Seek & Geek #10: Sturmey Archer Bicycle Hub

I took one of these apart a few years ago, and with all this talk about gears I thought I would do a bit more digging into the function of this stalwart of the honest and reliable shopper-bike.

PUPS #11: Documentation

A summary of my PUPS to date, following the design process from concept sketches to finished machine!

PUPS #10: Build Entire Machine

I finished my PUPS #9 with a to-do list, which was a pretty good starting point, and decided to keep this going in a word doc to let me keep track of what needed to be built and when. This worked really well, particularly since a semester of working in the shop has massively improved my ability to estimate how long it takes to make something! Here’s what my rolling to-do list ended up looking like by the end of last week – the last section is when I really nailed it, putting in conservative time estimates so that I managed to achieve all of them, even with setbacks.

Seek & Geek #9: Fresnel Lens Lighthouse Light

A few weeks ago my mum was over from the UK to visit, and as someone who loves ships and literature she decided a visit to Nantucket was obligatory. A highlight of the trip was the whaling museum, which had a range of artifacts from Nantucket’s whaling days, including this pretty amazing lighthouse lamp that was once used in one of the island’s three lighthouses. I saw it just after the lecture on bearings and power transmission, so thought it would be a good chance to unpick the design and layout of the gears

PUPS #9: Complete Machine Detail Design

On finishing my carriage and testing it out on the axis, I was pleased with its rolling smoothness but less pleased with a few things:

• Over-complicated and heavy carriage design
• Difficult preloading
• Difficult assembly
• Under-designed leadscrew nut holder

To fix these, I iterated on the design for my carriage and greatly simplified it. Rather than try to create my own box-like structure for the y axis, I decided to make use of the structural properties of a 4″x4″x0.25″ aluminium extrusion. While the extrusion is not as stiff as my original carriage design, it cuts down vastly on the opportunities for manufacturing and assembly error, by reducing the part count from 15 (with ~6 unique) to just 1. This obviously introduces more complexity to a single part, increasing the risk of a single bad operation messing up the design.

Seek & Geek #8: Sir David Mackay

OK, so this might be pushing it in terms of the definition of ‘Seek & Geek’, but I just found out that  David Mackay passed away today and I’m rather sad about it.

Mackay made a number of contributions to the scientific world, in the areas of machine learning and information theory, as well as writing the book that basically inspired me to study engineering – ‘Sustainable Energy – Without the Hot Air’. Interestingly, his approach to sustainable energy was broadly similar to that of Professor Slocum’s approach to precision machine design. The dominant theme in ‘Without the Hot Air’ is that, whatever your feelings might be about something (wind energy, electric cars, vegetarianism – or sliding bearings, structural layouts, actuation methods), you need a plan that adds up.

PUPS #8 – Most Critical Module

This week was the time to start building stuff for real!  I managed to spend all of Friday and Saturday in the hobbyshop, but that was no way near enough time to finish my ‘most critical module’, the y-axis of my machine. I’ll be back in the shop tomorrow and all of Friday again, so will hopefully make more headway soon – I feel like this ‘most critical module’ may end up being all I manage to complete by the end of semester.

PUPS#7 – Concept Detailing

Time is running out! The past couple of weeks have been a rollercoaster of inspiration, indecision and inaction. A poorly timed bicycle race has held up my fabrication big-time, but I’m now finally felling happy about my bearing concepts and have a detailed CAD model of my Most Critical Module to show for it. This week will be spent finalising some little bits, then fabrication will begin proper on Friday and Saturday – I may need to reign in my aims for how much of this machine gets finished before the end of the semester, but I’m confident of getting at least two axes finished. Here’s how the design has progressed in the last couple of weeks:

Seek and Geek #6: Inventables X-Carve

Who thought it could be so difficult decide how to make something move in a straight line? This week I’ll be looking more at the structure and stiffness of my router, but for this Seek and Geek I wanted to complete the picture as to the past week’s bearing madness. As fortune had it, the lab for another of my classes, Design of Electromechanical Robotic Systems, had just taken delivery of an X-Carve CNC router (!) and Prof. Hover was more than happy to let Lauren and I have a stab at assembling it.

PUPS #6: Detail Exploration

An update to the error budget spreadsheet has now introduced even *more* functionality, and adds another facet to wrap my head around. Compliance matrices for each axis mean the deflections due to loads can be accurately determined, and starts to flesh out the error budget further.