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LAN_403

Nikhil

Sun Dec 28 2008, 10:36AM

Registered Member #1751 Joined: Fri Oct 10 2008, 03:16PM
Location: India
Posts: 16

Recently i managed to extract some outrunners from old dvd drives. I would like to build ESC for each of them keeping the circuit simple and rugged.'Rugged' bcoz i'll be experimenting with the windings. I prefer not to employ feedbacks in the circuit ie no hall effect sensors and other speed monitors.
I know getting an ESC would be the best option but i need to try out building these drives. Like the stepper motor which can be run by any of the pulse schemes can the outrunner be also driven similarly maybe employing a couple of fast switchers(555's maybe) operating synchronously delivering the correct pulse to the correct winding?
Can anyone help me? Can a driver be designed without a feedback?

Avi

Sun Dec 28 2008, 03:18PM

Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410

you can indeed run them similar to the way a stepper motor is driven, however as load increases it is likely to fall out of sync.

Carbon_Rod

Sun Dec 28 2008, 05:10PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

The hobby 3-phase brushless electronic speed controls are low cost ($44.--).
Or build one using an MCU to switch the gate drivers for 6 MOSFET.

The CD and harddrive motors do not perform well in the stepwise manner.

Cheers,

Nikhil

Mon Dec 29 2008, 07:37AM

Registered Member #1751 Joined: Fri Oct 10 2008, 03:16PM
Location: India
Posts: 16

Carbon_Rod wrote ...

Or build one using an MCU to switch the gate drivers for 6 MOSFET.

Yes i agree, but how to do tat ?

Avi

Mon Dec 29 2008, 08:51AM

Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410

3 n channel and 3 p channel mosfets in a 3 phase bridge. the MCU should output double edge 3 phased PWM.

Nikhil

Tue Dec 30 2008, 01:27AM

Registered Member #1751 Joined: Fri Oct 10 2008, 03:16PM
Location: India
Posts: 16

Avi wrote ...

the MCU should output double edge 3 phased PWM.

Perhaps if u're more specific abt the MCU i can start looking for a good one that fits. I suppose the 3 phase bridge can be gated by the MC33395 which is MC driven , are the better alternatives? what do u suggest?

tesla500

Tue Dec 30 2008, 08:35AM

Registered Member #347 Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106

You don't necessarily need an MCU, you can buy chips such as the MC33035 to do 3phase PWM generation, no programming required.

I'd stay away from sensorless operation at first, sensored operation is simpler, as no potentially unreliable rotor position estimator is required; the controller knows exactly where the rotor is. All CD/DVD motors I've seen already have the 3 hall sensors installed. If they're buffered output (3 pin) they'll work with the 33035 directly, otherwise (if they're 4 pin) a simple comparator is needed to turn the differential analog signal into digital.

David

Nikhil

Tue Dec 30 2008, 03:10PM

Registered Member #1751 Joined: Fri Oct 10 2008, 03:16PM
Location: India
Posts: 16

Excellent !! The MC33035 is a good one employing hall effect sensors. Has anyone tried it? Well i am bit confused on whether or not to use the closed loop speed control. And how do i realise the pi n/w of 'current sense reference'?

Ok, the TA8466AF ckt is as simple as the MC33035 but i think it needs a control signal at pin5. I couldnt get what kinda cntrol signal is given over there, the datasheet i had didnt comment much on that. Unless the cntrl sig is of an MCU, i feel the ic is as good as the previous one. Anyone familiar with it?
The A8904 is another one WITHOUT sensors and the ckt seems equally simple as the prev ones but needs access to the centre of the wye.
What are the max rpm supported by these ICs? I would prefer the one with the max

tesla500

Wed Dec 31 2008, 01:28AM

Registered Member #347 Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106

I've used the MC33035 before, it was one of my early electronics projects. It worked fine, driving the spindle motor out of a laserdisc player. You don't need closed loop speed control unless you want very precise speed regulation. Open loop control is fine if you're driving an airplane propeller or a model car. The 'current sense reference' is for current limiting, to avoid sending too much current through the motor windings at low speed. It may or may not be needed in your application.

The TA8466AF datasheet isn't really written very well. Power is limited, 18V 0.7A max, with adjustable current control on pin 5 it looks like. It says it's designed for driving the drum motor in a VCR, which quite low power.

If you want to control the MC33035 from an MCU, you could make a simple PWM DAC to drive the 33035's PWM comparator.

I haven't used the A8904, but it looks good. Sensorless BLDC motors can have a hard time starting though, especially if driving a big load.

All of the sensored chips can run the motor very fast, probably into the hundreds of thousands of RPMs. I'm not sure about the sensorless controllers, and how fast the position estimator will work.

David

Nikhil

Wed Dec 31 2008, 02:57AM

Registered Member #1751 Joined: Fri Oct 10 2008, 03:16PM
Location: India
Posts: 16

Ok, think i'll spend some time with the MC33035. Are there other ICs similar to tis one? And just for my in4n- how to build the current sense reference? What abt the output buffer, how can i implement it?

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