Colin Mill

Hi Julian By RC servo standards that is a very expensive unit and not amazingly powerful. Also 0.6s/60 degrees is quite slow (standard RC servos are around 0.2s/60 degrees). It might be worth looking at the Hitec servos. They do some titanium geared servos that are quite impressive. One thing you need to bear in mind is that RC servo manufacturers are rather naughty in specking servos - they quote no-load speed and stall torque so the servo you are looking at will do about 1.2s/60 degrees at 60kg.cm load. My guess is that you will need considerably more grunt from the servo. If you want a really high-spec servo try looking at Maxon. They are a Swiss coreless motor manufacturer that do a very wide range of motors and gearboxes. Certainly they will have something to do what you need. However you want to do it the electronics is now very simple and cheap. Colin

I use heavy duty velcro (here) to hold the doors shut on mine and it works fine. There are quite a lot of grades of velcro and similar products. Some are so strong that you have to use a blunt knife to help separate the halves so I'm sure there would be a grade to do the job. Edited by - Colin Mill on 5 Jul 2007 15:39:43

I would expect the oil pressure when cold to be sat on the pressure relief valve pressure pretty much from idle up. Is that how your engine usually behaved?

IIRC the standard Caterham part is thin plastic - quite literally as much use as a Chocolate fire-guard. Not sure that Carbon is a lot better.

A friend of mine was involved in developing a printing machine that maintained the registration between the different colours electronically - each colour stage was driven by a separate motor. The registration accuracy was, I believe a fraction of a mm at a paper speed of several metres/s. He has moved on from that occupation but I'm sure can point you at some useful suppliers. If you like I can blatmail you his contact details. Colin

Hi James Let me know if you need any help with the sums - I'm a cr@p driver but I do sums 😬

I feel slightly conned 😬 😬

There is some info here. You will need to do some units conversion as its an American web page! The volume flow rate down a pipe under laminar flow conditions is given by Volume/second = (Pi*P*R^4)/(8*Eta*L) Where Pi = 3.142, P = the pressure drop between the ends of the pipe( in Pascals), R is the internal radius of the pipe (in metres), Eta = the dynamic viscosity of the fluid(in Pascal.seconds), and L is the length of the pipe (in metres). From a couple of sources I have that for viscosity conversion 1 cP = 0.001 Pascal·second Petrol (gasoline) has a viscosity of around 0.6 cP at room temperature or 0.0006 Pascal.second but is a strong function of temperature. Colin Edited by - Colin Mill on 26 Jun 2007 20:16:38

Well, the starter motor and its solenoid are nice big inductances so you can get a interesting jolt when disconnecting 😬 V=-L dI/dt and all that stuff.

If the stat is in the top hose and almost seals completely it is not getting a chance to 'sample' the output water temperature so there is a great chance of getting a major temperature overshoot. I'm sure the drillings are the way to go to ensure the stat sees the true output water temperature as soon as possible. As a general rule delays in feedback loops like this are a recipe for oscillation

I think the relay contacts in the MFU are a likely candidate as they are switching an inductive load (the solenoid) so they are likely to suffer some burn on releasing. I have been meaning to put a heavy diode across these contacts to divert the inductive kick away from the contacts. You need to fit the diode so that its reverse biased under normal conditions. Colin

There are a lot of different grades of loctite and other makes of locking compound. I would use Loctite 243 which is an oil tolerant medium strength retainer intended to give similar performance to nylocs. You could use loctite 290 which is a high strength retainer intended to wick into the thread after assembly but will be harder to disassemble than you might wish. Don't use loctite 270 (studlock) this is intended for permanent assemble and will give you a hell of a job to undo subsequently (its a blowtorch and lots of force job). Colin

If you can tell us what said 'device' is without ruining your reputation we could probably be more help 😬

There is a lot going for the "2 x 15 stone" approach. I had a minor involvement with the Huygens lander (that is now sat on the surface of Titan). They spent ages using finite element analysis to design the structure but part of the instrument mounting broke on the vibration test rig causing a bit of last-minute beefing up to be applied.

I think you would be better off to apply the same amount of effort to unsprung weight reduction of the existing de-dion setup. Alloy brake components and an alloy or composite tube would do a lot in that direction.

Well, if I was designing the thing I would use a regulated supply to provide the feed to the potentiometer so that the voltage across the pot was independent of the resistance value. Given how cheap this is to do I can't see a manufacturer cheapskating this as its going to cause more trouble than its worth. Lets assume that they allowed the full 12v across the pot the 15k one would pull about 0.8mA and dissipate about 0.1Watt. The 5k one would pull about 2.5mA and dissipate 0.3W. Neither the extra current nor the dissipation in the pot itself is enough to cause a problem (unless the ECU were deliberately designed to be fragile!). More likely they will have regulated down to say 5v for the sensors so the currents are even less. Colin

Looking at the EU3 circuit diagram I see that the throttle pot is a three-wire connection so I expect that they are using the pot in potential divider mode rather than variable resistance mode. This would make considerable sense in such an application as, with a high input impedance of the ECU input that monitors the wiper voltage the arrangement gives great immunity to poor wiper contact resistance etc. If the pot is used in this way then the actual resistance is not very significant. More important is the angular range of the pot. Colin

Hi Darren If you find it difficult to hit a brightness compromise that works OK day and night let me know - I think it would be fairly easy to make a little circuit that dimmed it for night time use. Colin

While there are some LEDs with built-in resistors most don't. Depending on the colour the voltage drop across a LED is typically 1.8v to 2v. 20mA through most LEDs gives you a pretty bright light so if the output of the unit is 5v you will need about a 150 ohm resistor in series with the LED to set the current. If the output of the unit is 12v then you will need a 560 ohm resistor to set the current. 2 watts at 12v is a current of 167mA so there is no problem about exceeding the 2 watt drive capability. Colin

While you could get problems on the earth side, by having the drop show up when metering relative to the battery negative it shows, in this instance, the high resistance is in the feed side. Colin

Went to a drag track in the USA one time and, yes, if it was not for all the silicone enhanced ladies walking around the place I would have nodded off completely 😬

Hi Roger Circuit is done with multi-turn pot for adjusting the trigger voltage. It covers 11 to 15v quite happily and I have set it to 11.5 for starters. The bit of veroboard is 25mm wide by 68mm long - input on orange and black out on orange and grey (the negative is switched with a N channel mosfet - a 46 amp one as that is all I had to hand 😬) Please drop me an email with your address and I'll get it sent! Colin

Hi Roger Probably the easy one is to use a voltage comparator or an op amp to compare a fraaction of the battery voltage (adjustable on a pot if you like) with a reference - a zener diode would be the easy one - and use the output to turn on the LEDs via a bipolar transistor or a mosfet. A suitable amount of hysteresis around the amp/comparitor should stop it coming back on as the voltage recovers after the load is removed. I probably have all the bits needed in my stocks here so if you like I can knock something up on veroboard for you - say for a modest bung to NTL 😬 Colin Edited by - Colin Mill on 15 Jun 2007 20:32:16

Yes 😬

If its a good old mechanical one with a speedo drive cable it can be caused by the cable being unhappy (after I lifted the front of a Hornet up by the speedo cable while removing the engine the speedo had a 20 mph bounce ever after!) Colin