Suspension roll

[The Artful Bodger]

Darryl, after writing my last post I have been thinking if it is true (about the neutral point)?

If the steering is turned while the front part is vertical the contact patch will move off the vehicle centreline due to the castor angle of the front wheel (or maybe that should be called 'trail' on a bike?). So there would be some steering effect on the rear at low speed when the front is vertical but maybe it will even out once the vehicle is moving and the front leans? I cant quite figure it out but either way I feel this would be insignificant or at least within the rider/driver's scope to allow for.

This is a very interesting subject and it may be necessary to braze up a simple test vehicle!

[darryl]

Artful, you are right about the axis of the pivot being inline with the front tire contact point for neutral steering of the rear end. The way I explained it was in error. The idea remains though about being able to steer the rear by varying the angle of the pivot axis.

You would probably start with the pivot axis inline with the front tire contact patch, then vary the angle to test the effect of steering the rear end. If one were to make this part adjustable on the frame, you could always weld it up solid once the proper setting was found. Same for the steering tube angle. If doing this results in a heavier frame than is acceptable, then you could always make up another frame with the correct angles built-in.

This might be seen as wasteful of material, but without having been able to go through a trial and adjustment process, you would never know if your design had the potential to be improved or optimized.

[Clevelander]

We're working the same page....

The observation you made about the wheels and side load is a vital one. On the vehicles where the rear wheels stay vertical they will for sure need to be more robust than a bicycle wheel.

You and I are working a very similar program though a somewhat different approach. I've decided (until or unless I find out it won't work safely) that I will be using cast wheels from a scooter. That is actually why I bought the new lathe I got, so I could rework the wheels to move the axle stub more to the middle of the wheel and to allow the addition of disc brakes and of course the steering knuckle/spindle assembly. As I mentioned (in another of these posts ?) I'm using a fixed double wheel assmebly in the rear to provide some stability but as you lean into the corner it will transition to only the inner of the two tires being in contact with the road to allow me not to require a differential.

The thing that perhaps most has me scratching my head at this point is having unequal lenght A arms to allow for a reduced scrub angle but still having to make allowance for the whole mechanism to lean into the corners and keeping the relationship of the steering in sync with the rest of the moving suspension (that is not ending up with the outside wheel bump steering as it were through the transition). Clearly this problem has been licked on that 4 wheeler....I'm interested to know just how they did it.

Stay tuned for more info as it comes.

[The Artful Bodger]

Darryl, I believe you are quite right regarding steering the rear end and I expect that regardless of front steering inclination the vehicle will be neutral when the axis of the leaning pivot passes through the front wheel contact point.

[EddyCurr]

Perhaps you might want to look up William F. Milliken. His book, "Equations
of Motion" publilshed by Bentley could be an interesting read for you.

Eddy,

Hey, I have that book too! He had a lucky escape with the B-29 test flights.
A very dangerous aircraft with its fire-happy Wright engines. I have The Last
Great Miller too.

Camber Car....I don't care, that just looks wrong!

The Bentley link was good too, some video interviews with Mr Milliken.

Peter

I haven't read 'The Last Great Miller' and will have to look it up. Mr Milliken's
adventures at WG & Pikes Peak with his Miller were great reading.

Anyone wishing to gain greater insight into how and why vehicles handle
could benefit from adding Mr Milliken and son Doug's book 'Race Car Vehicle
Dynamics' published by SAE to their library.

In either EoM or RCVD, there is a discussion of tricycle dynamics, IIRC.

.

[darryl]

Comes to mind that a person could give some steer to the rear wheel pair as the front is leaned. If you consider that the rear of the front framework ends in a section of rod, about which the rear section pivots, then by adjusting the angle of that section you could steer the rear to some extent. If the rod went straight back, parallel to the roadway, then leaning the front would not steer the rear at all. If the rod were tilted downwards, then leaning the front would steer the rear into the turn. That could be a little strange to drive- . If the rod were tilted upwards, then leaning the front would steer the rear away from the turn. Too much of this would probably make it undriveable. Making this angle adjustable would give you a way to fine-tune the feel of it.

Of course, castor and steering tube angle on the front wheel are critical adjustments as well in terms of handling. When I did my tadpole design, I also paid a lot of attention to this. Even though it doesn't lean, I'm sure that minor changes here will be very noticeable in the way it handles. Because my bike has very nearly the same wheelbase as the tadpole, I just copied the geometry from it. I have no way of making a valid comparison to say whether it's right or wrong, I can only go from how it feels when driving it. It feels alright, not twitchy or hard to steer.

One of my original intents was to provide a way to adjust the steering tube angle to 'dial it in'. At the same time there would need to be a way to change the position of the front axle (or axles). They could ride in slots like the rear axle on a motorcycle, making for some adjustability. All in all it just added more complexity to the design, and I didn't go that route.

This is a slow speed vehicle, so I suppose I could make some comparisons to a scooter or even a wheelchair- how much work actually went into designing those things for handling - probably not much. Personally though, I'd be fussy over how it handled.

Where a person is designing the vehicle to be capable of comparative speed, say more than 30K or so, I would think you'd want to refine these geometries to a fairly high degree.

[Peter S]

Perhaps you might want to look up William F. Milliken. His book, "Equations
of Motion" publilshed by Bentley could be an interesting read for you.

Eddy,

Hey, I have that book too! He had a lucky escape with the B-29 test flights. A very dangerous aircraft with its fire-happy Wright engines. I have the Last Great Miller too.

Camber Car....I don't care, that just looks wrong!

The Bentley link was good too, some video interviews with Mr Milliken.

Peter

[GNO]

leaning into the curve

Back in the late 50's or early 60's someone built some hybred '' Studeillacks'' these were equipped with mercury switches and a system to pull down the inside of the curve side of the car

[The Artful Bodger]

Motorised skateboards are not allowed due to too small of wheels. The city can't be bothered to actually fix the potholes around here, so they would rather just ban vehicles that would be fatally affected by them!

I was not suggesting a motorised skateboard but rather an examination of the principles on which they are steered.

[EVguru]

It would seem to be easy enough until you think about it for a minute or two. To make the vehicle lean into the turn means moving the weight of the vehicle into a tighter turn than that followed by the wheels, this is easy enough on a two wheel vehicle where a turn is initiated by first steering out of the turn then as the vehicle begins to topple reversing the steering and balancing things out with speed and centrifugal force. (***** plenty of scope for debate here****** ). I am not sure how the same situation could be induced on a three or four wheel vehicle that is, unlike the bicycle, inherently stable.

You do it by making the steering/suspension behave like a bicycle!

That has already been described in this thread!

Here's a nice tilting recumbent trike; http://www.youtube.com/watch?v=GCJp4tU4TE4

Also look for Piagio MP3 on youtube.

[Black_Moons]

Hmmmm... I think you are leaning towards the principles of a skateboard! That could be worth a close look I think!

Motorised skateboards are not allowed due to too small of wheels. The city can't be bothered to actually fix the potholes around here, so they would rather just ban vehicles that would be fatally affected by them!

[The Artful Bodger]

Hmmmm... I think you are leaning towards the principles of a skateboard! That could be worth a close look I think!

[Black_Moons]

It would seem to be easy enough until you think about it for a minute or two. To make the vehicle lean into the turn means moving the weight of the vehicle into a tighter turn than that followed by the wheels, this is easy enough on a two wheel vehicle where a turn is initiated by first steering out of the turn then as the vehicle begins to topple reversing the steering and balancing things out with speed and centrifugal force. (***** plenty of scope for debate here****** ). I am not sure how the same situation could be induced on a three or four wheel vehicle that is, unlike the bicycle, inherently stable.

Well, Yes, I think the solution here is in the fact that my vehicle will hopefully be a fraction of the drivers weight and just by having the driver shift there body, they will be able to put enough weight on the inside tires to greatly improve cornering and stability.

I also thought it might be an amusing exercise to have a steering column that tilted side to side, directly controlling camber of all 4 wheels via control linkages. Maybe Mk2 will try that out...

You would lean to balance the G force on yourself in a downward direction and drag the steering column with you.



Of course, While talking to the motorcycle/ATV shop owner down the road today about 'leaning 4 wheeled suspensions', he had an interesting tidbit to say:
"That is a stupid design. You will still wipe out, Just differently!"

He may very well be right in a way..

[EddyCurr]

W.F. Milliken's MX-1 camber car.

Under restoration

MX-1 at Goodwood

MX-1 at speed at Goodwood

I also see that in Sept 2011 Mr Milliken was inducted into the 'Legends of the Glen'.
Along with some guy named Andretti ...

.

[The Artful Bodger]

I was looking at making the car lean into the turns, ie try and move its center of gravity to the inside of a turn.

I am starting to think that with a light enough vehicle and soft enough suspension, the operator should be able to just lean the vehicle with his own weight. Maybe with some kind of seat tilt feature to make leaning more natural feeling.

It would seem to be easy enough until you think about it for a minute or two. To make the vehicle lean into the turn means moving the weight of the vehicle into a tighter turn than that followed by the wheels, this is easy enough on a two wheel vehicle where a turn is initiated by first steering out of the turn then as the vehicle begins to topple reversing the steering and balancing things out with speed and centrifugal force. (***** plenty of scope for debate here****** ). I am not sure how the same situation could be induced on a three or four wheel vehicle that is, unlike the bicycle, inherently stable.