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Feb 09, 2014, 09:26 PM
Wisconsin
Mini-HowTo

A tutorial on using eCalc


What is eCalc anyway? It is a web-based program to take multirotor design data and calculate some valuable information about the design. It was written by Markus Mueller.

eCalc is a powerful tool to answer questions like "will that motor work" or "what will my flight time be"? You can use it as a "what if tool" to design your multirotor. For example, what if I change the props from 13x4 slow-fly to 14x5.5 E props?

Although DJI, for one company, has introduced some very popular ready-to-fly multirotors, many other brands are still custom built by forum members from parts and most are very different builds from each other.

So, let's design a multirotor from scratch. We want to lift a Sony Nex5n camera.
The first thing to realize is that we need to know the weight of every part of this project. When you ask forum members "will this motor be good for me?" it is really hard to answer because you have to enter all the data into eCalc to find out. Unless somebody runs that exact set of parts in their own multi-rotor you probably won't get an answer - because other members honestly don't know.

So, let's start with a Tarot FY690 frame. A frame that can handle the wieght of the Sony Nex5N camera. There are, of course, lots of other frames that will work just as well. I'll also pick out a complete set of parts, somewhat arbitrarily, and then we can play with substitutions to see if we can improve our design.
Frame
1-Tarot TL68C01 (FY690) = 690g with landing gear.
2-Tarot TL68B14 Battery holder=25g

Motors and props
=============
6-Tiger MN3110-17 700kv = 80g each
6-12x4.5 CF Slow fly props =10g each

Power
=====
6-30amp ESC = 32g each
1-3s8000mah Zippy battery=600g
1-Power Distribution board=5g

Electronics
========
1-Receiver =15g
1- Flight Controller = 35g
1-GPS = 10g
1-GPS pole=10g
1-BEC = 5g
1-Power Module=10g
1-FPV Camera = 10g
1- Video Transmitter = 45g
1-Telemetry Transmitter = 21g
1-Video Switch =2g
1-HDMI converter for Nex5N=5g
1-IR Trigger for Nex5N=2g

Payload
======
1-Gimbal =300g
1-Nex5N body=270g
1-Sony Nex 16mm lens=80g


So what are our totals?
Frame and landing gear, battery tray and Power distrubtuion board =700g
Electronics weight =170g
Camera and Gimbal weight= 650g

So our total weight without our drive, that is without the motors, esc, batteries and prop, is 1520g. Quite a bit. That's what it takes to lift a Sony Nex5n or something like it.

So now that we have our data lets go to eCalc.
http://www.ecalc.ch
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Choose your language under the column "xcopterCalc".

Now we see the main data entry screen of eCalc:
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Let's put our data into the first category "General".
First: Leave cooling on "Medium".
Next: The number of rotors is 6 for our Tarot FY690 example.
Next: The Model weight is everything except our drive. From our list above, the weight of everything is 1520g except the drive.
Next: Change "inc. drive" to "without drive"
Next: Type in the elevation of your flying area above sea level ASL
Next: Type in the temperature when you fly and the air pressure if you know it.

First group done, not too hard, eh?

Now the battery group. In our example we are using a 3s8000mah so click on the drop-down menu labeled "Type" and choose the closest battery:
LiPo 3s8000mah - 35/50C
eCalc fills in the details. But we weighed our battery and we know it is not 196g per cell but 600g/3=200g; also from Hobby Kings site we know it is a 30c battery not a 35c. So let's change "type" to custom. It saves all the stock information about the LiPo 3s800mah - 35/50c but let us now edit and change the fields we know are different. So let's change "C-rate" from 35 to 30 and the cell weight from 195g to 200g.

Now on to the Electronic Speed Controllers, the ESC's.
The group is called "Controller" and the first choice is the drop-down menu labeled "type". We are starting out with 30amp ESC's. So choose "MAX 30A". It fills in weight at 40g but we measured ours and they are 32g so let's choose "custom" under "type" and change the weight from 40g to 32g each.

Now time for the motors:
In the "Manufacturer -Type (kv)" find
Tiger Motor and MN3110-17 (700) for the model.

OK. last group is the Propeller:
For "Type" lets choose "APC slowfly SF" and for Diameter 12" and a pitch of 4.7
Ours are two-bladed props so leave that box alone.
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Now it is time for some results. How will it fly?
Click on "Calculate" and see what happens
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It says we have an All-Up-Weight (AUW) of 2959grams. That is the sum of our payload of 1520g and the calculated drive of 1439g, 1520g+1439g=2959g. The Tarot FY690 should be able to handle that weight.
Our hover flight time is about 12.2m, but Markus tells us that all the results are plus or minus 10% and it depends on the accuracy of the numbers we entered. So it could be a minute less or a minute more. Our throttle at hover is going to 71% which is not too good. We would like it to be closer to 50%.
So what if we change our prop and go to a 13x4?
To find out let's go back to the propeller diameter and change it from 12" to 13" and the pitch from 4.7" to 4".
Now click "Calculate again"
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Our total weight has not changed, of course, it's still 2959g, but our throttle is now at 62% and our hover flight time has increased to 13.2m. Not bad. We can also see that when we use the maximum power we are consuming 142Watts of power and the maximum rating for the motor is 470watts so we are well below that. The temperature of the motor at maximum is still a cool 100degF so we are ok there.

What happens if we run a larger prop still? Can we fit 14" props on this FY690 frame? Let's say we can, but always keep in mind what will fit your frame, so let's find out.

Let's Change the Diameter of the prop to 14". Click "Calculate"
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We have once again improved our hover throttle down to 50% and increased our hover flight time to an estimated 14.2m and we are still only using 170.8w! What if we really get crazy and try a 20" prop?
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Ah, here we have gone too far, not to mention 20" props won't fit on the frame! Notice the warnings in RED.
The hover throttle is a very low 19% and the flight time is a wopping 20 minutes but the motor is overheating in max flight and the ESC's just burned up at 33.74A when we only have 30A ESC's.

Let's go back to using a 14" prop and see what happens if we use a 4s battery instead? So what is a roughly equivalent 4s battery? Well our 3s is 3x3.7v=11.1volts and power is volts x amps so the power of our 3s battery is 11.1vx8amps (8000ma)=88watts so 4s is 4x3.7=14.8v. So 88w/14.8v=5.9 amps or 5900mah. So a 6000mah 4s battery has about the same energy stored as the 3s 8000mah battery. So let's use that.
Change the prop back to 14" and the battery to the drop-down listing labeled LiPo 6000mah 30/45c and change the configuration from 3 to 4.
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What happened? Our AUW increased to 3056g so we are a bit heavier now. Our throttle at hover is ok at 30% but our flight time went down from 14.2m to 13.2m. We are now using more power at engine max 305.3w vs the 170w we were using before. So we are pushing the motor a lot more now. Looks like this 700kv motor runs better on 3s.

Lastly, let's use a similar motor and see what happens if we lower the kv rating of the motor to 470kv. Let's change the engine type to the Tiger MN3110-470kv.
Click "Calculate"
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How did we change the design now? The weight is the same. The throttle is not bad at 61% but the power used has dropped way down from 305.3 watts back to 143.8 watts and the flight time is 13.2minutes. This motor runs better at 4s than the similar 700kv version of this motor.

You can try different motors and see how the weight of the motor, the rpm per volt (kv) and the prop size are affected by the 3s(11.1v) vs 4s(14.8v) batteries. There tends to be a "best match" for each motor and it will perform poorly with less voltage and smaller props and more voltage and bigger props, above and below the best match. Use eCalc to find the best combination for your payload requirements and flying style.

We were looking at hover flight time for this example but your personal flying style with affect flight time. Under the "Battery" column in results are estimates of "flight time" taking into consideration more acrobatic flying style and "Mixed flight time" where some hover and some acrobatic flight are averaged together. Also it is good practice to test your flight time estimates by flying shorter flights and noting the power that is returned to the partially discharged battery. Then compare how much power you had left in your battery. Then recharge and fly a little longer and check it again, step by step, until the power you return to the battery is close to about 80% of the battery capacity. That is your limit. You don't want to discharge a Lithium Polymer battery (LiPo) above 80% discharge or you can damage the battery. It is not a good idea to take the numbers from eCalc and fly to the limit the first flight. If you made any mistakes you might have a in-flight crash as the real flight time turns out to be less than your estimated time and you run-out of power in the middle of the flight.

We could ask a lot more questions like what if I use a heavier gimbal at 600g, just add 300g to the "Weight" under general group. What size ESC do I need? Look at the Motor @ Maximum column in results and see what the maximum current is being used and then add 30%-50% to the figure to get some headroom. What happens if I run two batteries? Just change 1P to 2P under "Battery cell" group.

There a many more things you can learn from eCalc about a design. This is just a simple example focusing on a couple of important considerations.

I hope this little exercise can help you design and try different configurations for your next multirotor build or just help you learn how different battery, motor and prop configurations work together.

If you like and use eCalc why not click on that donate button to give Markus some encouragement and positive feedback!

Cheers

Next: "Using eCalc to optimize motor selection"
Last edited by mike_kelly; Feb 13, 2015 at 09:43 AM.
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Feb 13, 2014, 12:05 PM
Registered User
Thanks for taking the time to do this.

The prop selction variables (yoke twist and PC constant) is still a bit of a mystery. There are so many props that have the similar specifications but perform differently in practise.

Is there a useful generic prop setting where a prop without ecalc suppiled data is been considered?

Or is the size and pitch sufficient?
Feb 13, 2014, 05:50 PM
Wisconsin
How true. I think some of the variablility is the material that the prop is made from. Clearly there is a big difference between a more flexible nylon prop and a stiffer carbon fiber prop. I am not sure anyone has quantified those differences and they are not parameters that eCalc takes into consideration. Like motors it is difficult to get all the information needed for eCalc on many vendors products. I find eCalc a great tool but it can only take us so far and then empirical testing has to take place. Ya gotta try it and find out
Feb 14, 2014, 10:55 AM
Registered User
ItsSweetAvard's Avatar
I second helidex, thanks a whole lot for this tutorial!! I now understand eCalc a lot more, it's suddenly useful

I already have a scratch built Tricopter, and acro quad. I'm now looking al building a hexcopter for AP. This will help me, you have no idea.

On a side note, I was contemplating the Turnigy Talon Hex V1.0, but would you recommend the Tarrot FY690 over it?
Feb 14, 2014, 12:18 PM
Wisconsin
First it depends on what camera you want to use for AP, something very light like a GoPro or something heavier like a Canon S100 or heavier sitll like a Nex 5 or really heavy like a DSLR.

I have no experience with that frame but something to keep in mind for AP is that the heavier the load the bigger the props you need. Small props are fast and responsive, like a sports car, and big props are slow, powerful with a lot of torque and henceforth lifting capacity. The diameter of the frame determines the largest size of the props that will fit. Also a quad can take larger props for the same diameter than a hex due to the geometry, the arms are closer together on a hex so there is less room betwen them for props. So use eCalc with the camera, gimbal, FC and motors you want to use and the weight of that frame and determine what the best prop size is to use. Then try and figure out if you can use that size prop with the Talon frame. Check other Talon builds to see what the largest prop other people are using with it. HK lists 8" to 10" as the range.

You will see there are a number of Tarot builds where folks are using longer tubes for the arms or longer motor mounts to squeeze a little extra length so they can run larger props.

It is a balance, of course, you don't want to over-do it because weight is always your enemy. Bigger motors and frames weigh more, they therefore require bigger batteries which weigh more...soon you will find you don't gain much.

Good Luck and have fun designing!
Feb 16, 2014, 10:27 AM
Registered User
Thanks for the tutorial write up. I just started really using ecalc last week to build an extended flight time custom quadcopter using a 6S setup with 15 X 5 inch props since they are pretty standard, have a variety of styles, and carried by plenty vendors. With these parameters, I'm using ecalc to find a motor that will give the longest flight time. How important is the motor wattage limit and is the wattage limit known to be a conservative value?

I get this warning in eCalc:
"max. power over the limit of the motor. Please check the max. power limits defined by the manufacturer"

Then when I switch to the next biggest motor (which is going from 14 magnets to 22 magnets), my flight time takes a huge hit.

I also have been dialing in other setups built by some experienced people that extend flight time and eCalc reports the same warning about going over the motor wattage limit. This is where I question whether the wattage limit spec is just conservative or does the warning only mean anything if your going full throttle all the time. For instance, take a look at this guys quad.
http://fpvlab.com/forums/showthread....copter.-(video)

Here is a link to the eCalc I generated for his 1500g setup. I used a lighter battery since he uses Li-Ion cells.
http://www.ecalc.ch/xcoptercalc.htm?...tch=5&blades=2

I want to avoid going with bigger, heavier motors if I dont necessarily need to. Thanks in advance for any advice or suggestions.
Feb 16, 2014, 10:00 PM
Wisconsin
You are right on target. It can be a game of diminising returns going bigger. I'll write up a new blog entry about this subject because it is a good point. But to answer your question quickly the warnings are limits on the maximum. So that answer partially depends on how you fly. If you are doing Aerial Photography (AP) and you are hovering most of the time you are rarely hitting the maximum. But if you are flipping and doing acrobatics you are flying near the limits a lot more. So the warnings are just that a guide. If your motors are rated at 200w and you are getting a warning of 210w but you very seldom ever fly at the motors maximum then it is not such a big deal. But if you really fly to the limits you may be overheating and stressing out the motors risking failure.

Clearly if your design is using 125w motors and the eCalc results are showing a warning of 250w maximum then it is time to reconsider your choices.
Feb 17, 2014, 01:43 PM
Registered User
Makes sense....thanks for the advice...
Jul 10, 2014, 12:16 PM
Risk Taker, Prop Breaker....
WannaBeRC's Avatar
Hey Mike, Thanks for your write up. It has helped me a lot!!

A noob here with a few questions if I may. Or direct me on where to post.

1. In the Battery section. Do I enter the total battery weight in the weight box or do I divide the weight specified, by HK for example, by the cell count and enter that number? Or in other words, is the battery weight box wanting the total battery weight or the cell weight?

I ask after reading this from above and finding nothing but warnings if I enter the full weight.

But we weighed our battery and we know it is not 196g per cell but 600g/3=200g; also from Hobby Kings site we know it is a 30c battery not a 35c. So let's change "type" to custom. It saves all the stock information about the LiPo 3s800mah - 35/50c but let us now edit and change the fields we know are different. So let's change "C-rate" from 35 to 30 and the cell weight from 195g to 200g.

2. In the controller section I have a similar question. I am using a Q-Brain 4-way ESC. Does the calculator multiply the weight by four? If so, I should divide my Q-Brain weight by four and enter that value correct?

The eCalc AUW does not match my Excel spreadsheet. If anything I should be heavier than eCalc as I fudged heavy on connectors, wire, tie-wraps, mounting plates, etc. But I am not. Do you know how eCalc calculates the weights?

3. General section. When would I toggle to [Inc Drives] using this calculator? It doesn't seem to like it being toggled on no matter how I fudge numbers.

4. Prop section. What props have a degree value we would use in the 'degrees' box other than 0 ? I have not seen this spec.



Thanks again for the 'How To' !!!
Jul 12, 2014, 07:40 PM
Wisconsin
Quote:
Originally Posted by WannaBeRC
Hey Mike, Thanks for your write up. It has helped me a lot!!

A noob here with a few questions if I may. Or direct me on where to post.

1. In the Battery section. Do I enter the total battery weight in the weight box or do I divide the weight specified, by HK for example, by the cell count and enter that number? Or in other words, is the battery weight box wanting the total battery weight or the cell weight?

>>>>> It is the cell weight not the total. It will multiply by the cell count when it calculates.

I ask after reading this from above and finding nothing but warnings if I enter the full weight.

But we weighed our battery and we know it is not 196g per cell but 600g/3=200g; also from Hobby Kings site we know it is a 30c battery not a 35c. So let's change "type" to custom. It saves all the stock information about the LiPo 3s800mah - 35/50c but let us now edit and change the fields we know are different. So let's change "C-rate" from 35 to 30 and the cell weight from 195g to 200g.

2. In the controller section I have a similar question. I am using a Q-Brain 4-way ESC. Does the calculator multiply the weight by four? If so, I should divide my Q-Brain weight by four and enter that value correct?ht

>>>>>>>>>>>> Interesting, yes the calculator multiplies by four or the number of motors so you will need to divide the total weight of the all-in-one by four, in your case.

The eCalc AUW does not match my Excel spreadsheet. If anything I should be heavier than eCalc as I fudged heavy on connectors, wire, tie-wraps, mounting plates, etc. But I am not. Do you know how eCalc calculates the weights?

>>>>>>>>>>>eCalc is going to take the wieghts that you insert for just the drive system. So just the motors, esc's, props and batteries. Anything else including things like the flight controllers, bec's, gimbals and controllers, telemetry radios, fpv gear, anti-vibration systems and domes etc. All that stuff you need to insert in the first line under "without drive". This tells eCalc about everyting other that the items in the motors, batteries and esc dropdowns.

3. General section. When would I toggle to [Inc Drives] using this calculator? It doesn't seem to like it being toggled on no matter how I fudge numbers.

>>>>>>>>>>>>>> Include drive is only used when you already know what everything weighs. Then ecalc just uses your numbers and does not add anything up individually itself. Maybe your aircraft is finished and you can just put it on the scale to determine a very accurate total weigh. Then you just want to play with numbers for different props or such so there is no need to use the estimated weights built into eCalc.

4. Prop section. What props have a degree value we would use in the 'degrees' box other than 0 ? I have not seen this spec.

>>>>>>>>>>>>> I have not seen it either. It seems to me it is a manual way to describe pitch but that is just a guess.

Thanks again for the 'How To' !!!
My pleasure anytime. Glad you emailed me. I wish RCG would notify me when there is a new comment. Cheers
Jul 12, 2014, 09:53 PM
Risk Taker, Prop Breaker....
WannaBeRC's Avatar
Excellent!! Parts list being finalized now.......

Thank you sir!
Jul 14, 2014, 09:17 AM
Wisconsin
<<<4. Prop section. What props have a degree value we would use in the 'degrees' box other than 0 ? I have not seen this spec.>>>

WannabeRC, Here is Markus answer to your prop question.

Hi Mike,
folding props may have a additional twist in the yoke (centerpiece) that changes the effectiv pitch of the blade. these twisted yokes defines the twist in degrees, e.g. 42mm/+5

If your blade is a 15x8" your inital pitch of 8" gets a additonal 5 degrees angle of attack resulting in a effective pitch of more than 8".

cheers

Lg Markus
Jul 14, 2014, 02:45 PM
Registered User
One question. My figures are quite close to what you have on the model weight without drive, and off the top of my head mine is about 1300-1400g without drive.

I've found out that i get more consistent results by putting the total weight of the multicopter, in other words that is: frame&landgear+ESCs+motors+props+OSD+FPV tx+gimbal and camera, etc, in the model weight than if I separate each item. When I do this I get a flight time figure which is consistent with what I'm getting in real life, but I know this is not the right way to do this.

Now, here's where it gets confusing. If I put the weight of everything except the drive and related items, exactly like how you did it on your tutorial, then ecalc says I don't have enough power to hover, however I'm able to hover fine for over 18 mins with no motors, ESC's or battery overheating. What am I doing wrong?

So my question is, instead of placing the weight of everything separately, can I just do what I did above for good accurate results, or not. Any thoughts?

Attached is a screenshot of my ecalc results.
Last edited by jofs3d; Jul 14, 2014 at 02:48 PM. Reason: clarification
Jul 14, 2014, 05:59 PM
Registered User
I found out what I was doing wrong, I had to re-read the tutorial to see what I was doing wrong.

For those with the same issue as mine. My mistake was related to the battery weight, in particular placing the total battery weight on the cell weight!
I assumed I had to put the total weight of the battery in the cell weight category but I was wrong. Ecalc will calculate each cell's weight on its own after you put the right weight for each of your cells, very simple.

So now my figures are consistent.

Thanks for the tutorial btw!
Jul 17, 2014, 09:30 AM
Wisconsin
Quote:
Originally Posted by jofs3d
I found out what I was doing wrong, I had to re-read the tutorial to see what I was doing wrong.

For those with the same issue as mine. My mistake was related to the battery weight, in particular placing the total battery weight on the cell weight!
I assumed I had to put the total weight of the battery in the cell weight category but I was wrong. Ecalc will calculate each cell's weight on its own after you put the right weight for each of your cells, very simple.

So now my figures are consistent.

Thanks for the tutorial btw!
That is a common mistake so it is good to have commented about it to remind others. Glad your aircraft is working well, good flying!

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