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Author: Subject: Trike roll oversteer
Slimy38

posted on 4/7/13 at 01:00 PM Reply With Quote
quote:
Originally posted by Mr Whippy
Reading through everything it seems really the problem is having tyres for a leaning bike on a vehicle that doesn't lean to turn. When riding a motor bike at speed you don't actually turn the handlebar to turn, you lean the bike over and the bar turns with the bike. Try it, without leaning the bike the handle bar will not turn.

[Edited on 4/7/13 by Mr Whippy]


I'm afraid it's the other way round, you cannot lean a bike over without turning the handlebars (well, at least most of the time). Have a read of this;

http://www.superbikeschool.com/machinery/no-bs-machine.php

Sorry OP, I'm slightly off topic here, but just wanted to clear this one up.

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MikeRJ

posted on 4/7/13 at 03:47 PM Reply With Quote
quote:
Originally posted by smart51
Hi Mike,

The enormous bush you can see is there to allow the engine to move up and down a bit under shock loads. The trailing arm to engine bushes a really quite small and are hidden from view in the photo. The A frame pivots and the trailing arm pivots are not quite in line but the difference is very small. All the movement can be taken up by the mechanism that allows the engine to move.

I've just fitted a stiffer anti roll bar at the front. When I next go out, I'll see if that makes any difference.


I'm glad to hear this, I had visions of something expensive breaking!

Just a thought; is it possible that whilst you might have constrained the axle enough to prevent it "steering" in the obvious direction, could the engine/gearbox be twisting axially (i.e. twisting in the axis of a line running from the front to the back of the car) under load?

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Mr Whippy

posted on 4/7/13 at 04:33 PM Reply With Quote
quote:
Originally posted by Slimy38
quote:
Originally posted by Mr Whippy
Reading through everything it seems really the problem is having tyres for a leaning bike on a vehicle that doesn't lean to turn. When riding a motor bike at speed you don't actually turn the handlebar to turn, you lean the bike over and the bar turns with the bike. Try it, without leaning the bike the handle bar will not turn.

[Edited on 4/7/13 by Mr Whippy]


I'm afraid it's the other way round, you cannot lean a bike over without turning the handlebars (well, at least most of the time). Have a read of this;

http://www.superbikeschool.com/machinery/no-bs-machine.php

Sorry OP, I'm slightly off topic here, but just wanted to clear this one up.


If you ride a motor bike like me, just try and turn the handle bars at about 30mph without tilting the bike, it won't turn

The article you refer to is about folk leaning their upper body over to tilt the bike which as is stated is not right, you actually use your hips and move your lower body, the bike then follows, it's also how you can ride without any hands

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Slimy38

posted on 4/7/13 at 04:55 PM Reply With Quote
quote:
Originally posted by Mr Whippy

If you ride a motor bike like me, just try and turn the handle bars at about 30mph without tilting the bike, it won't turn

The article you refer to is about folk leaning their upper body over to tilt the bike which as is stated is not right, you actually use your hips and move your lower body, the bike then follows, it's also how you can ride without any hands


As a fellow bike rider, I think we may have to agree to disagree on that one! Although I do agree you can't steer without leaning the bike, otherwise it would just flop over! I just don't agree that you can steer with no bar input. Maybe just about to change lanes, you won't be getting round any roundabouts!

[Edited on 4/7/13 by Slimy38]

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Fred W B

posted on 4/7/13 at 05:05 PM Reply With Quote
Can you not find a Gopro camera somewhere and strap it on the frame looking back along the swingarm.? Then go for a ride and record what is actually happening to view later.

WRT discussion above I agree that pushing forward on the inner bar is the way to make a bike turn. I was amazed when I first read about that and tried it. It steers the front a little out from under you, makes the bike lean into the corner and then you go round the corner like you mean it! Try it sitting bolt upright on the bike and you will feel it too.


Cheers

Fred W B

[Edited on 4/7/13 by Fred W B]

[Edited on 4/7/13 by Fred W B]





You can do it quickly. You can do it cheap. You can do it right. Pick any two.

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on_eighty_runner

posted on 4/7/13 at 05:26 PM Reply With Quote
Hi there great project!
The back end on a scooter is not that rigid in torsion as A scooter doesn't need that much.
I had a gilera 180 with what seems to be the same rear swing arm mount and there was give right to left at the rear wheel.
As the 2 strokes only had one rear shock unit as the bushes wore in the mount you would see the wheel start to lean over under weighy giving odd tyre wear

I suggest you try to control the wheel a little tighter as it is probably moving around more than you realise in its new home
As it looks like Piaggio 4 stroke I assume it has 2 rear shocks.
These are quite close to the wheel axle
A rose joint linkage from the shock mounts to the right and left edges of the chassis (with these ends inline with the swingarm pivot)should very good control right to left
If you could take another pair from under the swingarm casing to the same right and left chassis points this will control the wheel vertically

You will then have in effect 2 large A arms holding the wheel in 2 axes but still being able the pivot around the third ( the swing arm)

Bushes may be good enough and will give better vibration absorption

The big rubber donut is quite soft and isolates vibration from the big single engines at idle. It is not fitted to 50ccs

Best of luck

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smart51

posted on 5/7/13 at 08:20 PM Reply With Quote
The stiffer anti roll bar has made a big difference to the handling. There is noticeable reduction in body roll but no change in ride comfort, which is nice. The high speed stability is improved too but it still isn't quite right. I'll have a think about it a bit more. I'ts definitely getting there though.






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MikeRJ

posted on 5/7/13 at 08:52 PM Reply With Quote
quote:
Originally posted by Mr Whippy
The article you refer to is about folk leaning their upper body over to tilt the bike which as is stated is not right, you actually use your hips and move your lower body, the bike then follows, it's also how you can ride without any hands


It doen't matter which bits of your body you try to use to lean a bike, if you don't countersteer using the bars then the best you'll ever get at normal road speeds is a turning circle the size of a supertanker. You HAVE to use the bars to steer, as the machine linked to above proves.

On a pushbike your body weight has a lot more effect, obviously, but even then if you are doing 20-30mph you won;t steer much by just leaning.

[Edited on 5/7/13 by MikeRJ]

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Dave Ashurst

posted on 5/7/13 at 09:45 PM Reply With Quote
Not sure if you've solved it now but if not then could you record the rear end motion with a strategically-mounted video camera under the car?
Would that help spot the source of movement? Better to cure it than mask it. Perhaps you could record movement from driving combinations with and without front anti-roll bar and a-frame.
I've got an old bullet cam, clamp mount and recorder somewhere. You can borrow them if you I can find them (we moved house!). Give me a call.
best
D

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Dick Axtell

posted on 6/7/13 at 12:52 PM Reply With Quote
Tilting Trikes

Hi. Been following your new project with interest. Then I recalled encountering a Dr. Edmund Jephcott, who tried (unsuccessfully) to promote his tilting trike, with patented tilt control mechanism.

Check out here :- http://www.maxmatic.com/ttw_moto.htm

Getting your trike to lean into the turn might alleviate your probs?





Work-in-Progress: Changed to Zetec + T9. Still trying!!

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smart51

posted on 26/7/13 at 04:44 PM Reply With Quote
OK now we're getting somewhere. I've stiffened up the A frame by putting a cross bar on it, turning it from a V frame to a proper A frame. I also strengthened the mounting brackets on the chassis. It has made a big improvement and the handling is now quite good. The springy effect when suddenly turning in is still there a little bit but it is not objectionable unless you're really chucking it in at around 60 or so. I'll still see of I can make it better still but I'm almost there.

Now the bad news. Everything is now very stiff and all of the single cylinder engine vibrations find their way to the chassis and through to the driver's seat. I'll probably have to make a whole n swing arm that allows some vertical movement of the engine but absolutely no lateral movement.






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smart51

posted on 16/12/14 at 12:17 PM Reply With Quote
Update after a bit(!) of a gap. I'd tried lots of things to stiffen up the rear trailing arm to solve the handling problem. All of them made is slightly better, but not enough. I finally got round to fitting a car tyre to replace the rear bike tyre. That made things worse. I suspect because it increased rear end grip, exscserbating the cause of the problem.

After some procrastination, I took the advice of a friend and stiffened up the chassis. I had assumed that as the trike has 3 wheels, there would be no twisting moment on the chassis. I was wrong. Thinking about it, cornering forces act on the CofG and on the 3 wheels, making 4 "points of contact" which is enough to twist the chassis.

Brace Frame
Brace Frame


I made an axilliary frame running the length of the body with 3 X braces. This was welded to the exisiting floor structure which looks a bit like a ladder chassis from underneath. It has made a noticable difference. The car has less sway at speed, though is still not 100%. I haven't tried any fast corners yet because the roads are wet, but on the next dry day we get, guess what I'm going to do Meanwhile, I need to think of more ways of stiffening my trike's frame.

So I've learned a lesson. Trikes need a chassis that is stiff in torsion.

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smart51

posted on 23/12/14 at 03:45 PM Reply With Quote
Now the chassis has been stiffened up, I've been playing with toe settings. A little toe out is better than parallel, which is better than toe in. Still more to do, but we're getting there now.
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smart51

posted on 30/12/14 at 11:30 AM Reply With Quote
Another day, another mod and this one has made a big difference. Stiffening up the rear of the chassis has improved the high speed stability so that it's almost hands free at 70. There's still a little more to do but I'm almost there.
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