How do you choose motor KV for a build? - FPV Questions

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[@Theextremepessimist]

I’m basically living on your channel at the moment.

[@taylormayhew369]

same

[@brucebaxter6923]

Short version, Prop tip,speed needs to be around Mach .85 Pitch to diameter is about 1:1.5 Run the lowest kv and highest voltage you can to get that speed

[@Mxoderberg]

I believe Chris Rosser has some videos on motors and also props that gives you a good understanding and a clue on what you should get.

[@anthonyzanze5946]

Another vid that I didn't know I needed until I watched it and then watched it again. Love your vids! Every one is like having your own ecyclopidia that's hands on and has pictures! The fpv community thanks you!

[@NotOfThisWorld567]

Just built a Babytooth 2mm. Have TMotor 1103 11,000 KV's on 2s. AUW of 62.06g. Using Gemfan 3018-2 bi blades. It is the quitest and fastest quad I own!!! I absolutely was blown away today by this little monster! I am a newb with quads but have a few builds under my belt now. I thought I'd like my Apex Micro 4" 5s with 2004's better but this little 3" has my heart. It's all about the power to weight ratio. FPVCycle's KaBob dude is THE MAN!! Look at his builds and try to follow his guidelines for MAXIMUM pleasure in the air. Thanks Bob!!

[@jackr4731]

That's me

[@killsme6957]

I love it how it was explained, honest and helpful.

[@WeatherWorld]

Very useful information here! Thanks :)

[@nickbrown7700]

You've helped me again, Joshua. Thanks!

[@Drizzer_Fpv-py7cy]

Can you make a video on how to pick the right prop without burning out your motor

[@SkeezyFPV]

Thanks! It’s only 08:41 and I already learnt something today, JB. Yesterday I went to a local hobby shop and learned ama model airplane guys don’t like quads hahaha. I’m a noob that’s been flying BNFs and I’m finally wrapping up my first build; an aos Cine25 with an o3 air unit. Now I get to learn about BetaFlight. Btw, thanks for teaching us about wtfos butter. I was able to roll back the firmware on my v2 goggles this past week even though I was already on the ‘bad’ version that couldn’t be rolled back prior. It worked ‘like butter’! 😂

[@anubhavsingh2916]

Motor yeyeye --------- it's hot 🔥😎

[@RCRitterFPV]

I use site "warp drive Prop tip speed calculator" aim for about 600 mph Max tip speed. I use 3.7v per cell.. 4s = 14.8 6s = 22.2 5" prop * 40,000 rpm = 595 mph... so 40,000 rom / 14.8 or 22.2 2700 kv 4s or 1800kv 6s they list 750 mph as redline when amp draw ramps up exponentially that would be 50,000 rpm on 5" 32,000 rpm for quiet efficient 2150kv or 1444kv...

[@b3owu1f]

The one thing I am unclear about.. batteries put out different C ratings.. how does that affect what motor/kv/etc as well? I see 100c, 50c, 125c, etc.. not sure how that affects the motor/kv, duration, speed, ability to NOT burn out the motor, etc.

[@n4t3RC]

@@b3owu1f that's a completely different parameter and is relating to the max amps that can be drawn from the battery (battery capacity X C rating = max amps). So for a 1500mAh 100C battery, the battery is rated for 150A max. This is independent from the voltage which affects the motor rpm

[@b3owu1f]

@@n4t3RC Really? I had thought the more C the more energy output the faster you could spin motors (or motors that can handle it) and thus potentially more speed? Is that not the case? I also assume the more C a motor could pull, the more energy it drains and thus battery would last less time (assuming full throttle pulling that much)?

[@n4t3RC]

@@b3owu1f A motor will only pull the amps it needs from the battery. Having a battery with a low C rating will mean the voltage will sag more which will prevent the motor from spinning as fast as it needs to. I guess in some way they are related, but only because a higher C rated battery can sustain higher amp draws and therefore the voltage will not sag as much. Its more of a case that the battery can cope with what the motor is expecting rather than the battery being able to put more energy into the motor.

[@b3owu1f]

@@n4t3RC Ah.. that makes sense. So a less capable motor could work well with a more capable battery because the battery has the headroom to handle whatever draw the motor needs right?

[@markuskoarmani1364]

higher KV motors need to spin faster to get same torque level as low kv motor and require higher voltage to match lower kv motor of same size motor. Low KV motors have more coper windings than higher KV motor giving them higher magnetic field resulting in stronger motor per spin. going through winds and pulling out of dives with low KV motor will do it with ease and lower energy. Yu can run higher pitch with low kv motor giving you even more thrust. Free style will choose low KV motor as speed is not as important as torque. High KV motor uses 16volts Low KV uses 25volts. 2400kv x 16v = 38400 max rpm 1850kv x 25v = 46000 max rpm 700mah 4s on my 1.5inch drone with 8000KV motor will hover 3.5min Same battery 700mah 4s on my 4 inch 1404motor 2750kv will hover for 7 min. drone 1/3 of weight with same batt has 1/2 the hover time over heavier drone and larger motor. Its a torque per spin raatio that counts and not KV alone.

[@GR33ZY.A1]

Running ARRIS 2306.5 1500KV motor on racing drone. Is says to use 4s . Am I able to use 3s lipo?

[@Kleinage]

@@GR33ZY.A1that’s a thicc motor, I’d stick to the recommended voltage battery.

[@cameronbest]

Are there any databases that people have put together where we can see this motor testing that JB is talking about?

[@bearbeefpv]

yes

[@paulhope3401]

Miniquadstestbench... hasnt been updated for a good while but should help provide a basic picture.

[@bhood7058]

You talk about testing different motors and props, that would be very expensive. Is their a formula that one could use to determine what size motor and prop one would need?

[@dilbertmcfly5986]

Which KV? prop inches * KV * Cell Count = Magic number ("56") 7 * 1.350 * 6 = 56.7 5 * 1.880 * 6 = 56.4 4 * 3.600 * 4 = 57.6 3 * 4.500 * 4 = 54.0 Working backwards, 56 = 2S * 3" (babytooth) * KV. KV = 9333 If very light quad, and light prop, you can go a bit higher KV. Heavy quad, especially CINE, go lower.

[@nevillecreativitymentor]

How can I resolve KV ...for a given AUW ? IS it impotant to know the Flying Speed? Is KV somehow related to the Can size? (this I have always wondered!!)

[@Quad8ightMix]

Need help...What aug size of cable use in iFlight Xing 1404 5500kv? Thanks for your future response

[@zbigniew4370]

Perfect explain

[@WindjumbieFPV]

I like high rpms so I just choose one of the highest KV in it’s rated class

[@Alexa-oz6sm]

1100kv motors for a 5inch drone which will be around 600gram and a 3s battery. Is that suitable?😅

[@breckfreeride]

How does this translate to fixed wing? Just go for thrust? 2207 vs deeper bells?

[@pir869]

I,m a total noob to fpv,not even tried out my sh eachine novice3 yet(had it for a year now). I'm an electronics technician,i don't work on micro controllers i design audio stuff for musicians and myself,though i would like to design a drone/quadcopter of my own. My novice3 came as per the eachine kit plus a T16 controller,i was wondering from looking at the novice 3 that as it is pretty much a modular design,could a cheapo drone from ebay be stripped to allow the RC control to control a larger power distribution board for larger motors and larger capacity batteries,also change out the camera from a pos to a decent unit. I can't find any good books on drone building at this level,more like lego kit implementation stye ideas,though it's not far from it as the parts plug together as such though not as simple in total system build. The whole thing comes from flight time and cost of 30+ minute FT drones,carbon fiber tube etc is cheap and i have a lathe and a mill,so titanium end fixings to quad body etc etc can be made quite easily to get bigger props and motors onto the cheapo body to keep weight down and make a longer flight time light weight ripper,sort of. If the power distribution board is modular and not part of a control board in general,though some cheaper drones might have a control/poer dist board like cheap PCs have integral video cards etc,but if the control and power dist are separate would you say this can be done easily,electricaly speaking,obviously high thrust motors could rip a flimsy motor arm mount off the body. I'm spit balling,but from a power management viewpoint it would seem that the input signals from the RC controller unit on a drone will be of a pwm nature with a combination or both of frequency control or mark space ratio control ,whatever combination is used to drive the motors the input signal i think should be a universal sittuation,with the power output control suited to the power needs of the motors. Over all a drone of under £100 uk seem plentiful ,like i say extended motor arms ,bigger motors and the necessary change of distribution board bigger capacity batteris and if needed a small buck converter to feed lower voltage components if larger battery capacity is too much for original controllers etc. Seems from a design angle of not knowing enough of the system as a whole ,but still an educated guess of a system implementation from control to power regulator upgrade,the basic idea looks interesting ,even if if kills a cheapo pos drone. Any ,and i mean any (possitive) input welcome,any direction pointers to literature on building from scratch. I should add i do make power controllers,that can be logic controlled or from analog push button,so the signal level shift from input to output is well understood,just not the whole concept for drones. Great vids,and subbed. Cheers.

[@madfpv3154]

I understand as something slows a motor down from the speed it wants to spin it gets hot. My question is so on the ummagod 2fiddy when you run 6s but limit the motor to the 69% or whatever it was will that make the motor run hotter as well? Or no because that is the FC limiting power to the motor?

[@jeffreygardinier4836]

I have a ? I have a DJI fpv drone. Can I put a bigger motors on this drone. I can’t find anybody that has done this

[@pepetelacrosse]

Once we know the rpm what? All websites tell you the rpm like this data would solve all our doubts

[@harleyqueen1337]

Is 2050kv the best for racing? Why not the 2500kv ?

[@american7169]

I have a 3" build that had flywoo 5500kv 1203's and flew really good but I wanted more power. So recently swapped with 1404 6000kv. Running on 3s. I notice no added power and my amp draw is way higher and flight time sucks now. Tried different props but still sucks.

[@Markq666]

I have 1404 4000 KV on my siren f 3 3” 4s

[@DanielBarrios83]

What batteries are you using and what flight time do you get?

[@willappleton]

hi.. seem like you might be able to help me please.. the esc/reciever i have says 7A/2S or 5A/3S is this ampage rating continuous current? if so, the 2s has higher power?? 2s current is 7a and 3s current less is 5amp??

[@willappleton]

why does the motor ratings show 2s 8v going up to 11.6 amp?>

[@funy0n583]

Didn’t tell us how to pick the correct motor you just told us to copy someone else 😂

[@daze8410]

00:16 Tell me you have a 3 monitor set up without telling me

[@slogan9105]

high kv just limit the RPM in BetaFlight

[@Kirmo13]

Ultimately, Kv is a shitty way of rating motors. Torque and power would be much more useful. In a car it's like comparing the max-rpm to fuel consumption ratio to determine which motor is more powerful.

[@memelol7167]

Can you gift me a drone on the wall behind you?😪😪

[@ourchannel8215]

my build is 600g 1850kv 6"prop, new 1100mah batery just fly 2-3 minit 🥴🥴🥴 what happening guys???

[@nicholasweiss4662]

I hope youre joking, but if not: That build is way too heavy for a 1100mah battery. Im not sure if that number invludes a gopro or not, but here is some advice: Check how heavy your frame is. Especially older Frame styles like the ZMR250 are very heavy and weaker than newer models. 1100mAh is kinda low for 6". 1850KV is on the high end for 6" on 6s, so either get low pitch props or go down to 5s or 4s. You could also change your motors to something that works better for 6s and 6" though that will be mkre expensive than getting low pitch props that will be more efficient anyways. Lastly: 1100mAh 6s is a common size for 5", but with the bigger lift and better efficiency of 6" props you could go higher, to 1500 or 1800mAh

[@Liam-it7yu]

Props to you for this well explained concise comment. I can just imagine the frustration in this poster’s comment and I can understand it. It can be pretty overwhelming at times to build out your own quad without using valuable resources like fpvknowitall builds and recommendations. Thank you for helping this guy out its nice to see the community helping new people out.

[@ourchannel8215]

@@nicholasweiss4662 thank👍