New ScaleRCHelis.com Electric Calc 08-20-08

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New ScaleRCHelis.com Electric Calc 08-20-08

Postby cquinby » Wed Aug 20, 2008 1:02 pm

Again, big thanks to Alex (Mac) for putting this into a program

Here is the long awaited update and follow-up to this thread: viewtopic.php?f=42&t=6071

First off this calculator should get anyone in the ballpark when planning a power system for their helicopter. Remember these are estimates how ever as you move along you can start to fine tune the settings to suit your findings.

Things that have been added since the last revision:
1. The ability to choose a target RPM % instead of only calculating for 100% rpm.
2. The ability to choose Metric weights.
3. The ability to modify the LiPo and A123 voltages on the settings tab rather than the config file as before.
4. Tips on each calculation to help explain the calculation.

srch_e-calc.zip


We will do a example here to show how to use the calculator. We will use a heli that uses a 2 stage transmision (actually model this after my -e-benzin) with 10s lipo setup. I know it flies at 17 amps and weighs in at 16.5lbs

We need to first determine our voltages for our batteries under load. 3.65v/cell for LiPo's seems to be pretty close. Some of the newer packs can sustain upwards of 3.80v when used lightly as we are in scale. To adjust this setting click the settings tab at the top of the screen. Here you can adjust the voltage per cell for LiPo and A123 cells. Also you can choose the targeted HS percentage and also if you want the Tip's to be shown and if you want Metric conversions applied.

percentage.jpg


First lets pretend we want to find the KV motor we need for a HS we want to run. We need to know the number of cells we want to use and also the HS we want. So in this case I want a HS of around 1160 at 90% throttle. We plug in our gear ratio first, in this case I am running the 83:21 gearing on the vario benzin. Do this by clicking the button next to the Gear Ratio field in Find Head RPM section.

gear_ratio2.jpg


gear_ratio.jpg


Now we enter our HS and cell count and click the calculate button which tells us what the estimated kV motor we need for our requirements. In this case I need something around 263kV

motorkv.jpg


So this will help you find the kV motor you will need.

If you already have a motor then you can use the HS calculator portion. Plug in your gear ratio, motor kV and the cell count.

hs.jpg


Now we want to calculate our estiamted amp draw based on weight and watt's per pound or Kilogram. First we need to know our model weight and give a estimated power usage in watts per lb. In this example I know I am running around 38 watts per lb. giving me around 17 amps durring flight.

watts.jpg


38 watts/lb is very low and when estimating your numbers I would use something around 50 to give you a reasonable assumption.

Now that we know what our estimated Amp draw is we can take this number and plug it into the Known - Calculations tab to get a estimated flight time using the 80% capacity rule. So in the case I take 17.18 amps and plug it into "Drain in Amps/hr" and then put our battery capacity into the "battery in mAh" field and click the calculation button. In this case I should expect about 14 minutes with 5000mAh LiPo packs!

time.jpg


Now if I was starting fresh I would have put 50 watts/lb to get my estimated amp draw and it tells me I should expect a draw of about 22.6amps. Now I take this and figure my flight time to be about 10.5 minutes. This would have given me a safe testing margin how ever I recomend you fly for 1/2 the estimated time and figure your data out from there.

So lets say that I flew for 5 minutes and burned out 2400mAh. I take this data and plug it into the Used Capacity and Flight time calculation. It then tells me I was averaging 28.8 amps.

time2.jpg


Now I can go back and plug in the 28.8 amps and know that I should be able to fly for about 8.33 minutes.

If you have any questions about the calculation you can click the Tips button next to each calculation to help you understand it.

tips.jpg
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby Mac » Fri Aug 22, 2008 9:44 am

Hope you all like the new version, If any one is having problems please post here and I will look into them.
Alex
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby tskg2 » Mon Sep 15, 2008 6:21 pm

Alex and Quimby-

huge thanks for this!

I've started to seriously look at converting all my TSK's to electric- so this will come in handy. I'm still working to get my head around kva, watts, and all that stuff.
But I have some clever lads around here that are helping me with all this. They are gonna do the math- then hand me the bits and bobs required for the job. Fingers crossed!! :)

Muchos gracias- G2
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby Rotor-1 » Fri Feb 06, 2009 10:04 am

I'm kinda late to this party.

What a sweet app!. Thanks for the effort guys and offering it up to everyone. :rockon:

George
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby gpetri67 » Wed Mar 17, 2010 10:55 pm

Many thanks for the application !
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby FelixGiant » Sun Nov 14, 2010 8:33 pm

Hi,

I do have a question after trying to use this nice program.
I was trying to find out the HS considering 500kv motor, 12s Lipo @3,65v under load and 12,25 gear ratio.

Putting those numbers into the program it gave me:
Motor Rpm @90% Efficiency = 15768 rpm.
HS = 1293 rpm

But:

(500 x (12 x 3,65)) x 0,9 = 21900 x 0,9 = 19710 rpm
I can't understand why!?
Having 15768 means 21900 x 0,72 is this right?

Can someone explain me why?
Thanks

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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby Joel Rosenzweig » Mon Nov 15, 2010 4:35 am

Motor Rpm @90% Efficiency = 15768 rpm.
HS = 1293 rpm


It calculated the HS with 80% on the ESC. If it were 100% on the ESC, you'd have 1609 RPM on the head.

500 x (12 x 3,65)) x 0,9 = 21900 x 0,9 = 19710 rpm
I can't understand why!?


That's 19710 motor RPM.

19710 / 12.25 = 1609 RPM (at 100% throttle on the ESC)

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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby FelixGiant » Tue Nov 16, 2010 1:45 am

ok,

thanks

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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby MXCobra » Mon Mar 14, 2011 9:47 am

Calculated vs Actual Headspeeds

My target HS was 1500 rpm @ 80% gov with 12S pack. Motor kv selected was 450. GR 9.5
Actual HS turned out to be north of 1900 at 80 % gov.

Switched to 10S pack, calculation predicted 1262 RPM, actual was ~ 1640 rpm, again at 80% gov.

Is this typical or did I miss something in the calculator?

Rick
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby cquinby » Mon Mar 14, 2011 9:53 am

yes, you were using governor mode. That throws everything out the window as the throttle % in governor mode acts more like the gain in a gyro. The ESC will run much higher on the throttle because of this (up near 95%). If you turn off Governor mode and run a flat throttle curve you will be much closer to your calculated value.
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby MXCobra » Mon Mar 14, 2011 10:43 am

So all I have to do is disable the gov on my ESC (my throttle curve is already flat at 80%) and I'll drop my HS 400 rpm? I'm really missing something about how the gov mode operates thru the ESC or maybe my radio setup .... but this is my first electric conversion. Is there anyway to predict HS with the gov enabled?

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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby cquinby » Mon Mar 14, 2011 10:54 am

Rick, I don't know of any way to determine that. Most of us use the Castle Controllers and setup via the Set RPM Gov mode.

Yes, disable the gov mode and I bet you will see your RPM drop between 300 and 400 RPM. Remember, when your batteries are fresh you will have a higher HS till they lever off after the fist 30-60 seconds, then your RPM should stay pretty well locked in for most all of the flight.

If you want to run the governor mode as you currently are setup then you need to change your gear ratio or motor KV (reduce it by about 15%) and you should be close to your target RPM. When you changed to 10s you in effect reduced the power by 17% (12/10 = 83.33% of the voltage available from the 12s setup).
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quin?by, verb, 'kwin-bE:
1 a: To crash (your helicopter) on the maiden flight.
2 a: To roll (your helicopter) over, destroying the main blades.
e.g. I quinbied my helicopter yesterday. Don't quinby the helicopter. He who quinbies often, has a good relationship with the UPS driver. If you're not quinbying, you're not flying hard enough.
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby MXCobra » Mon Mar 14, 2011 11:24 am

Thanks Chris,

I understand the power side, that's why I started with 12S. My gear ratio is already about as high as I can go. I'm using a Kontronik Jive 80HV and a Kontronik Pyro 700-45 motor in Hirobo S60-II mechanics. I custom built the motor mount for the 700-45. I may just live with the 10S setup and 1640 HS for now.

This learning curve can get pricey !

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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby Kananga » Fri Jul 01, 2011 9:40 am

Are there any plans to port this onto the iPhone? I think it would be a very popular and useful app whilst getting you some funds along the way (after apple take their 30% of course).
Going through a fpv multi rotor phase at the moment.
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby cquinby » Fri Jul 01, 2011 2:11 pm

Kananga wrote:Are there any plans to port this onto the iPhone? I think it would be a very popular and useful app whilst getting you some funds along the way (after apple take their 30% of course).


That has been the plan but my iPhone guy who will remain un-named has been busy for the past two years. If it was ever released it would be free. Trust me, I have wanted it on my iPhone since I bought the original iPhone. Oh well...
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quin?by, verb, 'kwin-bE:
1 a: To crash (your helicopter) on the maiden flight.
2 a: To roll (your helicopter) over, destroying the main blades.
e.g. I quinbied my helicopter yesterday. Don't quinby the helicopter. He who quinbies often, has a good relationship with the UPS driver. If you're not quinbying, you're not flying hard enough.
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby Kananga » Sat Jul 02, 2011 2:17 am

Poke him with a big stick until he ports the code lol.
I think everyone has those sort of projects, I've got one that would make opening combination safes easier but I need a computer program writing for the hardware I've come up with but can't do it myself nor find anyone that will help been on the back burner for around the same length of time.

I'll keep my fingers crossed but not my breath held lol.
Going through a fpv multi rotor phase at the moment.
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby controlledCrashes » Wed Sep 07, 2011 6:35 pm

Any interest in making this an Android app? Sorry no plans to move to iOS for me. It going to be slow going but I need a project
for a programming class that I am taking and this seems to be a good one. This would remain 100% free on my end.
The only thing I will get out of it is experience. Been programming over 10 years now but this is my first stab at Android and Java.
So I need something worthwhile to challenge me.

Mike
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby NOTAR » Sun Jul 08, 2012 11:26 pm

HI,

I get an issue with the pack voltage:
"List index out of bounds (0)".

I cannot change voltages. Also, I had to change points to commas for a calculation to work.
While calculating RPM with voltage, kV and gov. setting, I get no result.

Hope you can help me out:)
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby cquinby » Mon Jul 09, 2012 3:29 am

NOTAR wrote:HI,

I get an issue with the pack voltage:
"List index out of bounds (0)".

I cannot change voltages. Also, I had to change points to commas for a calculation to work.
While calculating RPM with voltage, kV and gov. setting, I get no result.

Hope you can help me out:)


are you trying to type in the voltage into the settings page? Use the arrow buttons to increase and decrease the voltage. The range is 3.00v per cell to 4.5v.

Make sure you have the number of cells entered into the Cell Count section. Not sure what you are entering commas into, I can't add them anywhere. If you can post a screen shot it would help.
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quin?by, verb, 'kwin-bE:
1 a: To crash (your helicopter) on the maiden flight.
2 a: To roll (your helicopter) over, destroying the main blades.
e.g. I quinbied my helicopter yesterday. Don't quinby the helicopter. He who quinbies often, has a good relationship with the UPS driver. If you're not quinbying, you're not flying hard enough.
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby NOTAR » Mon Jul 09, 2012 9:08 am

Ok so I restarted the program and now it works :huh: :

However, here's the message and the screenshots anyway.

You can see two screenshots, one of the battery setup (I used the arrows and yes, I cannot type a comma there, only numerical values it seems but then I get that error mentioned in my previous post).
The second screenshot is of the window where it should show voltage but it stays at zero, even if I click the calculator.

Greets
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby cquinby » Mon Jul 09, 2012 9:29 am

I have no idea how you are getting the commas into the fields.

Take those out and get the periods back in. Make sure you are hitting the Calculator button to calculate the data once your perameters are entered.
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quin?by, verb, 'kwin-bE:
1 a: To crash (your helicopter) on the maiden flight.
2 a: To roll (your helicopter) over, destroying the main blades.
e.g. I quinbied my helicopter yesterday. Don't quinby the helicopter. He who quinbies often, has a good relationship with the UPS driver. If you're not quinbying, you're not flying hard enough.
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby NOTAR » Mon Jul 09, 2012 9:34 am

Most fields already had commas. I used the calc button.
Now the programme works fine and I think this is the best one I've used so far!
I also would wish for an iOS app:)

Thanks for your replies!
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby Paulsheli63 » Sat Sep 19, 2015 1:25 pm

Hello Guys, can anyone tell me if this calculator will help me determine the gearing and motor kv, if I'm using a kontronik esc and motor? If I understand correctly, this Calculator was designed to calculate gearing and head for the cc esc. my motor kv 225, gearing 7.5 ratio, 12cells, 4x 800mm blades, turning the head at 1183 rpm is my goal. according to Scale rc cal, my motor and gearing will only give me 779 rpm, am I doing something wrong?

Paul
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby cquinby » Sat Sep 19, 2015 1:36 pm

Yup, doing something wrong... I get 1079 at 90% with that setup.

paul.jpg


The 90% is for a fixed endpoint throttle curve. How does this equate to a governor? For Castle you want that throttle percent between 80 and 95% to keep things happy (I target 87.5% so I have room to move up or down if I don't like the HS I get).

For the Kontronics and some of the other ESC's they tend to govern the top 20% of the ESC based on my tests. So 90% in the Calculator would be approximately 50% on your radio when in governor mode. 95% in the calculator would be approximately 75% on your radio.

Hope that helps and makes a little sense...
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quin?by, verb, 'kwin-bE:
1 a: To crash (your helicopter) on the maiden flight.
2 a: To roll (your helicopter) over, destroying the main blades.
e.g. I quinbied my helicopter yesterday. Don't quinby the helicopter. He who quinbies often, has a good relationship with the UPS driver. If you're not quinbying, you're not flying hard enough.
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Re: New ScaleRCHelis.com Electric Calc 08-20-08

Postby cquinby » Sat Sep 19, 2015 1:40 pm

Oh and if you want to target 1183, put the gearing, LiPo count and target HS into the second calculation. I changed the throttle percent to 87.5% and rand the data for you. You will want around a 250kv motor to accomplish that and have room to move up or down on the HS.

paul2.jpg
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quin?by, verb, 'kwin-bE:
1 a: To crash (your helicopter) on the maiden flight.
2 a: To roll (your helicopter) over, destroying the main blades.
e.g. I quinbied my helicopter yesterday. Don't quinby the helicopter. He who quinbies often, has a good relationship with the UPS driver. If you're not quinbying, you're not flying hard enough.
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