Biggest influences Tadpole turning circle ?

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Hi all

Assuming we had a perfect steering geometry/linkages what has the biggest influence of a tadpole turning circle ?

My guess :-
track width front wheels
diameter of front wheels
wheelbase

any others ?

Paul
 
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I would add "width of seat" because I run out of steering when the bars hit the seat.
With a skinnier seat/rider you can pull the bars further round their arc of travel.
If I take my seat off, the bars turn further.
 
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I assume

most important = track width front wheels
less important = diameter of front wheels
least important = wheelbase

Dan
is that width of seat or less than idea steering linkages ?



It's winter and thoughts turn to an enclosed tricycle ?
Drawn with 24" wheels so as can be seen quite wide and probably over long in front of pedals ?



Although this design would probably meet all my objectives apart from getting through the A cycle barriers

Paul
 
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Dan
is that width of seat or less than idea steering linkages ?
The steering is designed using the Ackerman Steering spreadsheet and the links etc. are optimal in accordance with that.
There is <5% variance from perfect ackerman right down to 2M turning circles (which it cannot do anyway).

Ideal AckermannThis geometry
radiusleftrightRErrorHB Angle
100000​
0.58​
0.579​
0.5793​
0.0%​
0.29​
20000​
2.84​
2.930​
2.93​
0.0%​
1.45​
10000​
5.59​
5.935​
5.94​
0.1%​
2.89​
5000​
10.76​
12.112​
12.19​
0.6%​
5.69​
3000​
16.97​
20.493​
21.11​
3.0%​
9.17​
2000​
23.64​
30.710​
34.75​
13.1%​
13.04​

It could be the bars are less than ideal.
 
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I would add "width of seat" because I run out of steering when the bars hit the seat.
With a skinnier seat/rider you can pull the bars further round their arc of travel.
If I take my seat off, the bars turn further.
You could alter the ratios on the steering arm between the bars and the wheel. Move the bar end further away from it's pivot or the wheel end closer. It would speed the steering up so less input was needed. If that goes too far though it can get twitchy but I'd suggest that if the bars are hitting the seat, whether the trikes or yours, then if there's no room or desire to widen the bars then there's scope on the ratio front.
 
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I'd say track width and wheel diameter are essentially the same limitation as in both cases the limitation is the inner wheel hitting bodywork or legs in a turn.

I wouldn't put a tadpole's front wheels at the front. It puts the rider too near the single wheel and gets unstable in a turn. It's massively more stable to get the rider between the two wheels. This does create a problem width wise in that the widest part of the trike other than the wheels is near the hips and bars and moving the front wheels there inevitably means a wider track than putting them near the feet where they can be more inboard and still provide clearance. From experience I'd not place the front wheels far from where a Warrior or Streetfox has them. Bringing the wheels back from the front will help turning circle.

I think ranking the limitations is perhaps to concentrate too much on what you place at the top when the reality is that the turning circle is a combination of all the factors.
 
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Dan

My definition of steering linkages [ not give at the time ] is it includes every thing from your hands to the wheels , ackerman whilst ideal is not a must ?

I rode a Windcheetah supposedly a bench mark for tadpole trikes ?
You either had mudguards and limited turning circle or no mudguards and it turned well , the price you paid ? the wheels burnt your thighs.

Popshot

Whilst I understand you comments and think a trike should be as safe as possible so unexpected things do not turn into an incident.
The position of the front wheel in the drawing is standard for that style of Velocar , and I am certainly no speed demon ?

Bringing the wheels back from the front will help turning circle.
not entirely , if it means the pedals are sat out front they swing through their own arc and limit where you start to turn ?

Paul
 
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The pedals are where they are regardless of where the wheels are and so is irrelevant in wheel placement from the point of the turning circle. Moving the wheels forward will only make it worse for turning circle and stability. It also means you need more chassis length and more chassis strength as it has to span a larger gap twix front and rear. Moving the wheels forward has only one positive in that the track can be narrower because you do not need factor the room for hips and bars. On the negative side you get length, weight, stability and turning circle. I suspect the velocar designer placed the wheels there because car makers of the time did and not because it made engineering sense.
 
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The pedals are where they are regardless of where the wheels are and so is irrelevant in wheel placement from the point of the turning circle.
Not explained myself properly.



If I meet one of these I can turn further inside it if the wheels are in front and stand a chance of getting round.
If the pedals are in front I have to turn earlier and so risk not making it ?

Paul
 
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I believe you are mis-imaginng how that turning will work. The rear does not "follow" the front but makes it's own circle. If you put the wheels forward then the rear starts it's turn earlier and you need more room. To try to visialise it try thinking of the wheels several feet forward like a mini limo. Same thing but exaggerated to imagine the effect.

One other way of imagining it is to imagine a bus and a lorry the same size. The bus will turn better because they are designed with a large front and rear overhang to shorten the wheelbase. You get the same effect with a swb trike over a lwb one.
 
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Even on this swb the pedals are not that far forward of the arc of the outside wheel so it gets the tighter turn associated with swb without the length penalties of lwb. The longer it is the more room it needs on the inside just like a lorry does.
 
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If you want the tightest turning taddy then use a 20" on the rear too and get the wheel right up to the back of the seat.
 
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Popshot - thanks for your input a different take is always welcome

Yes probably

I was trying to relate my experiences with a 2 wheel SWB where a couple of times I could not get close enough to the obstruction to turn with the pedals hitting a wall dead ahead.

Dan and I have done a bit of brain storming and have an idea just need to get it on paper and see if it can be made to work ?
There is talk of 16" wheels on the front and 16" or 20" on the back we shall see.
Of course 16" wheels will need suspension

As they say watch this space

Paul
 
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Ok think I have my head around this ?



Velocar tadpole or delta 3 or 4 wheels etc

So plan view chassis to left front wheel show both straight ahead and turned @ 45' , A is the wheel base

Projecting a line from front wheel through pivot @ 90' to wheel hits line projected from rear wheel axle giving the turning circle , conveniently if geometry can achieve 45' then turning circle = wheelbase.

From this we can predict changes to said geometry ?

angles less than 45' move lines intersection to right and turning circle becomes bigger

angles greater than 45' move line to left and turning circle becomes smaller

obvious @ 90' turning circle is 0 and so is ability to turn !

as can also be seen the greater the front track of the turning wheels Z becomes further away from chassis and so move the lines intersection to right and turning circle becomes bigger

The longer the wheel base moves the lines intersection to right and turning circle becomes bigger

On a delta this picture looks better as single wheel is on centre line so Z is in best place , so for the same front wheel angle a delta will turn better than a tadpole.

A tadpole is further hampered by Z's position ?

Across my feet is my narrowest point @ 18" so for a 32" front track the wheels only have 32-18/2 about 7" to move in [ mudguards of course reduce this further ].

The only way around this restriction is to move the front axle in front of the swept pedal area this increasing the wheel base DOH so maybe no gain at all ?

Still thinking Paul
 
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Dan

So which bit is confusing ?

Probably the same however :-
a) he uses math's
b) i want to be able to visualise the the difference changes make without having to drag a calculator out ?

Paul
 
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Look at the wheelbase - A and imagine making it longer on the drawing. This makes the hypotenuse a longer line making the turning circle - C longer and therefore bigger. The pedals are where they are regardless of whether the wheels are in front or behind them so placing the wheels behind is of no detriment at all to the turning circle. Indeed making the wheelbase as short as possible makes the turning circle as small as possible. It's irrelevant whether the pedals go into a turn before the wheels.

The longer the wheelbase the wider the entry into the turn needs to be as the inside of the trike moves towards the inside edge of the opening and the sooner, not later, it must start it's turn. In the picture the two top trikes are at the same forwardmost point. The bottom pair show the furthest point forward the two trikes then go as they turn. The lwb clearly goes further forward than the swb and therefore must start it's turn sooner than the swb. You can also see the added extra sideways movement to reach the furthest forward point the lwb takes meaning it needs a wider opening. Putting the wheels forward is a guaranteed way to not negotiate a hazard.

 
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Look at the wheelbase - A and imagine making it longer on the drawing. This makes the hypotenuse a longer line making the turning circle - C longer and therefore bigger. The pedals are where they are regardless of whether the wheels are in front or behind them so placing the wheels behind is of no detriment at all to the turning circle. Indeed making the wheelbase as short as possible makes the turning circle as small as possible. It's irrelevant whether the pedals go into a turn before the wheels
I may have made my point badly ?

On a Tadpole there is a limit to the angle a given wheel can turn.
Made up of:-
a) diameter of wheel
b) distance wheel can turn before it hit's something
c) steering control components

a) is easily got around by going smaller although @ 16" I would want suspension.
b) is help by a smaller a) however it all comes down to what is the wheel going to hit ?
frame ? body work , riders parts ?
c) well it is not as easy as it seems to devise linkages that get the most out of the steering and produce a equal diameter.

So b) if the front wheels are in front of the pedals that removes one restriction , question is are the gains worth it against the increase in wheelbase length ?

Paul
 
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So b) if the front wheels are in front of the pedals that removes one restriction , question is are the gains worth it against the increase in wheelbase length ?

Paul
Better to have a swb and wider track if turning circle is the key attribute IMO. Here I've made the SWB track wider to clear hips and legs. The trike turns even tighter as the wider track brings the centre of rotation in towards the rear axle. It also goes slightly less further forward overall during the turn. It does obviously mean a larger opening is needed though.

 
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