Well, I have three AMD 1561 accelerometers (can't remember the full spec - you can go to the AMD website and trawl through their stuff till you hit them) - there are about three different types, and I chose the ones with on-board output amplification, going +/- 3g (I think) which is more than sufficient for a Mini. They are mounted in the three axes and have a multiplexor for axis selection.
The gas struts - well, I just picked up a dead Ford Fiesta gas strut, which had about 9 inches of extension travel. That corresponded roughly to what the Spax shocks on my TR 6 can do (but they don't, of course
) and more than double the expected suspension travel of the Mini. I carefully drilled one end of the casing to release the remaining gas pressure in the struct, and then pumped out the oil (messy). I then carefully cut around the welded seal at the top of the strut casing with a diamond disc on a Dremel, and the thing came apart quite nicely. Although it's difficult to describe the guts of the thing, it is basically a rod with a one-way plunger valve on the end inside a tube casing. The weld seal was necessary for the oleo-pneumatic pressure. I washed and degreased the bits, and then fitted a plastic insulator pipe over the inner rod after removing the valve, but not the end stop. This meant I now had a free-moving linear rod-in-a-pipe setup with an insulated core.
I now hand-wound the insulator pipe with naked 4 thou copper wire (did this with the rod clamped in the drill bit of an electric screwdriver and with the screwdriver turning, gradually wound the entire length of the pipe. LOOOOONG time). Another drill-hole half way up the outer sleeve, insulated spring-loaded carbon brush from a vacuum cleaner goes through the hole to come in contact with the wound inner sleeve on the inner rod, and then tack-welded the cap back onto the sleeve. Bingo! Instant, linear 5k pot, with weather proofing. Cost - about a quid for the strut, 20p for the insulator pipe, a fiver for the copper wire (but enough for about 20 pots), and I raided the parts box for the spring-loaded motor brush. Linearity is not superb, and I had to play about a bit with the wound length to make sure the end stops corresponded to wound parts of the sleeve, but it is *much* cheaper than the real thing (around 220 quid a shot). The difficult bit has been working out how to safely (and rigidly) attach then to the shocks of the car. I have ended up using jubilee clips until I can think of something better (whadda bodge
).
I should be able to use Patrick's board with the empeg (given a reasonably stable reference voltage source) to measure the suspension travel and accelerative forces applied to the car (vertical, longditudinal and centripetal). If I have the same setup in each car I have an empeg sled installed in (TR 6 and the Mini at the moment) then I should be able to write an acquisition program for data logging whilst the cars are on the road, and then dump the the data for analysis when I get home. It should then be possible to tweak the gas shocks on the cars to get the best setup for the road conditions I encounter.
Although neither car has a CAN bus (too old), I will be trying to use the Motorola CANbus chipset (can't remember the numbers, so don't ask) to interface via one of the serial ports so that I can pick off CANbus traffic in the future. That's the intent - I wonder if I will manage to get that far? I also plan to look at manifold vacuum and fuel metering unit behaviour on my TR 6 to look and see if the fuelling behaviour of the system is optimum, but that really is a long way off....
. Worra plonker.
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