Simple Frame/Prop/Motor calculator for beginners

W

wolph42

Member
Disclaimer: beware I'm a beginner myself and created this out of necessity but I CAN have it wrong so recheck before you commit yourself to these numbers!!!

Yes there is ecalc, but getting started if really hard if you have absolutely no inclination of where to start. This calculator works when you have chosen a frame! It calculates the max diameter of props you can add to it (basic geometry, but slightly annoying to calculate). Secondly, based on manufacturers suggestions I noticed a linearity between prop diameter and KV for motors. Hence if you know the frame, you can calculate the max diameter for the props and from there you can pick the generally suggested KV for the motor. Obviously you can deviate from these calcs (although I would not suggest to go for bigger diameter props if your frame does not allow it ;-D) especially if you require a lot of thrust for a heavy payload you'll need to go low in the KV.

In the end, when you've selected all the components make sure you cram them in ecalc to get more exact number. This tool is really just intended as a rough guideline for beginners so you know where to get started!!

Here's the tool:
http://bit.ly/1gmDQ3E

feedback, suggestions are most welcome!!
 
Last edited by a moderator:


SoCal Blur

SoCal Blur

Member
wolph42 said:
Disclaimer: beware I'm a beginner myself and created this out of necessity but I CAN have it wrong so recheck before you commit yourself to these numbers!!!

Yes there is ecalc, but getting started if really hard if you have absolutely no inclination of where to start. This calculator works when you have chosen a frame! It calculates the max diameter of props you can add to it (basic geometry, but slightly annoying to calculate). Secondly, based on manufacturers suggestions I noticed a linearity between prop diameter and KV for motors. Hence if you know the frame, you can calculate the max diameter for the props and from there you can pick the generally suggested KV for the motor. Obviously you can deviate from these calcs (although I would not suggest to go for bigger diameter props if your frame does not allow it ;-D) especially if you require a lot of thrust for a heavy payload you'll need to go low in the KV.

In the end, when you've selected all the components make sure you cram them in ecalc to get more exact number. This tool is really just intended as a rough guideline for beginners so you know where to get started!!

Here's the tool:
http://bit.ly/1gmDQ3E

feedback, suggestions are most welcome!!
Click to expand...

Nice tool to get within the ballpark.

I think the linearity between motor KV and prop size kind of falls apart towards the larger wheelbase sizes. The KV ends up being a tad too high. I think you might be going about it a bit reversed. In my mind, it's really the Motor KV + Motor size that determins the basic prop size. Voltage also plays a part. Since you don't have a database of known motors, you might be able to create a table where the user enters the KV and motor size and even perhaps the voltage or number of cells of the battery and combined with the wheelbase to determine the recommended prop size. Don't forget, prop size is only one factor, the pitch of the blades is another, important consideration.

Still, It's a great effort and will be helpful to a lot of people that may be intimidated by eCalc.
 
Last edited by a moderator:

W

wolph42

Member
thanks for the kind replies

SoCal Blur said:
Nice tool to get within the ballpark.

I think the linearity between motor KV and prop size kind of falls apart towards the larger wheelbase sizes. The KV ends up being a tad too high. I think you might be going about it a bit reversed. In my mind, it's really the Motor KV + Motor size that determins the basic prop size. Voltage also plays a part. Since you don't have a database of known motors, you might be able to create a table where the user enters the KV and motor size and even perhaps the voltage or number of cells of the battery and combined with the wheelbase to determine the recommended prop size. Don't forget, prop size is only one factor, the pitch of the blades is another, important consideration.

Still, It's a great effort and will be helpful to a lot of people that may be intimidated by eCalc.
Click to expand...

linearity for larger wheelbasis: yes they do, but it was not really intended as such. Its basically twofold.
1. first determine the max size prop that the *frame* allows, always good to know when props start eating eachother. Obviously you could use different lengths shafts to omit this issue, but 'beginners' remember.

2. once youve got that you can dig into the motors. And obviously if the max diam is e.g 18, that does not mean that you should get 18 inch props, but you *can*. You at least have some foothold of where to start.
and indeed i do it in reverse but only because of my own experience. First i decide what kind of frame i want, then i have a lookat the parts and the only (direct) limitation is the prop size, so you take that as a start. Hence you derive the motor KV from the prop size.

keep in mind though that although the motors tell you which prop to get, if the prop is too big it wont fit, thats why i created the first part!!! so its certainly not (only) the motors who tell what props to get.

The latter part (create database) is where you enter the area of ecalc and is beyond this tool. This is just to get you started, for finetuning you really need to go to ecalc.
 
Last edited by a moderator:

SoCal Blur

SoCal Blur

Member
wolph42 said:
...keep in mind though that although the motors tell you which prop to get, if the prop is too big it wont fit, thats why i created the first part!!! so its certainly not (only) the motors who tell what props to get.
Click to expand...

I get that... but don't you think that first it should calculate the most efficient Motor / Prop configuration and then apply the wheelbase restrictions? So let's say a 15" prop is most efficient for the motor but the frame will only allow 14" props. So you display 14" props with an "*" stating that prop size restricted to less than efficient size due to frame size limitations... Just thinking out loud :tennis:

Again, I think it's a helpful tool for beginners. Thank you.
 

W

wolph42

Member
SoCal Blur said:
I get that... but don't you think that first it should calculate the most efficient Motor / Prop configuration and then apply the wheelbase restrictions? So let's say a 15" prop is most efficient for the motor but the frame will only allow 14" props. So you display 14" props with an "*" stating that prop size restricted to less than efficient size due to frame size limitations... Just thinking out loud :tennis:

Again, I think it's a helpful tool for beginners. Thank you.
Click to expand...

Yeah that's also possible. That's simply reversing the formula. Basically you could start with any of the three: motors,props or frame and derive the max. For the other two from that yes. I'll have a look.
 


SoCal Blur

SoCal Blur

Member
ahhh.... now we're getting somewhere! Suggested KV still seems a little high when you get to the larger wheelbases but I do like the new min wheelbase and motor calculations.
 

W

wolph42

Member
thank you.

I don't however know what your getting at as i don't give any relation between wheelbase and motor KV. I could add that if you can provide me with sensible data, e.g. a table with a couple of wheelbasis and their suggested motorsizes. The only thing im currently doing is suggesting which motor goes 'best' (factory suggestion) with whch prop diam. And i give the limitation of either a given prop diam or wheelbase. But no relation between wheelbase and motor.
 

SoCal Blur

SoCal Blur

Member
You do it indirectly. You give a prop diameter recommendation based on Wheelbase. Then if you plug that diameter into the tier below it, it gives the recommended motor KV. So, technically, I guess the relationship is really prop size and KV. It's not a big deal, because it is close...
 

W

wolph42

Member
SoCal Blur said:
You do it indirectly. You give a prop diameter recommendation based on Wheelbase. Then if you plug that diameter into the tier below it, it gives the recommended motor KV. So, technically, I guess the relationship is really prop size and KV. It's not a big deal, because it is close...
Click to expand...

Ah ok theres the misconception. I don't recommend a prop diam based on wheelbase. I tell you where the physical limits lie, that's not a recommendation. I do give the recommendation between motor KV and diam but not between wb and diam. I'll try to update the tool to clarify.
 

W

wolph42

Member
ok I've added an extra note explaining that the wheelbase - prop.diam. relation that this tool calculates is NOT the recommended size but the "mathematically possible" size.
 



P

p40whk

Member
Hmm, site doesn't open for me. I might be behind a firewall and it looks like this is in Excel format, any way to share it via google docs?
 


P

p40whk

Member
Thank you for doing that! It must be my firewall preventing me from accessing the original link. The web version worked for me once I made a copy. Nice tool, thanks for your work on this!
 


W

wolph42

Member
added prop diam vs lipo S count to the tool. Its a really flimsy correlation and it should have been better to set the relation between KV and S but that turned out to be even worse.

Anyway as is the entire tool intended: if gives you a rough estimate of where to start with choosing the parts.

I also added more data points so the results should be a bit more consistent. (not much change though meaning that the original set was actually already complete enough).
 
Last edited by a moderator:

W

wolph42

Member
more updates. Doubled the comparison with motors, updated the graphs (if anyone is interested) and added motor-lipo correlation.
(v3.5)
 

You must log in or register to reply here.
Top