get 8.86 minutes, but anything more than that and you overload the motors. Since you have plenty of lift capacity on hand, change the batteries to 6000mAh - 25/30C (still 4S2P) (by jiggling the numbers using the Custom setting to exactly match the linked battery) and you get 10.81 minutes.

Conclusion: those motors are good to get you going, but once you've ironed out all the bugs and foibles, I'd be looking to upgrade them to something with a bit more beef.

 

[Borneoben]

Hi Jes111

Many thanks for your help

you have helped me understand eCalc much better now. Im glad i didnt buy anything based on my original assumptions i would have been bitterly dissapointed!

I still couldnt work out how you managed to get a flight time of 10mins plus though?
Your attachement is a little too low resolution for my computer i cant make out the numbers?


However
I have been working on my frame design and realised that my weight estimates were a little out! I am now estimating that the AUW ready to fly with camera is more like 5.6Kg's!!!

I have also been doing more research into off teh shelf frame kits from teh likes of Droidworx and Cinestar etc to compare my frame weights.
They are in a different league! I dont know why I thought I could build something similar for alot less money!

Will have to search for a reasonbly priced machinist and change my design to suit carbon fibre then maybe i could build something with similar performance.

OR

I could just buy a kit of the shelf and get on with flying instead!!

Which is what I will probably do!

Anyway

Thanks again for your help.

Ben

 

[jes1111]

Sorry - didn't realise - Windows or the forum software squished the image. Attached again. To get to 10+ mins just change the battery from 3300mAh 4S2P to 6000mAh 25C - you get 10:13min - adjust the weight of the battery to the actual value (from the link) and you'll see 10:81

Don't be discouraged - there's a motor/battery/prop combo out there that WILL give you what you need - you just have to find it - wood is a great material - less dense than CF and plenty strong enough for the job. The reality is that the DW frames (and many others) could be built out of G10, wood or even aluminium and still fly just as well for just as long, provided a bit of real "engineering thought" was put into designing for the material used. Carbon fibre is an overrated material in this context and it's rarely used appropriately - it's just a "fashion statement"!

 

[ovdt]

The reality is that the DW frames (and many others) could be built out of G10, wood or even aluminium and still fly just as well for just as long, provided a bit of real "engineering thought" was put into designing for the material used. Carbon fibre is an overrated material in this context and it's rarely used appropriately - it's just a "fashion statement"!

I totaly agree with your statement about carbon fiber.

I built my frame using aluminium round booms but painting them was a pain. It took 2 days for me to complete the paint work. I'll consider using CF booms after this.. When the painting time added to the cheap alimunium booms, it costs me more. CF booms are born to be sexy; no need to paint them

 

[Borneoben]

Hi Jes

Thanks for all your help and advice and encouragement

I have been playing around with eCalc again and think i have found a decent system

Based on Tiger Motor 2820 830KV motors
60 amp ESC
14x4.7 props
4s 5000mah packs x2

I can get an indicated 10.7 minutes.

See my PDF attached

This would also alow me some lea way for the AUW of the airframe.
Even if my frame weighs upto 4kg without Drives i still get about 7 mins of flight time!

I am also assuming that this power system would then be very nice for other airframes If or when i choose to upgrade!

Thanks for the encouragement

Ben

 

[Borneoben]

I totaly agree with your statement about carbon fiber.

I built my frame using aluminium round booms but painting them was a pain. It took 2 days for me to complete the paint work. I'll consider using CF booms after this.. When the painting time added to the cheap alimunium booms, it costs me more. CF booms are born to be sexy; no need to paint them

I agree Carbon is pretty much always over kill for teh job but is expected in todays high tech world.

I think the all carbon Cinestar and Droidworx et al are very nicely thought out machines but i struggle to see how they are worth what they are charging. I can see how the FC's are worth the money but lets face it a multi rotor airframe is just a frame with no moving parts to keep teh motors and props in teh right place!

I really like the cinestar and the cinestar camera mount but i just cant see how they can charge over 1000usd for that camera mount.
I am tempted to draw up something very similar but dont want to face the inevitable copy cat comments from others and want the challenge of doing it differently!

Like i said multi rotor frames are just there to stop the motors and props from hitting each other!!

 

[ovdt]

Berneoben,

I'll recommend you a motor with lower KV. I recently purchased Tiger motor MT2826 / KV550. You can select AT2826 from the list with the APC 14x4.7 props on. Since they are reasonably priced, you will also see more efficient flying.

APC Slow Fly prop has RPM limit; so high KV motors may not be suitable for it.

Look at the figures attached.

View attachment 1097

 

[ovdt]

And also, a 40A ESC would be more than enough for the configuration I attached.

 

[Borneoben]

Wow that looks good ovdt

Thanks very much for looking into this

I will investigate further


Cheers

Ben