Folding Python delta trike

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Hi! I'm new here but I've occasionally been reading on this forum for the past few years. I've had a trike idea in my head for quite a while, and now I'd like to share it.

The idea: a Python delta trike, but make it foldable.

Design requirements:
  • Comfortably haul a 10kg 40L backpack, to go on hiking trips I otherwise can't do without a car
  • Be able to take it (plus backpack) on a Dutch train, which officially means no dimension over 85 cm
  • Max 75cm total width, to fit through shed door and comply with Dutch traffic regulations more easily
  • Fun project to build together with my dad, who is an experienced aluminium welder and has worked on bikes before
What I've learned about Python trikes so far:
  • The only other folding Python trikes I can find are Howard Stevens' Porta Velo's, but folded up they're still a little too big/wide for what I want. Have there been any other folding Python trikes?
  • Pivot point & seat should be as much forward as possible, to put more weight on front wheel. This is extra important because of the added weight of the backpack
  • Wheelbase should be as long as possible, also to put more weight on front wheel
  • Seat should be as low as possible for cornering stability, but not so low that there is no ground clearance
What I've come up with (first draft):
  • 20" front wheel, possibly with 5 speed gear hub with coaster brake
  • 20" rear wheels. Thinking about simple spoon brakes that push onto the surface of the tire, to have some emergency braking power and also as a parking brake
  • The rear wheels are on swing arms that can fold 180° forward
  • The seat folds forward too. Haven't designed the seat yet, but I'm thinking about something similar to a beach chair
  • Open space between the rear wheels for mounting my backpack
  • When folded, the backpack can stay attached to the seat and the whole thing acts as a luggage trolley running on the rear wheels


Stats of first design draft:
  • Pivot angle 60°
  • Trail -18 cm
  • Wheelbase 90 cm
  • Total width 75 cm
  • Seat height 20 cm
  • Ground clearance 11 cm at the pivot, 17 cm in the middle
Before I develop this idea further, has something similar been done before? Can anyone foresee any issues with this kind of design, besides possible loss of traction going uphill? Thanks!
 
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My Idea for the Python. Front hub, Nexus 8 with Roller brake. Or rim brake. Disk as last, rare option. (the drawing allows for a midmotor assist)

Spoon brakes, good for a vintage bike that only runs at a very gentle speed or for a parking brake. (how many bikes need that?) I would use any other kind of brake, including band or rim brakes on the rear wheels to assist the single front wheel brake.

All the rest looks well tought out.
 
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I have built and ride a Python trike,



and was about to present a concept suitcase python, my idea is that the python fits inside, be part of, a 85 x 54 x 30cm suitcase.
I will present my concept shortly.
 
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Sturmey Archer drum hubs on the rear wheels (expensive, but worth it). SA brake levers with "parking" button.
Lots of design challenges for you to overcome perhaps, but a great project. :)
 
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I'd use something much better than a coaster and spoon brakes but I understand how such things will keep cabling to a minimum and need no handlebars either. Personally I'd rather have cabling issues to solve than poor brakes. Your pivots for the rear wheels to fold will need to take a lot of stress and have very minimal slop in both the pivot and locking mechanism. You have no triangulation to the rear wheels to ease the load on those pivots unless the seat back locks to the uprights and is load bearing. The arms from the pivots to the wheels are an effective lever to stress those pivots and I would not like to see aluminium used there (I appreciate you haven't said that you will use aluminium and that you have only said your Dad is an experienced aluminium welder). I appreciate the CAD work showing a (presumably) wooden seat is not necessarily the finished design so perhaps you could build the seat as a mesh type with a metal frame which would then allow you use that frame as triangulation for the rear wheels thus fullfilling two jobs for the one item. The seat would need to pivot at it's front as the current design and lock to the uprights perhaps like a tent pole type system to provide that triangulation. That would ease the loading on the pivots substantially for almost no weight penalty (if it locks to the seat you could probably do away with a locking mechanism on the pivot itself saving weight) plus provide a better seat. Having a mesh seat would also mean having the use of the frame to mount the bag.
 
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Hi! I'm new here but I've occasionally been reading on this forum for the past few years. I've had a trike idea in my head for quite a while, and now I'd like to share it.
Welcome and interesting project.
I assume you have seen my Python thread ? no folders but ridden various one's many thousands of miles My Pythons

The idea: a Python delta trike, but make it foldable.

Design requirements:
  • Comfortably haul a 10kg 40L backpack, to go on hiking trips I otherwise can't do without a car
  • Be able to take it (plus backpack) on a Dutch train, which officially means no dimension over 85 cm
  • Max 75cm total width, to fit through shed door and comply with Dutch traffic regulations more easily
  • Fun project to build together with my dad, who is an experienced aluminium welder and has worked on bikes before
Not much weight and a very small volume for all that gear ? impressed if you can do that
When I last looked at Dutch trains you could take a bike free if it folded or spilt in 2 ? but not a trike ?
Would it be easier just to make it split in 2 at the pivot and carry it as 2 separate halves ?
I have ridden @ 70cm tyre centre to tyre centre [ giving a trike width [ hub to hub ] of 80cm]

What I've learned about Python trikes so far:
  • The only other folding Python trikes I can find are Howard Stevens' Porta Velo's, but folded up they're still a little too big/wide for what I want. Have there been any other folding Python trikes?
  • Pivot point & seat should be as much forward as possible, to put more weight on front wheel. This is extra important because of the added weight of the backpack
  • Wheelbase should be as long as possible, also to put more weight on front wheel
  • Seat should be as low as possible for cornering stability, but not so low that there is no ground clearance
I have seen a low resolution Russian video of a trike folding as you suggested however can't remember where I saw it.
The weight of the back pack & load behind the rear axle is negligible compared with the weight of the front end and your weight both sat in front of the rear axle so don't sweat that part
I have ridden with wheel bases between 91cm and 116cm , 91cm means your elbows are inside the rear wheels , 116cm is more comfortable over uneven ground no real difference seen in traction.
Seat height has been at 21cm [ front of seat ] from ground and main frame keel underside 13cm from the ground.

What I've come up with (first draft):
  • 20" front wheel, possibly with 5 speed gear hub with coaster brake
  • 20" rear wheels. Thinking about simple spoon brakes that push onto the surface of the tire, to have some emergency braking power and also as a parking brake
  • The rear wheels are on swing arms that can fold 180° forward
  • The seat folds forward too. Haven't designed the seat yet, but I'm thinking about something similar to a beach chair
  • Open space between the rear wheels for mounting my backpack
  • When folded, the backpack can stay attached to the seat and the whole thing acts as a luggage trolley running on the rear wheels
I have ridden with brakes only on the front wheel and don't recommend it , especially on loose surfaces ?
Much to easy to lock up the front wheel and using the jargon the Yanks like ' you slide to the scene of the accident '
Did you discover this ? Glens Delta Trike aluminium and with very cheap/simple rear brakes , he said they weren't very successful ? maybe because the rims were painted me thinks !
Have you look at the 2 wheeled Python seat ? very simple/light/easy to make and folds anyway ?

Stats of first design draft:
  • Pivot angle 60°
  • Trail -18 cm
  • Wheelbase 90 cm
  • Total width 75 cm
  • Seat height 20 cm
  • Ground clearance 11 cm at the pivot, 17 cm in the middle
Before I develop this idea further, has something similar been done before? Can anyone foresee any issues with this kind of design, besides possible loss of traction going uphill? Thanks!
I think you need to consider handle bars , I did try without and had my only near death moment when I could not correct a steering oscillation on a narrow road in traffic [ terrifying ].
feet are very imprecise when trying to steer with them , especially if free wheeling and hitting a bump upsets the steering , also I found when freewheeling down hill if there was any tendency for it to drift off track caused by small bumps/camber etc it was very hard to make small corrections especially as the speed built up.

Good luck with the build Paul
 
Last edited:
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Thanks for all the replies!

@pegasus: that is a pretty bike! And the suitcase trike design in your new thread sounds very interesting, I like the idea and I will watch your thread. For me, 10-15 minutes disassembly is too much and I'd rather have hinges and a slightly larger folded size. My current design is about 45x55x80 cm folded, it would be 35x55x80 cm if it wasn't for the wide seat and the middle frame bar.

@maddox, @DannyC and @Popshot you're right, brakes are important and spoon brakes are a silly idea. I'll use some other type of brakes on the rear wheels, thanks. The reasoning behind the coaster brake on the front wheel is indeed that it does not require a handlebar. I'm still thinking about keeping that coaster brake on the front and getting roller brakes on the rear wheels. That way, I can get away with a single handlebar, perhaps between the legs. Re: parking brake; maybe I can just put a rubber band around the brake lever when I park..

Your pivots for the rear wheels to fold will need to take a lot of stress and have very minimal slop in both the pivot and locking mechanism. You have no triangulation to the rear wheels to ease the load on those pivots unless the seat back locks to the uprights and is load bearing. (...) I appreciate the CAD work showing a (presumably) wooden seat is not necessarily the finished design so perhaps you could build the seat as a mesh type with a metal frame which would then allow you use that frame as triangulation for the rear wheels thus fullfilling two jobs for the one item. The seat would need to pivot at it's front as the current design and lock to the uprights perhaps like a tent pole type system to provide that triangulation. That would ease the loading on the pivots substantially for almost no weight penalty (if it locks to the seat you could probably do away with a locking mechanism on the pivot itself saving weight) plus provide a better seat. Having a mesh seat would also mean having the use of the frame to mount the bag.
This is exactly what I was thinking. There is triangulation already in the original design, it's just not very clear in my first image. Still haven't designed the seat yet, but you can see better where the arms would be in the image below. Indeed thinking about a mesh over an aluminium frame seat, like those reclining beach chairs. It will indeed hinge around the front end for folding and I'm thinking about a simple net for putting the backpack in.

The arms from the pivots to the wheels are an effective lever to stress those pivots and I would not like to see aluminium used there (I appreciate you haven't said that you will use aluminium and that you have only said your Dad is an experienced aluminium welder).
Again that's what I was thinking. Obviously my dad wants to go aluminium, but even with the triangulation I'm worried about the stress on the pivots and fatigue in the long run. My original frame design was aluminium, but I've updated it to steel; only the seat frame will be aluminium.



Updated design also shows rear wheel arm extensions. This allows for both a longer wheelbase and a shorter length when folded (two extremes shown: 80cm & 100cm wheelbase).
 
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Welcome and interesting project.
I assume you have seen my Python thread ? no folders but ridden various one's many thousands of miles My Pythons
Thanks, and yes of course! I haven't read all pages but Google sent me to your thread a few times. I will try to learn from your pivot woes. I like the lean steer trike, I think I've seen some other ones as well, but the design does not lend itself as well to folding.

Not much weight and a very small volume for all that gear ? impressed if you can do that
When I last looked at Dutch trains you could take a bike free if it folded or spilt in 2 ? but not a trike ?
Would it be easier just to make it split in 2 at the pivot and carry it as 2 separate halves ?
I have ridden @ 70cm tyre centre to tyre centre [ giving a trike width [ hub to hub ] of 80cm]
40L/10kg is not even that bad, there are some "ultralight" guys that go way lower! And depending on where I'm going, I may have a few more kgs of food/water.
Folded bikes are free in the train here, and usually split bikes are too. Officially, no dimension is allowed to be greater than 85cm but it is always up to the conductor. Regular bikes need a separate ticket, with limitations on what times you can travel with it.
I didn't think a lot about just splitting the trike in two at the pivot. It would make for a package of about 65x75x80cm which is allowed as luggage (no dimension over 85cm). But that's a lot bigger than my current folded design at 45x55x80cm. But do I really need it to be that small, especially if I could use it as my own seat on the train? I will think about this.
Would you say a trike 5cm narrower than yours is ride-able?

I have seen a low resolution Russian video of a trike folding as you suggested however can't remember where I saw it.
The weight of the back pack & load behind the rear axle is negligible compared with the weight of the front end and your weight both sat in front of the rear axle so don't sweat that part
I have ridden with wheel bases between 91cm and 116cm , 91cm means your elbows are inside the rear wheels , 116cm is more comfortable over uneven ground no real difference seen in traction.
Seat height has been at 21cm [ front of seat ] from ground and main frame keel underside 13cm from the ground.
Oh that's good to know about the weight! I think the seat in my design is a little more forward, with elbows inside the rear wheels at 80cm wheel base but not 90cm. I've updated my design with wheel arm extensions that allow 100cm wheelbase, so that should be comfortable. Very similar height/clearance dimensions, good to know that works!

I have ridden with brakes only on the front wheel and don't recommend it , especially on loose surfaces ?
Much to easy to lock up the front wheel and using the jargon the Yanks like ' you slide to the scene of the accident '
Did you discover this ? Glens Delta Trike aluminium and with very cheap/simple rear brakes , he said they weren't very successful ? maybe because the rims were painted me thinks !
Have you look at the 2 wheeled Python seat ? very simple/light/easy to make and folds anyway ?
I will never ride a bike again with just a single coaster brake, after losing a chain and being left with no way to stop. I didn't think about the loss of control braking with just the front brake though. I'll definitely look into rear brakes, but I really don't like rim brakes.
Re: the seat; is that the seat belt one?

I think you need to consider handle bars , I did try without and had my only near death moment when I could not correct a steering oscillation on a narrow road in traffic [ terrifying ].
feet are very imprecise when trying to steer with them , especially if free wheeling and hitting a bump upsets the steering , also I found when freewheeling down hill if there was any tendency for it to drift off track caused by small bumps/camber etc it was very hard to make small corrections especially as the speed built up.
Thanks for your insights, I did not consider that. I was thinking about a single handle bar with a brake lever (for the rear wheels) and a gear lever, but I wanted to connect it to the frame behind the pivot. I will connect it to the front wheel part instead! What do you think about fitting it to come up between the legs?

Good luck with the build Paul
Thanks!
 
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Suspension
“Comfort” is at the very top of my list of design requirements, so I’m thinking about suspension.

General: Schwalbe Big Apple tires to absorb at least some of the bumps in the road. Maybe even the widest 60mm one at the front.

Rear wheels: the long arms that connect the rear wheels to the front of the frame are not very stiff, so this adds some suspension, but there’s no easy way to dampen that movement at the frame. So I’m thinking of putting some sort of shock dampers under the rear attachment of the seat instead. Those little arms that go up to the seat (see image two posts back) are about the length of a seat post. Could I just put two suspension seat posts there – would that do anything? They would only be loaded with less than 30kg each and they’re meant for full bodyweight, so they might be too stiff even at the lowest setting?
 
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Thanks, and yes of course! I haven't read all pages but Google sent me to your thread a few times. I will try to learn from your pivot woes. I like the lean steer trike, I think I've seen some other ones as well, but the design does not lend itself as well to folding.
Please no lean steer , there is a fundamental flaw in the design which means you can either run out of turning or leaning oh and they dump riders e.g
  1. riding slowly you may need maximum turn but if you leaned to get it you fall out the seat.
  2. riding fast you may need very little turn however the speed means you need more lean
  3. very poor turning circle
look at the Mosquito velomobile - they say it works - however it is very low AND very wide !

40L/10kg is not even that bad, there are some "ultralight" guys that go way lower! And depending on where I'm going, I may have a few more kgs of food/water.
Folded bikes are free in the train here, and usually split bikes are too. Officially, no dimension is allowed to be greater than 85cm but it is always up to the conductor. Regular bikes need a separate ticket, with limitations on what times you can travel with it.
I didn't think a lot about just splitting the trike in two at the pivot. It would make for a package of about 65x75x80cm which is allowed as luggage (no dimension over 85cm). But that's a lot bigger than my current folded design at 45x55x80cm. But do I really need it to be that small, especially if I could use it as my own seat on the train? I will think about this.
Would you say a trike 5cm narrower than yours is ride-able?
Yes I would say so , I am currently @ 60cm and a high seat however my seat tilts.
It as proved to be very safe , I think a lot of the tilting I do is ' because it can ' rather than because it needs to.
I really need to remove the tilting by dropping the seat onto the main frame [ then about 30cm from floor ] and riding it to see if it is still safe :D


I will never ride a bike again with just a single coaster brake, after losing a chain and being left with no way to stop. I didn't think about the loss of control braking with just the front brake though. I'll definitely look into rear brakes, but I really don't like rim brakes.
Re: the seat; is that the seat belt one?
Yes seat belt one


Thanks for your insights, I did not consider that. I was thinking about a single handle bar with a brake lever (for the rear wheels) and a gear lever, but I wanted to connect it to the frame behind the pivot. I will connect it to the front wheel part instead! What do you think about fitting it to come up between the legs?
Insufficient leverage , I still steer with my feet something you will have to learn as initially your feet resist it turning and the steering feels heavy and dead.
get some where like an empty car park and practice , once foot steering comes naturally I found I could add/remove clothing eat/drink txt and take pictures and map read whilst riding then I think maybe a lever with much less leverage might work.


Paul
 
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Could I just put two suspension seat posts there – would that do anything?
It would, but remember you are using the back rest to push from, so it needs to be firm, specially on a python.
I have used 1 front v brake only, with no problems. Probable have disc and v brake on the front wheel on the suitcase python. Castor brake might be dangerous, because every time you push on the pedals you have to balance the force with your other foot to make the bike go in the direction you want it to go.
Handle bar. I only use it to steady the bike when riding fast, and to hold my brake lever and gear shifter, because you have to counterbalance your pressure on the pedals with the other leg, so when you pedal so fast that there is no more pressure on your pedals, or going down hill, you have risk for a wobble. The unbalance starts for me around 30kmh but light hands on the handlebar will dampen it.
Because you are using your feet to both pedal and steer, to look over your shoulder is in the beginning impossible and even when you are a comfortable rider it's still difficult, so a rear mirror is important.
A link to a mainly 2 wheel python webpage. http://www.python-lowracer.de/index.html , some good information there.
 
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Suspension
“Comfort” is at the very top of my list of design requirements, so I’m thinking about suspension.

General: Schwalbe Big Apple tires to absorb at least some of the bumps in the road. Maybe even the widest 60mm one at the front.
Everyone tells you no suspension needed just buy fat tyres.
This is not always true , depends where you ride and how heavy/hard/fast etc.

IIRC Big Apples [ in fact all fat tyres I can find ? ] do not have any puncture protection , maybe more important than a bit more comfortable ride than say 20 x 1.75 with green guard ?

Paul
 
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You're right Paul - no puncture protection on Apples. I'd class fixing a puncture at the roadside as a fairly uncomfortable option.
 
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Good point @stormbird and @Popshot. Big Apples used to come with greenguard (Big Apple Plus) but those are no longer in production. The Big Ben Plus 55-406 (20x2.15), Super Moto-X 62-406 (20x2.40), Marathon 365 and GT365 55x406 (20x.15) all come in with greenguard. There is also the Schwalbe Pick-up which is faster and apparently even more puncture resistant and those also come in 55-406 (20x2.15). From what I can read the Big Ben Plus is probably the most comfortable ride.

It would, but remember you are using the back rest to push from, so it needs to be firm, specially on a python.
I have used 1 front v brake only, with no problems. Probable have disc and v brake on the front wheel on the suitcase python. Castor brake might be dangerous, because every time you push on the pedals you have to balance the force with your other foot to make the bike go in the direction you want it to go.
Handle bar. I only use it to steady the bike when riding fast, and to hold my brake lever and gear shifter, because you have to counterbalance your pressure on the pedals with the other leg, so when you pedal so fast that there is no more pressure on your pedals, or going down hill, you have risk for a wobble. The unbalance starts for me around 30kmh but light hands on the handlebar will dampen it.
Because you are using your feet to both pedal and steer, to look over your shoulder is in the beginning impossible and even when you are a comfortable rider it's still difficult, so a rear mirror is important.
A link to a mainly 2 wheel python webpage. http://www.python-lowracer.de/index.html , some good information there.
Thanks, I did not think about some of those things so it's really nice to get feedback from people who have experience riding pythons.
I did read the original python site & openbike wiki, some nice info there.

Ok so the coaster brake is out too. I'm currently thinking 2x 70mm SA drum brakes from Ginkgo on the rear (90mm would be overkill because I ride mostly flat terrain) and a roller brake gear hub on the front.

I'll see if I can get two handlebars into the design, and a little mirror would indeed be nice.

I wonder if stiff suspension is worth it over a simpler design without suspension, if I already have balloon tires. But I guess those suspension seat posts (about 500g each) could work then.
 
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I have seen a low resolution Russian video of a trike folding as you suggested however can't remember where I saw it.
I found the video of the Russian folding trike! Also found the forum thread to the folding trike (link to translated version). Cool how similar it is to my idea.

They even made a second version with rear suspension.


Can anyone figure out how that suspension works?
 
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The pictures are not sufficiently detailed to see it. Best guess is there's a pivot at the end of the blue arm and is elastomer controlled.
 
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I did some reading of that Russian forum (yay Google Translate) and they don't explain how it works but apparently they spent a month on it, it was complicated and it didn't even work very well.

I threw out my earlier seat post suspension idea, because I want the connections between the frame and the seat to be rigid and only the rear wheel arms to be suspended. I tried playing around with the rear wheel attachments to see if I can get some sort of off-the-shelf spring/damper unit in there. I'd have to swap the tube-in-tube arm extension in my previous design image for another pivot. Here's a rough idea:


I also looked at those tube-in-tube elastomer suspension thingies from Rosta, and the elastomer suspension used on ICE trikes for inspiration.

But to be honest, I doubt it's worth the hassle and the extra weight for maybe 2 cm of travel. If I ever decide I need it I will look at it again, but for now I will continue without suspension.
 
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A double pivot on the rear wheel arms allows the rear wheels to fold facing out instead of in. This means that the frame at the pivot can be much narrower, and this allows for the addition of handlebars without compromising the steering angle.

Here's another design, this one has no suspension. It shows the much narrower middle frame, similar to the Russian design, with under-seat handlebars added. Maximum steering angle is 40 degrees, which sounds ok especially with the short wheel base? Seat removed to show the frame better.


Next up is designing the seat, and then finishing the pivots and locking mechanisms.
 
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