Helicopter Power & Setup Calculator :

Dark Horse RC

Battery Pack:
Amps (estimate) Watts avg... mA/min
  V | Full Flat
minutes avg. pack drain mAh used
Main Gear Teeth:
  Metric Imperial --(convert units)
Motor Pinion:
g AUWeight
oz AUWeight
Motor RPM/V:
Kv Watts/kg
Efficiency Factor:
mm rotor
inch rotor
Motor RPM:
kg/m disk load oz/ft disk load (hover)
Rotor RPM:
KM/H tip speed
MPH tip speed
Try the Advanced
Calculator prototype
KMH max FF
MPH max FF
Quick reference guide v1.6b (save the Mobile page version to your phone for offline use at the field)
Snap in stock values
Gear RPM Weigh/g Rotor mm Amps Data source |
Snap in stock values
  Gear RPM Weigh/g Rotor mm Amps Data source |
120 3500 200 330 5.0  
150 2800 700 700 12.0 forum
120 4000 265 430 4.5 thread2  
162 2700 1800 1070 18.0  
180 2600 360 560 5.2  
110 2000 1575 1060 17.0 thread
110 2500 375 620 4.8 thread
  180 2000 1800 1040 18.0 thread  
140 2100 300 527 3.6 thread  
93 2500 1600 950 15 thread  
140 2500 410 550 6.0 thread  
96 2000 2600 1200 20.0 thread  
    140 2500 385 556 6.0 thread  
140 2500 474 600 10.0 thread  
  ---------------- All Micro Heli Resources -------------------  
64 2600 28 180 1.14 thread  
Custom memory presets
96 1400 220 500 2.5 thread  
9 level
or Spawn New Calculator Email to a friend ;).


- Internet Explorer must 'allow blocked content' to use calculator scripts.
Save the Mobile page version to your phone.
- To easier compare setups, define two Restore buttons, use 'undo' and 'redo' buttons or launch 2 versions of the calculator page

- Things to be taken into consideration when assessing the calculator results:
Whether you aim for RPM at zero pitch or at hover pitch loading (at what flying weight?)
How accurate is the motor kv (rpm/v) rating, eg. some justgofly winds seem to vary.
Operational battery voltage under load, so try out the middle three radio buttons (pack voltage) for a better guide range.
The actual efficiency of the motor and other drag factors such as gear mesh and blade profile drag.
The calculator should really be thought of as an estimator at best.
- Brushed motor are in the 60-70% efficiency range and brushless may achieve 75-90% efficiency.
- An FP is normally geared to hover at 65-75% throttle.

- When using the pack voltage radio button Full to Flat you will notice that Amps and Watts are also recalculated to show a lower Amp draw at higher voltages. Note the effect is exagerated as the rotor RPM also increases at higher voltages and would use more Amps to over come drag, something not modelled in this simple version. The the Advanced Calculator prototype tries to do this more accurately.
- Some text fields can be typed into and auto update when clicked, tab'd away or just press return.
- Edit the average Amp consumption rate to estimate maximum battery pack runtime.
- Alternatively, if you know your setup's flight time when hovering then enter the number on mins and calculate back the average Amp draw (if 100% capacity could be used).
- Note that you can shift the pack voltage with the radio buttons, just a guide to Amp draw ranges, not for true runtime calculations as there is no way to correspond a pack voltage to remaining capacity under unknown loads.


- 'Efficiency Factor' means you can use the drop % as a throttle if you wish but remember to drop at least 10 to 20% for real world losses. 90% is about the best zero load performance your going to ever see (eg. 90% = (100% throttle)-(10% efficiency factor)). Note that ESC's throttle % are not normally as linear. Also the resulting RPM figure is meant to be a guide value under load like in hover. Zero pitch loading at 100% throttle may be a lot higher RPM. You just got to juggle what you know from your experience of your particular heli setup.
Given that the Kv of your motor may vary +/-10% from manufactures spec, the true condition of your batteries under load, if your belt tail drive is a bit too tight, any tail rotor demands or your ESC motor timing is set aggressively etc. etc. etc. all can significantly impact real life numbers. You get the picture though right ;)... ball park estimates.
For motor efficiency info try www.fastelectrics.com and

You can just about verify the actual RPM by taking low frequency sine wave audio measurements like the method described here. All you need is a good audio editor that can give you accurate sample lengths like Sony Sound Forge. eg. Low frequency EQ filter Hornet X-3D (27T on fresh charge) audio recording revealed a max of (44100/880 samples)*60 = 3006 RPM with hover loading.
Also check out grnbrg's grnbrg?$10 (Or less!) rotor tach, or try this thread ;).


Rotor RPM = (Motor RPM/V * Battery Voltage) / (Main gear Teeth / Pinion Gear Teeth) * (% Efficiency /100)
Runtime max without losses = (Battery Capacity Ahrs) / (Amps average) * (60 mins)
Or Amps average = (Battery Capacity Ahrs) / (Runtime) * (60 mins)

Tip speed KMH = (Rotor RPM * 60 mins) * ( (22/7) * Rotor diameter in mm) ) / 1000000
Tip speed MPH = ((Rotor RPM * 60 mins) * ( (22/7) * Rotor diameter) ) / 1000000) / 1.609344

Max safe Forward Flight speed estimate = Tips speed * 0.3, before the onset of uncontrollable cyclic handling from retreating blade stall (violent 'pitch up' effect 90º rotor offset to retreating blade), may occur between 0.3000 and 0.3333 of tip speed. Read the theory by Colin Mill, more here.
Remember that the rotor rpm will probably bog down under load and the heli may not be performing at full pitch for max FF. So with conventional curves the throttle may not be at 100% unless you run a flat 100% throttle curve. Try it and you'll see that it can be a fine balancing act between main rotor pitch and forward rotor tilt.


- There are 3 custom memory slots to save and restore custom model setups into your browser's cookies. Makes it easier to compare custom setups with one click and save model setups for another day (valid until the year 2022). There may be other malfunctions that crop up as old data is restored on a future modified web page, so may look odd. If this happens refresh the page and overwrite the old saved data with the newer format. Or try using one of the older versions. Note that the following link formats to the same page will save and restore different cookies (different domains): http://www.dhrc.rchomepage... or http://dhrc.rchomepage...

- If your Internet connection is not that reliable then you can always File->SaveAs this page to your hard drive and use a local copy when ever you like.

- Problems with metric Kg and mm? Try this online unit converter ;)

Need more battery and motor data? Try these other calculators and resources:

- Progressiverc.com plenty of motor, ESC and battery data.
- Estimate Electric Motor & Prop Combo from the useful Beginners' Guide to Model Aircraft.
- Electric Motor Calculator good for planes and props etc.
- KC's Power System Comparison Spreadsheet, useful Excel tool for heli's
- www.peakeff.com/ test motor efficiency and generate online graph data.
- Drive Calculator, or download for extensive motor prop modeling
- Mmotocalc.com download 30 day trial, good for flexible airplane data modeling.
- NASA's FoilSim II is a great applet to play with.
- Aerodynamics for Model Aircraft learn about Airofoils.
- Colorado Gliders.com has a wide variety of useful plane related Tools & Calculators
- WebOCalc, in the software section for a good plane setup estimation tool for motors and props etc.
- MrMel's Headspeed calculator

- e-Motor Calculator for Helicopter (Prototyp)
- HeliPort for Windows desktop and Windows Mobile 6.x, includes a audio sample calculated rotor RPM tachometer.

- Excellent spread sheet for rotor dynamics, uses blade element/momentum theory and includes tip loss and flybar. Very good stuff!

Other info:
- Helicopter physics: Colin Mills Practical Theories parts 9,10 and 11(other parts here), a must read!.

Credits & model development:
Please see this thread.

Copyright ©2007. Free for noncommercial use only.
We take no responsibility for any damage caused as a result of any predictions etc.

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