Jump to content


  • Posts

  • Joined

  • Last visited

Everything posted by DeTRacted

  1. The DfT have published some proposals on new regulations for vehicles, which includes controls on modifications (they call it tampering): "We will create new offences for tampering with a system, part or component of a vehicle intended or adapted to be used on a road." https://www.gov.uk/government/consultations/future-of-transport-regulatory-review-modernising-vehicle-standards/future-of-transport-regulatory-review-modernising-vehicle-standards#questions I expect it is only meant to apply to new autonomous vehicle systems but the wording looks very lax and you have to wonder how wide the effect wouid be if implemented.
  2. Don't forget the elephants though. (unseen university emoji)
  3. I can't help thinking this would be better discussed in the common-room but: I understand your point John and am familiar with resonance and harmonics and with pulses in cables which is a good analogue as the physics is similar. The reflection of fast pulses is much used in time-domain reflectometry and that goes for optics too because the same thing holds for fibres and light pulses. Similarly, standing waves are set up in cables under the right conditions but these must be steady-state. I can’t help feeling we are describing the same thing from different directions as it were. Standing waves are an effect, not a cause and do not exist in isolation. They are the interference pattern from the interaction of incident and reflected travelling waves (continuous sinewaves, not pulses) . It follows that If there is no wave travelling downwards and no reflected wave travelling upwards, there cannot be a standing wave. Considering each header pipe, I believe in practice any standing wave would be severely disrupted - often - by the short pressure pulses of gas, with a repetition rate and duration which will vary with engine speed - so the conditions are far from steady-state. There will be more pressure pulses occurring at different times and feeding from the other end of the pipe as the other cylinders exhaust so the result is likely to be very complex. If it was one pipe per cylinder all the way down things would be simpler to comprehend.
  4. Worbarrow bay is a special place. Lots of fossils. There is a small headland that juts out on the east side of the bay and on the east side of that there is -or used to be- a large wave-worn ammonite in the rock, about two feet across. It must be 40 years since I was last there so maybe it has gone now.....
  5. I’m not sure about that John. The diagrams you show are not of a travelling wave but a static or ‘standing wave’. You will only get a standing wave if the excitation is continuous at exactly the right rate - like blowing a flute. I think an exhaust is much more like a tubular bell where the exhaust pulses are the stick. There may be a resulting resonance in the tube but it would be more of a decaying sinusoid following each pulse. As with a bell, the pulse repetition rate which does the excitation does not change the frequency of the resonance. The exhaust pulse must travel - after all the gas does have to get out. Another analogue is of sending an electrical pulse down a cable. Provided the pulse rises quickly and is shorter than the transit time in the cable it will travel along largely unchanged until it meets a change in impedance (e.g. pipe diameter or joint in an exhaust). Then some of the energy continues but some reflects depending on the degree of impedance mis-match. You can also see this with a skipping-rope held at both ends, where if you tweak one end sharply you can watch the wave travel down the rope and then come back with reduced amplitude. The faster the pulse rise-time and the shorter its duration the more pronounced any reflection will be so for an exhaust it should really only be a high-revs thing. The reflected energy will interact with following pulses in a complex manner depending on when they meet. Surely tuning is the trick of getting the pulse to arrive back at the valve with the right polarity and spacing to give some rarefaction. ( I don’t think you can get a flute to suck at the player’s lips can you ?)
  6. An ordinary full-size momentary centre-off toggle switch but I did extend the toggle.
  7. I wanted a two-way centre-biased momentary toggle switch for my J-type box, flick down for OD on , flick up for OD off, plus the logic from the interlocks. That way I don't need a warning lamp as operation is obvious, so this is what I did:
  8. Yep. 12 dots - four on each of the top, middle and bottom horizontal lines.
  9. They aren't actually moving around, it is just that you can't distinguish them unless you are looking directly at them. Something to do with less detail being available in peripheral vision?
  10. ...and your concern was correct as witness the Iranian centrifuge plant full of Seimens PLCs, sabotaged by the Stuxnet virus. The problem isn't necessarily the system itself either but the daft b*****s who insist on it being connected it to the internet, though even an air-gap doesn't help there is an unprotected USB socket.
  11. The problem with the latching relay is you need a pulse to re-set it when the interlock opens, for the 'logic' function - which is what the transistors do. I don't think there is any other way to do that. You also need to find a way to automatically ensure it always starts in the 'off' position, because as-is it stays where it was last set. That circuit is for a TR 'box with the off-in-neutral function. In your sketch, if the latching relay is ON and the interlock kicks RL1 off because you change gear, the next time you operate the switch it turns the latching relay off again so you don't get OD. You would have to push the button twice to get overdrive on again. I think you might soon find that irritating - sometimes one push needed, sometimes two.
  12. Here is a way of having sequential on/off switching with a single momentary switch (in this case on the gear-stick but it could be anywhere). It uses a bi-stable relay and was designed for a J type but is easy to adapt for an A or D type. The two transistors shown could be replaced by a single TIP120 :
  13. Are you over-thinking this? I can't see what you are trying to achieve with the third relay. If you have the interlock opening between 3rd/4th the circuit automatically drops out as you go through neutral without the need for another relay, since power for RL1 is removed when the interlock opens. What you don't have without the clutch switch or an equivalent on the dashboard, is any means of turning off the overdrive yourself except by changing gear. (By the way, the TR/saloon box already has interlock opening in neutral between 3/4 AFAIK - at least, the ex-2000 box in my '3A does)
  14. ... and dare I say it , rather OTT in my opinion (but each to his own). Perhaps it's because my electronics training came long before PICs were even dreamed of but I was always taught to keep things as simple as possible, commensurate with the function required. Two relays is all you really need for the 'logic' as per Andy's circuit above. Even if you want to get complicated and have only one momentary switch to operate it on and off, the most you need is a couple of transistors in addition. Since this is a fixed-function device there is absolutely no need for programmability, and voltage glitches don't affect relays.
  15. Ah you can't do the both-through-the-interlock suggestion then. The solenoid takes too much current.
  16. That looks sort of OK except the indicator lamp in series with relay 2 coil. As drawn they would both have to be 6v items. Both relay2 coil and the lamp need to be in parallel to be 12v ones. (If it is a J type I would have taken the earth returns for relay 1 and the solenoid both through the interlock switch. That way the OD is still inhibited in 'wrong' gears even if the relay sticks closed. )
  17. At that price it can only be crap and If you value your eyesight you will steer well-clear John. That is a class-4 laser and is only really safe if used in a properly constructed and interlocked enclosure which ensures line-of-sight contact or specular reflections from the nice newly-cleaned shiny metal surface are prevented. At the very least you need special laser-safety goggles which attenuate light at the laser wavelength, and which will probably cost considerably more than that machine for a decent pair.
  18. As Mike said. An RCD compares the current being drawn from live, with the current returning through the neutral. If there is a difference the lost current must be flowing to earth and more than 30mA difference will trip-out a normal RCD. There are different ranges though - you can also get 10mA RCDs for extra protection or 100mA RCDs for circuits where 'nuisance tripping' is a problem. The fact that you can re-set your garage RDC after which everything works OK, shows that there is no basic wiring fault, else it would keep tripping, and that this is probably just a nuisance trip due to inrush current - again as Mike said. Anything with a filter capacitor in it can cause that. The switch panel in the photo looks a bit long in the tooth but I think the 25A switch on the left could be an RCBO as it has a test button. (An RCBO combines the function of an RCD and an MCB circuit breaker for overload currents). The fact that this doesn't trip means either the inrush current is occurring somewhere in the circuit prior to it or perhaps it has a different range to the RCD in the garage. It also may be stuck - you need to exercise RCDs periodically by using the test button to keep them free. The switch on the right is just a 16A MCB and the middle one looks to be the main contactor. It might be worth considering upgrading the panel with more modern switchery though, as you really don't know the state of those...
  19. John - I think that content is in your personal space on Google. You can see it because you are logged in to the account but no-one else can access it, so a link doesn't work.
  20. The clamp-type knurling tools are definitely best as there is much less strain on the lathe. Can't say I've done any on brass though. Ali is easy.
  21. For android phones there's a 'free' gizmo called Android File Transfer available for Mac and PC - just plug the phone into USB and you can drag-and drop files. Works fine with an android phone on my Mac, I've not tried it yet on a PC.
  22. It's not quite as easy as that on a '3a John. The take-off for the pressure gauge is a banjo fitting on the oil filter head so the required adaptor would be quite complcated.
  23. Sorry garbled the last bit and can't edit it. - e^6 would be 403/million or about 26000 for the UK.
  24. That doesn't work with the graph John. The vertical axis is "Log deaths per million (of population)" so 5 on the graph would be 100,000 or 10% fatalities. Some of those dots look to be well in excess of 6 which would be more than 100% fatalities. Something wrong somewhere.....? It might be log to base e perhaps in which case 6 is about 26,000 ?
  • Create New...