Outer rotor (outrunner) motor control circuit
Outer rotor (outrunner) motor control circuit
(OP)
I am an electronic ignoramus. I wish to use a motor such as this http://www.hobby-lobby.com/brushless-axi2204.htm for a hifi turntable. These motors are primarily aimed at the radio control aircraft hobby market, so the only controllers I can find are for use with R/C systems. Can anyone suggest a source of motor controllers for this sort of motor which allow accurate speed control, running from the AC mains rather than batteries?





RE: Outer rotor (outrunner) motor control circuit
Gunnar Englund
www.gke.org
RE: Outer rotor (outrunner) motor control circuit
RE: Outer rotor (outrunner) motor control circuit
Benta.
RE: Outer rotor (outrunner) motor control circuit
RE: Outer rotor (outrunner) motor control circuit
Gunnar Englund
www.gke.org
RE: Outer rotor (outrunner) motor control circuit
RE: Outer rotor (outrunner) motor control circuit
which at 3000 to 7000 RPM exhibited less than 2 microsec
variation from rev. to rev.
It wasn't difficult...
RE: Outer rotor (outrunner) motor control circuit
Gunnar Englund
www.gke.org
RE: Outer rotor (outrunner) motor control circuit
RE: Outer rotor (outrunner) motor control circuit
They are far less expensive than alternative brushless motors.
($200 as I recall for a 1HP capable motor)
One big issue is the need for cooling. They are intended to be mounted on an RC aircraft with signficant airflow for cooling, you are going to need to add a fan and other details...
I was thinking that I would add a something, whether a magnet&hall sensor or quadrature optical for comutation rather than run sensorless.
My highest level of curiosity is about the durability. Unlike the brushed RC aircraft motors, the only wear item should be the bearings.
(assuming you do not let the magnets get hot, they are NdFeB, and as soon as the get above a relative low temperature, no magnet.
Really curious about the technology in the speed/comutation controllers that are sold to go with them.
RE: Outer rotor (outrunner) motor control circuit
Mike Halloran
Pembroke Pines, FL, USA
RE: Outer rotor (outrunner) motor control circuit
Gunnar Englund
www.gke.org
RE: Outer rotor (outrunner) motor control circuit
RE: Outer rotor (outrunner) motor control circuit
I understand your application a bit better now. My comment on sensorless BLDCs stands, however.
It is possible to drive BLDCs very smoothly using sinewave drive, but this is only feasible using motors with commutation sensors (Hall sensors, or whatever).
You might look to Toshiba Microelectronics, they have a range of controllers for sine-wave drive. You do need to add a sensor circuit to the motor, though.
Benta.
RE: Outer rotor (outrunner) motor control circuit
RE: Outer rotor (outrunner) motor control circuit
I.e. if substantial acceleration is not involved, one cycle should look pretty much like the next. I.e., you may not know where the rotor is in space, but you know approximately where it is in time.
Mike Halloran
Pembroke Pines, FL, USA
RE: Outer rotor (outrunner) motor control circuit
RE: Outer rotor (outrunner) motor control circuit
In fact, most synchronous motors work without position sensors. The trick in your case is to feed the motor a voltage that corresponds to the flux derivative as the motor turns at the desired speed.
In most larger motors, that would mean a sine waveshape. In these smaller motors it probably means that you need a distorted waveform to get a smooth running (to avoid rumble). Such a waveform is easily synthesized and needn't add much to the cost.
Gunnar Englund
www.gke.org
RE: Outer rotor (outrunner) motor control circuit
to phase-lock to a back-EMF sensor and if necessary generate a sine-wave of any reasonably small distortion.
As everywhere, it is a compromise between performance and
complexity i.e. cost.
During acceleration the rumble doesn't matter so the PLL
may be switched in only after the nominal speed is reached.
<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032
RE: Outer rotor (outrunner) motor control circuit
My comment on sine-wave drive and the need for sensors come from the fact, that with sine-wave drive you have no meaningful back EMF and can not use it for commutation. Sensorless BLDC drive only works with trapezoidal drive, which again leads to torque ripple that is unwanted in your application.
The working mode for the sensorless controllers that I know is as follows:
1: DC exitation. This means, that the motor is brought to a know state by applying DC to the coils and thus rotating the rotor to a known place.
2: acceleration. A 3-phase (others are possible) frequency ramping drive voltage is applied to the motor, accelerating it.
3: At a certain point, the back EMF is large enough to be used for commutation. The motor is now in normal running mode.
Now, in this application, you could replace (3) with just forgetting the commutation and regard the motor as a synchronous one. It might work. However, just applying the frequency ramp and not bring the motor in a known state first is questionable, so a bit of extra logic is required for the circuit.
ncbuska: if we are looking at a BLDC as a synchronous motor in this case, why do a PLL? As I said, the back EMF would be meaningless, and the generated frequency for the motor would suffice. The feedback from the motor would just be the generated drive signals, and they are known already from the drive circuit.
Benta.
RE: Outer rotor (outrunner) motor control circuit
You are of course right: sine-wave drive doesn't generate
back-EMF and trapezoidal drive has varying acceleration
within a cycle.
It is again a matter of design to select a compromise
between the two extremes where the back-EMF is detectable
and the force variation is still acceptable.
The closer we come to the sine wave, the noisier will
be the back-EMF sensor. The PLL filters out this
jitter.
<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032
RE: Outer rotor (outrunner) motor control circuit
Right, but I still question the PLL. If the motor is running synchronously, there is no need. If the motor is out of synchronism, you don't know where you are anyway.
The premise here is to run a BLDC as a synchronous motor, and it that case the drive controls the rpm. I don't see the need for an extra control loop that is unable to do anything.
Regards,
Benta.
RE: Outer rotor (outrunner) motor control circuit
commutated waveform. The Pll is a relative easy way to filter this noise out.
<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032