Need help with a kill switch circuit for a motorcycle

Discussion in 'Automotive Electronics' started by Luke Anderson, Oct 28, 2015.

  1. Luke Anderson

    Thread Starter New Member

    Oct 28, 2015
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    Hello everybody! I am new to the forum, I'm building a motorcycle to compete at the bonneville salt flats in Utah. Its a honda CX500 converted to electronic fuel injection with a Megasquirt controller. The issue I am having it with the kill switch circuit. The rules require the kill switch to kill the ignition and the fuel pump.
    The ignition is the stock cdi and kills when its grounded out.
    The fuel pump kills when power is taken from the relay.
    The lanyard kill switch is closed when activated.
    The handlebar kill switch can be open or closed when activated.
    The key switch is open when shut off.

    The ideal situation would kill power to the pump relay and ground the cdi, using any of the 3 switches, key, handlebar, or lanyard.

    I attempted to figure this circuit out on my own but its over my head. Any help would be appreciated!
    Thank you,
    Luke
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Doesn't the ignition require power from the battery just like the fuel pump?
     
  3. Luke Anderson

    Thread Starter New Member

    Oct 28, 2015
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    I wish it did.this is the old style cdi box, with the box wired directly into the generator wiring. It's independent of the the battery and the rest of the wiring harness.
     
  4. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    The "lanyard kill" is the crappy one.

    I would probably wish the fuel pump one to be a bit more sophisticated. e.g. IGN on, turns fuel pump on for some fixed time. It stays on if there are ignition pulses and it turns off vial kill switch. Ignoring that one.

    I think you can use a combination of "diode or-ing" and/or sequential interlock. The Lanyard has the wrong logic.

    So, the IGN turns on the fuel pump relay via a +12 diode OR. The handlebar kill switch can also be diode or. A DPDT relay can deal with the ignition So, the relay covers the fuel pump and the CDI system.

    To simplify, I would see if another Lanyard system is available, otherwise you need to invert. I;d probably use an OPTOMOS relay there with a lot of attention to protection components. Maybe even an automotive grade high side switch.

    Another possible option is a "safety relay" https://en.wikipedia.org/wiki/Safety_relay Sometimes they have lots of different inputs. One aspect of the relay is force guided contacts. It might be your best bet. The "safety relay: is a complex beast.
     
  5. Luke Anderson

    Thread Starter New Member

    Oct 28, 2015
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    Excellent! That really helps! Here is what I'm thinking, tell me if its wrong. I'll get a new lanyard that is open when activated, then put the key, handlebar switch, and lanyard in series to the DPDT relay. That will control one side power to the pump, and one side ground to the ignition.
    That way if any of the 3 switches are open the relay will cut fuel and spark.
    Thank you for the help, I have been putting off finishing this harness for months because of this!
     
  6. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    http://www.play-hookey.com/digital_electronics/dl_gates.html

    Diode or positive logic is the pic on the left top of the page. You can extend that concept so any signal triggers the relay. e.g. the + trigger(s) goes through a diode, the relay coil and ground. There still should be a reversed biased diode across the relay coil.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    Some motorcycles of that era had high voltage windings on the generator to charge the CDI unit directly without an inverter running from the battery.

    The kill switch basically shorted out the CDI capacitor.

    The energy transfer type with the points, LT winding and generator coil all in parallel also used a shorting type kill switch.

    The regular Kettering type ignition had a break type kill switch in series with the + feed to the coils.
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @Luke Anderson

    I know this bike well, although I owned it for a summer. I never had to do any work on it other than an oil change. I have to ask. Why this bike? It is a fairly standard '80s looking bike. The interesting bits are that it has a liquid-cooled longitudinal v-twin (with shaft drive). The only 500cc that I remember having dual discs up front. Not exactly the base I would have selected for a speed run.

    Now, the real question, do you by chance have the very limited and very expensive turbo erosion that was quite a bit better in every aspect?

    I am interested to hear your story. Pictures would be interesting too.

    For the rest, here are photos of a standard CX and the turbo CX.

    image.jpg

    image.jpg
     
  9. Luke Anderson

    Thread Starter New Member

    Oct 28, 2015
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    The bike is the standard cx500, but has been modified with a turbo. The bike will run on methanol, and will run in the SCTA class MPS-PBF 500. That stands for modified partial streamliner, pushrod blown fuel, 500cc or less. This class was chosen because the speeds in the pushrod classes are lower, and I can afford to be competitive. The Honda cx was chosen because its liquid cooled like you mentioned, and also 4 valves per cylinder. Other pushrod 500cc engines are limited to buell blast, and older British twins and singles, all of which are air cooled 2v as far as I know. The biggest challenge has been gearing the bike high enough for top speed. The rear wheel is modified with 23" rim, transmission swapped from a cx650 in an effort to bring the top speed up to 149mph. The front end is from an 02 cbr954.
    As it stands now the record is 132mph, I believe we have a good chance against it! 11412299_10153358688352154_1993732609215227948_n.jpg IMG_20150603_210826761.jpg IMG_20150603_211041359_HDR.jpg
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    Do you just reassembly the bike, because it looks pretty new, specially the engine?
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    The CBX550 I had was twin front disc, but they were fully enclosed in the front hub (D.O. for the single rear disc).

    It truly was a monumental PITA to do any work that involved taking a wheel out!
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    That engine was only used by Honda in the US from 1978 to 1983 - think one sub-model was available until 1985.

    @Luke Anderson
    Good job on the front-end conversion. The brakes were not great and the fork needed more stabilization than it had - especially anything over 90 mph.
    The CX500 engine is a good choice for upgrading. The same block was used on the turbo and that made nearly double the horses of the standard version. Some engine blocks are not over designed like that so they pull themselves apart when under severe stress/strain when the ponies are increased.

    Let us know how it works out. When are you competing?
     
  13. crutschow

    Expert

    Mar 14, 2008
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    What engine RPM redline are you shooting for?

    Does the engine have an oil cooler?
    If not are you considering adding one? It might help keep the pistons within the confines of the cylinder if you pushing the engine to the max. ;)
     
  14. Luke Anderson

    Thread Starter New Member

    Oct 28, 2015
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    We plan on competing next August at Bonneville Speed Week, weather permitting. Both major events at the salt flats have been canceled due to flooding the past two years in a row!
    The redline will be in the 9000-9500 neighborhood. No oil cooler for now, ill be running a 15w40 Shell Rotella full synthetic. One of the benefits of running methanol is the cooler operating temperature. The radiator has been upgraded regardless.
    Its been a fun project, Ive learned a lot, did a lot of fab work that I never had the chance to do before, and its my first project with fuel injection.
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
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    I think some brands of anti-freeze work better than water if you use them neat.

    Usually the maximum temperature the cooling system can run without venting, is set by the pressure rating of the thermostat cap - you can run it hotter with a cap calibrated for higher pressure.
     
  16. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Some creative ducting of the airflow around the radiator will help too. The aerodynamics at 150 mph are completely different than at 90. The fins are very close together and you will likely have very turbulent flow which slows velocity. Watch your temp gauge. Maybe a race day at Brainard Int Raceway (central MN) will let you open it up to see what it can do. There is a mile-long straight away there with a full speed right turn (20-degrees or so) at the end. Keith Code describes it as the best turn in racing. Anyhow, a closer option before going all the way to Utah.
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
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    Formula 1 cars don't have any radiator fans - they rely entirely on the airflow from going somewhere fast.
     
  18. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Yes, that was my concern. I think his radiator is likely designed for old 55mph speed limit laws. Fan, tightly spaced fins, small overall. All air essentially flows around the radiator as turbulent flow is achieved between the fins.

    And, since the fans blades will not blow air faster than the bike is traveling, they further block the air flow.
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
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    The pictured model with the fairing looks like it goes some way to scooping airflow into the radiator.

    Looks like there's a canard on the front mudguard to help out too - but that may just be the same sort of thing as go-faster stripes.

    For even higher thrashing it - some carefully positioned duct tape may be needed to stop scooped air going anywhere other than the radiator fins.
     
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