Motors Watts means Power, yes?

Derek

Well-Known Member
I'm trying to decide what motors I should be purchasing for a quadcopter build that I'd like to do but I'm horrible at determining this part of the hobby.

I've heard it said, if a motor/prop shows 400 watts (test run on my watt meter/tester), that motor/prop combo can lift a 4lb model. Is that accurate?
 

RandyDSok

Well-Known Member
Watts and power are the same thing.... but...

To calculate thrust ( what you are asking ) and speed will depend on what prop it is and how fast it is turning.
 

Smoggie

Well-Known Member
As Randy said.. Watts are units to measure power, like inches or centimetres are units to measure length.

Power and thrust on the other hand are not the same thing and cant be directly linked. For example at one extreme it's possible to lift over 100lb with 400W if you have a large enough and slow enough tuning props. For proof of that check out the Atlas human power helicopter that lift a few hundred pounds with only one human power (maybe 500W?)
 

Derek

Well-Known Member
Ok. I appreciate your replies. Unfortunately, those aren't the answers that I was looking for and that's entirely my fault. I need to get more specific.

I want to build a large size racing quad. Most likely, 550-600mm sized, on 6S, and I need help selecting motors/props. I had an idea for a motor/prop combination but, based on the math (if I did it right), it will most likely be a VERY inefficient setup and I'll likely damage the batteries pretty quickly....so, I've given up on that particular setup but I've not given up on the project.

To select motors/props, you'll probably need to know the AUW of the quad. I can't give you that number because I don't have it built (not even started, lol). If I had to guess, I would guess that the AUW of the quad, with a 6S battery on board, will be in the area of 5-6lbs. Being a quad of this size, there will be enough clearance for 12-14" props.

Can you guys help me select some motors that will suit my project?

I was looking at these motors yesterday with curiosity:

Quanum MT Series 4108 475KV Brushless Multirotor Motor Built by DYS
 

Smoggie

Well-Known Member
That motor would fly it but if you want something fast you are going to need something rated for around 1000W, so a much bigger motor.

APC published some really good prop data: APC Propellers The list includers their range of multirotor props (suffixed 'MR'). A 470Kv motor on 6S would spin the props approx 9000-1000RPM, so you can pick the prop and see what thrust and speed you could get, and the power required.
 

Tony

Staff member
160 amps, now that thing would have some lifting power. And those props are bigger than my 540 props lmao.
 

RandyDSok

Well-Known Member
Now to step back into reality...

While on the surface it may seem to be a simple question, in fact it's much more complex question that many may think unless they've done a lot of custom scratch builds before. There is a ton of info available on the internet about what users have used for any specific make/model of a RC craft as well as the info ( if they provide it ) from the manufacturers may recommend. The trouble is that the info isn't available from any one location or place... That is a pretty large question when you are talking about a known make/model... add to this that now we are talking about a model that hasn't been made or completely spec'd out and now coming up with an answer becomes close to impossible.

This is what I did when I was looking for the impossible when it came to scratch building an airplane ( which there is much more info on than there is on multi-rotor craft ).... I take the information that I know or have a close estimate of.... then I look for existing models that match ( as close as possible ) the same set of specs that I'm looking for. Now that info gives me something to base a search on and then I can see what others have done for their craft and how well they feel it works.

When looking for actual motor data... you probably won't find it ( or much or it at least ) listed with the cheap motors found on sites such as HobbyKing, Gearbest, Banggood or similar sites... More often than not, those companies can care less about providing any real information, nor do the manufacturers of the products they carry. If you want real info on motors, look at the websites for known quality manufacturers first... When you find motor specs that you think will work, if you wish, you can now use that info to find the cheaper motors from these other places, just don't expect the quality or performance of a top end product in the bottom end products that many of these places carry.


It' s not going to be an easy search in many cases.... but often the end result and the experience you end up getting do pay off in other ways. I didn't do a lot of this myself ( just a foamy or two ), but my Dad did nothing but this during the last years that he was able to enjoy the hobby ... even today he still creates some of his own foamy planes to play with but at 84 years old, he doesn't do much of it.
 

Derek

Well-Known Member
Randy...I sure do value you replies.

When it comes to my scratch built planes, I do a similar thing when I'm searching for electronics. I take the specs of my "built" plane and simply compare it to actual models that are sold and then order electronics that are similar. So far, that method has worked real well. You are quite right about the lack of info on the net about multirotors, especially custom built scratch builds.

Perhaps I should just get my custom quad built and then search out electronics. That way I have an airframe weight.
 

RandyDSok

Well-Known Member
Perhaps I should just get my custom quad built and then search out electronics. That way I have an airframe weight.

That's probably where I'd start... then look to see if you can find a comparable model and see what specs they have for their motors etc. It would give you a place to start.


Come to think of it... that's not where I'd start... I'd start with an airplane... LMAO ( couldn't help it )
 

Derek

Well-Known Member
Come to think of it... that's not where I'd start... I'd start with an airplane... LMAO ( couldn't help it )

ha ha ha...I saw humor in that!

I'll work on getting my custom quad frame built. However, once the frame is done, I won't really be able to compare it to anything else on the market because I've not seen another 6S big quad. There is a guy that I've seen on YouTube, he's built a 700 sized quad and runs two 6S packs. I've asked about his quad and he replied back, "Due to safety and liability issues, I'd rather not share the specs of my build." To an extent, I can understand that.

I'm not looking to make my build go 100+mph but if I could get a solid 40-60mph, that's probably going to be intimidating enough to satisfy me.

Here is the video of that guys 700 class quad:

 

RandyDSok

Well-Known Member
I'll work on getting my custom quad frame built. However, once the frame is done, I won't really be able to compare it to anything else on the market because I've not seen another 6S big quad.

Then you should look at the DJI stuff... ie the Inspire or any of the commercial series... all are 6S ( although the Commerical ones are octi and not quads )
 

Tony

Staff member
And stupid expensive as well Randy. Way more than building yourself. IMO, they are about a grand over priced.

That video has me wondering about his response. In the end of that video, it says something about a release date. Has me scratching my head.
 

RandyDSok

Well-Known Member
And stupid expensive as well Randy. Way more than building yourself. IMO, they are about a grand over priced.

Considering that most of theirs are complete packages with radio, camera and everything else... they probably aren't that far out on price.... But the point was that there are 6s systems out there which, given a little research... means there are some specs that could be used to start parts shopping from.

I've seen both a Phantom 2 ( a 3s setup with the basic camera stuff ) and an Inspire 1 ( unknown on which setup ) and both worked great out of the box. The owners just needed systems that worked and didn't want to have to build it themselves. The Phantom owner was using it for genealogy research at cemeteries to capture videos of the headstones that they could later transcribe and document the locations of each gravesite. The Inspire was being used by an oil and gas company for whatever they were using it for ( we didn't get into that part but they started with a Phantom and had moved up ).
 

Derek

Well-Known Member
I've looked around and I've seen that there is an E800 motor (3510-250kv) motor that they use for the Inspire2. I've seen no specs on that particular motor that show max voltage, max amps, thrust, nothing.

I was looking at BuddyRC (love these guys). They have a T Motor MN3520-11 400KV motor that can run 4S-8S. Max Amps - 38 and they show a table of specs of testing 6S with 15, 16, and 17" props. Here is that motor:

T Motor MN3515 KV400 Brushless Motor

I'm thinking this T Motor might not be right for my build because I'm expecting 12-13 props
 

Derek

Well-Known Member
That video has me wondering about his response. In the end of that video, it says something about a release date. Has me scratching my head.

The "Release Date" was the date the Brian first shared the video of his build.
 

Tony

Staff member
Ah, okay. I was thinking he was going to release the plans or something on it at the time.

Another thing I noticed was that the large quad was not very fast. I'm sure it's powerful as all hell, but just didn't seem that fast. I know you were talking about up to 60mph, not sure if that quad could get that done.
 

Derek

Well-Known Member
I fully wish that Brian would release build plans for his 770 build. That would be awesome to see. I did message him and I asked about his electronic setup. He replied, telling me that he didn't want to share the details due to safety liabilities. To an extent, I understand that, but if he were to share details and I were to build the quad and something "bad" happen, in no way could he be held liable. It wouldn't be his fault if I went out and did something stupid with it. All that he did share was that he was using a Naze32 fc and 2 - 6S packs, to handle the amp load.

I'm going to continue to look for motors because I am going to build this thing. Practical? Probably not! Will it handle like a mini quad? ha ha ha, not a chance! Will it hit 50-60mph? Who knows! But....It's a unique idea and a unique build....and, since I got the wife's approval....I can't help myself.
 

Derek

Well-Known Member
I'm still shopping around for motors but I'm running out of sites to look at. Can anyone share some sites that I could look at for big 6S multirotor motors?

I've looked at:
Hobbyking
Hobbypartz
GraysonHobby
ReadyMadeRC
BuddyRC
StoneBlueAirlines
HeliDirect
 
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