I would hate to take all the fun out of it for you, but have you considered using speed controls for RC airplanes and cars? The make things a lot simpler with a power input, a motor output, and a connector that plugs right into your RC receiver. The controllers for cars usually are only good for 6-8 cell packs, but some of the plave controllers are good for a lot more. I have a very small speed control that was about 25 bucks that is good for 25 amps. Without the cables it is about an inch by an inch and a half and a quarter inch thick. It also powers the RC receiver from the motor battery right through the servo connector. Try Tower Hobbies if you want to look at a bunch of different kinds. Ted Mawson wrote: >Thanks Duane, > >The LT1158 looks like a really good choice. You can see the data sheet for >it at http://www.linear.com/pdf/lt1158.pdf . There's a Full H Bridge >example circuit diagram given on Page 19 with examples of how to implement >current limiting protection - very important - and there's also info in >there about driving more than 1 MOSFET in parallel. Apparently the LT1158 >can drive up to 4 MOSFETs from each gate driver. > >I also considered the IR2112 device from IR but their datasheet is far less >clear; the thing basically does the same as the LT1158 although the LT1158 >avoids the thorny issue of potential shoot-through (where both MOSFETs are >on together effectively tying Vcc to ground - goodbye MOSFETs!) by some >smart logic timing. What I also really like is the ability of the LT1158 to >take input directly from a sensing MOSFET to provide overload current >protection. > >So, my project starts to take form. I will use 4 LT1158s driving 4 x >IRCZ44s sensing MOSFETs on the high side and 4 x IRFZ44 non-sense MOSFETs on >the low side. This should be good for a 20-30A controller and I can double >or triple up on the MOSFETs once I've proved the design. > >I'm now also clear that the best way to generate the drive PWM signals will >be to have L+R PWM drive signals for speed and L+R FWD/REV logic signals >for each motor. > >Now the PIC bit is another question. Can anyone point me to a clock timing >diagram for a typical RC servo output? I know that each servo gets a pulse >between 1 and 2 msecs but Chan 1 pulse comes before Chan 2 pulse etc. This >leads me to think that I can use interrupts to call the output PWM changes >and use regular code for the input detection. Once I've detected a pulse in >on Chan 1, I know that it will only go low somewhere between 1 and 2 msec >later and THEN I can start to worry about Chan 2.... or maybe I should >consider just straight line timing code the whole damn thing? > >Lost yet? Let me recap. I'm trying to control a 2-motor robot such as you >see on Battlebots. What I want is for a PIC to take 2 servo channel inputs >that correspond to F-R and L-R and generate PWM + FWD/REV logic which will >feed the LT1158 via protection logic control (see bottom of data sheet page >19) which will feed the two motors vi MOSFETs. Hmmmmm, I wonder what should >happen when say I'm going full speed ahead and I let go the stick? Should >the PWM just stop? or how about it brakes the motor(s), or what if one >selected reverse while going full ahead? Maybe a brake pedal would be cool >on a 3rd channel? > >Now - anyone know where I can actually buy LT1158s? If they're an arm and a >leg, maybe I may have to go back to the IR2112 and brew my own shoot-through >avoidance circuitry - not that big a deal really. > >Thanks to y'all for advice so far. > >Ted Mawson PICman@portfoliopm.com > >----- Original Message ----- >From: "Duane B" >To: >Sent: Friday, February 08, 2002 8:52 PM >Subject: Re: [PIC]: Robot Motor Controller > > >>I don't know if this will help you'll out or not, but you might want to >> >take > >>a look at eh Linear Tech part LT1158 - a Half Bridge N-Channel Power >> >MOSFET > >>Driver. I'm using it in my design, well 4 of the actually, in conjunction >>with IRCZ44 - SenseFET's. The are rated at 60V, 50A, Rds(on)= 0.028. >> >>I controlling the LT1158 with a National Semiconductor LM629 Precision >> >Motor > >>Controller, which, in turn, will be ran be a PIC. >> >>Duane >> >> >>----- Original Message ----- >>From: "Ted Mawson" >>To: >>Sent: Friday, February 08, 2002 10:40 AM >>Subject: Re: [PIC]: Robot Motor Controller >> >> >>>David Harris wrote... >>> >>>"What kind of current do you want?" >>> >>>Answer... >>>I'm thinking in the 100-150 Amp range. Basic outline is for a PIC that >>>senses 2 standard R/C servo channel pulses on 2 inputs and converts this >>> >>to >> >>>signals for 2 H Bridge drives, 1 per motor. >>> >>>Questions that I have at the moment are... >>>1. Whether to poll the inputs or trigger the pulse width count using an >>>interrupt? >>>2. Whether to drive 4 PWM outputs or just 2 with a 3rd direction >>> >control > >>>(per motor)? The latter has the advantage that it is less likely to get >>>into a drive for all 4 FETs in the bridge. >>>3. How to handle the current in the output stages? MOSFETs like the >>> >>BUZ11 >> >>>can take 30A, 50 Volts, and have an on resistance of 0.03 Ohms and there >>> >>are >> >>>many more out there that can handle 80V and 50A. I'm thinking of >>>paralleling up 2 or 3 MOSFETs per channel with the resistance of a >>> >>carefully >> >>>designed PCB providing some kind of current sharing resistor capability. >>> >>It >> >>>seems like a no brainer to use opto-isolators to separate the PIC output >>>from the MOSFET gate drivers. >>> >>>Enough detail? >>> >>>Ted PICman@Portfoliopm.com >>>www.portfoliopm.com >>> >>>----- Original Message ----- >>>From: "David P. Harris" >>>To: >>>Sent: Friday, February 08, 2002 11:27 AM >>>Subject: Re: [PIC]: Robot Motor Controller >>> >>> >>>>What kind of current do you want? >>>>David >>>> >>>>Ted Mawson wrote: >>>> >>>>>Hi Bob, >>>>> >>>>>Your description is exactly what I was thinking of. I'd be very >>>>> >>>interested >>> >>>>>in seeing what you've got so far. >>>>> >>>>>Have you got the H bridge FET drive stuff fully worked out? I have >>>>> >>some >> >>>>>specific ideas in this area, seems to me that it should be possible >>>>> >to > >>>make >>> >>>>>a very high current H bridge by using MOSFETs that can have on >>>>> >>>resistances >>> >>>>>of 0.03 Ohms! >>>>> >>>>>Ted >>>>>----- Original Message ----- >>>>>From: "Bob Blick" >>>>>To: >>>>>Sent: Thursday, February 07, 2002 10:16 PM >>>>>Subject: Re: [PIC]: Robot Motor Controller >>>>> >>>>>>I've done something like that for a fighting robot. Takes two R/C >>>>>>receiver channels and generates pwm for two motors. Treats one >>>>>>stick as fwd/rev and the other stick as left/right. One motor goes >>>>>> >>on >> >>>>>>each side of the bot. Also monitors the current on the h-bridges >>>>>> >and > >>>>>>limits current. Has extensive amounts of code designed to reject >>>>>>spurious signals coming from the receiver. >>>>>> >>>>>>I was planning to do a web page about it. If you can wait, then it >>>>>>would come with some explanation, but I can send it to you if you >>>>>>want to figure it out yourself. >>>>>> >>>>>>Uses a 16F876, coded in HiTech C. >>>>>> >>>>>>Cheers, >>>>>> >>>>>>Bob >>>>>> >>>>>>On 7 Feb 2002 at 18:10, Ted Mawson wrote: >>>>>> >>>>>>>To save me re-inventing the wheel, can anyone point me to a PIC >>>>>>> >>>project >>> >>>>>that takes 2 Radio Control servo pulse inputs (from an R/C receiver) >>>>> >>and >> >>>>>generates the PWM drive for 2 DC motors running in H bridge mode via >>>>> >>>FETs? >>> >>>>>>>Thanks, >>>>>>> >>>>>>>Ted >>>>>>> >>>>>>>-- >>>>>>>http://www.piclist.com hint: The list server can filter out >>>>>>> >>>subtopics >>> >>>>>>>(like ads or off topics) for you. See >>>>>>> >>http://www.piclist.com/#topics >> >>>>>>> >>>>>>-- >>>>>>http://www.piclist.com hint: The list server can filter out >>>>>> >>subtopics >> >>>>>>(like ads or off topics) for you. See >>>>>> >http://www.piclist.com/#topics > >>>>>> >>>>>-- >>>>>http://www.piclist.com hint: The PICList is archived three different >>>>>ways. See http://www.piclist.com/#archives for details. >>>>> >>>>-- >>>>http://www.piclist.com hint: The PICList is archived three different >>>>ways. See http://www.piclist.com/#archives for details. >>>> >>>> >>>-- >>>http://www.piclist.com hint: The PICList is archived three different >>>ways. See http://www.piclist.com/#archives for details. >>> >>> >>-- >>http://www.piclist.com hint: The PICList is archived three different >>ways. See http://www.piclist.com/#archives for details. >> >> > >-- >http://www.piclist.com#nomail Going offline? 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