TIP: Increase your multicopter run time 25%

Caution!!!

You can do damage to your electronics if you are not careful and are not paying attention when following this article. Make sure you have calibrated your ESC's at 100% of the throttle limit before attempting this or else you will not get the resolution or equal performance of this setup.

Background..

I have several batteries and after I ran through all my 3s batteries, I would have to return to the charging station. This kind of stunk because, I was not done flying when I was out of 3s batteries. So I decided to see if there was a way I could my 4s batteries on my 3s setup. So I figured out this method and it worked!! I also have more run time!!

I do not recommend this for a newbie because of the amount of thinking, math, care, and ability to program your radio that is involved.

I have tried this on 2 different setups and it works great!

Setup for this example.

Hobbywing quattro ESC -I love this ESC and will by more www.valuehobby.com the wiring is a lot cleaner and a good length so you can build a larger quad. The heat sink is a little heavy for my liking but it disperses heat very very well. It was 39 bucks when I bought it. (See the first picture below of the ESC) Make sure that your ESC can handle a 4s battery. Most ESC's are either 2s/3s or 3s/4s in this range. I would run a minimum of 18amp ESc for this application.

KK2.0 multicopter board - Hobbyking's awesome controller. I flashed it with the 1.5 firmware.

cf2930 800kv motors - Value Hobby Good 3s motor. 

Transmitter that has heli mode and has an IDLE up option - I am using a DX7i for this.

10x4.5 CF props - So the CF props cost more but are worth it to the more experienced pilot. I have read several peoples thoughts and reviews about them. I have found that people are not drinking the CF prop koolaid but, in my humble opinion, you can do some things you cannot do as well on regular plastic or fiber props. One of the main things I noticed is you are able to decend a lot faster and smoother than other props. Your acceleration is a lot better too. Your top speed will increase. Your amperage draw is increased though. So keep that in mind if you are taking your multi out for a spin and are horsing it around. For a calm easy FPV flight your runtime is increased slightly. My opinion is the props are lot more efficient and you are not losing MAH's due to prop flexing. These props do not flex or bend. They are very strong and actually can be repaired with thin CA glue if you break one. I found 4 sets of 2 from Rctimer for 29 plus shipping. The shipping is slow from them but again worth the price to me. 

Side note - You can mix your CF props with your plastic props front to back if you are carring a camera this is more efficient if you have more weight on the front of your multi. So I have put 2 CF props on the front of my quad where my gopro sits and standard props on the back. Ideally you want your weight evenly distributed though.

3s 2200 and 4s 2200 - you get these where you like. 

Shipping note - I like Value Hobby by the way. The do not have a huge selection but, their prices are fairly cheap and I do not have to wait for the hong kong shipping machine. If I order something on monda it is here by wednesday usually for only 3.99 shipping on average depending on the size of the item. I live in indiana and they are based out of IL.

 QUATTRO ESC

Here is where this gets a little complicated. Get out the calculator for this. 

NOTE: This is my method. It is my way. It does not mean it is the best way.

I set my quads max throttle points to be 80-90 percent of full throtlle. That way at full throttle the controller still has room to send correction signals to the esc's. If you are at full throttle there is no where to go past 100%. So that is why I limit my to 80-90% depending on the setup.

I will break this up into 2 seperate parts. The math portion and the multicopter setup portion.

Math portion -

As I stated earlier I limit my quads to 80%-90% of full throttle.

For this example we will use 80 %

What we know....

The motor is 800kv

The battery we are using is a 3s 2200 11.1v

The battery we want to use is a 4s 2200. 14.8

max rpm of the 800kv motor on 3s is 9440 rpms (11.1v x 800kv = 9440)

max rpm of the 800kv motor on 4s is 11840 rpms (14.8v x 800kv = 11840) 

14.8v is is too much for these motors and will burn them up. (In theory anyways)

So what we need to find the percentage that we need to limit the 4s throttle setting too so we do not burn up our motors. 

 So a simple equation to figure all this out looks like this. You can figure out the meaning of life with this equation if you want too. It is one of my favorites. I am not a mathematition nor claim to be. It is the only really useful one that I learned in algebra.

So to use this equation you just plug in your numbers and solve it.

So if you want to figure out what rpm 50% throttle is it goes like this.

A=50 (50 %)

B=100 (100%)

C= 

D= Max rpm (battery voltage X KV of the motor)

We need to solve for C

So the operation always works like this.

(A*D)/B = C

(50 x 9440) / 100 = 4720

So 35% throttle would be like this

I will break this out a little so that everone understands.

(35 x 9440) / 100 = C

(330400) /100 = C

C = 3304

Ok knowing all of this information now we need to limit or percentage of throttle to get the desired RPMs on the 4s battery to 9440 rpm so it matches the 3s max rpms.

So now we need to use the same equation and plug in the numbers that we know.

We need to figure out what percentage of throttle gets you to 9440 on a 4s battery. 

So this is what we know-

max rpm of the 800kv motor on 3s is 9440 rpms (11.1v x 800kv = 9440)

max rpm of the 800kv motor on 4s is 11840 rpms (14.8v x 800kv = 11840) 

So now we solve for the percentage of RPM this time.

In the equation we would want to solve for A this time.

A=

B=100

C=9440 

D=11840

You always multiply diagnolly and divide by the third number that is left.

So now we do this.

(B*C) / D = A

(100 X 9440) / 11840 = A

(944000) / 11840 = A

A= 79.929

So basically 80% 

So when your stick is set to 80% on your radio using a 4S battery it will turn the motors, in theory, at 9440 RPM's and it is equal to 100% on a 3S battery. Which is within limits of the motors!

Ok now here is where it gets tricky. Remember when I said that I limit my throttle to 80% on my quads on the 3s setup? We have to make that 80% happen for the 4s setup as well. So we need to go back and run the equation again and this time run it on the 3s numbers to figure our RPM's at 80% of the 3s configuration. 

A=80

B=100

C=

D=9440 (3s 11.1 x 800)

(A*D)/B=C

(80x9440)/100=C

(755200)/100=C

C=7552

This will be the actual desired RPM of the 4s setup now and will be what we set up in our radio.

So now we need to figure out what the percentage of throttle is that we need on the radio again.

A=

B=100

C=7552

D=11840 (4s  14.8 X 800)

(100x7552)/11840 = A

(755200)/11840 = A

A=63.783

So round to 64%

So our target Max % of throttle is 64% for a 4S battery to operate exactly the same as a 3S battery with a 80% throttle max setting.

The Radio - 

Ok so we came up with the number of 64% to be the limit we need so that we can fly the 4s batteries without causing damage.

This is pretty simple. 

The way I did it was to use the idle switch and set my normal flight mode to be the settings for the 4S battery.

That way if you forget your quad will not burn the motors up because you forgot to flip the switch. My radio will sound an alarm if it is in idle up when first turned on. So my idle up is set Normal for 4S and position 1 is 3S.

All you need to to do now to make this work, is set your normal mode limit to 64% for 4S and IDLE up 1 to 80%.

Your multi will fly exactly the same with as 4s battery and a 3s battery with its switch in the proper position.

The unforseen benifit I was having out of all of this was the increase in flight times by roughly 25%.

Import note - Callibrate your ESC's with no throttle limit set initially. So set the max to 100% first. Calibrate the ESC. Then once complete set your limits. Else your are not sending the proper values to your ESC's from your radio.

Enjoy I hoped this helped.

-Casey

Here are some front and back photos of one of my quads.