On Fri, Oct 22, 2010 at 10:56 AM, vasile surducan <[email protected]>wrote:
> > > On Fri, Oct 22, 2010 at 10:06 AM, Sebastien Lelong < > [email protected]> wrote: > >> Hi Vasile, >> >> 2010/10/22 vasile surducan <[email protected]> >> >> Hi Seb, >>> >>> Looks to me that you have understand well that different DC motors will >>> give you different EMF values: >>> >>> http://sirloon.net/loonaweb/sirblog/experimenting-back-emf-motion-feedback >>> <http://sirloon.net/loonaweb/sirblog/experimenting-back-emf-motion-feedback>So, >>> that's it, a poor method using an analog feedback, if you want universal >>> solutions seems to me you have to switch on digital feedback, which as far I >>> know can't be EMF. >>> >> >> Do you mean something like encoded wheels ? bemf is really nice to have >> because it's not invasive, you can control any DC motors without modifying >> the structure (which is great when hacking RC toys) >> >> >>> You can't do it without modifying dividers. >>> >> >> Is electronic that limited ?? C'mon, there should be a trick ! >> > > Variable gain amplifier. It modifying dividers in software keeping the ADC > resolution constant. Still a s**t... > :) > > There is another way: when read EMF the motor acts as a generator. Loading it with a variable resistive load (switched digitally using some transistors) will decrease the EMF level as you wish. However that will brake the motor as well, as high as the load becomes lower. Probably with 2 loads you can use two different DC motors. Do you intend to manufacture some kits? > Vasile > > > >> >> >> Cheers, >> Seb >> >> >>> Vasile >>> >>> On Fri, Oct 22, 2010 at 7:57 AM, Sebastien Lelong < >>> [email protected]> wrote: >>> >>>> Hi guys, hardware guys, >>>> >>>> >>>> Years ago, I built a DC motor control board, with back-emf sensor: >>>> http://sirbot.org/sirbot-modules/dc-motor-controller-board/ >>>> >>>> This board (and firmware) generates proper PWM signals to control 2 DC >>>> motors, and in the mean time, collect data about produced back-emf voltage, >>>> using ADC. There's no such power control of DC motors (which was actually >>>> done using RC tank transistors themselves), it's just about signaling. >>>> >>>> Using this board, there's a warning I'd like to get rid of today. It >>>> says "This board uses ADC (Analog-to-Digital-Conversion) to evaluate >>>> motor's >>>> speed. Voltages produced by motors are often far greater than those ADC can >>>> handle. There are voltage dividers on this board which keep those in >>>> correct >>>> range. These voltage dividers are designed so voltage produced by motors >>>> can >>>> be up to max 12V. If your DC motors produce more than 12V, you'll need to >>>> adjust voltage dividers' values or you will damage this board. You've been >>>> warned !!!" >>>> >>>> That is, if I'm using 24V DC motors, voltage coming to ADC will be too >>>> great and could damage the PIC (or worse, I could get wrong data). On the >>>> other side, using 5V DC motors, I'll obtain a narrow spectrum of values, as >>>> it's always divided by 2 (a little more). >>>> >>>> How can I perform a voltage normalization ? Whatever the incoming >>>> voltage produced by DC motors, I'd like it to be proportionally mapped to >>>> [0,5V]. I'd like this be dynamic (I don't want to unsolder/solder some >>>> resistors each time I plug a new DC motors). >>>> >>>> Please explain to me with very simple words :) >>>> >>>> >>>> TIA >>>> Cheers, >>>> Seb >>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "jallib" group. >>>> To post to this group, send email to [email protected]. >>>> To unsubscribe from this group, send email to >>>> [email protected]<jallib%[email protected]> >>>> . >>>> For more options, visit this group at >>>> http://groups.google.com/group/jallib?hl=en. >>>> >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "jallib" group. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]<jallib%[email protected]> >>> . >>> For more options, visit this group at >>> http://groups.google.com/group/jallib?hl=en. >>> >> >> >> >> -- >> Sébastien Lelong >> http://www.sirloon.net >> http://sirbot.org >> >> -- >> You received this message because you are subscribed to the Google Groups >> "jallib" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]<jallib%[email protected]> >> . >> For more options, visit this group at >> http://groups.google.com/group/jallib?hl=en. >> > > -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
