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@simon_brooke@mastodon.scot
2025-08-27 06:48:16

Having not written anything about my #tricycle project in months, I've now written two posts in two days. Here's the first:
#BikeTooter
Rethinking the tricycle drive train

Rethinking the tricycle drive train
I've been rereading my posts on design of a tricycle, and especially this one; and I've been looking again at this picture, of Seventy Seven's removable front subframe which carries its front wheel, steering, and transmission systems; and I've been thinking. This will be a short post documenting my thoughts.

@simon_brooke@mastodon.scot
2025-10-15 12:03:24

I've just bought test materials to evaluate the relative strengths of a flax/balsa sandwich composite versus a carbon/Nomex (aramid) sandwich composite.
Yes, I know the carbon/Nomex will be stronger, but would the flax/balsa be strong enough for my #Tricycle project?
#BikeTooter

The Biodegradable Tricycle
One of the design goals of my tricycle is as a prototype for sustainable transport. To be sustainable, it has to be fully recyclable, and the simplest way to make anything fully recyclable is to make it biodegradable: nature will do the recycling for you.

@simon_brooke@mastodon.scot
2025-09-24 16:02:51

I'm still learning #OpenSCAD. This part, the lower knuckle for the four-bar linkage of the #Tricycle, isn't as smooth and aerodynamic as I'd like. But it's good enough, certainly for now.
The blue colour is just to make it easier to work with; the finished part will probably be c…

A CAD drawing of the lower knuckle of the four bar linkage. The body of the knuckle is an aerofoil teardrop in plan, with a radiused top and a rounded bottom. A boss on the outer (left) side surrounds the hole for the wheel axle. On the inner (right) side is an aerofoil stub to which the aerofoil section lower bar will be bonded. In the top of the knuckle is a radiused cavity in which the pivot on the lower end of the lateral bar will rotate. The part, which is coloured blue with yellowish-gre…
A view of the same part from in front. The hole for the shaft on which the lateral bar pivot will rotate can be seen.
The same part viewed from the lower front left.
The part in context. The lateral bar, wheel, and brake disk can all be seen, as can the lower bar, although this doesn't yet correctly join to the knuckle.
@simon_brooke@mastodon.scot
2025-09-16 14:27:49

I haven't actually written a new blog post about the #Tricycle project, but I have greatly amended and extended the last one.
#BikeTooter

Learning from CAD
As I reported in my [last essay on the tricycle project(../../2025-09-03-details-details/), I now have a CAD tool which I'm learning to use. So, learning to use it, I'm beginning to be able to visualise the tricycle, if not yet concretely, at least as an assembly I can look at and study. And doing that brings up several things.

@simon_brooke@mastodon.scot
2025-09-17 10:04:09

So, at last I have a rendering of the #Tricycle which includes a (so far fairly crude) model of the hull. This makes the whole thing much easier to visualise. Progress is being made.
I'd like to get the CAD model a little more complete, but actually this is enough to move onto an ergonomic prototype.
I'm about to start buying actual parts for this damn thing. It may actually h…

A rendering of the tricycle with the subframe inside a streamlined, teardrop-shaped green hull, and the four bar linkage holding the rear wheels embracing the tail of the hull.
@simon_brooke@mastodon.scot
2025-09-18 14:25:41

OK, a sidequest on the #tricycle project: I'm going to have to do data capture, storage and display. I need to log speed, cadence, battery voltage, and some indicator of power consumption. I need to display at least speed, cadence, and projected range. I can do speed and cadence off hall effect sensors. I want to use #Lisp

@simon_brooke@mastodon.scot
2025-09-04 12:22:46

Two more blog posts on the #Tricycle project over the last few days: firstly, I have found a CAD tool that works for me:
journeyman.cc/blog/posts-outpu

Drawing the tricycle
I have, as I wrote in my last post, real difficulty with learning 3d modelling software. Every system I've tried has a really steep learning curve, the commercial systems are extremely expensive making them very hard for me to evaluate, and some of my cognitive quirks just get triggered when trying to use them.

@simon_brooke@mastodon.scot
2025-09-10 21:05:38

Progress on the #tricycle project is mainly in thinking about and working on the subframe. One thing that I'm sure is the right decision is to give the subframe a flat mounting flange, which will bolt down onto a matching pedestal within the hull. This will make the subframe easier to fabricate, and easier to mount/dismount - which I think will be needed for any work on the wheel or tyre.

…
New Computer Aided Design rendering of the aluminium subframe, now with a flat mounting flange. It is a gangly collection of welded rectangular section aluminium extrusions, surrounding a wheel, a bicycle chainset with an enormous chain ring, and an epicyclic gearbox mounted in front of the chainset, and driving the wheel by way of a secondary chain. Both chains run on the left hand side of the drivetrain.
A Computer Aided Design rendering of a carbon fibre subframe laid up over an extruded polystyrene armature. It has an identically the same mounting flange to the aluminium design, except this one is laminated carbon, and it wraps identically the same mechanical parts in the same arrangement.
@simon_brooke@mastodon.scot
2025-10-06 19:44:51

The first actual physical part for my #Tricycle project has arrived today. This is an axle — actually a Cannondale Lefty axle — and it's nominally the front axle, although it doesn't really matter which axle it ends up being because they will all be identical.
#BikeTooter

A long narrow truncated cone of black anodized titanium(?), with flats for bearing seats turned into it at each end, and a rough sand-cast cylindrical mounting extension sticking out of the thicker end. It is lying on a varnished wooden surface.
@simon_brooke@mastodon.scot
2025-09-06 07:31:27

Having designed a good-enough CAD model of the subframe for my #tricycle as a welded aluminium structure, I'm now thinking that it might be better constructed as carbon fibre laid up over an XPS polystyrene armature.
The benefits are that I can do composites myself, whereas I can't weld aluminium; and that the composite would probably be both stronger and lighter. The downside is th…

Another illustration of the aluminium framed subframe. Both sprockets on the epicyclic are now shown, but the epicyclic still floats in space with no visible means of support. The secondary chain sprocket on the road wheel is also shown. The chainring is now a ring and not a solid wheel, making it easier to see that's behind it. The chainring now lines up correctly with the primary sprocket on the epicyclic, and the secondary sprocket lines up with the sprocket on the road wheel: there is room …
@simon_brooke@mastodon.scot
2025-09-05 11:20:45

CAD model of the #tricycle subframe. The chain ring is very nearly as big as the front wheel (80 teeth!). It drives an epicyclic gearbox mounted in the nose of the vehicle, which also has a disc brake. The epicyclic will drive a secondary chain via a sprocket mounted to the left hand spoke flange, but this is not yet shown. There will be no ratchet on the secondary chain, so the disk brake on the…

A CAD visualisation as described in the body of the post. Most of the structure is coloured grey, to represent aluminium tubes. The cranks and pedals, and the tyre on the wheel, are coloured black. The epicyclic body is coloured red to represent a Rohloff, although for budgetary reasons it will probably end up being a Shimano Nexus 11.
@simon_brooke@mastodon.scot
2025-10-04 17:17:57

If anyone's been following my progress on the #tricycle project, I'm currently drooling over the very adjustable recumbent ergonomic rig shown in this video. I'm wondering whether I can make myself something even nearly this adjustable!
#BikeTooter