Couple of questions...starting with one

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wolph42

Member
Hi newcommer here. I've only recently plunged into this whole jungle of parts and terms. I've started a thread here, basically also to be helpful for other who just start out.

On the way though I see stuff which gets me wondering what it means. So I'll just post those questions here:

Q1.: just encountered this: http://www.hobbyking.com/hobbyking/..._2209_980Kv_14Pole_Multi_Rotor_Outrunner.html
which is a 'short shaft version'. Now I get that the shaft is shorter, but what are the implications of that?? From the specs and the drawings it appears that the length of the shaft is actually 0, if so, to what do you attach the propellers?

Q2: thrust: its quite clear that it depends on the combination of motors and propellers. I'm thinking of a hexacopter which probly comes around 2.4kg meaning I need at least 5kg thrust which means that each motor has to have at least 833g of thrust. But its very hard to find any specs in regard to that. Can someone advise me in this? Either name some motors or a site where you can calculate this (im aware of ecalc but that still eludes me).
 
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SoCal Blur

SoCal Blur

Member
wolph42 said:
Hi newcommer here. I've only recently plunged into this whole jungle of parts and terms. I've started a thread here, basically also to be helpful for other who just start out.

On the way though I see stuff which gets me wondering what it means. So I'll just post those questions here:

Q1.: just encountered this: http://www.hobbyking.com/hobbyking/..._2209_980Kv_14Pole_Multi_Rotor_Outrunner.html
which is a 'short shaft version'. Now I get that the shaft is shorter, but what are the implications of that?? From the specs and the drawings it appears that the length of the shaft is actually 0, if so, to what do you attach the propellers?

Q2: thrust: its quite clear that it depends on the combination of motors and propellers. I'm thinking of a hexacopter which probly comes around 2.4kg meaning I need at least 5kg thrust which means that each motor has to have at least 833g of thrust. But its very hard to find any specs in regard to that. Can someone advise me in this? Either name some motors or a site where you can calculate this (im aware of ecalc but that still eludes me).
Click to expand...

1) The motor comes with a Prop adaptor (look at the other pictures of the motor on the site) That's how the prop is attached.

2) If the specific motor doesn't list thrust at various percentages of RPM, and eCalc does list the specific motor, then I would try to find similar size motors from other manufactures to get an idea. If not, buy a motor that does have specs listed.
 

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wolph42

Member
thanks for the swift answers!

1. ok. I thought that every motor came with a prop adapter (or if they didn't then you need to get one separately).. Keep in mind that I've never had my hands on these things, so its pictures only and the short shaft however eludes me. Had another look at the three pictures but there's not one with the entire thing assembled so no its not quite clear.
But basically it does not matter whether you buy a short shaft or not??

2. could you make a suggestion? E.g. any particular brand that's alway good (obviously you still need to pick the correct model, but preventing buying brands that are known to be faulty will help).

Q3. Is there any website/manual that explains eCalc. I've checked the help and well it *helps* but far from enough. I mean even the first question: 'motor cooling' what does that mean? (e.g. its in the specs of the motor? or its derived from the configuration? and what does 'good' mean?) or 'field elevation' (mASL). Well I can continue in this.
 

SoCal Blur

SoCal Blur

Member
wolph42 said:
thanks for the swift answers!

1. ok. I thought that every motor came with a prop adapter (or if they didn't then you need to get one separately).. Keep in mind that I've never had my hands on these things, so its pictures only and the short shaft however eludes me. Had another look at the three pictures but there's not one with the entire thing assembled so no its not quite clear.
But basically it does not matter whether you buy a short shaft or not??

2. could you make a suggestion? E.g. any particular brand that's alway good (obviously you still need to pick the correct model, but preventing buying brands that are known to be faulty will help).

Q3. Is there any website/manual that explains eCalc. I've checked the help and well it *helps* but far from enough. I mean even the first question: 'motor cooling' what does that mean? (e.g. its in the specs of the motor? or its derived from the configuration? and what does 'good' mean?) or 'field elevation' (mASL). Well I can continue in this.
Click to expand...

HA! I just noticed that you're in Nederland. I was born in Den Haag (the Hague).

They all typically come with some sort of prop adapter. The longer shaft motors were probably designed for airplanes. You usually don't want a long shaft for MultiRotors....not that you can't use them but then there is one more thing to bend when you crash.

T-Motor is a good brand but also expensive. I like SunnySky motors. They are similar to T-Motors but much more affordable. Here's where I get mine: http://www.buddyrc.com/ Many of the motors have the thrust charts listed.

As far as eCalc goes, most of it will make sense after you do more research on things like motors, ESCs, and batteries. Oh, and mASL = mean (average) Above Seal Level. Things like how high you are above sea level (air gets thinner as you go up) Pressure, Density Altitude, all effect the efficiency and thus flying time. Basic Aerodynamics.
 

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PeterLester

Member
DIY Multirotors are significant challenge..... It is literally a multi-discipline engineering task involving Mechanical, Electrical, aeronautical engineering. But hobbyists tend to be very savvy and innovative....To get around the multidiscipline engineering work use eCalc.... but be prepared to dig in and practice with it until you gain perspective on how total flight time is affected by the all up weight, motor and prop sizes etc. eCalc help section is brief as you indicate.

First try to decide exactly how much payload you want to carry, then aim for a specific hovering flight time. You will be surprised how fast the cost of your MR system will increase as the MR total AUW - All up weight increases. Choose your motors and batteries wisely. Many buy undersize batteries c/w too many spares, use them a couple of times and then discovered they have to move up from 3S to 4S and eventually all the way to 6S..... and used batteries are hard to sell at a good price.

High KV motors are best with 3S batteries. As you move up the MR AUW you need to shift towards 6S and also low KV motors...... much more efficient = better flight time
 

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wolph42

Member
SoCal Blur said:
HA! I just noticed that you're in Nederland. I was born in Den Haag (the Hague).
Click to expand...
currently residing in Delft so that pretty close. You're now in Canada? We're currently looking to move there...funny.
edit: silly mistake CA is California.

Thanks for the tips. As this will be my first build I do not want to go too expensive, on the other hand if I buy too cheap (or better said, too crappy) and the whole thing crashed it will be even more expensive. So I'm trying to find a sweetspot.

@PeterLester. Thnx for the tips. I noticed though (but could be entirely wrong) that low kV motors also tend to be more efficient with bigger blades 12"+. Is that (more or less) correct?
The build I'm considering (F550 frame) is limited to 10".

to me it appears that everything is connected to each other (pretty big *duh* there) and that based on the frame and AUW you should be able to derive the most efficient configuration. Which basically is the first step. E.g. *simple* remarks like: "Running en electric Motor below his optimal efficiency current results in a faster increase of wast power than running it over this point." (ecalc help) help a LOT. but as there is no *real* manual for ecalc maybe I should just start a topic and update it on the way... do you have any suggestions to find more info about ecalc e.g. is there or post or faq that sheds some light on it?
 
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PeterLester

Member
Lower KV motors driven by higher voltage motors are designed for increased torque versus speed and more torque allows you to rotate larger props and/or props with more pitch. Re: ecalc.... just ask MRF users specific questions...and there may be many...I don't think you will get more help data from eCalc beyond what has been posted already.
 

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wolph42

Member
PeterLester said:
Lower KV motors driven by higher voltage motors are designed for increased torque versus speed and more torque allows you to rotate larger props and/or props with more pitch. Re: ecalc.... just ask MRF users specific questions...and there may be many...I don't think you will get more help data from eCalc beyond what has been posted already.
Click to expand...

clear thanks.
 


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