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Help needed with electronics and RC stuff (planes) for personal transport project Answered


I need a hand with getting my head around how RC plane motors are rated. I am looking at a 4000kv motor. is that 4000RPM Per volt from zero or from a nominal 6v starting voltage?

This is for a personal transport project in the vein of this one - http://hacknmod.com/hack/make-diy-electric-bicycle/
That motor looks like it is very high on the wattage front!

I have found several cheap motors and controllers on ebay that I think may be suitable

do you think that they would be able to do something similar (upto 25mph), providing that the vehicle DOESN'T have to be started from standing?

A full instructable for a personal ride project is hanging on this info...

Any help is greatfully received!



7 years ago

So its been to years. not to bump a dead thread but anything ever come of this idea? i fly rc and picture the motor not being able to overcome the drag of the bike itself much less a rider?
thank you Brian


Reply 7 years ago

I had no forthcoming information, so this has been put on the extended back-burner....
I might make something of it though in the next year or so...


9 years ago

Here is my maths for the motor...

please poke holes in it (if you can) this is for a single 7.2V 6 Cell NiMh battery pack

I have assumed a 20A operating current for the motor and horrible efficiencies for everything!
so, as long as it can turn the wheel, this is "worst case" I'm sure it will run for longer though.

it's a little hard to see, but all the info is there. Spreadsheet available on request - if it makes things easier!

Target Speed (MPH) Target Speed (M/s)    
25   11.38    
Wheel Diameter (in) Wheel Diameter (cm) Wheel Circumference (m) Target Speed (m/s) Revs / s 
26   66.04   2.07   11.38   5.48 

Rotor Diameter (in) Rotor Diameter (cm) Rotor Circumference (m)   
4   10.16   0.32   11.38   35.63 
3   7.62   0.24   11.38   47.51 
Motor speed (RPM/V) Voltage (V) RPM   
4000   7.2  28800   
Num. of batt. / pack Voltage (V) Battery power (Ah) Total Packs  
6   1.2  2.3   1  
Continuous current (A) Voltage (V) Max Power (W) battery power (Ah) A/Ah  Run Time (Theory) (Mins)
20   7.2  144  2.3   8.7  6.9
Run Time (mins) Motor efficiency Max Motor Revs / S Needed Revs / S duty cycle for PWM (%) Multiplication factor
6.9  0.6   480   47.51  9.9   10.1
efficiency run time (Mins) Total Run time (Mins)    
4.14    41.83    

Estimated Run Time
with load (@ 10% eff) (Mins)  with load (@ 15% eff) (Mins)  with load (@ 20% eff) (Mins) 
4.18    6.27    8.37 


9 years ago

Looking at the product page it says Continuous output current: 35A.  At 10V this would give you 350W, which is enough for an electric bicycle type project.  I doubt it would run at 40000RPM under these conditions, though, because it would be under a lot of load- the RPM/V figure is probably under light torque load.  I also don't see how a motor weighing 25 grams can handle 30 amp loads...


Reply 9 years ago

The ESC can handle 35A continuous, but the motor seems to run best at around 10A and bursting upto 40A (for a max of 60 seconds before it burns out!)

weight of motor is 65g :-)

I have calculated the PWM duty cycle to obtain around 450RPS is about 8% using a 3" drive wheel, and the motor is designed for a 6-8" propeller, so it should turn with sufficient torque to turn a bigger/more massive wheel without overheating.

is there any way of uploading a spreadsheet to the forum?


9 years ago

after realising my sums were wrong (Meters per second and revs per MINUTE dont work together), I have fiddled my numbers and the ratio from the motor to wheel is 1:8.7

I'm gong to try and use a 3" (75mm) drive wheel from the motor.

the vehicle should be travelling at around 5-6mph before the motor will kick in, so the loss of torque due to the larger drive wheel shouldn't be an issue.

I have deliberately engineered horrible efficiencies into my numbers to get the estimated run time. (60% efficient motor, and only a 10% efficiency with a rider on the vehicle) and runtime comes out to around 15-20 minutes @ 25mph

The efficiency shoudn't be that low as it's a wheel travelling on a horizontal surface, but it pays to be pessimistic in estimation!

as always, any help or insights are greatfully received!


9 years ago

basic pic as commented

The small red circle at the back is the motor. This will hopefully direct friction drive the bike wheel.

This is based upon the "Magic wheel" that is available (and was mentioned elsewhere on instructables)

After seeing several videos, it seems that it could do with being "electrified" to make it more stable (less pushing) and easier to ride (as both feet are on their platforms)


9 years ago

I think you might be more concerned with the torque it produces.  I don't know if you need to gear it up or plan to use it as a direct drive.  I've never tried to hold on to an R/C plane-heli prop but I'm not sure if they can power a bike fully loaded with rider.


Reply 9 years ago

Well, gearing it won't be an issue...

I'm friction driving the bike wheel from the shaft of the motor or suitable drive wheel - making it a gearbox (around 670:1)

Direct driving a bike wheel at more than 4000RPM would be somewhat scary!

I'm sort of wondering if a plane-heli motor can sustain movement without having to have an enormous amount of "extra" power (which you would usually require to overcome the inertia of being static.)

These "450" style motors are for use in models upto 2Kg (4.5Lbs) if they (with wing geometry) can launch a plane, then I'm hoping that they can move a big wheel!

More help always wanted, Thanks for commenting

I'll add a drawing tomorrow of the layout and idea.