Post by thread:[EE]:PWM and DC Motors.

Hi all ... I know this subject has been discussed many times before, I have been through the archives but still find myself puzzled !! My problem is this - can anybody help me out with a correct routine for determining the best pwm frequency for a particular motor. Eg - I have a 12volt brushed Dc motor of unknown size ( Watts should be easilly determinable with a bit of Ohms law ) I wish to drive it forward only, using pwm and fets ( pwm being generated by CCP engine ) - I am not EE trained but am comfortable with electricky, it strikes me that there are several variables which can be combined into a loose rule of thumb. Well thats it - simply put, which is the best freq to drive a Dc motor using pwm and how to determine it ?? Thanks for your time. Steve ----------------------------------------------------------------------- Information in this email may be privileged, confidential and is intended exclusively for the addressee. The views expressed may not be official policy, but the personal views of the originator. If you have received it in error, please notify the sender by return e-mail and delete it from your system. You should not reproduce, distribute, store, retransmit, use or disclose its contents to anyone. Please note we reserve the right to monitor all e-mail communication through our internal and external networks. ----------------------------------------------------------------------- -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

In a message dated 01/15/2003 16:40:03 Eastern Standard Time, .....Steve.GoringKILLspam@spam@BSKYB.COM writes: > Well thats it - simply put, which is the best freq to drive a Dc > motor using pwm and how to determine it ?? > The frequency really doesn't matter. It gets smoothed out by an RC filter anyway. If you are using the CCP module from a PIC I would run it at least at 1500 cycles/sec at a 50% duty cycle. I think the minimum frequency you can run with a 20mHz resonator is about 1230 cycles/sec. Sid Weaver W4EKQ Port Richey, FL -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> I know this subject has been discussed many times before, > I have been through the archives but still find myself puzzled !! > > ... > > Well thats it - simply put, which is the best freq to drive a Dc > motor using pwm and how to determine it ?? Short answer: a few 100Hz. Long answer: there are lots of factors that have been beat to death here as recently as a few weeks ago. A high frequency heats the switching element because it spends too much time in transition between on and off. Too low a frequency and the motor reacts to individual pulses instead of their average. An additional wildcard is audible noise. There is no way to guess this because it depends on things that are not specified, like how tight the windings are held. So after much calculations and wringing of hands you end up with a few 100Hz. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

> The frequency really doesn't matter. Um, I bet .1Hz or 1MHz wouldn't work too well. > It gets smoothed out by an RC filter anyway. Huh!!? Unless you're talking about linear drive (and we were specifically talking about PWM drive) there is no RC filter. The pulses get smoothed out by the inertia of the motor, and to some extent by the motor coils acting as inductors. > If you are using the CCP module from a PIC I would run it at least > at 1500 cycles/sec at a 50% duty cycle. I think the minimum frequency you > can run with a 20mHz resonator is about 1230 cycles/sec. The 1230Hz figure sounds about right from memory, and should be fine for driving a motor. The only drawback at that frequency might be an annoying audible whine. At a few 100Hz PWM frequency you can do it in software and therefore drive a bunch of motors from the same PIC. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Olin Lathrop wrote: > > Well thats it - simply put, which is the best freq to > > drive a Dc motor using pwm and how to determine it ?? > Short answer: a few 100Hz. Shortest answer: RTFM. If DC motor is clearly allowed by specs to be "PWMed", then it should be "PWMed" at specified frequencies, otherwise it shouldn't be "PWMed" at all. > Long answer: there are lots of factors that have been > beat to death here as recently as a few weeks ago... Beaten to death approach should be revisited, I think. World has changed. Now there are cheap & efficient DC/DC converters that could be controlled by PIC to efficiently deliver variable DC to DC motor. Please, don't be hard on me for specs' orthodoxy and non-orthodoxy with beaten to death obvious to all unwritten rules. Mike. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

I use 2.8kHz in my controls for model motors from 50W to several kW. http://www.rc-hydros.com Andy At 04:46 PM 1/15/03 -0500, you wrote: {Quote hidden}>In a message dated 01/15/2003 16:40:03 Eastern Standard Time, >@spam@Steve.GoringKILLspamBSKYB.COM writes: > > >> Well thats it - simply put, which is the best freq to drive a Dc >> motor using pwm and how to determine it ?? >> > >The frequency really doesn't matter. It gets smoothed out by an RC filter >anyway. If you are using the CCP module from a PIC I would run it at least >at 1500 cycles/sec at a 50% duty cycle. I think the minimum frequency you >can run with a 20mHz resonator is about 1230 cycles/sec. > > >Sid Weaver >W4EKQ >Port Richey, FL > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

>The 1230Hz figure sounds about right from memory, and should be fine for >driving a motor. The only drawback at that frequency might be an annoying >audible whine. At a few 100Hz PWM frequency you can do it in software and >therefore drive a bunch of motors from the same PIC. I do 2.8kHz in software just fine, while measuring a RC servo input signal with 6uS resolution. Andy -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

Andy mentioned a key point: what resolution does the application need? Doug -----Original Message----- From: Andy Kunz [TakeThisOuTmontanaEraseMEspam_OUTFAST.NET] Sent: Wednesday, January 15, 2003 5:20 PM To: RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU Subject: Re: [EE]:PWM and DC Motors. >The 1230Hz figure sounds about right from memory, and should be fine for >driving a motor. The only drawback at that frequency might be an annoying >audible whine. At a few 100Hz PWM frequency you can do it in software and >therefore drive a bunch of motors from the same PIC. I do 2.8kHz in software just fine, while measuring a RC servo input signal with 6uS resolution. Andy -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservEraseME.....mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservmitvma.mit.edu with SET PICList DIGEST in the body

>Andy mentioned a key point: what resolution does the application need? >Doug Nothing fancy - I am actually driving a prop shaft on an electric outboard motor and intend to have a couple of push buttons for increase / decrease speed and on / off. Had intended to use 8 speed settings from 50 to 100%. Steve ----------------------------------------------------------------------- Information in this email may be privileged, confidential and is intended exclusively for the addressee. The views expressed may not be official policy, but the personal views of the originator. If you have received it in error, please notify the sender by return e-mail and delete it from your system. You should not reproduce, distribute, store, retransmit, use or disclose its contents to anyone. Please note we reserve the right to monitor all e-mail communication through our internal and external networks. ----------------------------------------------------------------------- -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservEraseMEEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

>Nothing fancy - I am actually driving a prop shaft on an electric >outboard motor and intend to have a couple of push buttons for >increase / decrease speed and on / off. > >Had intended to use 8 speed settings from 50 to 100%. I believe you will want something in the 1000-3000 range with those motors. Andy -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservspam_OUTKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> Shortest answer: RTFM. > If DC motor is clearly allowed by specs to be "PWMed", > then it should be "PWMed" at specified frequencies, > otherwise it shouldn't be "PWMed" at all. I've never seen a spec for a motor that mentioned PWM one way or the other, let alone specify a frequency range. > Beaten to death approach should be revisited, I think. > World has changed. Now there are cheap & efficient > DC/DC converters that could be controlled by PIC to > efficiently deliver variable DC to DC motor. And those DC to DC converters work by passing pulses from an on/off switch into a filter. Since the motor inertia and coil inductance will act like a filter, you can dispense with the filter part of the DC to DC converter. Now you're left with pulses going straight to the motor from the on/off switch. Given that, PWM is an easy way to get "linear" control over the motor. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspamspamBeGonemitvma.mit.edu>

Olin Lathrop wrote: > And those DC to DC converters work by passing pulses from an on/off switch > into a filter. Since the motor inertia and coil inductance will act like a > filter, you can dispense with the filter part of the DC to DC converter. > Now you're left with pulses going straight to the motor from the on/off > switch. Given that, PWM is an easy way to get "linear" control over the > motor. And you get benefits from angular ripple, which helps with loads that have large static or dynamic friction. It also eliminates losses from the DC-DC supply inductor etc. :o) -Roman -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestKILLspammitvma.mit.edu>

At 08:13 AM 1/16/03 -0600, you wrote: >> I use 2.8kHz in my controls for model motors from 50W to >>several kW. > >Does a 1kW motor still count as a "model" ? ;-) 1kW is a small motor - it's only going to put about 1 HP out. We run motors that will pull 90A sustained at 24V input (2.1kW in), and I make the controls to handle it. Most of us only run 1kW motors though due to cost. Check them out http://www.rc-hydros.com for the ESCs, http://www.montanadesign.com for the Boat Hobby section. I have them in planes too. Right now I'm about half done with a P-51, 43" span. It will be HOT! Andy -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestSTOPspamspam_OUTmitvma.mit.edu>

At 10:57 AM 1/16/03 -0500, you wrote: >> Shortest answer: RTFM. >> If DC motor is clearly allowed by specs to be "PWMed", >> then it should be "PWMed" at specified frequencies, >> otherwise it shouldn't be "PWMed" at all. > >I've never seen a spec for a motor that mentioned PWM one way or the other, >let alone specify a frequency range. Actually some of the micro-sized motors used for flying indoors cannot use PWM. But since they are so small they use linear outputs and they work just fine that way. I can't remember the name to save my life right this minute. Any indoor flyers here? Andy -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestSTOPspamEraseMEmitvma.mit.edu>

>Does a 1kW motor still count as a "model" ? ;-) 1kW is a small motor - it's only going to put about 1 HP out. We run motors that will pull 90A sustained at 24V input (2.1kW in), and I make the controls to handle it. It has occurred to me that with modern battery, cable (steel, kevlar, or spectra), and ("model") motor technology, "batman" like gadgets ought to be well within reach (ie given a secure attachment "up there", a handheld thing ought to be able to lift the mass of a normal sized human at a credible rate of speed. A sort of miniature hand-held winch.) Then I start to think about how sturdy the mechanical construction would need to be, and I get worried :-) BillW -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestspamBeGonemitvma.mit.edu>

>spectra), and ("model") motor technology, "batman" like gadgets ought to be They have 1 cubic inch electric models (bumblebee size) which carry surveillance equipment - audio and video! That's the other end of the spectrum. One of my friends was the first guy over 100 MPH in an electric model boat in November. They are closing in on the 125 MPH records that the internal combustion boats run! Andy -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestEraseMEmitvma.mit.edu>

On Thu, 16 Jan 2003, Andy Kunz wrote: > At 08:13 AM 1/16/03 -0600, you wrote: > >> I use 2.8kHz in my controls for model motors from 50W to > >>several kW. > > > >Does a 1kW motor still count as a "model" ? ;-) > > 1kW is a small motor - it's only going to put about 1 HP out. We run > motors that will pull 90A sustained at 24V input (2.1kW in), and I make the Sound totally inefficient ! What brushes have those motors ? best, Vasile -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Thu, 16 Jan 2003, Andy Kunz wrote: *>>spectra), and ("model") motor technology, "batman" like gadgets ought to be *> *>They have 1 cubic inch electric models (bumblebee size) which carry *>surveillance equipment - audio and video! That's the other end of the *>spectrum. *> *>One of my friends was the first guy over 100 MPH in an electric model boat *>in November. They are closing in on the 125 MPH records that the internal *>combustion boats run! Do you use dynamic stability devices ? How can you run such speed other than in a bathroom (perfectly flat water) with such small boats. Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Fri, 17 Jan 2003, Peter L. Peres wrote: > On Thu, 16 Jan 2003, Andy Kunz wrote: > > *>I have them in planes too. Right now I'm about half done with a P-51, 43" > *>span. It will be HOT! > > How does the weight compare to a gas engine ? I'd think having enough battery capacity to draw 90A for 15 minutes of flying would be more than it could get off the ground! That's impressive. -- Mitch -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Fri, 17 Jan 2003, Mitchell D. Miller wrote: *>On Fri, 17 Jan 2003, Peter L. Peres wrote: *> *>> On Thu, 16 Jan 2003, Andy Kunz wrote: *>> *>> *>I have them in planes too. Right now I'm about half done with a P-51, 43" *>> *>span. It will be HOT! *>> *>> How does the weight compare to a gas engine ? *> *>I'd think having enough battery capacity to draw 90A for 15 minutes of *>flying would be more than it could get off the ground! That's impressive. I strongly suspect that 90A is the takeoff power, they would use 40-50% of that for fast cruise. Still 40A for 15 minutes is respectable (10Ah battery at least). Peter -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>*>One of my friends was the first guy over 100 MPH in an electric model boat >*>in November. They are closing in on the 125 MPH records that the internal >*>combustion boats run! > >Do you use dynamic stability devices ? How can you run such speed other >than in a bathroom (perfectly flat water) with such small boats. No, not at all. They are hydro and aerodynamic. It is not as easy as with an airplane, but they are designed to minimize pitching effects. Actually, a slight ripple helps the boat run a little more free than perfectly flat water. After a while you get a feel for "record water." ANdy -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

At 03:13 PM 1/17/03 +0200, you wrote: >On Thu, 16 Jan 2003, Andy Kunz wrote: > >*>I have them in planes too. Right now I'm about half done with a P-51, 43" >*>span. It will be HOT! > >How does the weight compare to a gas engine ? The motors weigh about the same, but the "gas tank" for the electrics is killer. Andy -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>I'd think having enough battery capacity to draw 90A for 15 minutes of >flying would be more than it could get off the ground! That's impressive. We don't fly 90A for 15 minutes. 4-5 minutes of 125 MPH fun is PLENTY believe me! The 90A is what we will peak in boats. Airplanes are tame compared to boats. I'll probably run 30-40A max on 12V the way I fly. Andy -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>I strongly suspect that 90A is the takeoff power, they would use 40-50% of >that for fast cruise. Still 40A for 15 minutes is respectable (10Ah >battery at least). It's the same motor, but that doesn't mean we use it as hard. The power out depends on how you prop them, plane or boat either one. Andy -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>> 1kW is a small motor - it's only going to put about 1 HP out. We run >> motors that will pull 90A sustained at 24V input (2.1kW in), and I make the > > Sound totally inefficient ! What brushes have those motors ? 75% efficiency is a poor motor. 85% typical brushed, 90-93% on the brushless. You can check the motor type out on the Plettenberg website. Andy -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

{Quote hidden}> -----Original Message----- > From: Vasile Surducan [SMTP:@spam@vasile@spam@spam_OUTS3.ITIM-CJ.RO] > Sent: Friday, January 17, 2003 12:19 PM > To: spamBeGonePICLISTKILLspamMITVMA.MIT.EDU > Subject: Re: [EE]:PWM and DC Motors. > > On Thu, 16 Jan 2003, Andy Kunz wrote: > > > At 08:13 AM 1/16/03 -0600, you wrote: > > >> I use 2.8kHz in my controls for model motors from 50W to > > >>several kW. > > > > > >Does a 1kW motor still count as a "model" ? ;-) > > > > 1kW is a small motor - it's only going to put about 1 HP out. We run > > motors that will pull 90A sustained at 24V input (2.1kW in), and I make > the > > Sound totally inefficient ! What brushes have those motors ? > > best, Vasile > Vasile, he is not suggesting his 1kW motors require that much power, he was talking about different motors. Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= Any questions about Bookham's E-Mail service should be directed to .....postmasterspam_OUTbookham.com. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistserv.....TakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body