Electric power steering on a Beta

[peteracs]

Thanks for the update, you sparked a subject which I have thought needed to be aired and resolved. The top mounts which are currently available from memory have not had a good reputation for reliability. It would be interesting to explore actually having a batch of top mounts made especially if they can be made at sensible price by modifying an existing mount.

Are there any suggestions where to start on this?

Peter

[mangocrazy]

Hi Ian/Peter,

Thanks for the correction. I think I'm starting to get my head around it now. If this were motorcycle steering geometry it would hold no terrors for me, but the addition of a pair of wheels confuses me greatly...  

Ian will probably be able to confirm or deny this, but what you are doing by increasing castor angle on the front wheels of a car is equivalent to increasing the rake on motorcycle forks; i.e turning your sports bike (steep steering head angle) into a chopper (shallow steering head angle). This gives slower, heavier steering but with a predilection for stability and going in a straight line.

Graham

[WestonE]

Hi Graham

As a Mountain biker and holder of a motor cycle License unfortunately the comparison does not work well because bikes steer mainly by response to leaning except for slow speed parking. Cars use turning wheels around an axle point. Caster introduces twist for pressure on the contact patch and changes the wheel angles through turning to introduce negative camber which works against roll to maintain the contact patch. There is a complex relationship between toe in/out / camber and caster before we get to Ackerman angles. There are conditions we want to avoid like bump steer, sudden changes in camber through suspension travel or bush movement or wheel turning. We want the steering to bite into a turn (toe in/out setting & miss matched front/rear track ) with a flat tyre contact patch if possible and maintain strong grip and lead the car through a turn despite body roll.

You need to do some reading because this is a complex inter linked subject. Chad from The Monte Hospital commissioned an analysis of the Monte design from an Aston Martin Suspension engineer before building some excellent modifications to dial out the mistakes

Lancia were pioneers in balanced responsive handling including miss matched front to rear track and wishbones mounts that change load through the wheel travel, but had to build to a budget and ensure comfort. No Power Steering meant compromising the front suspension design. Front wishbone location was/is terrible under load and the cars squat under power (lack of anti squat geometry and little rear spring pre-load). If you want to see some of the design fit a strut with no spring and move the wheel through different positions with a trolley jack changing the strut compression.

Years ago I built in rear spring pre-load with short strut rods, had Barry Waterhouse nylon wishbone bush supports and added 1.5% negative camber after converting to Power Steering. Caster gives a bigger win than just negative camber because it maintains the tyre contact patch better. I deliberately built my car with twin adjustable rear links, fully adjustable coil overs, stronger wishbones with fully supported bushes and multi position front top mounts. This was so I could adjust toe camber and caster. I have gone for an educated guess on spring rates and the platforms on the struts allow adjustment of rake (some nose down attack maybe) and corner weighting. Because of the sliding rear anti roll bar you can even fix 'set back' on a Beta. That is when one side of the car is shorter wheel center to wheel center which creates a desire for the car to steer toward the shorter side.   

Ian knows what he is doing with the adjustments he is trying and it is valuable insight. I will only be able to test again when the car runs!

Eric     

[mangocrazy]

Hi Eric.

OK - I was grossly over-simplifying things I now realise. Time to take a crash course on 4 wheel vehicle steering geometry and suspension dynamics, I think...

Graham

[squiglyzigly]

I think the Electric power steering experiment is now at the end of its development for my Berlina.
Thanks to Chris who donated a 3.5 turns coupe steering rack to the project, so I now have the final piece of the jigsaw in place.
After a quick strip, clean inspect, grease and re-assemble with new boots it now takes it’s place in the engine bay with a few shiny heat shields, powerflex anti-roll bar bushes and some sound proofing for good measure.
The end result. It now steers quicker just like a coupe albeit without any real effort. You do still have to swing your arms about abit as it’s still 3.5 turns and not 2.5 turns like a modern car, but I’m very happy with the result.
It’s as good as I could of hoped for and ultimately I think it was worth the time spent experimenting.

I’m only sorry I didn’t get the car together in time to get down to Mark’s betaboyz open day. Next year I will definitely be there, and if anyone wants to give the old girl a drive then the keys will be available to any beta owner interested.

[squiglyzigly]

Nothing to see here, the interesting stuff is under the dashboard 

[WestonE]

Hi Ian

Brilliant as always. I am intrigued by the heat shields. Are they attached to the steering arms? I have some modern crinkle surface heat shielding saved for rolling up over the subframe and rack then kicking out below the fuse box. But this will be fixed in place and will involve fun with the gear linkage. I can see me wasting plenty of cardboard designing it!

Eric   

[squiglyzigly]

hi Eric
Yes the heat shields are attached to the steering arms. I tack welded a couple of M8 nuts on top of the arms to allow the heat shields to be bolted on. The shields are 2mm ally sheet and yes it did take me several cardboard attempts. Even then when function tested with engine back in they managed to touch the gear linkage when the car was jacked up with the suspension on full droop and full lock. Luckily its quite easy to remove the bolts/shields and make final adjustments.
The exhaust downpipe and flexi are also wrapped.

On my VX I made a similar pair of shields with wings cut into them to allow fixing via jubilee hose clips. But this isnt as good because its a knuckle grazing affair and the jubilee clips are very close to the 4 branch. Next time the VX engine comes out I shall tack weld the nuts on the arms.

[peteracs]

Neat solution for the steering boot protection. Food for thought for future mods.

Peter

[WestonE]

Hi Ian

Where you have the 2 black studs holding the sound proofing I have 2 x 6mm rivet nuts now that I intend to hold my up and over heat shield. We will see if it becomes a change of plan as many things have. It is nice to have bright ideas I can switch to.

Eric   

[squiglyzigly]

Hi Eric
Yes I did consider exactly the same route with rivnuts and a fixed heat shield. I changed my mind because as you know there is very little space between the rack and the exhaust. Maybe your custom made 4-1 will free up a centimetre or two. But as you can see on a standard setup there’s really not much space to play with and I didn’t fancy my chances getting a fixed shield to clear both the rack and the engine whilst they move around.
 I am intending to put another shield fixed to the bulkhead just next to the gear linkage but I’ve left it out for the moment because there’s a conveniently placed grommet that I’ve run my afr gauge wiring through. Once the carb is setup I will remove the afr wiring and put the shield in to finish the heat protection.

As my dad always said to me “there’s more than one way to skin a cat”.