Adjustable stepper motors

[Xen]

Hello lads,

Sorry to start a new thread like this, but I really need your help. I own a Ford Sierra Cosworth group A (rally car), and I have rear Bilstein magnesium coilovers ready to go on the car for the next event, but they have been modified in a rather unusual way in the Cosworth world. I had to speak with an ex-Ford Motorsport engineer about them, and he told me they have fitted "LAND ROVER" stepper motors inside, so you can live-adjust them in-car.

I had never seen this before, and was very lucky to come accross that engineer, because they seems to be very rare. The problem is that there are 5 wires going out of each shock, and I have absolutely no idea of how they are connected. I would say I have to use relays, fuses, and switch to choose between the few positions of the stepper motors, but have really got no idea. Here is a picture to show you the wires :

I would think the BLACK one is earth, RED is live 12+, but then what about the 3 others ?

I know I don't own a Land Rover, but you must have heard of these adjustable stepper motors before ?

Any help is welcome, and I would be very greatful to this forum if I can connect these shocks to go back rallying.

Thanks in advance,

Matt.

[HoSS]

If really is a stepper motor thats fitted, then no - its not as simple as putting relays.

A stepper motor is driven by an electronic circuit which provides pulses on to a set of coils (2 or more) in the motor.

I dont knof if someone like Maplin does a stepper motor driver kit these days...

Otherwise you will need a tame electronics engineer to build you something.....

[Dave W]

Like HoSS says, not that simple to drive a stepper motor... made worse by the problems of identifying the kind of stepper motor !

You should be able to identify the type of stepper (assuming it has no controller on it) with an ohm meter. If all 5 wires are used then what you have is a 5 wire unipolar stepper motor. BUT I've never come across such a thing on a Land Rover which makes me wonder if they've used a 5 core cable for the more common (on a Land Rover) 4 wire bipolar stepper.

If it's a 5 wire unipolar then one of the wires will be common and the rest will each be connected to the other side of a winding to the common. If you measure the resistance between any 2 wires you will get a resistance (around 20-50ohms is typical for a 12v stepper). If one of the wires you have selected is the common then you'll see half the resistance you will see across tow coil wires.

If it's actually a 4 wire bipolar, you'll find that the wires will only show a resistance (not open circuit) between the two wires in each pair with no connection between them.

Driving each type of stepper motor is different although a unipolar 5 wire can be driven using a rotary switch, it's easier to drive them using a simple circuit with a simple switch input to tell it to step in whichever direction. Using a small PIC device to control it would probably be best as this can then remember the last state of the stepper so it doesn't have to calibrate it's position each time. Without this you might have to press the button a few times until it makes a difference after turning the power off.

Can you actually see the stepper motor or is it buried inside the unit ? Without being able to see what it's doing, identifying which coil is which will be almost impossible on a 5 wire stepper.

[Dave W]

Just been chatting with a mate of mine who is into rally cars, he suggested that it might be worth looking at the Escort Cosworths as a source of info because the later Sierras were used as a test bed prior to the changeover and that piece of technology may have been used on the later escorts.

[simonr]

Two options once you have determined what sort of motor you have. I suspect they will be bipolar and only use 4 of the wires.

Milford Instruments sell a number of microcontrollers as well as stepper drivers.

Alternatively, use a CNC stepper driver board such as this one on eBay which has a pair of buttons which step the motor forwards and backwards!

I've found in the past that the channel change knob from old CB's sometimes have outputs for step and direction, and sometimes a simple up/down. Once upon a time, I used a CB knob connected to a stepper motor which adjusted the air-fuel ratio on a carb so I could set it for max mpg under different conditions by dialing up a 'channel'.

I suspect a couple of up/down push-buttons would be sufficient for your application though!

Si

[Xen]

Wow, thanks to everyone for all the answers already. Very happy with that.

Well, before posting that new thread here I tried all the possible ways to know how to connect these before asking here. I haven't tried to ask Land Rover but I think it would be worthless. I contacted Bilstein about these, and they phoned me back telling me they had never made such shocks, and that the stepper motors were fitted by some tuners to compete with late top specs group A cosworths. I also spoken with an ex-Ford Motorsport about these, and he told me they were Land Rover ones, but nothing more, as he said it was very rare, and not used on the Escort.

Yes, a lot of development made on the Sierra has been used on the Escort, but these shocks haven't been homologated by the FIA, so not been used on the works car (I do have the complete FIA homologation papers for all the parts).

So yes I will mesure this weekend all resistances between the wires and post the results there, here are 2 more pictures of the top of the shock where you can see where comes out the wires, but I don't think it helps very much.

I asked on another "french speaking forum" (I come from Switzerland but my native language is french, grrrr) but they all have never seen stepper motors used on Land Rovers, so this forum proven to be the place where I could get the answers, which is great to know.

So I will mesure everything on saturday and post the results there, but thanks again for all the answers already.

[integerspin]

Try reading 'jones on stepper motors', google it. it will enlighten you.

I would guess it's unipolar, which should mean 4 of the wires will common to one of them with pretty much the same resistance.

[Xen]

I mesured today the resistance of all the wires of the 2 coilovers, and came up with this result :

Only the RED and BLUE wires are directly connected togather. I mesured 20 Ohms as a resistance on each coilover, but no resistance for all the other wires.

[Dave W]

That suggests that it's something other than a stepper motor at the end of the wires, maybe it has an onboard control board.

Do you think it's safe/possible/advisable to take the top off the shock absorber and get to whatever is housed inside ?

I'm assuming that, as it's at the top of the shocker rather than in the hydraulic end it's a modification made to a shocker that was already manually adjustable rather than a major mod to the hydraulics.

[forkrentfitter]

if they are genuine grp a ford parts they will have a 909 prefix on the part number which will be on the shock,the info is still available through m sport,i did some work with gordon spooner years ago and a mate still works on ford rally cars now,he has no recolection of them,spooners did a lot of the development work on the sierra and the escort,is some one misleading you i wonder?where did you get them from?

[simonr]

I mesured today the resistance of all the wires of the 2 coilovers, and came up with this result :

Only the RED and BLUE wires are directly connected togather. I mesured 20 Ohms as a resistance on each coilover, but no resistance for all the other wires.

Another option for making such a thing would be a simple solenoid which opens an additional valve. Then use pulse width modulation to vary the effective damping coefficient between the valve open and valve closed rates.

If one were making such a thing, putting it at the rod end is easiest as the valving will be in the piston. Make the rod out of a tube and you can 'talk' to the piston from that end.

I would try connecting 12v to the two wires and see if you can feel the rate change moving it manually.

Si