Operating motors with no propellers
- Thread starter 3rdof5
- Start date
No, they will automatically shut down after a short time with no props.
The motors are speed controlled, and are pefectly happy to run unloaded. It's also a good way to listen for any noisy bearings.
As has been said- the motors require no load to operate. Speed is tightly controlled by line frequency. They will not over rev and destroy themselves like a DC motor or unregulated petrol engine might. Simple analogy is the spindle motors on my SNC routers, they are three phase 2 pole so at 300hz line frequency they run at 18000 rpm whether they are loaded by the cutter or free of the job. The phantom motors are simply miniatures versions of the spindle motors.
It is recc'd not to hit max throttle for too long as the motors will approach their KV rating ... but general test running is no problem at all.
As another says they do have speed limiting but its based on the AC style of 3 wire power to them. The power is basically pulsed and will only hit a max figure and that's it.
Nigel
As another says they do have speed limiting but its based on the AC style of 3 wire power to them. The power is basically pulsed and will only hit a max figure and that's it.
Nigel
Approach KV rating? There is absolutely no fear of the motors over revving. They are driven by a sine waveform, rotor speed is locked to line frequency. The no load speed will be identical to that as with props for any commanded throttle setting. The drive waveform looks nothing like you ordinarily see from a typical BLDC ESC. It is very clean, I was surprised when I hooked up my oscilloscope to the motor fly leads.
Over-revving is not what I said or intended.
No BL motor reaches its KV rating ... because of load ... but running without load allows the motor to approach KV rating rpm.
For those others confused ... KV is basically RPM per Volt. In theory a 1000KV motor could give 1000rpm for each Volt applied ... in practice it falls far short of that due to load.
Allowing the motor to rev up to that should be fine but budget motors have been known not to like it ...
Nigel
No BL motor reaches its KV rating ... because of load ... but running without load allows the motor to approach KV rating rpm.
For those others confused ... KV is basically RPM per Volt. In theory a 1000KV motor could give 1000rpm for each Volt applied ... in practice it falls far short of that due to load.
Allowing the motor to rev up to that should be fine but budget motors have been known not to like it ...
Nigel
I can confirm the motors run at the same speed with no props. I didnt rev it right up, just tapped the throttle to hear the difference, let em idle for a few seconds and stopped em. They sounded quite happy.
I can upload here many videos of Brushless motors running with different props and you can HEAR the difference in RPM let alone that I actually own and use a laser tacho which clearly shows change in RPM ...
But back to running the motors without props - as found - it is ok ... just not recc'd to go full throttle for long.
Nigel
But back to running the motors without props - as found - it is ok ... just not recc'd to go full throttle for long.
Nigel
This is bot a consideration for a phantom 3. Propellor or no propellor fitted the motor speed is deermined exclusively by the throttle position. The point you seem to have missed is that the motors are driven by a sine wave, not simply chopped DC as with basic ESC. The speed is determined by line frequency and number of poles, as is the case with any synchronous AC motor.
So what ur saying is that these are actually synchronous ac motors and are actually powered by on board ac invertors with variable frequency?
They are BLDC motors driven by variable frequency sine wave drive (inverters controlled by an SOC). The speed is, as with any AC synchronous motor determined by line frequency. The motor back- EMF and phases currents are constantly interpolated to determine rotor position and modify the drive signals to very accurately regulate the RPM. While the TI motor drivers mimic a tupicall RC ESC they are significantly more advanced in their operation.
You aren’t comparing apples with apples here, the phantom 3 motors are not driven by a basic ESC, RPM is very accurately controlled independent of shaft loading.
I agree thats a very innovative and high tech design. Go DJI!
Your words not mine.
I am well aware of how ESC works for Brushless motors and the DJi motors are plain BRUSHLESS motors - there is nothing fancy about them whatsoever ..... apart from the CW and CCW shaft threading.
A sinewave creates the ON / OFF pulsing that the AC 3 wire BL motor requires ...
Second - the speed of a brushless motor is determined by the frequency of the 'pulsing' or as you like to keep iterating ... sinewave.............. AND the voltage applied. As the load increases in for example larger prop - this creates a voltage drop and speed is consequently less.
The DJI as with any well designed QUAD should have 4 equal motors to reduce the work load of the Flight Controller. The accelerometers and other sensors talking to the FC along with the command input you give determines the motors speed and in so doing the thrust to solve the requested action.
Brushless motors are brushless motors QED. DJI do not have any magic design BL motors ... you could rip DJi motors out and fit Turnigy ... Mongoose ... any other similar KV sized BL motor and you would achieve similar results.
Nigel
??? DJI have some magic BL Motor ?? Since when ?
Basic ESC ? If you are implying that I don;t know the difference between a BRUSHED and a BRUSHLESS ESC ... then sorry - you are grossly mistaken. Having suffered years of BRUSHED motors and controllers in car rcaing / boats and even very early pioneer days of e-flight ... then been around as BL motors and Lithium tech took over ... I actually object to your assumption.
The RPM pf a DJI or any quad / multi-rotor is controlled by Flight Controller and its solving the flight according to your stick commands. The FC will adjust the power fed to each ESC to arrive at correct speed for that action.
The ESC in fact acts based on the command signals sent to it ..... and they ARE basic BRUSHLESS ESC's ... only difference is that are board mounted instead of separate...
My 450 Quad has the motors from my P3S and each controlled with own Aerostar 20A ESC and in turn the ESC's receive their command signals from the Betaflight Flight Controller .......... in basically same way the Phantom does !!
Nigel
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