Magnetorheological Shocks, some parts and ideas

[ace_xp2]

I was hoping to actually be able to post doing this to my car this winter. But it seems that I'll be heading out to the hinterlands for work this year. So rather than keep ahold of the idea, I figure I'll put it out there for any whom are curious.

I've been looking at Magnetorheological shock absorbers for quite a while. They represent a number of interesting possibilities to mess with transients, or hell, even just to make spring changes that much easier.



The biggest barrier to entry has been the price of the shocks themselves however, as the corvette mag shocks and similar mag vehicles start at the 5-600 range per corner. Now while that was about what I was looking to spend in the non mag range (say afco doubles), it's a little steep just to test the envelope of damping I can get away with in a given shock.

Enter cadillac, who decided that the escalade EXT really needed to have a magnetorheological shock system, and luckily, that they could sell it much cheaper. ACDelco sells them for a scant 270 a piece for rear shocks:
https://www.acdelcodirect.com/produc...truts/25871432
That's a cheap entry point to see whether they'll have the damping range that can suit the critical damping ranges that we'll be after. Plus a large truck is hopefully already higher in terms of force rates than a typical passenger car, given the weights involved.
Finding out what we can get away with will take a basic shock dyno, something this:
http://www.circletrack.com/howto/828...ng_shock_dyno/
Though finding out an accurate initial value could prove trying. Alternatively you could build something like this:
http://honda-tech.com/showthread.php?t=2325055
Though that is mainly overkill, since we will be able to vary the velocity response at will, our main concern is seeing just how much resistance the shock can generate between 0-5v.

That brings us to the next big problem, controlling the shocks themselves. They need a 5v pulse width modulated signal which controls the damp rate of the shock. Increasing the duty cycle increases the damping rate, luckily the shock response is apparently pretty linear, so there shouldn't be any annoying peaks or dips in shock response to program around. As for what to program, I'm unsure on that point.

I've been thinking of using something along the lines of an Arduino, which has the pwm capabilities, but can only supply about 40ma of current. Now I think that's where you'd use say a tip120 transistor to act as a relay and provide the dampers with the current they need. I believe at that point you'd need an additional 5v source to run thorough the tip120, not really sure though. An arduino leonardo would provide more than enough output and input pins, I'm just a little concerned about the duty cycle and general hardiness of these. They seem to be pretty tough, it's just not something you'd want to fail at an unexpected moment.
http://www.adafruit.com/products/849#Description
http://www.digikey.ca/product-detail...120-ND/1052441
http://www.ebay.com/itm/DC-DC-Conver...-/171002548980

As for inputs the sky is the limit really, you could pretty much add just about anything you want since an arduino like the leonardo has a dozen input pins. start with the requisite potentiometers on each corner to measure suspension movement (gm stock ones would likely work, but you could put something less robust up and out of the way with pushrods) and add whatever you want to use as a variable for the damping rate.

Here's a Delphi presentation on the subject:
https://docs.google.com/viewer?a=v&q...-FRxUrbAXaEb6g
and an interesting thesis on mag shocks which goes into some of the algorithms and even shock design:
https://docs.google.com/viewer?a=v&q...h_5LlqNjmsKGGA
Who knows, maybe this'll help someone else with too much time on their hands