Time for a quick update.
I spent some of my available time this week building a frame jig. As mentioned previously, the intention is to use it to make a PVC tube mock-up of the cardboard frame design. From there, the plan is to show it to my tame engineer to see what he reckons. Then I can listen to his recommendations and certification requirements, and build any required changes into the design before starting to make things in ChroMo.
Well, that was the plan. Things went wrong when I downloaded the free jig blueprints – the designer’s brief specified 50 x 50 mm box for the main frame, but didn’t mention a thickness. Keen to get started, I raced out and brought the closest suitable steel could find, which turned out to be 50 x 50 x 1.6 mm galvanised tube. I had some old welding rods in stock at home, so elected to stick weld the thing together instead of TIGing it – stick being much quicker in this application.
Anyway, problems were immediately obvious. Gal steel is a pain in the spadgebox to weld, not to mention that the fumes contain lead oxide, which can cause brain cancer and nervous system disorders. I took this into account, and set up a suitable ventilation system prior to starting (check your material safety data sheets kids!). Didn’t matter – it turns out that this steel is far too thin for this application. Despite being clamped and gradually tacked, it moved about a lot during welding. The end result was not as square as I would have liked, and flexed a lot once I’d finished – too much for what I want it for. Also, the combination of old rods, gal coating, and my muppet welding skills meant that the final result ended up looking like arse. I consider the time and money spent on this to be dickhead tax, and will incorporate the lessons learnt into the next version. I’ll make it using heavier material (which I’ve sourced), and will add triangulation to the original design to get rid of any potential for flex.
I’ve also spent some time developing a project budget. In my experience, failing to plan is planning to fail. Also, plans are redundant, but planning is essential – meaning that no plan survives first contact with reality, but considering the what-ifs before starting is a healthy survival strategy. As of today, I reckon that I know where to get about 80% of the parts and material I need for Gurty, and am in a position to start buying bits as my cash flow permits. Two thoughts here – it’s advantageous to base projects on popular/raced engines, as the OEM and after-market parts supply options are much better. For example, the engine in Gurty is thirty years old this year, and I don’t have any real problem buying the OEM parts I need. I do have to shop around, but they are there. There are also many after-market options available for parts and tuning that make my life just a little bit easier in terms of building and tuning for bigly power.
Of course, only time will tell whether the things I can see online can actually be brought and delivered in time. I was torpedoed by this recently when buying tools. I found an online supplier with the things I wanted showing as being in stock, and placed my order. Then waited for delivery. And waited. And waited some more. After reaching out, I was informed that supply was not currently available for all the things I ordered. To which I responded that those things were still showing as stock items on the vendor’s website, and that I’d like a refund. I got my coin back nearly two months later, but what a ball-ache. This brings me to my second point – things almost never, ever go strictly according to plan. Keeping an eye on my project time/cost/quality constraints, and having a plan to mitigate any risk, gives me the best chance of success.
Concurrently, I’ve also done up my budgets for the big wheelie bike, and the two land-speed record (LSR) bikes. Speed Week 2023 starts today at Lake Gairdner, but I obviously won’t be making it given that I’m, typing this from my home office 2,200 km away. However, I have a cunning plan – I’m about 75% on the budgets for these bikes (the remaining 25% is comprised by the unknowns inherent to building a frame from the ground up, and from boosting the engines), and I’m still working on building them. Moreover, I’ve found a place where I can test to my heart’s content without breaking the law or upsetting anyone. The use case for Gurty is pretty simple, and relatively easy to both test and verify. I won’t spoil the story by getting into specifics of that mission just yet, but it simply involves getting from A to B. The mission for the big wheelie bike and the LSR bikes is more complex, and is much harder to both test and verify. Given their intended purpose, the LSR bikes, in particular, are quite difficult to test in anything other than real-world conditions. There are two wind tunnels within 200 km of me – as far as I can tell, neither of them are available for anything other than research and teaching purposes, so my chances of getting access to them are slim. More to the point, it’s debatable as to whether or not such testing would be of any value. So, real-world testing is the only way forward. And I’ve found the place to do it. More on that later.
You may recall that TT24 is back on the agenda. Two updates need to be discussed here. First, my shipper is offering to send my bike to Barcelona in early May-2024, as opposed to sending it straight to the UK. Considering that we originally intended to travel in such a way as to meet up as a family at certain places (i.e. Mrs Wife and kidlets would fly, and I’d ride and meet them), this raises obvious questions around the overall trip plan. I’m still in discussion with Mrs Wife on this one – no doubt she’ll tell me what I think in due course. Right now, my thinking is to take a longer trip, see more of Europe, and take in some of the Irish road racing before heading over to the Isle of Man for the TT. I’ve done this before, and can highly recommend it. It’ll probably cost me some family bribery, but I reckon I can get this approved. The second update is that the accommodation I had for this year was rolled over to 2024. Unfortunately, the owners of the venue had had some family strife, and it is no longer available. I’ve rolled my deposit over to secure whatever digs become available, and don’t anticipate not having a place to stay. Still, even this far out, I’m slightly nervous about not having my TT24 accommodation locked in. Also, Steam Packet ferry tickets for 2024 went on sale on 6th of Mar-2023, so if you want to go, you better get in quick. This is relevant because, based on previous experience, coming to the Isle of Man from the mainland UK via Ireland can be easier than coming direct from the UK mainland. Something to think about.
I had some reader questions from the last update which I’d like to address. First one – why do I need so much suspension travel? Well, I’ll be taking Gurty places where more suspension will be better than less. I chose 300 mm as the arbitrary target for two reasons – it’s more than any stock motorbike I could find/buy, and I wanted to see if I could do it. Second question – why stuff around so much to get the anti-squat and zero chain slack? Well, as per Foale’s comments, the bigger the suspension movement, the bigger the effect that suspension movement has on anti-squat performance and chain slack. So, I had to take this into consideration in my design from the outset. Just copying an existing design would not achieve the benefits I’m looking for, and would likely incur more problems if I just tried forcing more suspension movement into it.
Third question – what will performance of the leading link front suspension be like? Well, in this design, function has determined form. I need the chassis to be light, strong, simple, and able to accommodate the required engine package and suspension movement. Reading Foale’s book led me to the decision that the leading link would be the way to go for the front suspension. I did consider a trailing link setup for some time, but it ended up looking too hard to package it neatly and still be able to maintain the OEM wheel base and engine/radiator position. All design is compromise. The cardboard mock-up video shows that it is at least feasible – I have lingering concerns regarding the strength and rigidity of the leading link, but, so far at least, the idea is do-able.
Further explanation probably requires that you read Foale’s book, as he explains it much better than I can. However, he does note that having the forks attached to the steering stem (as I do) means that braking and suspension forces still go through it. This means that it has to be strong, and likely heavier than alternative designs as a result (as my design probably is). I can live with over-engineering, but I can’t live with a premature failure of a flawed or weak design. It’s also the simplest design combination that I could see, but I’m happy to be proven wrong on that. Foale also talks about the potential benefits of leading links, including much better rigidity, stability, and control than standard forks. Anti-dive can (and will) be built in, and stiction performance is generally better than forks in his estimation. Foale does mention that leading links are generally not ideal where large suspension movements are required due to the larder range of motion of the axle with respect to the link pivot (i.e. the axle moves in a semi-circular arc, not a straight line), but I suspect that this won’t be a major concern considering where I want to take this thing. Foale also talks about the effect that link length can have on angular suspension movement – the shorter the links, the greater the movement, and the less anti-dive effect which can be achieved. I did consider this, and tried to keep the link as long as possible while still keeping it packed in the required space and giving the required suspension movement. Once again, everything is a compromise, and I’m prepared to live with a bit less anti-dive.
Fourth question – how do I understand Foale’s calculations? Well, the short answer is that I don’t – I didn’t even try, because I’m a certified turnip. Instead, I started with the design brief (i.e. 300mm wheel travel front and rear). Next, I decided to try for anti-squat and zero effect on chain slack throughout that range – just because I could. As noted above, I looked at designs that could feasibly achieve this, then looked around for suspension units that I could buy which would let me achieve this range of movement. Once I had all this, I started drawing various designs – lots and lots of drawings. This evolved into cardboard models, and culminated with the video you saw last time. In short, I didn’t have to understand the maths – I just had to know it works. I did this via the video, and will try to validate it with a physical 3D model next. I could try modelling it in some sort of software, but that seems like an extra step – I’m unlikely to learn any more about the design my modelling the thing virtually than I would be actually cutting bits up and gluing them together. Besides, I’m not competent with any of these software packages, and don’t have the time to gain those skills. I can lean on my engineer for finite element analysis when the time comes, so this is the path of least resistance for me.
Apologies if I’ve forgotten any questions. Hit me up, and I’ll answer them next time.