3s vs 4s Battery for Long Range 3in FPV Drone Responsiveness
What would give better responsiveness, a 3s 18650 jp30 pack, or a 4s one? This is for a 3in drone with 4600kv motors, and i am looking to do long range (5 to 10 km) but still dive down things. Or should i just stick with 4s lihv (an 850mah maybe)?
Note: I am using 350mw analog so anything over 5km is pushing the video to its limits, is it worth having a stupidly long flight time at the cost of a sluggish quad?
6sett. (modificato 6sett.)
the smallest 18650 packs I could see were 3s-4s 3000mah at 160g-200g, Im assuming your dry build weight is around 200g, so you'd be looking at doubling the weight and having a much lower discharge rating. for "responsive" you want 7-8:1 thrust to weight, 400g auw is probably more like 4:1 at 100% throttle on those motors, which would probably kill the battery with the lower discharge rate.
I like my 4s 700-900mah lihv for 3" a lot!
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6sett.
Autore
My build is currently 156g, and a 3s 18650 pack with the jp30 cells would be around 145g, AUW would be around 300g. What do you think of this for flying up mountains etc? I have a 4s 720mah and i can get about 4.5km round trip flights on it at about 7mins flight time. What sort of flight times could
you get cruising with a 850mah?
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6sett.
@SundryTea Please dont take this personally, but there are some variables/contradictions here that make me want to suggest more experience before pushing long range and mountain diving. It is just a very risky type of flying and generally people that do what you’re looking for are building drones specifically designed for it. Your range on this build is going to be limited by factors other than the battery, like the 350mw vtx, anything over 1.5-2km should be pushing its safe limits. Flying out 5-10km and diving a mountain probably isn’t possible on that drone, no matter the battery you pick.
When someone says mountain diving and 5-10km, I think of a 5”-7” with a +1w vtx and 6s-8s batteries.
To answer the question directly, a higher capacity 4s li ion might give you a longer hover time, but the drone will no longer have responsiveness and might fall out of the sky. Especially if you have to keep it at a high throttle and overheat stuff or fry the battery. The batteries you’re trying to compare aren’t really comparable and will make the drone fly completely differently between li ion and lihv/po. You’re still doubling the weight with the li ion and a 6:1 ratio isn’t very good, plus you’d probably only be getting that at 100% throttle.
If you have money to burn, try the li ion, if not, stick with the lihv/po. The 850 mah should give you an extra 1-3 minutes and you’ll still have high C discharge and all that. Even between my 4s 720 mah and 850mah I notice some difference in flight characteristics.
If I’m wrong about any of this or missing some info, I apologize, just want people to fly safe and happy!
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5sett.
Autore
Ok, i was just looking at drones like the deepspace roc 4 and wondering if my drone could do that. Thanks for the input!
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5sett.
try some different props types as well, like bi blades. I should have asked what drone you have because there are other things you can try to get more range, even if it isn't diving the matterhorn. a higher wattage vtx can help with more range, but more importantly the penetration and reliability. nothing wrong with pushing the set ups you have, if you can look up the motor chart for your motors, you can calculate how much weight you can carry on different voltages and prop types.
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5sett.
Autore
@AurilFPV currently limited on range by battery, i have a homemade 5 turn helical antenna on my goggles (ev800d) and have flown to 2km on lipo. I like the prop idea and will give that a try, and also get a 850mah 4s, it should help a lot because my current 720mah lihv is a bit degraded. I have a really long antenna on the quad, so my signal is just as good when flying toward and away from myself. What are your thoughts on a 1100mah lipo?
Also the oscarliang.com motor chart recommends 450 to 850mah for freestyle for a 4s 3in triblade build with a lower kv motor (3000 to 4200, i have 4600)
As far as adding a higher power vtx goes I cant fit anything larger than the current zeus nano in the frame. I can increase video range with a 7 turn helical though, so i will probably make one of those.
Thanks for the feedback!
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5sett.
Oscar Liang is awesome, but there should be charts from the manufacturer specifically for each motor model and kv as well. Thats really awesome making the antennas for the 800d! you definitely know your rf stuff, explains the range youre getting. What are the motors?
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5sett.
Autore
Found a chart for the lannrc 1404 4600kv + motors, and it is from testing with a 4024 prop. I currently am using 3016 props so it isnt all that useful.
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5sett.
well thats frustrating, I hate it when they do that. but we do know you will get less thrust with the 3", so this does give you some numbers to go off of. Pull: 398g x4 = 1,592g at 100% throttle. Thats what you divide by the drone weight to get the thrust to weight ratio, the higher the more responsive. The 3", depending on number of blades, pitch, etc, is probably at least 30% less powerful than the 4" on the chart. So your ideal total weight with battery is 140g-185g for responsiveness, but the absolute max should be around 278g for just cruising. I would also just assume the max amps for the motor in general are around 15A, so you want a battery that can do 60A burst discharge and is rated higher than you think your average throttle will be. If youre unsure, add current/temp sensors to the osd and keep an eye on them, there's also an 'average throttle' option for the post flight stats menu in betaflight.
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5sett.
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Unfortunately i cannot get any good 18650 pack that weighs less than 124g. I could make a 145g liion, but it would be 3s, further reducing thrust. Drones like the Deepspace Roc4 sit at around 4:1 thrust to weight on a 4s 3000mah liion pack, at an AUW of 380g. They use 4024 bi blade props, and 3000kv motors.
My drone isnt built for long flights like that drone is, so i think i will just stick to lihv until i get a bit of long(er) range experience under my belt. I may reconsider in the future, but that will work for now. Who knows, maybe ill just build a 7in! Thanks for the help!
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5sett.
its genuinely impressive that youre getting the range on the 3" that you are. I think thats why I was confused in your initial post, most people aren't making their own antennas, but that explains it. I was in fact wrong lol.
If you really wanted to, you could also try to see if your current components would fit on a 4" frame and transfer them, but I personally think it's more impressive maxing the 3". Your problem isn't the majority of flying/cruising, it's the 10-30% of the time that you need to pull out of a dive or quickly get over an obstacle/hiker, etc.
Looking at your 3" and rf abilities, you'd probably be pretty happy with/enjoy building a 7". Bigger platform opens up possibilities for different components and payloads like 3.33mhz or gemini and potentially carrying a relay or meshtastic node, if youre into that as well.
If you want to look at better baseline video systems as well, Rush is very well reviewed for analog vtx, especially for having a clean signal. Hdzero is probably the most innovative goggle brand right now, their built-in analog receiver is great and the platform seems friendly to experimentation. They even make their own antenna filters, which is a nice touch I guess.
Post the goggles and homemade antenna! It'll get some attention here and Im certainly interested in seeing it!
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5sett.
Autore
Ill post an update with the antenna setup and a long range flight as soon as i get that battery in, and a longer distance. Im ordering a 1100mah 4s lihv 60c, so my build will even stay sub 250.
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