How hard is it to drive a 3-ph brushless motor?
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From: dagmargoodboat on 9 Dec 2009 22:56 On Dec 9, 7:54 pm, Robert Sneddon <f...(a)nospam.demon.co.uk> wrote: > In message > <ba49cbaa-f1da-44d5-8106-90fb5711b...(a)z10g2000prh.googlegroups.com>, > dagmargoodb...(a)yahoo.com writes > > >A micro-stepped stepper would be ideal: smaller, lighter, cheaper, > >more rugged, and mechanically more reliable than something with a > >gearbox turning 8k rpm. > > The original poster specified high reliability over a period of years; > I don't see a 600:1 gearbox lasting that long without maintenance or > replacement. It will also exert a significant frictional load on the > motor that will change over time due to wear and lubricant expiry, > causing more control problems down the line. In addition a DC motor > capable of running at up to 8000rpm continuously for years on end will > be very expensive; what are the MTBF figures for such motors? 10,000 > hours, 50,000 hours? > > A stepper motor gets rid of the requirement for a gearbox; fewer moving > parts are a good thing, but the long-duration operation means whatever > the prime mover is it will have to be a hi-rel part and they are never > cheap whether it is a stepper motor or a DC brushless motor. > -- > To reply, my gmail address is nojay1 Robert Sneddon Yep. Not cheap, but cheaper than a high-rel 8Krpm motor + gearbox. Speed control? Trivial, of course. -- Cheers, James Arthur
From: dagmargoodboat on 9 Dec 2009 23:01 On Dec 9, 9:24 pm, S...(a)ControlQ.com wrote: > On Wed, 9 Dec 2009, dagmargoodb...(a)yahoo.com wrote: > > > A micro-stepped stepper would be ideal: smaller, lighter, cheaper, > > more rugged, and mechanically more reliable than something with a > > gearbox turning 8k rpm. > > > There are plenty under 35mm. Do you need super-smooth rotation or > > super-precise shaft positions? If not, the world's yer oyster. If > > so, maybe even then, too. > > > -- > > Cheers, > > James Arthur > > Perhaps a BLDC motor, like the one found in any old hard drive might > do the trick ... and the back-emf commutation method should work ... > > Cheers, > Rob Sciuk For BEMF commutation, the motor's got to turn some minimum speed, which suggests you'll need to spin faster and gear down. That's more parts. If the OP can tolerate the stepping motion (torque ripple), many-pole motors (steppers) really shine here. They've effectively a lossless gearbox built in (the many poles), with zero moving parts. -- Cheers, James Arthur
From: -jg on 10 Dec 2009 04:19 On Dec 10, 8:24 pm, Peter <nos...(a)nospam9876.com> wrote: > Are there some widely used stepper > motor controllers which would give me +100% to -100% rpm with a -10V > to +10V control voltage? Most stepper controllers are either SPI, or Step.Dirn types. If you wanted Linear control, then a V to F converter could give a micro-less solution. (or, you use a small uC with a ADC and a reload Timer, to build the V to F) http://www.onsemi.com/PowerSolutions/parametrics.do?id=407 eg AMIS-30542 has Step.Dirn control and also a SPI to configure the modes. or, something from here ? http://www.allegromicro.com/en/Products/Categories/ICs/motor.asp -jg
From: Paul Carpenter on 10 Dec 2009 12:34 In article <pan.2009.12.09.21.56.29.114217(a)example.net>, richgrise(a)example.net says... > On Wed, 09 Dec 2009 20:03:34 +0000, Paul Carpenter wrote: > > > > I am seeing a customer tomorrow who have an ASIC solution for doing this > > used for missiles so long life time product. Let me know if you want a > > datasheet or other details. > > Missiles? They have a very short lifetime, indeed! (albeit, they might > be on the shelf for awhile.) Now, _satellite_ should imply a very, very > long life. Most miltary and avionics has 20+ years which spares have to be made for the Nimrod is a 60's airframe and some of its avionics is still the same design. Some production runs for avionics I have seen being planned last year for 2015. You need to make exactly the same thing to avoid having to recertify the whole aircraft. In some cases to ensure making parts the manufacturer or their production supplier of sub systems, literally do last buys on WHOLE Wafers of chips to ensure supply for 20 years. .... -- Paul Carpenter | paul(a)pcserviceselectronics.co.uk <http://www.pcserviceselectronics.co.uk/> PC Services <http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font <http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny <http://www.badweb.org.uk/> For those web sites you hate
From: Paul Carpenter on 10 Dec 2009 12:45
In article <f370i598l3qthnuojpql0gogddo40cbnuk(a)4ax.com>, nospam(a)nospam9876.com says... > > Paul Carpenter <paul(a)pcserviceselectronics.co.uk> wrote > > > > >Quite common to get 3 phase pattern by PWM or Timing Pattern generator > >and gate this with PWM clock/DC to change the RMS level (part of torque) > >and adjust 3 phase pattern frequency for RPM. Watching your torque and > >RPM relationships for load and current speed to avoid stall. The 3 phase > >pattern is easy to do even for reversing in software or hardware. > > > >I am seeing a customer tomorrow who have an ASIC solution for doing this > >used for missiles so long life time product. Let me know if you want a > >datasheet or other details. > > > >> >> And I would quite like some kind of closed loop motor speed control. > >> >> Even though the torque is small, the application needs the speed to be > >> >> within about 10%. This can be done with back-EMF; should not need a > >> >> tacho. > > > >+/- 1.3 rpm at 13 rpm or higher rpm at the actual motor? > > Unfortunately I did not make it clear enough that this is at the > output shaft of the gearbox. I am currently looking at a 600:1 gearbox > so the motor would run at ~ 8000rpm. As I have seen in other posts you may be doing lower RPM than that. If you are wanting RPM limiter and speed control then maybe a sensored motor would be easier as you will have feed back for RPM directly, three of them for redundancy. > Now that I have "converged" on building my own controller, using one > of the integrated chips that exist, the biggest problem is getting the > mostly American companies to talk to me. Micromo pushes me back to > their UK agent who does not reply. Last time I had a go at this > project (1/2008) the same thing happened. I know of at least one ASIC for sensored with control signals, available in UK, email if you want details. -- Paul Carpenter | paul(a)pcserviceselectronics.co.uk <http://www.pcserviceselectronics.co.uk/> PC Services <http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font <http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny <http://www.badweb.org.uk/> For those web sites you hate |