"Wagon" steering on tadpole... bad idea?

[TylerDurden]

I never see it, but I don't know why. I always see knuckles and links.

 

[dirtdad]

I never see it, but I don't know why. I always see knuckles and links.

Unless you make some mods to it you wont get Ackermann corrected steering that way. The inner wheel should ideally turn in a tighter radius than the outer wheel. It makes a bigger difference as you turn sharper. As the effect gets worse, usually the outer wheel starts to get dragged partly sideways as it is not going the direction it is pointed, and the tire wears out really fast. Plus handling is really unstable.

 

[TylerDurden]

I also wonder if it's more significant on a 4-wheel vehicle, than a three-wheeler.

Knuckles..........Link.............................................Waggin'



:?

 

[dirtdad]

Hmmm...waggin must do an Ackerman kind of thing, too. The outer leg must cover more distance in a corner. I wonder if you can tell by watching him?

 

[Link]

Her.

 

[Stevil_Knevil]

I used to have one of these.. but it was delta. Rode it so much, I wore a groove down the center of the front wheel - which turned into a split

My uncle glued a 20" Comp 3 onto the front wheel and it was better than ever! Great scoot for 'drifting'..

.. never thought of flipping it around and adding electric power- until now Thanks, TD

"Wagon" steering? NOT a bad idea.

 

[curious]

Just looked-up Ackerman correction in google. At a first glance to me it looks like it is only needed if the wheelbase is maintained equal on both sides of a vehicle in a turn. If entire axle pivots like suggested in this post the thing will turn around the virtual point defined by the intersection of two lines defined by front and rear axles with all three or four wheels strictly perpendicular to the turn radius - sort of an ideal case. But maybe I am missing something.

 

[dirtdad]

I think you are right. Ackermann is needed when each wheel rotates around a separate vertical axis, but maybe not in this case. Ya gotta love simple solutions.

 

[cerewa]

You guys are right, that "wagon" steering eliminates the need for Ackermann steering correction. Instead, the wheels will handle as well as the rear wheels of a car do - no need for them to point in a non-parallel direction for turning. http://en.wikipedia.org/wiki/Ackermann_steering_geometry has a good explanation of Ackermann steering.

If you make a trike with non "wagon" steering, AND without ackermann steering correction, it might still not be much of a problem - being so much lighter and smaller than a car, I don't know that it really matters much for a one-person trike. Once you get into the realm of gross-vehicle-weight of 500 pounds and up, this stuff probably really matters.

The trike you envision, Tyler, may still have crappy handling though.

 

[fefifofob]

Ackerman shouldn't be a problem because both wheels will turn about the same point. The axle will be in line with that point. If you are turning about a 10 foot circle, the axle will point at the center of that circle and both wheels will be perpendicular to the circle.

But, there's another problem. With single axle steering, there's no self centering action. The wheels would just as much like to turn more as less. This gives more of a feeling that the vehicle is 'unstable' and would like to tip over, especially at speed.

 

[curious]

Plus effective track width is reduced progressively with decreasing turn radius thus reducing stability. It may still work OK though with some limits on minimum turn radius.

 

[Link]

I used to have one of these.. but it was delta. Rode it so much, I wore a groove down the center of the front wheel - which turned into a split

My uncle glued a 20" Comp 3 onto the front wheel and it was better than ever! Great scoot for 'drifting'..

{{snip}}

.. never thought of flipping it around and adding electric power- until now Thanks, TD

"Wagon" steering? NOT a bad idea.

LOL, they're selling those at Wal-Mart again for like $100.

My broke-ass family never got me anything good like that when I was little. I wanted a Power Wheels. Of course, I probably would have added a battery or two or three.

...

Mebbe being broke had nothing to do with not getting cool stuff...

 

[JennyB]

But, there's another problem. With single axle steering, there's no self centering action. The wheels would just as much like to turn more as less. This gives more of a feeling that the vehicle is 'unstable' and would like to tip over, especially at speed.

That's the killer. If you've ever ridden one of those cargo trikes with the big box up front you'll know that once one front wheel meets more resistance than the other there is a large force trying to steer the trike in that direction. If it's not corrected quickly then the trike just turns more quickly, and you're out the side door!

Wagon steering works best on wagons (where the tractive force holds the axle straight) or on slow, heavy things with lots of hydraulics.

 

[TylerDurden]

Jenny's point on tractive force makes mucho sense. While the steering can be made to center by moving the pivot ahead of the axle, it may be very unstable without a long lever for control.

 

[TylerDurden]

Hmmmm..... gears, maybe. :?

Edit: Great graphic, Stevil... lol

 

[TylerDurden]

I actually prefer delta, so here's an updated version of Stevil's Greenie:

The axle is mounted on a slope, so the longitudinal elements (chassis) tilt in the direction of the turn.

 

[MidniteTweeker]

Rear-steer recumbent trikes have been around a while.

http://www.sidewindercycle.com/

Never ridden one myself. I hear they have an extremely short turning radius. Also hear stability can be an issue.

MT

 

[TylerDurden]

Here's a delta with a twist... the tilting-trike/funcycle/dirtrike geometry actually has a "wagon steer" aspect to it. The angle of the pivot controls both the degree of tilt and the degree of axle turn.

 

[curious]

Let me see - if the center of mass of the loaded "thing" is below the line connecting the pivot point and the front wheel ground contact the "thing" should have positive stability without pivot suspension springs (except for some form of a damper).

 

[curious]

But if leaning and steering are interlocked how do you initiate a turn ? By leaning the body or by a lever leaning the entire front part including the body ? The "thing" may have some interesting feel to it

 

[dirtdad]

Here's a delta with a twist... the tilting-trike/funcycle/dirtrike geometry actually has a "wagon steer" aspect to it. The angle of the pivot controls both the degree of tilt and the degree of axle turn.

Something like that would be nice. I have a tadpole and was frustrated that you could not lean into a corner. If it works right, it will make it more stable, less likely to tip over.

 

[curious]

I vaguely remember when I was a kid I've seen a movie (vintage 60s or 70s) where they had a velomobile that had a conventional two wheel layout but with a pair of small auxillary stability wheels that can be raised and lowered on demand during the ride.

 

[JennyB]

Here's a delta with a twist... the tilting-trike/funcycle/dirtrike geometry actually has a "wagon steer" aspect to it. The angle of the pivot controls both the degree of tilt and the degree of axle turn.

I knew I'd seen this somewhere before

 

[TylerDurden]

Yes... the Banana-Peel, AKA Funcycle, AKA (DIY) Dirt-trike has been around, but mostly as a novelty. It usually has two handles connected to the rear axle that can be used to force the pivot action.

I like the leaning aspect and hope to create a feasable 2-seater (side2side) with a simple steering linkage that can be used by both or solo-rider. (I think a two seater that leans would be very fun. )

These early sketches were made before I grokked the relationship between the lean and the axle. The body might be made with aluminum-clad EPS.

 

[docnjoj]

Here's a delta with a twist... the tilting-trike/funcycle/dirtrike geometry actually has a "wagon steer" aspect to it. The angle of the pivot controls both the degree of tilt and the degree of axle turn.

Something like that would be nice. I have a tadpole and was frustrated that you could not lean into a corner. If it works right, it will make it more stable, less likely to tip over.

U can lean into a corner a tadpole. U cant have the seat near horizontal, but at 45 degree seat back angle, u can "hike out" a good deal and change C/G to prevent tipover and slide out. I wore my tires out doing this!
otherDoc