Post by thread:Ignition timing, 2nd iteration....

Thanks everyone for all the responces and offers for help. I think I will try to tone this down a little. Make it a bit easier. How about taking the signal from the dist. with mechanical and/or vacume advance working, and proccessing that signal by adding delays. Safer and less complicated. What I am trying to do is smooth out the power from my motor. The car is a drag car with front engine, rear wheel drive. At well over 1hp and 1ft/lb torque per 10lbs weight, and street radial tires, accelerating from a dead stop is very difficult. I read that pro street stock racers use timing computers to help with traction, and guard their curves with their life. These computers are not cheap. I think they start at $700.00. So, perhaps using the original curve from the dist, and tailoring that before it goes to the ignition module would be a good compromise. John

part 0 4766 bytes Tony's code is very clever, and just shows what can be achieved via software alone.  However, as he himself has stated, it was only designed for relatively slow reving engines.  The trouble with the software only approach is that you have to complete all calculations and keep a pretty accurate counter in between firing cycles.  The Motorola uP such as the 68HC332 have a TPU (Time Processing Unit) which is extremely powerfull.  It can actually run an engine in steady state with no CPU intervention, leaving the CPU bags of time to perfrom some very intensive maths. I think a good compromise could be met using a PIC with the Capture/Compare units, which would at least offload a good deal of processor time.  I have been thinking about a PIC based system on and off for ages, but never seem to quite have the time to sit down and work through it.  Maybe this is a good time to put our heads together? Your application of traction control might actually be slightly more simple.  I presume you need to reduce power once the wheelspin has started.  You only need to retard the igniton from the mechanical configured settiing to reduce power.  You might even get away with introducing fixed delays that are not proportional to engine speed, which accumulate the longer wheel spin progresses? Regards Mike <UL> {Original Message removed}

> From: "John Pearson" <spam_OUTxeroTakeThisOuTCMC.NET> > Thanks everyone for all the responces and offers for help. > I think I will try to tone this down a little. Make it a bit easier. > How about taking the signal from the dist. with mechanical and/or vacume > advance working, and proccessing that signal by adding delays. Safer and > less complicated. > > What I am trying to do is smooth out the power from my motor. The car is a > drag car with front engine, rear wheel drive. At well over 1hp and 1ft/lb > torque per 10lbs weight, and street radial tires, accelerating from a dead > stop is very difficult. I read that pro street stock racers use timing > computers to help with traction, and guard their curves with their life. > These computers are not cheap. I think they start at $700.00. > Do you need to tweak the timing for that? I'm just thinking out loud here. Since you have maximum traction when there's no wheelspin, maybe you could devise a system that compared the rotation of the front and rear wheels and slightly backed off the throttle if it detected any slipping, checked again and backed off if... etc. If it detected no slipping and your foot still hard down on the pedal it could nudge the throttle up again until wheelspin started again. Maybe the lag of the throttle action would make this unrealistic but until it was banned (and after too, if the rumours are correct) Formula One reacers used something similar (but no doubt much more complex) to great effect at the start of races. .

andy howard <.....musicKILLspam@spam@soon.com> wrote: > > I read that pro street stock racers use timing computers to help > > with traction, and guard their curves with their life. > > Do you need to tweak the timing for that? Andy: He doesn't have many other choices; traction-control is banned in his form of motorsport, but ignition timing curves, gearing, and rev limits are "free" (i.e., they can be set to whatever he likes) in most classes. > I'm just thinking out loud here. Since you have maximum traction > when there's no wheelspin, maybe you could devise a system that > compared the rotation of the front and rear wheels and slightly > backed off the throttle if it detected any slipping, checked again > and backed off if... etc. > > If it detected no slipping and your foot still hard down on the > pedal it could nudge the throttle up again until wheelspin started > again. That's the way the traction-control system on my car (and most others) works, and it's fine for keeping the wheels from spinning on ice or other slippery surfaces. It sucks, though, for drag racing... For many reasons, some of which are: 1. Wheelspin on launch is NECESSARY for the fastest times 2. The deformation of the rear tires under heavy acceleration changes their circumference (in the wrong direction), so the traction-control system will incorrectly see slippage when there is none 3. Maximum traction isn't developed with no wheelspin, anyway; the most acceleration is developed when the tires are slightly slipping -Andy === Andrew Warren - fastfwdKILLspamix.netcom.com === Fast Forward Engineering - San Diego, California === http://www.geocities.com/SiliconValley/2499

> Michael Rigby-Jones wrote: > The trouble with the > software only approach is that you have to complete all calculations > and keep a pretty accurate counter in between firing cycles. Not neccessarily. The last software I wrote precalculated a set of variables and these are used at run time - virtually no math while running. The data is then available exactly when needed. As I mentioned earlier, I can keep track of RPM, pos or neg advance, vac adv, dwell and rev limit in about 50 instructions. That is about 25uS @ 8MHz, but it still becomes an issue at high RPM. To test the software, I had two signal generators running. One at 500RPM and another about 6000RPM simulating the timing for a V8. I used a switch to change signals and as far as I could see the PIC coped OK. I didn't have a storage CRO to see the changeover glitch though. On the test bench the PIC could run a single 4 stroke upto 35,000 RPM. The system has been quite popular with old car enthusiasts because of hard to find distributor parts, and with people running engines on gas because 2 data sets can be stored and changed over even when the engine is running. I have had ideas on doing another one with more features, but the time it takes for development to cover a reasonable spectrum of engines.....oooh the pain. The last time I was 'playing' with this idea I was using a 16C74 and I could change the timing parameters even while the engine was running. There are four basic things needed to make a system work. Good programmer Electronics wiz Someone who knows engines inside and out. Time, time and more time. Even so, it was probably one of the most interesting projects I have done. Not too bad when you consider the whole shebang used only 1021 words of ROM. -- Best regards Tony http://www.picnpoke.com .....salesKILLspam.....picnpoke.com

{Quote hidden}> -----Original Message----- > From: Andrew Warren [SMTP:EraseMEfastfwdspam_OUTTakeThisOuTIX.NETCOM.COM] > Sent: Wednesday, 3 May 2000 9:05 > To: PICLISTspam_OUTMITVMA.MIT.EDU > Subject: Re: Ignition timing, 2nd iteration.... > > andy howard <@spam@musicKILLspamsoon.com> wrote: > > > > I read that pro street stock racers use timing computers to help > > > with traction, and guard their curves with their life. > > > > Do you need to tweak the timing for that? > > Andy: > > He doesn't have many other choices; traction-control is banned > in his form of motorsport, but ignition timing curves, gearing, > and rev limits are "free" (i.e., they can be set to whatever he > likes) in most classes. > > > I'm just thinking out loud here. Since you have maximum traction > > when there's no wheelspin, maybe you could devise a system that > > compared the rotation of the front and rear wheels and slightly > > backed off the throttle if it detected any slipping, checked again > > and backed off if... etc. > > > > If it detected no slipping and your foot still hard down on the > > pedal it could nudge the throttle up again until wheelspin started > > again. > > That's the way the traction-control system on my car (and most > others) works, and it's fine for keeping the wheels from > spinning on ice or other slippery surfaces. It sucks, though, > for drag racing... For many reasons, some of which are: > > 1. Wheelspin on launch is NECESSARY for the fastest times > > 2. The deformation of the rear tires under heavy > acceleration changes their circumference (in the wrong > direction), so the traction-control system will incorrectly > see slippage when there is none > > 3. Maximum traction isn't developed with no wheelspin, > anyway; the most acceleration is developed when the tires > are slightly slipping > > -Andy > Correct, it is around 6 to 10% slippage Dennis > === Andrew Warren - KILLspamfastfwdKILLspamix.netcom.com > === Fast Forward Engineering - San Diego, California > === http://www.geocities.com/SiliconValley/2499

> > 3. Maximum traction isn't developed with no wheelspin, > > anyway; the most acceleration is developed when the tires > > are slightly slipping > > > > -Andy > > > Correct, it is around 6 to 10% slippage > > Dennis > Just wondering - is this a known formula / observed rule in drag racing or can it be applied more generally? A little off topic now but I have often pondered this and tried to figure out my own explanations, thinking how a micro based traction control system might tackle the problem of fast starts for ant kind of race car. Though a slightly different situation, my experience is with two stroke 250cc moto-x bikes that develop 45-50hp. The formula for a fast start on soft dirt / grass surface is a high gear, say 3rd or 4th, and full throttle. As land speed increases the revs drop back slightly to that magical max engine torque / max traction magic value and for a while acceleration greatly exceeds that possible with zero slippage. (My brother and I have verified this by extensive side by side standing start tests on a grass air strip!) My guess is best acceleration occurs somewhere around 20%-50% slippage shortly after the start for as long the engine torque can keep up this condition. Similar technique works when stuck in mud at the bottom of a slippery gully. Put the bike in first gear and it wont budge no matter what the revs, do the 3rd/4th gear full noise trick and it's amazing how traction develops. Probably quite different to the drag car situation but I'm still interested in the laws at work here. Oh yeah, to get back on topic you could super glue DIP packaged PIC16F84's, with legs pointing up, to the drag track for more traction. You'll need around 35000 of them for two rows 0.25 mile long, but the good part is you don't need to program them. Brent Brown Electronic Design Solutions 16 English Street Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile: 025 334 069 eMail: TakeThisOuTbrent.brownEraseMEspam_OUTclear.net.nz

Brent, I know you have something here. I have heard road race drivers will stay a "gear-up" in rain to help with traction. I have always thought that if I put a taller first gear in I would gain time and traction; However, this is not 'tunable'. I would suffer when track conditions are real good. John ---------- {Quote hidden}> From: Brent Brown <RemoveMEbrent.brownTakeThisOuTCLEAR.NET.NZ> > To: PICLISTEraseME.....MITVMA.MIT.EDU > Subject: Re: Ignition timing, 2nd iteration.... > Date: Tuesday, May 02, 2000 6:29 PM > > > > 3. Maximum traction isn't developed with no wheelspin, > > > anyway; the most acceleration is developed when the tires > > > are slightly slipping > > > > > > -Andy > > > > > Correct, it is around 6 to 10% slippage > > > > Dennis > > > > Just wondering - is this a known formula / observed rule in drag > racing or can it be applied more generally? A little off topic now but > I have often pondered this and tried to figure out my own > explanations, thinking how a micro based traction control system > might tackle the problem of fast starts for ant kind of race car. > > Though a slightly different situation, my experience is with two > stroke 250cc moto-x bikes that develop 45-50hp. The formula for a > fast start on soft dirt / grass surface is a high gear, say 3rd or 4th, > and full throttle. As land speed increases the revs drop back > slightly to that magical max engine torque / max traction magic > value and for a while acceleration greatly exceeds that possible > with zero slippage. (My brother and I have verified this by extensive > side by side standing start tests on a grass air strip!) My guess is > best acceleration occurs somewhere around 20%-50% slippage > shortly after the start for as long the engine torque can keep up this > condition. > > Similar technique works when stuck in mud at the bottom of a > slippery gully. Put the bike in first gear and it wont budge no matter > what the revs, do the 3rd/4th gear full noise trick and it's amazing > how traction develops. > > Probably quite different to the drag car situation but I'm still > interested in the laws at work here. Oh yeah, to get back on topic > you could super glue DIP packaged PIC16F84's, with legs pointing > up, to the drag track for more traction. You'll need around 35000 of > them for two rows 0.25 mile long, but the good part is you don't > need to program them. > > Brent Brown > Electronic Design Solutions > 16 English Street > Hamilton, New Zealand > Ph/fax: +64 7 849 0069 > Mobile: 025 334 069 > eMail: EraseMEbrent.brownclear.net.nz

Andy, To avoid too much lag I wonder if this would work. How about just skipping the firing of a plug... like an interupt. You could detect rotation ratio front to back and if it is way out of sink you could interrupt the firing of the next plug? Dont know if this mechanicaly would be detrimental. <SNIP> >I'm just thinking out loud here. Since you have maximum traction when >there's no wheelspin, maybe you could devise a system that compared the >rotation of the front and rear wheels and slightly backed off the >throttle if it detected any slipping, checked again and backed off if... >etc.

part 0 3208 bytes Skipping firing cycles will cause unburnt mixture to be pumped into the exhaust which could cause some nice loud back fires.  This is never very good for exhaust valves, or indeed the the exhaust system itself.  This method used to be used by add-on rev-limiters, but much better methods exist.  One traction control system I have seen actually uses a secondary throttle which is normaly wide open, but can be closed by a servo to back off power. Mike <UL> {Original Message removed}

---------- {Quote hidden}> From: Allen Demers <RemoveMEfarmbooyEraseMEEraseMEIX.NETCOM.COM> > To: RemoveMEPICLISTspam_OUTKILLspamMITVMA.MIT.EDU > Subject: Re: Ignition timing, 2nd iteration.... > Date: Wednesday, May 03, 2000 6:52 AM > > Andy, > > To avoid too much lag I wonder if this would work. > > How about just skipping the firing of a plug... like an interupt. You > could detect rotation ratio front to back and if it is way out of sink > you could interrupt the firing of the next plug? Dont know if this > mechanicaly would be detrimental. > > <SNIP> > >I'm just thinking out loud here. Since you have maximum traction when > >there's no wheelspin, maybe you could devise a system that compared the > >rotation of the front and rear wheels and slightly backed off the > >throttle if it detected any slipping, checked again and backed off if... > >etc. This is how my current rev limiter works. It cuts the spark to different cylinders. It is very effective, I know, cause when I get the wheels spinning I go right into the limiter.

If you don't have any way to control fuel injection (via electronic injection, or primary/secondary throttle system), controlling the ignition time gives you "some" relative slack on the torque (followed by throttle delayed control). In any way you "should" burn the mix "inside" the combustion chamber, if not, as Mike already said, you can say "goodbye" to the exhaust valves in a short time; "Cam is up, exhaust valve is closed (from inside the chamber), explosion at the exhaust pipe generate pressure in both ways, it forces the exhaust valves springs opening the valves down the cylinder and it can bump the piston head surface, returning it bumps the pushrods against the cam, so double problem, or worse, if intake valves are open the explosion pressure would go back all the way inside the injection system... not a good thought, not even talking about dirt entering the chamber". To control the ignition time, or you use a multi-slotted timming (opto) disk, with one tick per degree or so, or use a software algoritm to create the required delay. In this case, remember that this delay is defined in "milliseconds" while rotational delay is defines as "angular", so in degrees, minutes, seconds. You need to measure the actual time between two ignitions, divide that time by 90 (4 cylinders engine), so you will have milliseconds per degree, then you can generate the expected delay in "degrees" by delaying the relative milliseconds to the next ignition time. To "advance" degrees, you actually "retard less" degrees in a system that runs with a fixed delayed degrees. Easy. Processing power? at 10,000 RPM, 4 cylinders engine, you have as much as 1.5 millisecond per ignition time, this is not plenty enough for all the math and control for a PIC running at 16MHz? You could probably run an average of 10,000 instructions in this period of time. Wagner {Quote hidden}> Michael Rigby-Jones wrote: > > Skipping firing cycles will cause unburnt mixture to be pumped into > the exhaust which could cause some nice loud back fires. This is > never very good for exhaust valves, or indeed the the exhaust system > itself. This method used to be used by add-on rev-limiters, but much > better methods exist. One traction control system I have seen > actually uses a secondary throttle which is normaly wide open, but can > be closed by a servo to back off power. > > Mike > > {Original Message removed}

John Pearson wrote: {Quote hidden}> > ---------- > > From: Allen Demers <RemoveMEfarmbooyTakeThisOuTspamIX.NETCOM.COM> > > To: EraseMEPICLISTspamspamBeGoneMITVMA.MIT.EDU > > Subject: Re: Ignition timing, 2nd iteration.... > > Date: Wednesday, May 03, 2000 6:52 AM > > > > Andy, > > > > To avoid too much lag I wonder if this would work. > > > > How about just skipping the firing of a plug... like an interupt. You > > could detect rotation ratio front to back and if it is way out of sink > > you could interrupt the firing of the next plug? Dont know if this > > mechanicaly would be detrimental. > > > > <SNIP> > > >I'm just thinking out loud here. Since you have maximum traction when > > >there's no wheelspin, maybe you could devise a system that compared the > > >rotation of the front and rear wheels and slightly backed off the > > >throttle if it detected any slipping, checked again and backed off if... > > >etc. > > This is how my current rev limiter works. It cuts the spark to different > cylinders. It is very effective, I know, cause when I get the wheels > spinning I go right into the limiter. In circuit cellar there was an article about an HC11 controled ignition/fuel- injection system, cant remeber now but i think it was around 2 years ago. check http://www.circellar.com regards /Sten