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How to choose your LiPo, ESCs, motors and props?

#1
Hi guys!

I'm a new (and a noob as must say) around here and I have a beginner question for you :)
I'm actually building my first quad with the Knuckle H-Quad frame created by the flitetest crew. The thing is, I followed the recommendations regarding the LiPo, ESCs, motors and props but I would like to know how do you do to know what is a good combination?

I already know this website which is very useful but there are so many different possibilities than I'm a bit lost :confused:
 

xuzme720

Dedicated foam bender
Mentor
#2
You are not alone. And sadly, because of the variables involved, it's not going to be an easy answer. Equipment selection is something that many pilots, even experienced ones, struggle with. Stick with the recommended parts or comparable items. As you learn more about the motors and how they work, you'll be able to assess and pick a power train to suit what your needs are.

The shortest answer I can give you is this. Determine what you need your envelope to be as far as faster spinning smaller prop or slower turning larger prop. Larger/slower is good on multi's that need lifting capacity, while faster/smaller is more agile and nimble. Once you have that, you'll also need to make sure you have selected a combo that can lift the frame and components you have planned on using. ESC size is determined after motor/prop selection due to needing those specs to decide what size you need. Then battery selection based on motor/prop/esc selection and time aloft needs. You'll need a battery that can provide the current draw without risking damage to itself, and also that can give you the necessary flight times you want. It's always a balancing act, because if you go with a larger battery for more time in the air, you are now lifting more weight and will be using more amperage, which will shorten flight times. In that case it might be better to change to a lower Kv motor(slower) and larger props for more lifting power. So, it's something that needs to be planned start to finish then go back and make sure any changes can be handled by the components you have or want to use.

I'm not saying it's impossible to learn, or so complicated that you can't do it. Just take it a step at a time, and see if the parts work. In time, as you learn more about how they interact, it will get easier to determine exactly what will work for what you need.
 
#4
Thanks for your answers, espacially xuzme720!

I do start to understand differences between motors / props based on your comment over the agility VS lifting power. One question though: To increase the lifting power, 3 blades props can be a good choice for a quad or is it better to stick with 2 bigger blades props?
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#5
Tomtom,

You will increase the trust by adding another blade, but the motor current (and the battery's "time to empty") will increase faster than the added thrust.

For instance if a notional setup is switched from a 2 to a 3 bladed prop of the same size and pitch, you might gain 20% more thrust so you can now cruise/hover at a much lower throttle, but your full throttle run time could still drop by 30-40%, and your actual flight times could drop significantly as well. Both this efficency loss and prop flutter effects will get worse with incresing RPM.

Not to mention, three bladed props are a *BEAR* to balance.

Three bladed props *do* make sense at times:
- when space is limited (boom length too short or frame gets in the way), but you still need to increase lift
- you want the props to look cool and don't care about a shorter flight time -- on scale fixed wing aircraft, this is important.

For heavy lifitng, if your motor can tollerate moving the prop up in diameter, it's a better way of generating more thrust/lift.
 

Cyberdactyl

Misfit Multirotor Monkey
#6
I bought 3-bladed props for my first build. I hate them. They are very sensitive to prop wash. And when first learning to fly multi-rotors you're generally in a motionless, or close to motionless hover quite a bit with some up and down movement, making learning even more difficult.
 

rcspaceflight

creator of virtual planes
#8
I don't have it all figured out either. I've only been flying for almost a year. But I can share what I do know, and hopefully I can keep it simple and helpful.

According to David and Bixler, you start with the propeller, then you find the right motor for it, then the right ESC, and then the right battery.

You can use a simple thrust calculator to have a rough idea of what to expect thrust wise from any given prop. Here is the one I like to use: http://personal.osi.hu/fuzesisz/strc_eng/

Also, when looking for a prop, it's good to know that long props give you more pulling power. It's like riding a bike in first or second. A short prop can handle spinning faster, but it's like riding a bike in tenth gear. The long props get the plane to full speed right away, but can't go very fast. Short props can go a lot faster, but takes quite a while to get there.

I found what David said in the third podcast extremely helpful. He said something like 2 inches on the pitch of the prop is equal to 1 inch on the length. As far as the load/resistance the prop creates on the motor. Basically, if your motor can handle a 9x5 prop, then if you want to go up to a 10 inch, the pitch needs to be 3 in order to equal the same load/resistance/performance (watt wise). Or you could drop down to an 8x7. At least that is my understanding of what David meant. It doesn't sound quite right, but close.

Finding the right motor can be hard. Especially if you're looking for the most efficient. I think all you can really do in that regard is read reviews of a motor. See what other people got out of them and with what setup. You can buy a motor and then find out which prop size is the most efficient for it, but that might not be the right prop for your plane/copter.

Basically look for the KV rating you want out of the motor, and then find one that can handle the prop you want.

For ESC and Battery, you need a watt meter to know how many amps the motor draws with that prop. Don't worry, I don't have a watt meter. I base what I use from what other people do and what is recommended for the motor. But usually, I just use a 30amp ESC regardless. I'd rather have an ESC that can handle more amps than what is used. And as far as batteries, I always buy the highest "C" rating that they have for the battery I want. Yeah, I end up spending more. The last battery I bought was $20 and if I bought the one with the lower "C" rating it would have been $10. But I figure it's worth the extra money to know I'm not going to overdraw the battery and kill it. It's an investment for a longer lasting battery.

I hope this info was helpful to you. It can be difficult and take a while to know what the right setup can be. I know I've overheated a motor or two and I burnt out an ESC.
 

rcspaceflight

creator of virtual planes
#9
Re-looking at that calculator I recommended, I want to point out that it asks for "RPM". You have to multiply the motor's KV with the amount of volts you are using. Example, a 3 cell battery is 11.1volts. If I have a 1300KV motor, then I multiple 1300 with 11.1 to get the RPM (at full throttle). And I want to say that I usually guess with which prop I'm using. It doesn't look like it changes the amount much.
 

colorex

Rotor Riot!
Mentor
#12
So far episode 3 has been the geekiest of the podcasts, but they've all had valuable things mentioned in them.
I listen to them while I'm resting. The funniest thing so far for me was the Canadian stereotype David referenced in #004 - "Canadians, they're sorry" :p It's a common stereotype that Canadians are very polite and apologize for everything :D
 

rcspaceflight

creator of virtual planes
#13
For some reason I like Bixler's jokes in the podcasts. I think it's because I didn't expect him to have that kind of sense of humor.

Chad: "I don't know how Bixler does it."
Bixler: "Caffeine and Jesus."