neil.cavanagh Posted June 3, 2008 Share Posted June 3, 2008 After the interia cut-off being tripped by running over the curbs at Pembrey on sunday I am planning on fitting a by-pass swtich to allow it to be disabled. I assume the the switch is simply that.. the wire runs in to it... through the switch and then back out. If the switch is closed the engine runs.. if it is open it doesn't. So I am proposing to fit a switch in parallel to the interia switch. This would mean I could run with this extra switch in the OPEN position most of the time, which would meant that the interia switch would be in control. But then for timed events I could close my extra switch, which would effecitvely by-pass the inertia switch. Do any of the electical gurus see an issue with this? What current rating switch do I need? Link to comment Share on other sites More sharing options...
mav Posted June 3, 2008 Share Posted June 3, 2008 Really bad idea, IMO. Better to relocate it to the cockpit like the race cars do. Then you can reset it from the drivers seat if you trip it... Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 3, 2008 Share Posted June 3, 2008 Neil, What you have planned will work, but the switch needs to be high current rated as the inertia switch sees the full current of the fuel pump (which is of course daft when the entire circuit is controlled by a relay). Link to comment Share on other sites More sharing options...
Englishmaninwales Posted June 3, 2008 Share Posted June 3, 2008 Neil In the event of a big shunt you could end up with broken fuel lines and petrol at 4 bar pressure spraying over a hot engine........... ☹️ As mav says, resite it. Malcolm Link to comment Share on other sites More sharing options...
neil.cavanagh Posted June 3, 2008 Author Share Posted June 3, 2008 Why a bad idea Mav? Many people disable them totally. With my approach you'd have the option to: 1) leave it enabled, and flip the switch if it trips during a run. (The swtich I'd use would be easier to operate with driving gloves on than the interia switch) 2) Disable it before a run.... if you expect issues.... like at Pembrey. Last year 5 people (I recall) had the inertia go at the same point of the track. This would allow you to attack with more confidence, and not risk losing a timed run due to cut-off going. Yes, there is a risk that whilst competing with it disabled you might have a massive crash that leaves you unable to reach the cut-off switch whilst petrol keeps pumping out. But this is minimal, and with an emerald that cuts the fuel pump if it doesn't detect that the engine is running, a perfectly acceptable risk to me. Link to comment Share on other sites More sharing options...
neil.cavanagh Posted June 3, 2008 Author Share Posted June 3, 2008 PC. Would 20A do it? here Link to comment Share on other sites More sharing options...
neil.cavanagh Posted June 3, 2008 Author Share Posted June 3, 2008 Malcolm... as least they would be a Doctor close by if I needed one!... 😬 😬 *wavey* Link to comment Share on other sites More sharing options...
Adrian Williams Posted June 3, 2008 Share Posted June 3, 2008 Neil mine is disabled all the time so your idea is certainly better than that, as you say as long as the engine stops the ecu will kill the pump anyway. Putting the inertia in the cockpit is a waste of time because once it trips your run is ruined anyway which is what you were trying to avoid in the first place. I would have thought the 20A switch you found will do the job, the fuel pump fuse is only 15A and the LED in the switch will tell you when you've overridden the inertia switch. Adrian Link to comment Share on other sites More sharing options...
david nelson Posted June 3, 2008 Share Posted June 3, 2008 Neil mine is also disabled when sprinting. I just reconnect it for road and track use. David Link to comment Share on other sites More sharing options...
Englishmaninwales Posted June 3, 2008 Share Posted June 3, 2008 Neil I didn't know about the Emerald cut off if no crank sensor signal...... 😳 Malcolm Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted June 3, 2008 Share Posted June 3, 2008 Mine is always disabled. I took the inertia switch out and wired the connections to a dashboard switch to let me turn the fuel pump off when working on the car. I've heard too many stories of them bouncing off on the track. The fuel pump is controlled by the Weber Alpha ECU anyway, although I don't know if stopping the engine will stop the fuel pump in my case. I think it will. If I stall the car, the fuel pump does stop. On my setup, the inertia switch deactivated the fuel pump via the relay so a small low ampage switch was all it needed. ----- VDU 7X Pics More VDU 7X Pics Edited by - Alex Wong on 3 Jun 2008 17:11:32 Link to comment Share on other sites More sharing options...
Colin Mill Posted June 3, 2008 Share Posted June 3, 2008 The ideal thing would be for the inertia switch to tell the difference between a curb and a serious machine-bending arrival. I guess the inertia switch as it is will trip on a near instantaneous event over a certain number of g. I suspect that a modest amount of anti-vibration mounting would ensure that a longer high-g event is needed to trip the inertia switch. Link to comment Share on other sites More sharing options...
Simon.Rogers1 Posted June 3, 2008 Share Posted June 3, 2008 What inertia switch Colin I would agree with your thoughts. But They are just to sensitive. Now a different product or spec switch would be good! Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 3, 2008 Share Posted June 3, 2008 The fuel pump current will probably be steady at around the 5A mark, but the circuitry should have a healthy overhead. Link to comment Share on other sites More sharing options...
Jason Plato Posted June 3, 2008 Share Posted June 3, 2008 I simply tie wrapped mine at some venues that had harsh kerbs I have since taken it apart and "adjusted " its sensitivity. Its quite straightforward to do once its in bits on the dining room table . do it whilst your wheels are in the dishwasher 😬 here is C7 TOP Taffia rear gunner Link to comment Share on other sites More sharing options...
Colin Mill Posted June 3, 2008 Share Posted June 3, 2008 Well, there are three-axis accelerometer chips available these days that are designed for the airbag deployment market and are thus dirt cheap (about 3 quid in quantity and falling all the time). It would of course be no great problem to set an X g for Y milliseconds criterion and make the thing have a sensitivity that was right for the job. Link to comment Share on other sites More sharing options...
Myles Posted June 3, 2008 Share Posted June 3, 2008 t would of course be no great problem to set an X g for Y milliseconds criterion and make the thing have a sensitivity that was right for the job. Or you could just fit a standard inertia-switch and not have to bother plugging your laptop in to reset the bugger... *tongue* 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7s Ecosse™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Colin Mill Posted June 3, 2008 Share Posted June 3, 2008 If it only tripped in a real crash you wouldn't be very worried about resetting it anyway. 😬 Having said that, what objection would you have to pressing a switch on the unit to reset it just like the current unit ? Since I'm messing about with some 3 axis accelerometers at the moment (for helicopter applications) I might have a go at making something like this. Link to comment Share on other sites More sharing options...
Simon.Rogers1 Posted June 4, 2008 Share Posted June 4, 2008 You may have a ready market of say 60 sprinters Link to comment Share on other sites More sharing options...
paulyb Posted June 4, 2008 Share Posted June 4, 2008 But who of them is going to offer to crash test it...... Link to comment Share on other sites More sharing options...
robmar Posted June 4, 2008 Share Posted June 4, 2008 well there are plenty of suspects who you could put it on and you know eventually they will crash as an aside I have crashed my 7 (rear end into a wall at spa at about 40) and into the bushes at longcross at about the same speed and neither time did it trip the inertia switch however over the rumble strips at curbugger rob Edited by - robmar on 4 Jun 2008 10:02:44 Link to comment Share on other sites More sharing options...
Colin Mill Posted June 4, 2008 Share Posted June 4, 2008 As a bit of light relief from the current accelerometer job I have been giving a bit of thought to this. I guess the criteria would depend on the type of car as downforce would shift the g figures of interest. However, I think all we need to do is decide on a g-force and a speed of interest. To kick some numbers about I guess for any car without aero you would have to reckon anything above 2g in any horizontal direction has to involve nerfing something. So if you start integrating the accelerometer output (to give the change in speed) once this threshold g is exceeded and this integral exceeds the threshold speed - say 15mph - before the g value falls below the threshold again then the unit trips. So at 2.5g this would take about 0.2s for the unit to trip, at 5g about 0.1 seconds and so on. As for the vertical signal I guess if it goes to zero or negative g for say a second you have just parked it upside down or driven off a cliff so it can trip. Edited by - Colin Mill on 4 Jun 2008 13:41:32 Link to comment Share on other sites More sharing options...
Simon.Rogers1 Posted June 4, 2008 Share Posted June 4, 2008 Colin - our data loggers regularly show spikes of "g" well over 2. But i guess its the length or duration of the spike that you look at? It really is the rumble strips that are the pain in the arse. Link to comment Share on other sites More sharing options...
neil.cavanagh Posted June 4, 2008 Author Share Posted June 4, 2008 as for zero g... I guess the biggest/longest jump is The Snake @ Longcross... and I should think that is in reality only a tenth or so of a second. THough feels longer!!! Link to comment Share on other sites More sharing options...
Colin Mill Posted June 4, 2008 Share Posted June 4, 2008 But i guess its the length or duration of the spike that you look at? Yes, that is the important thing and I believe would allow you to have a threshold that would ensure you don't get Robs problem of having a significant "off" that doesn't trip the switch. My guess is that the rumble strips are producing some rapidly alternating, mainly vertical g and this is easily suppressed in the software. I'm actually feeling quite good about my current little accelerometer project (I was pulling my hair out over it earlier today but it's sorted now!) so perhaps I'll be able to make a start on the code tomorrow. Link to comment Share on other sites More sharing options...
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