HELP!!! Newbie brain fry!!!

[ROVguy]

Ok, so Ive been looking into the forums for a while now and trolling the internet trying to get as much information I can about MRC's before I end up purchasing. Ive pretty much decided to go with the DJI F450 or F550 kit with Naza+GPS and bits 'n' bobs (Ive got a £1.5k budget so this could change unless I decide to jump into FPV straight away). Ive found a lot of information during my research and it is slowly penetrating my thick skull. However, trying to get my head around the Lipo - motor - prop = thrust + flight time correlation is making it hurt!!! I just dont get it! I think the 2S, 3S, 4S thing is the number of cells and thereby the voltage of the battery? Im not entirely sure what the other specs are, although I know the mah is the capacity of the battery, the bigger the number the larger the capacity, but also more likely the greater the weight? The 25/35C, 30/45C bit confuses me a bit, is it the amount of current the battery can provide?

Basically what Im trying to find out is what goes with what with respect to the battery, motor and prop. Do you go with a larger prop and slower motor to have greater lift or smaller prop and faster motor? What battery type would you need? If you change your battery type would you need to change your FC given the change in voltage? Given a few comments previously on here Im presuming the size of the prop also has a baring on the stability of the MRC and its performance and handling in the wind?

As you can tell my heads a bit mushed up and I think Im starting to lose it a bit. Any help any of you guys could provide would be very much appreciated.

Richard.

PS. Whats the general consensus of Radio Transmitters? I was thinking of going with the Spektrum DX8, but after having a look around on here Ive noticed a lot of people use Futaba and that you can incorporate UHF modules with them to get greater range? Theres this DHSS and FASST malarkey. Which way do I go? Would it be better to go for something with more channels for future usability or just stick with the 8 for now and upgrade again later? I can get the Futaba 8FG Super 14-channel S-Bus including all the gubbings for an extra £130 over the DX8. And whats this S-Bus, PPM, PCW all about? Whats the advantages disadvantages?

Sorry for dumping all of this on you.

 

[Bartman]

top

 

[kloner]

slid right by

2s = 2 cell, 3s = 3 cell and so on. Each cell is 4.20 volts, fitting... lol

25c, 30c and so on is a way to tell you the maximum amp load it can support. it is calculated like that cause the actual number depends on the mah. If i have a 1000mah 25s, it does 25 amps. if i have a 2000mah 25s i got 50 amp service and so on. to make ya a tricky one in case your following along with a calc, i use 4000 mah 40c,,, 160 amp service. Whats all this mean at the end of the day, the internal resistance inside the pack. the components that tie the celles together, the quality of the products used, the quality of the polymers, it's a little of everything that makes it happen. From the day you get a fresh pack till the day you throw it away, anything yo do wrong increases that internal resistance so a 40c pack gets down to a 30c pack then a 20c pack then it won;t support what your flying and you throw it away. normal use it falls single digits slowly over time, one over discharge, overheat, anything bad will increase IR by double to tripple digits at which time the pack is done. I look at individual cells and when i get one rising uncontrollably and hit hits a double digit it goes to ground equipment or trash

What motor/prop/battery...... in general the higher rpm and smaller props fly better, but at a point don't make enough thrust to lift what you want to fly. A typical 450-550 runs 900 kv +-100...... flies all around good but start adding much weight and your draws go up, it gets to the point you can't make enough watts to lift what you want. in a naza, and most likely alot of others you want it to lift and hover at mid stick, gives the motor the most control over itself, if it needs to drop a motor to stay level, it has alot of range to change them all through the algorithym the fc is using. speed this, slow that, everything sits niice and as smooth as can be. if it's running too high in the throttle range, it can pretty much only slow a motor, not alot of room to increase the other and vice versa for to low of a hover throttle, like hitting a hill in 12th gear in a 18 wheeler, your looking for a lower gear fast and your mr doesn't have those........

changing cell counts involves changing props and that does involve changing gain settings, not neccesarily fc's.

the difference between spektrum and futaba is night and day. not so much in the feel although that is growing on me,,,,, it's the link between the radio and receiver is just rock solid. fasst is there old technology. it is proprietary and the rx's are expensive. FHSS is what all the aftermarket long range systems use. it is reliable and what i want

sbus is a single wire that comes out of a receiver into the FC, it is proprietary to futaba which is why dji calls it D-bus, in the case of an 8fg it has 14 channels coming out of one wire......

ppm is a common long range receiver protocal just like sbus. one wire coming out of the receiver carries all the channels the rx has.

pcw is servo wires lanquage, it is ppm or s-bus interpreted at the rx,,,,,,,, if you use this mode to get those 14 channels to something, you'd use 14 servo wires from RX to FC

The biggest reason to have way more channels than you need is alot of fold. they have more switches and dials to assign stuff to. they have a future with you longer than you think, you never know what your next hobby is. if it's big planes, eaach control serfuace have multiple servos. Having the extra channels makes setting up and using a breeze without a bunch of aftermarket parts to let you trim each servo, etc. there is just so many reasons to get the biggest you can i can't even think of them. Probably the biggest thing though is feel. Gimbles with more bearings, smoother movements.

 

[DesJardins]

I have wanted to try Futaba for flight even though my DX8 hasn't caused any issues but that people rave about Futaba and it's reliability/distance.

I ran all Futaba 4PKS Tx's for racing but I hear Futabas Air Tx's are a little more
complicated to start with

 

[kloner]

range wise,,, i used spektrum ar8000 on a jr 11x so only had dsm2, but it'd failsafe alot, i've seen alot of spektrum guys here not have much range. I've gone 2200 feet, but failsafed turning around everytime. i've seen a guy come here and tell us he went a mile with a dx8,ar8000 in dsmx, but i also have ran into alot using that and getting 2200 feet just like me before it started glitching all over and entering failsafe in and out. I'e ran into alot of futaba guys that fly a mile away. I tried to get a verified by me distance in the wide open desert i fly and when i got one chance to check it out, the eagle tree sat wouldn't lock in but i know i went further than 2200 feet a few times, just not sure how far, that was with a 8j using fhss and the stock receiver it came with

the fhss i think carries over from ground. it's a algorithym that runs to keep it hopping channels so it doesn't interfere, same as fast, dsm2, dsmx just royalty free. whatever that is JR went to same thing, spektrum owned dsmx and the break up between the two companies forced JR to move on with there technology

I'm pretty sure futaba is going to fhss as a standard though nobody told me, just makes since in the market environment that is shaping now.

 

[DesJardins]

Very tempting

I always trusted my Futaba 4PKS over all the others and it seems like Futaba is ahead of the game with a better tech moving forward.

 

[ROVguy]

Thanks Kloner, I very much appreciate the time you took to write that, its a great help. So basically S-BUS/D-BUS or whatever, is a manufacturers proprietary method to multiplex the control signals and transmit through air or down one wire, saving space etc.
The battery thing is also a great help, would I be right in saying then that you start with the motor you are running, see what the max current draw the motor can handle x the number of motors and match the battery to suit and increase the mah of said battery/s depending on what flight time you want and use its weight as a limiting factor with respect to the flight time. If you need more thrust to contend with the increase in weight then you'd increase the size of the props and change the motors so the speed rating suits and start the whole process again. Please correct me if Im wrong in any of that.

The Transmitter issue is a difficult one. Regulations are a lot stricter I believe over here in the UK. We are restricted to 25mW VTX's so that in itself limits the range we can fly to horizontally or so I believe and we have a 400ft ceiling so I cant go very far that way either (legally) would there be any benefit in my looking/paying for a FHSS system when I cannot take advantage of its benefits? What is the range of the 8FG super (or any other 2.4GHx transmitter) anyway? The number of channels thing I totally understand and its one of the reasons why Ive suddenly thought to change from the DX8 to the 8FG Super, I have aspirations of having a full on AP system with 2/3 axis camera mount etc and I could always make use of the other channels one way or another I guess. With regards to feel, I cannot comment on either as Ive never held either of them. I may pay a visit to the local RC Hobby store in Barnsley (Ive got Fast Lad Performance on my door step) and see if I can get a feel of them.... once I get home (just 3.5 weeks to go!! Not that Im counting! ;D )

Again thanks very much for your help.

Richard

 

[kloner]

it does seem more for teh hobby and less for the same small group oof guys wallets. I used to be a die hard horizon guy. if they had it, i knew i'd be taken care of but that's not the case anymore. Seems like since the dx8 fiasco they had when it was released made them tighten there belts tight. I used to buy $150 servos and if you had a problem, didn't even have to think about being taken careof then it stopped and they just wanted to sell you new ones at a discount...... ok..... never mind. stuffs not that good

the grass is greener and i wouldn't hesitate to switch. in my case it has a great feel and going form an 11x to the cheapest futaba was weird at first, but the performance made me forget all about it. Got kids, dogs on a boat, figured i needed one that could get dunked and me not loose sleep over replacing.

 

[kloner]

we cross posted so i didn't answer ya there

yes, cleaner, less wires to fail, lighter and makes less interference with a bunch of little antennas laying there in the form of servo leads.


motors, yea and no, you need to make sure your buying enough watts to lift your goal. then you need to weigh prop space to voltage of packs you run to make your kv decision. in rc helicopters, 450 size used to all be 3s and 2800 kv motors, then 4s and 2000kv motors, now they all run 6s and 1200-1400 kv motors.... why, more watts and less draw. I'd look at lifting weight in the same light. You can work it out in e-calcs and apps, or ask if your not familiar, just need to know everything it'd lift weight wise, how many motors, to fly or hover, etc. and somebody here is doing it and knows a good choice

i don't think fhss is more, in fact i know it is less. fasst receivers are $110-$300,,,, the futaba fhss like used in 6j, 8j and i believe next years radios is fhss from the factory, 8ch receivers start at $30

the lrs fhss stuff i spoke about is another deal all together, i was pointing out that is open and not proprietary source, it is the future for it's reliabilty........ i think the old fm 72 and whatever you guys had, 26mhx i think was fhss... not new, but reliable. jr added some proprietary ways of looking at it and had some thing like fasst and dsm back 30 years ago

The feel is this, when i back off the tension form my sticks to not make them so hard to move, it stops centering on it's own fast. on my jr you can back them off so far you can barely feel the tension and when you let go, it centers perfect.

When you move a stick on a higher end radio, it feels like you paid it...... like pabst blue ribbon vs. micro brew

that euro video stuff is better answered by somebody form your region. we run 1 watt max but everything else the same as your description not by law, but by ama code

 

[ROVguy]

Thanks again Kloner, your a star! I think I will reserve judgment on the transmitter thing until after Ive had some in my hands. By the looks of it you can only get a max of 8 channel FHSS systems with Futaba and I think Id rather have the channels than the range at this moment in time so it may well be the FASST based transmitter or equivalent. Besides, if youve only got an 8 - 15 min flying time, how far can you go before your having to turn back?
The CAA regs over here are backed up by the law, if you break the regs... you are breaking the law. I will stick to whats written down in the regs and if its 25W VTX's and a spotter, then so be it. I dont particularly fancy getting friendly with Big Leroy in my local Nick!

Thanks again!

Richard.

 

[kloner]

Besides, if youve only got an 8 - 15 min flying time, how far can you go before your having to turn back?

Thanks again!

Richard.

i can get about 2 - 2.5 miles by calculator,,, only been 1.5 so far,,,,,, but i'll do it just to do it

 

[DesJardins]

Shoot within a 60 seconds I have seen somebody go so far it was a spec in the sky.
Pretty crazy

And it was hard to see through binoculars

 

[kloner]

When i leave fpv and just fly off, i see it for about 10 seconds and it's gone. Sometimes i'll hear people around say oh there it is, but i'm like a mile away, they must see a speck, i can't see squat except out the monitor

 

[ROVguy]

Crikey! I didn't think you could cover that kind of distance in so short a space of time. It's a scary thought if I'm honest, it's a hell of a lot of land to cover to find a crashed/missing copter!


Sent from my iPhone using Tapatalk

 

[kloner]

ya know, that's a good point but in all honesty, If it was easy to loose a model, kloner would have lost alot of em. if the flight controller doesn't failsafe in an auto pilot situation like we have now in these, they fall as soon as you can't figure out the right way to move the stick. not self leveling MR's and even Single rotors don't stay on axis very long, ever. planes are the furthest thing i've gone after and it's not usualy very far away..


Now i've heard of self leveling mr's climb out and leave, i've heard of single rotor helis that get in a massive piro hold level, climb and leave, like a bad failsafe setting........ but normal every day flying and loosing, really hard to do without a failure of some sort with the planets aligning and you walked under a ladder, broke a mirror