Things which are blocking the tricycle project

The tricycle project is extremely experimental and ambitious. It may not work at all. It may work technically, but I may not like it. It may work technically, but I may not be well enough to make use of it. If I commit to it, it will cost all my spare resources of both time and money for probably a year.

So let's once again lay out the things which are, for me, at present, blocking it, and consider whether those are reasonable; and, as part of that process, consider the steps and milestones which are needed to achieve a working vehicle.

Health

At this moment I've been ill for a month, and not fit to ride a bike. I believe I am recovering, but after this long an illness, recovering fitness will take a while. Obviously part of the reason for building a (mostly) human powered vehicle is to help me maintain fitness into old age; but if I don't reliably have sufficient fitness to use it, it's not a good investment.

Edited to add on Monday of this week I took the village's big cargo bike into Castle Douglas with my trailer attached, taking in all my recycling accumulated over several months and returning with shopping and a 25 kg sack of cattle treats. That rig is pretty much the same weight as the trike would be, so I can do this!

Learning Computer Aided Design

All three dimensional modelling software is really hard to learn, for me. I think it is for most people, but I know that I really struggle. Before building moulds — which is a considerable investment in time and money — I have to have a design into which I am confident I can comfortably fit myself and all the mechanical and electric components of the machine. That seemed to me to require a computer aided design model; and although I am thinking about how I could avoid it, it still seems to me that a CAD model would be desirable.

After all, the designer of Beano designed the machine, built it... and then sold it to a smaller man because he could not fit in it. And Woodstock is a second iteration; Russell Bridge previously built a very similar machine called Snoopy, which he sold after a very short period because he was dissatisfied with it, I think for fit reasons.

However, there is an alternative: build the ergonomic prototype (which I'm going to have to do anyway); sit in it and take careful measurements to establish the volume that I occupy, build a set of frames from those measurements, and then eyeball the building of a mould around those frames as traditional boat builders have eyeballed the shapes of the boats they've made. That is possible and I could do it but I think I must make yet another effort to learn CAD.S

The female mould

When I first set out a plan for this project, I assumed I could use a male mould for the hull. People who have done similar things advise me that this is not good enough. I will need a female mould. But to make a female mould, I do first need a male mould to mould the female mould over. So that's not just an extra major operation, but it's a lot of extra materials and thus cost. Of course, the female mould does not need to be nearly as light or nearly as strong as the final hull, so it can just be glass fibre. Which means it doesn't double the cost, but it does pretty nearly double the work of moulding the hull.

A working prototype of the four bar linkage

The Lego steering prototype did pretty much demonstrate that the four bar linkage would work in principle, but it didn't demonstrate that it would handle the necessary loads. I remain extremely concerned about the very unfair loads on the upper pivots, which I suspect were the major problem with the Mosquito tricycles. In my earlier notes I suggested that a 100mm long hinge pivot — with PTFE bushings or bearings — might be sufficient. I'm now very skeptical of that, I think it should be much longer.

But, the hinge pivot has to be straight, and the surface of the hull is curved. Furthermore the axis of the pivot must be parallel to the vertical centre plane of the hull at rest, but raked back about 45° from the vertical. And working that into the surface of a compound curved hull without horribly upsetting the aerodynamics seems quite a challenge.

So I need to build a prototype of the four bar linkage, including those upper pivots; and I think I need to build that into a working 'functional prototype' of the whole chassis. So the timber functional prototype, which in the earlier plan I thought I could dispense with, now feels essential.

So that's now two major assemblies which I hadn't expected to have to do which I now see I do have to do. The timber functional prototype need not be very expensive because it can be built essentially of rough sawn timber and bits of scrap bicycles, but it will still cost time.

However, if we have a timber functional prototype, not only can it be initially built with cheap and junky models of the final front subframe and rear four-bar linkage to test ideas and refine the design, but it can later be used to test the intended final front subframe and final four bar linkage tested on it before I have to commit to the cost of buying the materials for the hull is lay up, so that if last minute design changes are needed they can be made.

This also allows us to have go/no go decision points both before committing to buy the mechanical parts for the front subframe and the four bar linkage, and later before committing to buy the (expensive!) materials to lay up the female mould, and the hull.

So the revised plan looks like this:

Milestones

That looks kind of doable. It would need no significant life events to happen for two years, and, while the tricycle might be more or less usable by spring of 2027, it would take some time to shake the inevitable bugs out of it.

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