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Old Feb 16, 2012, 03:01 PM
Innov8tive's Avatar
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At 8.3 pounds you are looking at 3768 grams of flying weight which is 942 grams per motor that needs to be lifted in the air.

From the Data that I collected on the Cobra 2820/12 motor at 11.1 volts with an APC 13x4E prop I have put together the following charts and graphs.

This first one is a complete chart of the prop performance at 20%, 40%, 60%, 80% and 100% throttle.





This next graph shows the thrust produced in grams versus the throttle position. From the numbers above we need 942 grams of thrust per motor to hold in a hover. Looking at the graph, if you start at about 950 grams on the left side, and trace the line accross, it will intersect the blue line on the graph. If you go straight down from that point to the bottm scale, you can see that it take about 63% throttle to make that much thrust.





The next graph shows the efficiency level of the prop in grams of thrust per watt of power at different throttle settings. If we start at the 63% throttle point at the bottom of the graph, and go up to the blue line, and then go from there off to the left, the red line intersects the graph at about 7.8 grams per watt of input power.




Now we know that the motors will be operating at 7.8 grams of thrust per watt of power. Since each motor needs to make 942 grams of thrust, if you take 942 and divide it by 7.8 you get 121 watts of power needed per motor. With 11.1 volts in the 3-cell pack, 121 watts will take 10.88 amps per motor. this is a total of 43.5 amps in a hover for all 4 motors.

If you have a 3-cell 7800mah battery, 43.5 amps is a 5.6C discharge rate, and if you take 60 minutes and divide that by 5.6C, you get 10.75 minutes to completely depleate the battery. If you use the 80% rule, then you should only fly for 8.6 minutes to leave 20% of the energy in the battery.

If the weight you gave is for a pair of 3-cell 7800mah batteries, then you can double these numbers and get about 17 minutes of flying and still use only 80% of the battery capacity.

Is that good enough Randy?


Lucien
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Old Feb 16, 2012, 04:38 PM
ramovan's Avatar
United States, NV, Pahrump
Joined Aug 2004
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Quote:
Originally Posted by Innov8tive View Post
Is that good enough Randy?
Lucien
Yes, that's more than "good enough". Told you guys Lucien was good at that run-time math!
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Old Feb 16, 2012, 06:44 PM
FPV addict
Joined Mar 2011
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Where the bow down smilie, lol. Seriously thank you Lucien, hopefully you get this bigger motor mounts in soon so I an get the quad flying again, and get ready for my live demo for DARPA on the 3rd. Man is time flying, pardon the pun.
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Old Feb 19, 2012, 12:01 AM
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San Diego
Joined Oct 2009
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It got a little quiet in here after Lucien dropped some knowledge on all of us. I stopped by Innov8tive skunkworks today and picked up a few new payload mounts. I now have my NL 500mm quad setup the way I want it. I went with the way Randy has his as I think its the best way to get the GoPro image away from the props on the 500mm. I will probably still have a little in the conners, but I can deal with that. My AUW now with FPV gear on is 4.5 lbs. I stepped up the props to 10x4.5sf. This now produces 7.8 lbs. of thrust. This puts my AUW under 60% of the thrust. That should make maneuverability much better. I also have a Dude Power 3s 4200 35c (Thanks Randy) powering the motors and a 3s 1000 for video. A bit overkill for the video, but I had the packs laying around. For now I plan to use the GoPro as the FPV cam, but once I get some more funds I will add a dedicated FPV cam on the top front payload plate. Here is a few shots of my setup.
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Old Feb 19, 2012, 12:15 AM
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Resqhopper - What is that plastic dome behind your quad? Is that a subwoofer or something?
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Old Feb 19, 2012, 12:24 AM
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San Diego
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Resqhopper - What is that plastic dome behind your quad? Is that a subwoofer or something?
yes. Sub for the computer's speakers.
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Old Feb 19, 2012, 02:43 AM
Jesus Freak
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Southern CA
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Is anyone using Next Level 30a esc and a DJI Naza??

I can't get the Naza to arm, and just trying to eliminate stuff. My Naza assistant setup is exactly the same as a friend of mine. His will arm mine won't
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Last edited by AtTheCross; Feb 19, 2012 at 02:48 AM.
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Old Feb 19, 2012, 07:20 AM
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What radio are you using. If you are using a DX8, and I think a 7 as well, there are internal blocks preventing you from moving the stick all the way to the bottom. In the assistant it will show full movement but when you go to arm it will see 2 different travel distances. I had the same issue with my DX8 and wookong. Tour going to have to open up the back of your transmitter and remove the blocks, 2 small screws hold them in place.
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Old Feb 19, 2012, 09:43 AM
Jesus Freak
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I'm using a dx7, think your onto something, but in a different way! I gave up last nite and went to bed, was lieing there thinking ( how could I just go to sleep) and remembered someone couldn't do something because of cyclic rings being installed. I don't have cyclic rings but I have some big thumb knobs installed. They may be limiting travel, will check later this morning, and if that doesn't work will see about the blocks

Read in this tread someone is using NL 20a esc my friend is using 40a esc, anyone confirm they are using NL 30a with the naza?
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Old Feb 19, 2012, 11:04 AM
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Originally Posted by AtTheCross View Post
I gave up last nite and went to bed, was lieing there thinking ( how could I just go to sleep)
Too funny Cross!

I think we've all been there, dang Quads and visions of FPV flight keeping us awake at night

Is your throttle trim/slider all the way down?
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Old Feb 19, 2012, 11:19 AM
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Resqhopper

Nice clean build there Buddy!

Is your 4lb 5 oz including batteries (I'm a little jealous )

Yeah it did get a little quiet around here, took me 5 days to process what Lucian said
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Old Feb 19, 2012, 11:21 AM
Jesus Freak
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LOL yeah those visions of the perfect flight, the dumb moves and the aha moments caused many sleepless nites

Nope all sliders are down in the tx as well as travel limits set to 100%
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Old Feb 19, 2012, 11:30 AM
FPV addict
Joined Mar 2011
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Those wake ups SUCK!! i have a 1 1/2 year old who still wake up at time at night, usually around 4:30, and there are many times i get up feed him and cant get back to sleep so i come down and try to get some work done.
Haven't worked to much on my NL quad, going to start working on it once im done writing this, but i did get a new FPV bird done. Its called a wing jet and i though it would be awesome for some fast low level FPV flying. Its a balsa bird and external EDF unit. Went together in about an hour, then 30min with a dremel and soldering iron to cut the canopy, make some cables, and fit everything in. Using a RMRC700VX camera, 430Mha 3s, and 400Mwatt 1.3 transmitter. Only going to use her for close, low, fast FPV flights so no need for a HUGE transmitter. If only the weather was crappy today she would be up in the air.
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Old Feb 19, 2012, 11:31 AM
Jesus Freak
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I'm hoping I found the problem, will test after church. I have thumb knobs on my sticks and when I go to the extremes the touch, so I'm hoping that it's limiting travel and that's the arming problem
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Old Feb 19, 2012, 12:02 PM
Jesus Freak
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Southern CA
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those sleepness nites brings this joke to memory from another thread


Wife's Diary:
Tonight, I thought my husband was acting weird. We had made plans to meet at a nice restaurant for dinner.

I was shopping with my friends all day long, so I thought he was upset at the fact that I was a bit late, but he made no comment on it.

Conversation wasn't flowing, so I suggested that we go somewhere quiet so we could talk. He agreed, but he didn't say much. I asked him
what was wrong;

He said, 'Nothing..' I asked him if it was my fault that he was upset.

He said he wasn't upset, that it had nothing to do with me, and not to worry about it.

On the way home, I told him that I loved him. He smiled slightly, and kept driving.

I can't explain his behaviour I don't know why he didn't say, 'I love you, too.'

When we got home, I felt as if I had lost him completely, as if he wanted nothing to do with me anymore.

He just sat there quietly, and watched TV.

He continued to seem distant and absent.

Finally, with silence all around us, I decided to go to bed. About 15 minutes later, he came to bed.

But I still felt that he was distracted, and his thoughts were somewhere else.

He fell asleep - I cried. I don't know what to do. I'm almost sure that his thoughts are with someone else.

My life is a disaster.

Husband's Diary:
The heli wouldn't start, can't figure it out.
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Last edited by AtTheCross; Feb 19, 2012 at 12:24 PM.
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