9: Prototype Teardown

The arrival of the Zeb fork last time meant we had to jump ahead a little bit, missing out the original Prototype Teardown blog. But it's an important step that you can't miss out so here goes...

The way things have been this summer, the Slacker Project blog has been a little neglected. We've been testing and working on the bike, but we haven't found the time to share our progress as much as we should (judging by the amount of emails we've had). The good news is there’s plenty to come in the next few months and we'll be sharing what we've been up to with all things Slacker.

Setting The Scene

Roll back the clocks to BC (before corona): it's last Winter, when the global pandemic was just a whisper. The nights were long, the days were short, the air was crisp, the soil was moist. Finally it was the delivery date for the Slacker prototypes.

That day we spent much time at the window, our breath condensing on the poorly insulated single glazing of Alderson Road (our old workshop). Back then our days were spent worrying about Brexit huddled around oil filled radiators. But this day was full of anticipation and hope; hope for a world where every rider owned a DH bike; a better world where plastic Enduro bikes don't infest bike parks like a plague, the DH bike reinstated as the one bike best suited to uplift-assisted riding.

At 2:35pm the unmistakeable brake squeal of a long wheelbase Citroen Relay entered the yard. We rushed to the window. Could it be? Yes it was... the warm yellow glow of the rarely seen DHL delivery van, a beacon of hope! Without a second thought we all took to the stairs as fast as our well-worn skate shoes would take us, the sounds of waffle-soled gum rubber on poorly constructed stairs could be heard throughout the building. The door flung open, a mob of three men and one dog rushed across the yard, before Nigel (DHL delivery driver: loves flat ales and gravy on chips, supports United, holidays twice a year in Benidorm, didn’t vote, pins his hopes on the postcode lottery) could even open his Tardis-like van. The doors swung open revealing a sea of brown cardboard. There it was in all its glory, the box containing the samples, bearing all the battle scars expected of any package that had made the arduous pilgrimage from Taichung to Sheffield in 3 days. A quick scribble of the pen and it was ours.

First up: Tear Down

When we receive any prototype the first thing we do is what we call a teardown. It's not the most exciting step but it's important and can't be skipped. The hardest part is to resist the overwhelming temptation to just build the thing and go for a ride - after waiting weeks or even months to get to this point, it's important to wait one more day while we check everything is as it should be.

The teardown process is basically a complete disassembly of the frame where we check the tolerances of all parts, measure, weigh and inspect each component. This allows us to not only confirm the prototype has been built to spec but also evaluate the ease of assembly/disassembly, and familiarise ourselves with what has been a drawing on a computer and a set of 3D-printed parts up until that point.

To get started (after we've got over the initial excitement) we fit a shock and then cycle through its travel to confirm clearance and alignment, and once that's done we can start with disassembly. The first part of disassembly is to break down the frame into four parts: front triangle, rocker, chain stay and seat stay. Once you have broken down in to those four parts you can start getting into more detailed disassembly, removing dropouts, cable guide hardware, pivot bearings and so on. Once the frame is stripped completely, we weigh all components and check tolerances on each one.

This is an prototype which means the frame is built without much of the tooling we would have in place for production. As much as anything it's a proof of concept sample, so we need to know if the project's even viable before putting thousands of dollars down for tooling. As a result we're reliant on the skill and experience of the fabricator and although producing a complex sample like this is always done by the master welder, the potential for errors is there. With that in mind we pay special attention to check geometry and pivot locations as well as alignment whilst the frame is being disassembled.

Remember, as an entirely new design, this is the first time the factory has ever made one of these so it's not just a physical prototype for us to test; we're also prototyping the manufacturing and QC processes. It's at times like this when you really appreciate having a good factory to work with.

Once this is all done and documented we've got a baseline. We know everything is as it should be on day one and we have a fixed point if any issues arise during testing or there are challenges down the line.

What did we find?

First impressions are important so we were relieved that the frame looked so good out of the box. We knew it would be a bit overbuilt and rough around the edges - early prototypes always are - but we had got the overall 'look' right; the proportions felt right, the tubing profiles and joints were as good as we had hoped in 3D and the lines flowed as we had intended. You really need to see the bike built to make that final judgement on stance but if there was a real design problem, we'd have known straight away. 

The frame was manufactured to correct specification/geometry and all parts within tolerance. This is normal and what we would expect from our factory; we are very fortunate to work with a factory with a wealth of experience who (at least in our opinion) are one of the best. To date we are yet to have any tolerance issues with prototypes which really is testament to their abilities as a manufacturer - especially when you consider the complexity of projects such as the Slacker. Nevertheless, it's important to check.

One issue we did find when disassembling was actually one of the main pivot bearings outer race was 0.2mm out of spec meaning the bearing fit with the frame wasn’t as snug as we would have liked. In practice this would have probably been ok but for peace of mind we replaced it anyway. This wasn’t an issue we have come across before but just goes to show the importance of this process in highlighting any potential issues. It may seem like a trivial issue but if this hadn’t been spotted on day one and we had issues during testing - bearings moving within the bearing seat - that might have led us to question the pivot's design.

Weight

As with any early prototype it is on the heavy side. Over-engineering comes naturally for us I think and an obsession with durability and strength for this project maybe ran away with us a little. But we also knew we were going to prototypes earlier in the design process than we normally would, so we expected these first samples to be a bit on the agricultural side. Breaking down the total weight of the frame into all its constituent parts helped us to evaluate where that extra timber might be and where we should focus our efforts in the next round of design work.

The frame as it stands today weighs in at 4.9kg. Factor in powder-coating and we're probably looking at a 5kg (11lb) frame which would give you a 38-40lb bike. Obviously, that’s a little overweight so before we move to second-gen prototypes a large part of the development will be shaving off some of that mass. We aren’t aiming for the Slacker to be a featherweight but its clear from this process that there are savings to be made. As a target we'll look to take out around 600g before the next round of prototypes. We have a few ideas on how to achieve this, but more on that later...

As a first prototype the main purpose here is proof-of-concept, a mule to work out kinematics and geometry and a vehicle for us to test any new ideas.So the teardown is more or less what we'd hope and expect from a first draft. As you'll see in the next few chapters, we've built them in different ways and done a bunch of ride testing to there's a lot of learning to come. Barring any epic fails we would hope to move on to second- and possibly third-generation prototypes aimed at refining details and moving the whole project closer to something that's production ready.