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  • Tech Electronic question

    I was wondering how hard it would be to make a module with an output to trigger a 20amp auto relay at a specific rpm

    Just curious if it would be a simple design I could build if someone could draw the plan. Autometer make shiftlights with changable resistances (to light up at 7000rpm, 7500rpm, 8000rpm etc) that I believe runs off the ignition pulses or something but I don't want to have to butcher one of those, theyre not cheap.

    Basically I want to use it to trigger a nitrous system. I have a microswitch so it wont work till WOT, a gear position sensor so its only triggered in 2nd or 3rd gear and above and hopefully the rpm trigger so that it only works above, say 6000rpm.

  • #2
    Never mind.. I found out MSD make a "window switch" with plug in rpm modules to switch on AND off. And they're only $80.

    Sweet

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    • #3
      Ah, use the horn button! Simple.

      I've got something here if you want to play with it. It came out of a car I had years ago. Pommy Triumph, not used to our hot Aussie weather and it was fitted with an A/C unit. A/C in England anyway, it switched the A/C off when idling so it didn't overheat the engine and then switched it on above a certain rpm, (set by a pot on it). Now without doing any math, I'm sure it would do the job hooked up to one coil of a V2 seeing as it was hooked up to the coil of an inline six.

      OK I'll do the math 6 cylinder at 1500rpm = 4500 pulses per minute (75pps) 6 X 1500 then / 2 for 4 stroke. That's what I had it set at from memory. A V2 with 1 coil per pot firing only at compression at 6000rpm = 3000ppm (50pps). It would be in the range of adjustment for sure.

      Want me to send it up with the rest of the "junk" later this week? It'll save you $80.
      "I spent most of my money on Scotch, women and cigarettes. The rest I just wasted"

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      • #4
        Thought I'd better find it after shooting my trap off. Found it. I once thought of using it to bring on the fan automatically when the revs fell below a certain value on the TLS (at idle). But I don't do enough stop start riding and when I do, I don't panic about the 100C if it reaches it anymore.
        "I spent most of my money on Scotch, women and cigarettes. The rest I just wasted"

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        • #5
          I did a little experiment on the way home tonight on the Vmax. On a quite part of the freeway I dropped down to 2nd at 60 or 70 klm/h and pressed and held the horn button while nailing it. Don't think I like that idea, either its just the Vmax or I really like to be hanging on. I always ride with 2 fingers on the clutch lever and that only leaves 2 and no thumb. I also want to be able to change gears while on the gas and trying to shuffle fingers and thumbs is gonna be a pain. I want to make it as automated as possible once I arm it. So I need 3 interlocks. WOT switch, gps - 2nd or 3rd gear and above only, and only above 5000 or 6000 rpm (very important) and I have to make sure it switchs back off before the revlimiter kicks in and starts dropping pulses to the fuel injectors (if thats how the revlimiter works) or else with the nos still flowing @ 10,000rpm it will lean out. I seem to hit the limiter enough as it is.

          Sure send it up if you don't need it, I'm sure I could get my head around it and if it saves me $80 all the better.

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          • #6
            I'll send it up, except it doesn't really have a window as such, like a low and high limit, just the low limit. But hitting it with gas on the limiter is probably only a waste of gas worst case?

            Your 2nd or 3rd and above wishes are going to be hard. All I can think of at the moment is an ATRE, 1st to 3rd gears remapped to 4th (the lowest possible gear to re-map to I think from memory) then you use the output to the LED indicating no remapping to drive a small relay that switched your larger relay for the gas. So your relay would only be active in 4th, 5th and 6th and neutral and false neutrals.

            The only thing is if you hit neutral at WOT the ATRE says no re-map in neutral or a false neutral and the ATRE is missing the signal woo hoo, WOT, Gas and no load!
            "I spent most of my money on Scotch, women and cigarettes. The rest I just wasted"

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            • #7
              What about the high beam flasher? A microswitch in your mouth clench hard and get gas! Maybe even between your butt cheeks?
              "I spent most of my money on Scotch, women and cigarettes. The rest I just wasted"

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              • #8
                Very funny....lol

                Apparently hitting the limiter with the gas still flowing is one of the things that blows up engines, due to the extremly high cylinder pressure when using nos, if you suddenly lean it out (revlimiter cutting the pulse to a cylinder injector) the pressure goes through the roof, especially on a twin which develops higher pressures than an I4 anyway, and you can end up in a situation where the rear cylinder conrod destroys the microswitch assembly that you've carefully mounted between your butt cheeks...

                And if it cuts the spark to one of the cylinders as a way of revlimiting, what happens to the unburnt fuel and nitrous when it comes back on ? Better to be safe than sorry I guess

                Thats just what I've read anyway.. open to correction


                Btw do you know what the resistance values coming from the gps are in 1st, 2nd, 3rd etc and neutral

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                • #9
                  OK, I understand now about the limiter business.

                  Pinched this from a previous post, was MilesB's research

                  This is what I have (didn't measure it, found it on the net)

                  Gear - Voltage - R to Gnd

                  1----- 1.8 ----- 560
                  2----- 2.26 ----- 830
                  3----- 2.99 ----- 1500
                  4----- 3.68 ----- 2700
                  5----- 4.38 ----- 6800
                  6----- 4.7 ----- 15000
                  Maybe a modified gear indicator that lights leds in succession could do the job if it reads the GPS and not the Speedo to Rev ratio?
                  "I spent most of my money on Scotch, women and cigarettes. The rest I just wasted"

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                  • #10
                    Always use a good window switch with NO2. Make sure you set the upper limit a good way back from the rev limiter (and test it out slowly with a light first instead of the solenoid!)

                    As you say, if you hit the limiter with the gas flowing, get ready for an explosion. Usually with cars, it explodes the intake manifold and sends it through the hood. I wouldn't like to see that on a bike.. you might learn to fly, or at least, get the crap scared out of you.

                    Engine damage is usually caused when the rev limiter cuts fuel, not spark. That's when it really leans out. Don't ask me why the manifold blows in cut-spark limited engines.. I can't remember the reason. It looks pretty mad though. Rips the manifold open at the seams.
                    Used to ride a '01 TLR

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                    • #11
                      When the ignition is cut out, there is still fuel and N2O being dumped in, so once the spark kicks back in there's an abundance of fuel and oxygen just waiting for that spark to explode....
                      Mickey
                      AEC (AW) US Navy

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                      • #12
                        Hi Folks,

                        So you need a RPM window-switch with a condition for certain gears for the nos right?

                        Guess you found it for $80 right? if you still want to go at yourself i could upload a schematic that hopfully would work (without warrenty;-)) for a solution.
                        Twins are twice as fun

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                        • #13
                          Originally posted by DaGaz
                          Hi Folks,

                          So you need a RPM window-switch with a condition for certain gears for the nos right?

                          Guess you found it for $80 right? if you still want to go at yourself i could upload a schematic that hopfully would work (without warrenty;-)) for a solution.
                          I've found the window switch but it has no provision for a detecting what gear its in ... still need something that will triger a relay or close a circuit etc in 2nd or 3rd and above only preferably switchable. If you have any ideas I'd love to see them. I'm still working out my wiring circuit and I won't be installing anything for a few weeks anyway.

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                          • #14
                            Rupes, see if the local wrecker has an old GPS it's mounted behind the clutch basket.

                            See if you can get it open, you may be able to replace the resistances for 3rd 4th 5th and 6th with links. You could then use the GPS wire.

                            If you fit my SATRE, you don't really need the GPS connection to the ECU unless you switch the SATRE to the off position, it uses the Neutral indicator wire to switch the relay send or not send the resistance value to the ECU.

                            I'm sure Balls Performance here in Melbourne modifies the GPS when he does a TRE mod, but that's on Gixxers and I think they have a different unit?

                            Still thinking!
                            "I spent most of my money on Scotch, women and cigarettes. The rest I just wasted"

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                            • #15
                              Colin Linney at 10/10ths also does the same thing with the GPS, he changes the resistance values, sort of like a permanent tre. I'll look into that too.. Cheers

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