RunRyder RC Helicopter Topic - would appreciate confirmation of calculations

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e-Minicopter Joker > would appreciate confirmation of calculations

sky vision
Heliman
Location: Ontario - Canada

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Bear with me, I'm second-guessing myself here and would appreciate input:

I have the MJ2 with Pletti 370/40 motor, Power Jazz ESC, 12T pinion and 12S TP batteries.

According to old posts I have read, I found this equation to determine headspeed:

510 kv x 44.4 v = 22644 motor rpm

reduction 12T of 13.56 = 1670 max head speed, x 0.8 = 1336

Helicopter seems to run smoothest at head speed of 1350-1400.

Is this in fact the correct equation to use?

10-23-2009 02:00 AM

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Wingman77
Elite Veteran
Location: Pulaski TN US

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how many teeth are on the main gear?

hs=load voltage(about 3.5v a cell)x kv x pinion /main gear

34.6% of all statistics are made up on the spot

10-23-2009 02:03 AM

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sky vision
Heliman
Location: Ontario - Canada

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msin gear is 67T

10-23-2009 02:16 AM

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Wingman77
Elite Veteran
Location: Pulaski TN US

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you sure about that? it must be wrong because that would put your headspeed at 4k

34.6% of all statistics are made up on the spot

10-23-2009 02:19 AM

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sky vision
Heliman
Location: Ontario - Canada

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I'm sure - I recounted and main gear has 67T.

In the equation I was using, I had the reduction that Gerd of Minicopter identified for the 12T pinion as being 13.56.

10-23-2009 02:30 AM

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Wingman77
Elite Veteran
Location: Pulaski TN US

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dude 67/12 don't equal 13....
67/12 =5.6 you either need a much smaller pinion or a lower kv motor.

34.6% of all statistics are made up on the spot

10-23-2009 02:32 AM

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Blade_Master1
Elite Veteran
Location: Canada

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Just go here

http://www.readyheli.com/Online_Hea...ulator_s/81.htm

Avg RPM you will see with 100% throttle and no governor: 3776 with current set-up

if you use an 8S lipo Avg RPM you will see with 100% throttle and no governor: 2517

it seems to me you picked a motor for a 6S power system average HS would be 1888 with that gear ratio

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10-23-2009 02:38 AM

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Wingman77
Elite Veteran
Location: Pulaski TN US

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lol he does not need that he needs a different motor.

34.6% of all statistics are made up on the spot

10-23-2009 02:42 AM

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Blade_Master1
Elite Veteran
Location: Canada

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you will want a motor with a KV rating between 250-300KV for that size

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10-23-2009 02:44 AM

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Heliman
Location: Ontario - Canada

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I've copied Gerd's post from earlier (August 2007) here:

"Reductions are then 1:12.52 with 13 tooth pinion and 1:13.56 with 12 tooth pinion.
Motor speed is 510x35=18000 rpm (about)
Recommended rotor speed is then 1450 x 0.85 = 1230 rpm for 13 tooth pinion and 1320 x 0.85 = 1120 rpm for 12 tooth pinion.
The factor 0.8, you know probably, is the factor you need as reserve for the governor mode of the esc. When your flight style is more powerful (3D) you should better use the factor 0.75, if you fly very gently like Maxi-Jokers normally fly, you can use the factor 0.85.
For 12s the recommended speeds with 0.85 are 1470(13T) and 1340rpm(12T)."

This is the link for the thread: http://www.runryder.com/helicopter/t366448p1/

The volts here are for the 10S, it would be 42 for the 12S.

Therefore, using this equation, 510x42= 21420/13.56 = 1580 x 0.8 = 1264.

Is there something else I'm missing here?

10-23-2009 02:49 AM

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Blade_Master1
Elite Veteran
Location: Canada

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Quote
510x42= 21420/13.56 = 1580 x 0.8 = 1264

I believe it's Motor KV X Volts @80% / gear ratio = HS
you are putting the efficency after the HS it is 80% of motor not 80% of HS

Also it should be calculated using nominal voltage which I believe is 3.7 per cell

also your gear ratio is incorrect 67/12= 5.58

So it should read 510KV X 37V =18,870rpm -20%= 15096 rpm /5.58 =2,705.35 HS

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10-23-2009 02:57 AM

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Heliman
Location: Ontario - Canada

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Blademaster,

I went to the site you recommended, and when I input the "final gear ratio" of 13.56, I come out with very different numbers than you are talking about. (The MJ2 has 4 gears, 12, 34, 14, and 67T).

10-23-2009 03:28 AM

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Blade_Master1
Elite Veteran
Location: Canada

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ahh there is some confusion going on with the final gear ratio

what is your final ratio if it is 13.56 which is rather high ?

510KV X 37V =18,870rpm -20%= 15096rpm / 13.56 gives you a head speed of 1113.27 rpm

so if you're certain about the final ratio you need a higher KV motor

let's see
1100kv X 37= 40,700 rpm - 20%= 32560 rpm / 13.56 gives a HS of 2401

trying the same formula
you would need about an 850KV motor

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10-23-2009 03:39 AM

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Heliman
Location: Ontario - Canada

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Quote
what is your final ratio if it is 13.56 which is rather high ? 510KV X 37V =18,870rpm -20%= 15096rpm / 13.56 gives you a head speed of 1113.27 rpm

The ratio of 13.56 was provided by the manufacturer of the helicopter - but I got the same value through your link by clicking on "gear ratio calculator" and inputting those numbers - 12, 34, 14 and 67.

Secondly, the batteries are 12 cell, not 10, which will have an impact on your calculation.

These are the results I obtained by inputting these numbers into the calculator link:

Quote
Voltage for this calculation (avg):3,33/cell with a total of 39,96 Nominal voltage: Spoolup RPM 100% throttle no governor (44,4v): 1670 Avg RPM you will see with 100% throttle and no governor: 1475 Max normal bogging applied you will see RPM at: 1202

From these values, it would appear that the 1400 headspeed I'm running is right where it should be - I think.

10-23-2009 04:13 AM

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Blade_Master1
Elite Veteran
Location: Canada

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right on the numbers are confirmed
sorry don't know why I did 10S instead of 12

1400HS is a little low is this for a scale heli ?
what size ?

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10-23-2009 04:41 AM

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Wingman77
Elite Veteran
Location: Pulaski TN US

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it is a joker so it is huge.

34.6% of all statistics are made up on the spot

10-23-2009 04:56 AM

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Blade_Master1
Elite Veteran
Location: Canada

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huge like a 90 ?
don't they run 1650 -1850 HS ?

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10-23-2009 05:00 AM

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nooobs
Elite Veteran
Location: Toronto, Canada

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Quote
huge like a 90 ? don't they run 1650 -1850 HS ?

Yes, huge like 90.
No, they do not run 1650-1850.
This is not a 3D bird.

Sky Vision

Since you're running the Pletti, it's recommended to use 10s. If you use 12s the motor will run very hot and low throttle percentages.

With 10s you'll need to use either 13T or 14T.

Gears:
1 - motor pinion
2 - 34T
3 - 14T
4 - main gear 67T

Gear ratios:
12T = 13.56
13T = 12.52
14T = 11.62

I'm assuming you're spinning at least 800mm blades.

Have you thought about using a Xera 4035/3Y-400 motor? I ask because if you already have 12s LiPo packs then this would be the way to go.

Read here for some info on this motor.
http://www.runryder.com/helicopter/t545157p1/

10-23-2009 05:28 AM

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sky vision
Heliman
Location: Ontario - Canada

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Thank you BladeMaster and Wingman for your comments and assistance.

Noobs,

Yes, I am using 800 blades, and yes my throttle is a bit low, at 75%. However, the motor is not running hot to touch after a flight, just warm. The batteries are quite warm at the end of the flight. Would the throttle level have something to do with this?

Will check out info on the Xera. What is its weight?

What is your throttle percentage with your set-up?

10-23-2009 11:40 AM

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pkfrizzlefry
Senior Heliman
Location: Newington, CT (Central Connecticut)

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no reason

its nice to know the math behind it but no need for a calculator anymore...

Check out dark horse
http://dhrc.rchomepage.com/calc.htm
http://dhrc.rchomepage.com/calcAdvanced.htm

best HS Calculations i ever seen and need

Fly, Fly then Fly some more!!

10-23-2009 02:56 PM

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e-Minicopter Joker > would appreciate confirmation of calculations

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