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

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On the way back from mothers Tilt#6 had a material failure leaving it [ and me ] across the middle of a road junction with the trike like this.
With the trike like what?

No picture to go with the statement; and we all enjoy a good laugh. ;)
 
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So you think me sat on this :-



in the middle of a road junction is a good laugh ?
 
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Bugger! I assume it came apart at a relatively slow speed? I hope so anyway. I can't think of any way to reinforce that other than by extra thickness metal as you suggest. Better fully examine the other half of that pivot too.
 
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Maddox - Yep
Popshot - thankfully very low speed , what is worrying is that I cross 27 roads in each direction on the ride [ 3 times a week ] how many do I cross where I think ' oh I can beat that car ' well I ain't if this happens !
It could have turned out very differently 😢



This is looking down on it during construction , these plates were welded into the angle iron with me sat comfortable with it on the work bench propped up to get suitable angles for welding , now it is on the end of the front frame a huge lump of heavy unmanageable steel.

The current plan is to weld it back on then make a 3mm cap to cover both it and the ends of the angle iron , that way the caps will be welded to both the sides of the angle iron and all the way around the piece that broke off - effectively making it 6mm without trying to weld a new piece inside the angle iron as this was.
Probably do the same to the bottom one as well , the other advantage is it keeps the inside faces the same distance apart - needed to get the rod end bearings in the right place to bolt up to the rear.

The first Python front a different design has not broken here , however the rod ends are very exposed to the weather and it does not have the turning circle of this one as the front frame fouls on the rear frame.

Paul
 
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With the trike like what?

No picture to go with the statement; and we all enjoy a good laugh. ;)
Not of you in the middle of a road, no. When I looked at your post last night ONLY the bottom picture of the 3 above was present. So I had no idea what had actually failed or its importance.
I can now see a lot more pictures and yes, that must have been very un-funny when it happened. Especially if there was no warning or symptom detected beforehand.
 
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So I was able to clean up the broken pieces and get them assembled again for welding



As can be seen there was some porosity so it may have started to crack in the left corner , however it is clear to see it snapped just after the reinforcement provided by the angle it was welded to.

I welded this side and then welded the inside edge [ the back of the fracture ] I ground this side smooth and made another 3mm plate that overlapped both the plate and the angle then welded all the way around effectively making the plate 6mm.

As was suggested I then looked at the bottom plate , well it did not look to have started to fracture ?



Although it has lost some paint , it was very bent ?



The left nut and spacer squeezed a bolt onto the fixed upper plate whilst the right nut pushed the lower plate back into line.
I then plated this one as best I could , although the mud flap brackets and other assorted hardware stopped the torch getting in to all areas.

Hopefully having plated the outside the inside dimensions will be correct for this to go back together ?

I need to drill a hole in the main spine for the new rear elastomer position and weld in a tube keeper for the hex connector then I can try for re-assembly.

fingers crossed Paul
 
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When you see the thinness of the materials that standard bikes are made of you would think that 3mm metal in this critical area would be sufficient.
But clearly it wasn't, or some degree of load related movement caused the plate to repeatedly bend , fracture and eventually snap. Lucky escape indeed, as it could have happened at speed downhill and in traffic.
You live to fight another day. :)
 
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Pauls 'front steering' is a shear break.

Most bikes thin metal sections are under compression force, hopefully.
Easy to spot where you would need triangulation in some instances, so don't panic.

I'd designed an 'improved steering' for a future trike and will heed the warning as it has lugs that will have shear forces.
But I had planned to use a better material than mild steel (EN3, 070M40, C22) anyway as I can guess the force will be great there.


Think the two plate top and bottom of the 'green' will be 4mm Hardox or RQT material.

Martin.
 
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When you see the thinness of the materials that standard bikes are made of you would think that 3mm metal in this critical area would be sufficient.
Therein is demonstrated the engineering perfection of the diamond frame where all the forces are dissipated down the tubes. Nothing is thick steel because it doesn't need to be. Pretty much anything we make is a fudamentally weaker design relying on the strength of individual pieces of steel and the quality of the weld.
 
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Hi all

Thanks guys for the input.

I have repaired it in a fashion that increases the plate from 3mm to 6mm hopefully this will banish this gremlin.[ although if I make this area strong enough it only moves the stress elsewhere ?]



So I need to find out why it happened ?
a) so will it happen again ?
b) can I stop it ?
c) is tilting a contributory factor ?



Looking into the side of the joint these are the forces/loads attempting to push the joint into the ground.
Now looking at my construction
1)the 3mm right angle is of infinite length compared to the 3mm plate
2) the M12 bolt and rod end bearing is also infinite length compared to the 3mm plate

This is the reason it broke where it did and not across the bolt hole , which theoretically was weaker due to the M12 hole in it.

Other forces are also at play



On the left the 2 wheels at the rear are on level ground and so the frame is horizontal and so the front wheel is vertical [ unless turning ] .
On the right the left hand wheel has encountered a bump causing the frame to tilt upwards , this tilt is transmitted to the front through the pivot and attempts to twist the front end to follow the rear.
Of course the 3mm part of the plate feels these forces the most a tearing action across it.
gee it has a hard life :(

So to tilting ?
Now tilting involves the elastomers allowing me to go off centre , now my gut feeling is that as long as both rear wheels stay planted on the ground the left example above tilting has no part to play in the failure.
Unless tilting causes one of the wheels to lift off the ground then we are at the right example above and so tilting could cause tearing forces across the 3mm plate.
To the best of my knowledge I have never had the Tilt#6 on 2 wheels.

So am I right ?
Where are the forces going now ?
What will happen tomorrow ?
Paul
 
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So the real focus of this weekend should have been a longer seat sub-frame :-



I got some brownie points taking SWMBO out both Saturday and Sunday morning so got time to both repair and improve !
The original elastomers where in the two left holes , now they can be in the 2 outer holes.



Annoyingly I have now lost the rear pannier rack stay and the source of the seat hitting the frame troubles DOH.
I know the gap was 1.25" so I need to make up some other parts to attach to the seat rear and rack spaced that far apart and see if they collide....



I spent some of Saturday putting Tilt#5 back together [ foreground ] as insurance against not getting both the repairs done and the seat extension.
As I only have one set of elastomers of those values I then had to dismantle Tilt#5 to recover them and reassemble Tilt#6
I will be buying some more when I can determine if 400kg [ one pair ] is needed of whether the extension means I can drop back down to 300kg for the pair.



So again we are ready to hit the streets Monday , although I think I will temper my riding for a bit and take more care crossing roads I don't have 9 lives ....

Paul
 
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Hi all

Thanks guys for the input.

I have repaired it in a fashion that increases the plate from 3mm to 6mm hopefully this will banish this gremlin.[ although if I make this area strong enough it only moves the stress elsewhere ?]



So I need to find out why it happened ?
a) so will it happen again ?
b) can I stop it ?
c) is tilting a contributory factor ?



Looking into the side of the joint these are the forces/loads attempting to push the joint into the ground.
Now looking at my construction
1)the 3mm right angle is of infinite length compared to the 3mm plate
2) the M12 bolt and rod end bearing is also infinite length compared to the 3mm plate

This is the reason it broke where it did and not across the bolt hole , which theoretically was weaker due to the M12 hole in it.

Other forces are also at play



On the left the 2 wheels at the rear are on level ground and so the frame is horizontal and so the front wheel is vertical [ unless turning ] .
On the right the left hand wheel has encountered a bump causing the frame to tilt upwards , this tilt is transmitted to the front through the pivot and attempts to twist the front end to follow the rear.
Of course the 3mm part of the plate feels these forces the most a tearing action across it.
gee it has a hard life :(

So to tilting ?
Now tilting involves the elastomers allowing me to go off centre , now my gut feeling is that as long as both rear wheels stay planted on the ground the left example above tilting has no part to play in the failure.
Unless tilting causes one of the wheels to lift off the ground then we are at the right example above and so tilting could cause tearing forces across the 3mm plate.
To the best of my knowledge I have never had the Tilt#6 on 2 wheels.

So am I right ?
Where are the forces going now ?
What will happen tomorrow ?
Paul
Not sure if I am thinking correctly about this but I would have expected the bottom plate to be trying to pull apart and the top plate to be compressed together. Which is the opposite of what appears to have happened? I hope today's ride to your Mother's is uneventful. (y)
 
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Not sure if I am thinking correctly
Correct your not ?
about this but I would have expected the bottom plate to be trying to pull apart and the top plate to be compressed together.
Both plates have the same forces on them as they are inline ?
Which is the opposite of what appears to have happened?
Once the top plate had parted I was still sat on it , however then the lower plate was doing all the work and so bent as it had not started to fracture ?
I hope today's ride to your Mother's is uneventful. (y)
Nervous but achieved.
I would seriously look at your mount before you rode it , it is possible it cannot resist the forces either ?
It has already been proved lacking when you first sat on it ?

Paul
 
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Both plates have the same forces on them as they are inline ?
Not sure this means they have the same forces TBH.
I would think that the top one is trying to rotate rearwards, the bottom one is trying to rotate forwards around a centre point between the two fixings.

You can prove this by slackening the rod-end bolts, the top one will naturally be pushing in, but the bottom one will be pulling out (I think). A feeler gauge in the top one will tell you whether it is being pushed or pulled.

I would seriously look at your mount before you rode it , it is possible it cannot resist the forces either ?
I most certainly will keep a very watchful eye on it after hearing of your "brown-trouser" moment; but.... mine is quite different to yours as it is:
a) all 4mm plate.
b) Bolted to the frame at either end through its baseplate.
c) The plates the bolt passes through are both webbed to the baseplate on either side at either side of the fixing bolts (further strengthening it I think).
d) The pivoting element presents as a solid compressed mass between the two end-plates and not as two discrete rotating attachments (like I think your does). The internal races of the two bearings are pressed together against the "internal race separator" and the "through-bolt" ensures the cheeks/endplates of the pivot carrier are tight against this solid mass. While it is is free to rotate (and does so easily) it does not "wobble" on the bolt.

It's why I called it a "PPP" ;)

Having said all this though.... Where mine will most likely fail is where the front frame attaches to the outer casing of the PPP tube.
But the frame is 25mm square tube @2mm thick with about 4" of weld fixing it to the PPP tube.

While not an exhaustive test I did get a "fat-boy" to jump up and down on the frame at the pivot before I ever rode it.


 
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Some triiangular gussets would reinforce it but may hinder lock without further work such as shaving the other side or extending the rod ends slightly. Even relatively thin metal here would add a lot of strength.

 
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Wow! so similar to my existing deployment. ;)
Properly stiffened with gussets the things are unlikely to bend.
 
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Thanks all for your input , however it is not there now I am bothered about ?

If I make that strong enough to resist the forces when ridden , the forces move to the next weakest area ?


Question is where is that and will it stand up to the punishment ?

To put this into context it is not a new trike/design ridden off the drive and had a failure on the first ride ?
This front end formed the basis of Tilt#2 , Tilt#4 & Tilt#6 and a best guess it has done about 940 miles + Holland 2022 since it first saw service on 20th Sept 2021.

Paul
 
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While the old saying "a chain is only as strong as the weakest link" is entirely true, it is the discovery of its location that takes the time.

It would appear to have failed at a point where the forces were/are most concentrated.

As you have fixed that, I would look next at the mating parts to this failure and where they attach for any signs of deformation or stress fractures.
Beyond that I am afraid that you are in a wait & see situation. Regular inspections would appear to be in order. :(

Not the most welcome answer I am sure, but it may be the only one that works.

In perspective, as you say there have been nearly 1,000 happy miles travelled on this beast, and only one failure (albeit a bad one).
Would it give you comfort/confidence to try and overload the trike with a heavier rider and/or a heavier rider seated plus a helper stepping on/applying weight to the frame junction to see if anything "gives"?

Not sure I like "potentially destructive" testing but if its all you have and it restores confidence perhaps it is necessary.
 
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