My life with Python trikes Mk1 , Mk1.5 , Mk2 ?

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Hi both

Well it was an attempt to apply Brads ideas to my Python , others had reported it worth the time/weight/effort etc.

Probably a poor implementation as it was clumsy heavy and just to bl**dy noisy !!! I hate unnecessary noise whilst riding.

Chopped it out and rode it without.

I like this :-



However I need a way of stopping the steering ! and it needs to be completely mounted for and aft , so not impinge on the luggage area ?
 
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Weld a plate behind and another in front to the bit that moves up and down, extending along the notched beam towards its centre. The plates should stop any steering as a channel will be formed around the end of the notched beam. Some lubrication or some packing (will leave it to you) should stop most of the noise.
 
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If going that way I'd expect the system to need some decent bushings. It'd need better bushings than a swing arm as the swing arm has massive leverage making the bush move around it's bolt and movement is minimal. A sliding pillar has zero leverage and large movement. It'd be difficult to keep such a system lubricated so I'd opt for phosphor bronze. Again you'd want to make the sliding part as long as is practical to minimise any desire to bind when the force isn't perfectly aligned with direction of slide. You could eliminate twist completely by using two sliding pillars per side. It's extra weight but the best solution I can think of. You could make each pillar a bit daintier as the load is shared by two of them.

I still think a swing arm is the better solution though and would only take up the width of the suspension unit from a side to side perspective.

One out-of-the-box idea would be to use swing arms but instead of bolting them to the chassis through a bushing, weld them to a straight piece of anti-roll bar from a car. That anti-roll bar would need to have tabs welded to it to bolt to the chassis to both mount it and stop it turning. The tabs would need to be central to still allow the majority of the bar to twist and it'd need good bushes near the "swing arms" to hold the wheel in alignment. The swing arms would need to be more structural than if they were actual swing arms as they'd be taking a loading and holding the wheel in alignment. There's going to be some experimenting and zero damping but all cheapo bike suspension units have zero damping anyway. This has the advantage of taking zero room side to side preserving every scrap of luggage area. It's essentially the torsion bar system the Beetle uses for it's rear end. It does have the benefit of being an anti-roll device. There's probably a number of reasons it won't work but I thought I'd throw it out there.
 
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If going that way I'd expect the system to need some decent bushings. It'd need better bushings than a swing arm as the swing arm has massive leverage making the bush move around it's bolt and movement is minimal. A sliding pillar has zero leverage and large movement. It'd be difficult to keep such a system lubricated so I'd opt for phosphor bronze. Again you'd want to make the sliding part as long as is practical to minimise any desire to bind when the force isn't perfectly aligned with direction of slide. You could eliminate twist completely by using two sliding pillars per side. It's extra weight but the best solution I can think of. You could make each pillar a bit daintier as the load is shared by two of them.
Yes I had though of a parallel pair and was not convinced a home builder could get them parallel enough for it to work ?
Yes I had considered lubrication a problem.
I had thought of a kingpin constructed from some some precision tubing sliding on a 12mm bolt shank and a separate 12mm rod end sliding on the another bolt shank and bolted to the kingpin

I still think a swing arm is the better solution though and would only take up the width of the suspension unit from a side to side perspective.
probably , however the obvious solution ?

It's essentially the torsion bar system the Beetle uses for it's rear end. It does have the benefit of being an anti-roll device.
Intriguing I have always been impressed with tanks and the VW using torsion bars.
I assume they were made from spring steel ?
I though I had read the VW had flat bars clamped inside a tube , so you could add/subtract bars to alter it's spring rate ?
 
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The rear of every Beetle I've seen used twin round bars splined differently at each end. Perhaps the very early ones used something different. By carefull repositioning of the swing arm on it's splines and the same at the centre you could raise or lower the rear at will. IIRC they're far too beefy for a trike application but anti-roll bars go down quite thin as they're only backing up a beefy suspension unit on a car. I think they go down thin enough for your use. The key would be to get a good bush near each end to control the swing arm acceptably. Without a good bush and sturdy swing arm the wheel would be somewhat free to wobble. Typically an anti-roll bar uses a split bush on a car which wouldn't do here. You'd also have an issue getting a bush on after welding a swing arm to the bar. Perhaps you could weld a square taper from a bottom bracket to each end of the bar (you'd need to chamfer the bar and taper to keep the welding no wider than the bar itself) and start the swing arms off with a pair of crank arms making the arms then removeable so you could get the bush on/off. If you got long enough crank arms and the right pedal axles they'd do the whole job from roll bar to wheel. It'd certainly be both different and impressive, not to mention economical with it's use of space.

I think you're right about alignment issues with a twin slide. It'd probably involve a lot of tacking and retacking as you test slide it.
 
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For what it is worth.
Why not create an independent suspension such as the Citroën 2 CV. Instead of hinging the central arm, you can move the two axes up and down separately and connect them with tie rods and compressed coil springs. A view from behind would be something like this.
 
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You'd need to mount the springs a fair way below the axle pivots or you'd get little pull on the rods for a big deflection of the wheel. You'd need to separate the springs to allow the wheel to drop to prevent the rods clashing or better still to offset one to the immediate front of the axle and one behind. The main boom would also need to support the wheel side face of the spring. A swing axle has built in camber changes fundamental to it's design. A swing arm changes wheelbase slightly as it moves which is to all intents and purposes no issue for the rider but a swing axle's camber changes are more of an issue. If there's 2 inch of movement either way there's 16 degrees of camber change. The entire axle moves through the luggage area, admittedly only by a couple of inch or so but taking that room nonetheless. It's been a while since I had to follow a 2CV but my memory tells me they always rolled in a corner like a ship trying to capsize. I owned a '66 Beetle which surprisingly was one of the least roll prone cars of it's day.
 
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Hi all

Keep the ideas coming I can't ignore or pooh pooh them if I don't read them !

Also there is someone on here who will swear blind I am stubborn and single minded , ignore that thought please 😧

So doing some Googling of Velomobile suspension most use the Quest McPherson strut at the front , however when you look inside them they are simply a container for a combination of die springs and small elastomers...

So the light bulb flicker slightly .. they look just like the inside of a front fork leg ?

I would only need a leg per side and most of the fork is not actually required so I could lighten them considerably ?

Now before the chorus gets up to speed and volume , this is purely for an experiment and is being done with whats available and CHEAP !!! sadly 20" for now as they were easier to find , I do have some 26" one's that may be better quality but can't get to them easily.



So this is all I need and there is still some meat that can be trimming off, it weigh's 420 grams



so this is the inside and has a die spring [ well similar ] and a elastomer , the dimples are where the top is riveted into the chromed tube.
I left enough above the top spring mount that I can drill a 8mm hole and use a 8mm bolt to fasten to a bracket ?



looking at the first picture the inside is not fully home however you can see the red bit does not have enough room for 1" of travel.

So I need to slowly trim the red bit down till at full travel does not hit the 8mm cross bolt in the end of the shiny bit.

I can also trim some off the shiny bit to lower it's weight.

I drove a 2cv derivative for many years and had no problem with it's cornering , you weren't a good driver if you had not ground the door handles down some what :ROFLMAO:

So now I have a pair of retarders what am I to do with them ?

Swing arms parallel to the centre line outboard where the wheels are would be good for luggage space conservation , although it is tempting to mount them inboard just to keep it all clean ;)

Ideas please
 
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Paul: Another thought for you to read and ...

What about trailing arms? Use pedal arms for the purpose, a bottom bracket for mounting the arms at each side of the cargo area, and fit a spring between the free end of the pedal arm and something to work against? Or, if you can find a suitable one, a torsion spring for the pedal arm to twist. You might be able to re-purpose gate hinge springs for it. Shouldn't be anything difficult in such a contraption er, construction.
 
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Hi all

Now this is interesting ?


from here :- Cyclekarts

Paul
 
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The following video that came up when I looked at the one above might suit you for rear suspension. I think it is, effectively, a Panhard Rod system. Virtually identical to that on the rear of a 1968 Toyota Crown that I once owned, so I know it works. He mentions wishbones to stop fore/aft axle movement but the Toyota had trailing arms.

 
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I think it is, effectively, a Panhard Rod system. Virtually identical to that on the rear of a 1968 Toyota Crown that I once owned, so I know it works. He mentions wishbones to stop fore/aft axle movement but the Toyota had trailing arms.
Lots of steel and not really independent ?
 
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Isn't the use of a fork leg and swing arm the same as a swing arm and typical suspension unit, but more effort for the same end result?
 
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If you are NOT looking for any tilting function then the "struts" you are proposing seem an ok way of getting some level of independent suspension if each side is attached to a rigid frame that does not itself twist or pivot.
What method would you use to attach a wheel's axle to the strut and keep it pointing straight ahead?
 
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Isn't the use of a fork leg and swing arm the same as a swing arm and typical suspension unit, but more effort for the same end result?
Well if you remember my original ramblings were to try and replicate the Morgan sliding kingpin suspension that takes a level of hacking more that I want to go....

So the mind drifted to looking at Velomobiles and so I ended up here.

My thoughts are this :
typical suspension unit
These have very high spring rates from 350lbs right up to 850lbs IIRC ?
On a bike one unit does the whole of the rear end , so if I want independently spring the rear wheels I will end up with 2 units.
They weigh the same , although there are no fixings yet
Typical cheap units have no damping , so no advantage there
fork legs seem to have elastomers inside , I assume as a progressive bump stop
fork legs have better weather protection so can be greased.
fork legs are slimmer [ could be useful ]

regards Paul
 
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I take the point about spring rates for rear shock units. They're typically too high to use with no leverage. Angling them by 45 degrees would half the rate. Are you intending to use the fork as a strut? By that I mean pivoting the swing arm at both ends unlike a swing arm and typical unit which would be pivoted only at the chassis end?
 
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Another thought.
What if you turned a pair of fork legs sideways, welded a bar across the lower halfs with a hole central to mount the wheel through (put the original donor's axle back in the drop-outs for alignment before welding the axle mount). Weld that bar at a height to get the fork legs fairly low below the axle so the top isn't overly high and then weld the top to the chassis. Hey presto one instant double sliding kingpin. If the spring rate is too high take one of the springs out and run it on one spring. Ideally you'd want to weld the top at two different heights so the weld itself isn't taking the strain of sideways jarring. You could also invert the forks and do it that way, welding the axle mount to the shiney bits and the chassis to the painted bits. It'd make the assembly overall taller but not unreasonably so and if that can be accommodated would give more scope to weld to the chassis at two well spaced heights providing better resistance to jarring along the axle direction. It'd also sound cooler saying you run upside-downies. Also technically better as there'd be less unsprung weight. Kiddies 20" wheeled units would probably be ideal for it as they'd have enough travel, be overall shorter and have better spring rates. Haven't you just chopped one in half?;)
 
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popshot - good stuff and keep it coming.

No I think I don't want it as a strut

Though of turning forks into sliding pillar briefly....
However it is not possible to weld to the red part - well on these it isn't as they seem to be lined with some plastic making a very tight fit with the chromed part of the insides ?
..and weighty x 2 !!!

So what to do ?


I think this would work ?

advantages wheel is well located without any strut input

pivot for swing arm can be a normal suspension pivot shell with ball bearings inserted [ I have one already like this they look like standard bearings ] so just need to convert a normal shell to ball race.

cut down suspension leg is currently 8.5" without mounts I reckon I can keep it under 10" therefore it will remain within the wheel arch , no encroachment on luggage space - however it is very dirty in there ?

mount for suspension leg at chassis end does not have to be very tall ?

might even be able to use a steel pedal ?

but will it work ?
 
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If you are NOT looking for any tilting function
NO NO NO NO NO NO ...........

remember The Alamo the tilting MBB trike ?
If I made the Python tilt it would become a bicycle and I cannot ride a Python bicycle.

[QUOTE="DannyC, post: 4273, member: 893]What method would you use to attach a wheel's axle to the strut and keep it pointing straight ahead?[/QUOTE]

Woah you are getting way ahead of me there , although I have had another light bulb moment .......



Long , long , ago in a distant galaxy...

I built this it was meant to be a wide iLean tilting rear end , I believe it's still lurking in a shed ?

One reason it did not get pursued was due to a brain fart it ended up as wide as the normal Python rear , so not much need for tilting 😕

Another reason was I had to much slop in the connecting bar across the rear , and I suspected it was to light for the job of coupling both the BB axles together ?

So dump the connecting rod slightly lengthen some wheel cranks and we have the makings of a suspension rear end ?
 
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Assuming you have no swing arm pivot at the wheel end you have very little movement of the suspension for a lot of wheel movement. You'd need to get the suspension well above the swing arm to get any compression of it. If you have a pivot at the wheel end of the swing arm you have no compression at all.

With the ex-iLean you could try to find an anti-roll bar and weld it in in place of the square bar. If you can then use muscle power and get a sufficient deflection you cut the ironmongery off and weld the BB shells to the chassis plus a central mount for the anti-roll bar to chassis. With only a little ingenuity the central mount could use a large bolt winding against the chassis to make the rear suspension adjustable up and down to ensure you can get it set at a perfect height allowing for compression or just to move it up a tad if loading the thing up for an adventure. Those bottom brackets are better than the best bushes for the job. You'd have excellent location with them and some long crank arms. The only if / but / maybe is finding a correct thickness anti-roll bar which is going to be trial and error. Simple and impressive plus anti-roll device to boot.
 
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