Every morning I have to cycle five and a half painful minutes to the engineering campus. 'Could I possibly introduce some British comfort into this experience?', I thought. The obvious solution was getting an Aston Martin - which I would have done given the necessary pocket money. Since that was not given however, I opted for the next best option: a driving sofa. It was also going to be my first own car, and I would build it myself. At this point, I want to mention my friend Arno who supported me a lot throughout this project simply by believing in and hoping with me. It helps immensely to know that someone believes in your dream just as strongly as you yourself.

After watching a few YouTube videos, it became apparent to me that household tools wouldn't suffice for this project. Since I was not getting the most cooperative impression from the school of engineering, I decided to consult the Edinburgh College of Art metalworkshop. Over there I met the metal tech, Catriona Gilbert, who took my proposal surprisingly serious and agreed to training me on the necessary equipment once I was ready to start. I said "see you in half a year then", and that marked the end of a simple interaction that would allow me to make my dream come true.

I came to the conclusion that everything would need to be designed around the sofa - since I really did not want to build a sofa. One day, while I was getting a covid vaccine booster, I came across the Edinburgh Furniture Initiative store - a charity for 'cheap, quality, used furniture'. Music to my ears. So I walked in and fell in love with this blue sofa in the corner stacked on top of three other sofas. I loved that it was absolutely huge for a two seater, allowing space for luggage etc. So I bought it immediately for 70 quid.
The next question was of course where to store the sofa after taking dimensions. After all, the chassis (the driving bit) was not designed yet whatsoever, that would take some time. Edinburgh's Meadowshare - a facebook group - came in handy here as always. We luckily found a passionate couple with storage space to keep the sofa in. I got my Italian friend Massimiliano involved, and we transported the sofa through town on a 'borrowed' airport trolley from student accommodation.

Once the sofa was secured, the actual work started: Before doing anything, I have the Motorcycle Single Vehicle Approval by the Drivers and Vehicles Standards Agency a thorough read (a marvellous piece of literature). The important message right now: The maximum allowed vehicle width without mirrors is 2 meters. Lucky that the sofa turned out to be 1.97 meters wide!
At this point, I was planning on using a Honda generator engine, but I decided later on that the lawnmower engine sound would annoy me too much! So I opted for a bike engine, with the added benefit of included clutch and transmission. I also calculated the parameters for an electrical drive, but decided that getting stuck in the countryside with empy batteries wasn't for me.
On the modelling side, I fell in love with skeleton modelling which allows me to drive all component sizes through one master sketch.

The CAD models were (somewhat) ready - now the exciting bit. Massimiliano was helping me out again, albeit this sort of manual labour was quite out of his natural element. Catriona taught us how to use all the tools in the metalworkshop - MIG welder, sheetmetal bender, drill press... I even got an intro to operating the plasma cutter. For the school of arts, our ambition for precision was unprecedented - but Catriona understood. My stated goal was to stay within 1mm of the CAD model for all dimensions. With careful tack welding and a bit of material science, that actually worked out! We also managed to mount the 125cc engine I got off Ebay. The dimensions were too complicated to model, so Catriona helped me to "wing it" and we built an engine mount by trial and error. A key challenge was to find small enough wheels that are also marked as road-legal. I finally found some trailer wheels (which are not marked as such though), and I paid for them with a 100 quid voucher I won for completing a uni survey!

After a Spring and Summer of intensive building and designing,the school year was coming to an end - and the sofa naturally was not yet finished. Due to a lack of storage (and not wanting to pay a man with a van also), Massimiliano and I pushed this monstrum through the streets and across The Meadows to store the sofa in my flat. Sadly, our plan of driving it through The Meadows with a running engine did not work out, and as I later found out, could never have worked out: Disassembling the engine revealed that the flywheel was designed for a fuel-injection system that required an expensive, high-performance ignition and injection computer. I attempted to build one with an arduino and acquired some extensive knowledge about fuel injection and timing mapping, but decided to flip the engine on eBay and get a carburettor-powered Suzuki instead. That worked out well, and I managed to sell it with a 50 quid profit! The sofa would remain in my flat for one year while I was studying abroad at Cornell University, so that I could continue working on it when I returned.

Having the sofa stored safe and sound, I spent a final week on the engine subframe and rear axle. However, I noticed that I was lacking steering components and some pre-built assemblies actually functioned in different degrees of freedom than I had expected. I realised at this point that a substantial redesign would be necessary, but left it at that because I had to leave for my year abroad: Cornell Univesity! To be quite honest I had not informed myself much about the destination and was expecting a chill year abroad getting to know some East Coast culture. I could not have been more wrong! This place was absolutely intense. The teaching was excellent, everyone was giving 110%, professors replied to emails on a Sunday evening within 20 minutes, 16-17 hours of work a day... An academic transformation with a $90k/year sticker price + your soul. Criticism aside, it changed me as an engineer: We were taught in a much more rigorous, application-driven way, and a fascination for Aerospace and Embedded Systems grew on me. Nevertheless, I got to know a few people closer who gave me quite intimate insights into what lives one can live in this country. I am so grateful for these connections!

As mentioned previously, I had left Edinburgh with the realisation that my sofa was not going to work out how I thought it would. A substantial redesign was necessary, which I called Model 3 (Model 2 was a poor design I came up with at Cornell, never implemented) and I changed my approach: Instead of solving mechanical constraints with solutions I invent from scratch, solving issues when I run into them, I would research industry solutions extensively and then modify these for my needs. I decided to acquire a go kart double wishbone suspension kit and modify it to the width of the sofa. Furthermore, I would implement an Ackermann steering linkage to maximise traction while cornering: Driving in a curve can be viewed as driving in a circle with a large radius, but the circles each wheel on an axle is travelling on have different radii. Therefore, there is a specific difference in steering angle between both wheels that has to be implemented for every steering wheel position. I spent three nights getting a first-order trigonometric intuition and then a 2D CAD sketch for fine-tuning to finally design the linkage from sheet metal.

I do not only take the train from Germany (where I grew up) to Scotland because of the climate. Stepping out of Waverley Railway Station is just overwhelming - a yearn for action overcame me, and after sharing an excellent take-away with my good old flatmate Henrik, I set to work the following day. During the design phase, I had developed some Python scripts that gave me more accurate weight predictions. Coupled with Finite Element Analysis for the frame structure, these informed my decision to rebuild the frame from smaller, 40% lighter steel cross-sections. What followed was a 6-week, 8 hours a day marathon of metalworking in the day and designing and refining at night.

As mentioned, I had ordered a new engine, original Suzuki with 8k miles on it. Henrik, my expert for engines, helped me get her running, and the feeling of success when this thing started spitting flames like a machine gun in our backyard was marvellous. Sure, the timing was still a bit off, but she ran!! This also marked the point where I got a lot closer to Yordan, a fellow engineer and crazy genius. He helped me with adjusting the clutch springs and generally helped me with welding the frame, as well as some hardcore 16-hour painting sessions later on.

My six week marathon was sparked by exceptional workshop availability during August of which I took full advantage. Contrary to the first time, my beloved plan-execution approach worked out so nicely. It is quite fascinating to see the things you are envisioning coming true at such a pace. I rebuilt the whole vehicle from scratch, with loads of information gathered from the first attempt. Getting the double-wishbone suspension aligned at a 4-degree kingpin angle symmetrically challenged my manufacturing skills to the limit. One-handed welds in awkward angles, estimating heat dissipation and material contraction... It was so satisfying when it all worked out in the end. The CAD model had turned into reality, precisely. Bending the exhaust properly was another brain twister - thank you Catriona for your impressive geometric intuition! Lastly, the custom sequential gear shifting mechanism worked out easier than I had anticipated - so satisfying!

The metal chassis frame was finished, but there was one thing I had neglected completely: the actual sofa! One day was spent where the three woodwork technicians helped me dismantle the sofa and apply reinforcement wherever possible. I had not deemed it necessary, but one of them mentioned quite rightly that the current stability of this piece of furniture might suffice for a living room, but not quite for burnouts on the M25!

After first experiences with the actual sofa, the next step was to turn this into a luxury vehicle - with the appropriate cushioning. To maximise its chances of survival in the wild, I stripped the sofa down to the wood. In two 8 hour non-stop painting sessions till late into the night, trying to capture good weather windows, Yordan and I waterproofed the sofa with woodstain and painted the frame. Now the elements could not do much harm to it anymore.

You cannot believe how quickly blank steel rusts. Half an hour outside, already that stuff starts showing up. In an arduos fight against the rust, Yordan and I sanded, ground and painted in tandem, whipping paint into every corner we could cover till late at night with our phone torches at 5% charge. The frame looked as beautiful as a nice English black fence in Surrey afterwards. During this time, I also managed to acquire a steering wheel from an old VW Beetle, as well as an indicator stalk switch from a Dacia Duster 2008.

The thing I worried most about in December was certainly not my four exams, but how I will deliver on my promise of making this sofa comfortable. I did not know anything about upholstery, and I quite frankly don't have a hand for it. Mentioning my struggles, a medicine student in the makerspace interrupts me: Panav owns an industrial sewing machine and is experienced and confident in upholstery projects. Why am I so lucky? He was prepared to take the lead here and not only assist me, but work out detailed plans on how to tackle this. We envisioned four layers: A structural layer of black airport flooring (I had acquired this in a village close to my grandparents in Germany, with a lot of begging. Don't ask me how Lufthansa didn't prevent me from bringing it all as hand luggage.), a layer of blue foam, a waterproof cover from pool toy plastic material, and finally the dark blue cover the sofa came with. In an intensive three week act, we managed to put this plan into action, ending with a robust and comfortable piece of furniture.

The electronics are a chapter I had massively underestimated. Designing a relatively complex network of relays and combining these with constraints like wire lengths and associated voltage drop, automotive connectors, ground noise and power draw introduced many interdependencies for construction. This means that it is not entirely clear what the next step is because many things depend on each other. The main thing I learned for my engineering career: incremental testing! Design the smallest component, implement it, test it, then go a step bigger. Test everything with regulated power supplies, preventing fried components and having to hunt down obscure issues later during integration testing. This process is still ongoing, I'll keep you updated...

Another detail I underestimated was the speedometer: Oddly, most speedometers nowadays are still driven by a mechanical cable rotating in a sleeve. They move the needle via a fixed gearing mechanism, which is unhelpful considering the very motorcycle-unlike size of my trailer wheels. Since this gearing would be near impossible to adjust, I considered getting a newer type of speedometer that takes readings via a magnet on the wheel and a hall-effect sensor similar to a bicycle computer. Unfortunately, these proprietary devices have fixed wheel sizes to choose from hardwired into the chips, if there is any choice at all. I concluded that I would build my own speedometer circuit, and bought a 1970s Classic Mini speedometer which I completely took apart and cleaned up with the grinder. Very soon, I will connect automotive gauge stepper motors (x27.168) to the needle controlled by an arduino that processes magnetic pulses.

Two and a half weeks of trying to get the engine running... devastating. Richer mixture, leaner mixture, spark timing, starter battery charging, pilot screw... I tried everything. The engine would just not run. My flatmate Henrik, expert of 1950s motorcycles, was also at a loss. I turned to my last resort: Posting on r/motorcycles on reddit. Ohlav, a biker from Brazil, got back to me with clear instructions. Smaller carb, smaller jets, tuning strategies. Something combusted. Neither on time, nor regularly however. After days of live support from Ohlav, me uploading videos of the newest settings to google drive, he giving me feedback what to change, we managed to get it running. On a good day. At some point, I got it pretty reliable. Arno was in town, and I wanted to show him the engine running. He was quite excited, so I thought, "why not try driving it?", and it drove. The clutch and gears without indicators whatsoever took a while to get used to, but the success was evident.

Sadly, my wonderful uni life was bound to end at some point and before I had even graduated in June, I started work life at GE Aerospace in Cheltenham. The move to the South was significantly complicated by my unusual piece of furniture, so I hired a man with a van to drive the sofa down. Packing was no where near completed two hours before the van arrived, but somehow it all happened in time. Starting my job two days after moving, I now had to find a flat and a place for my sofa alongside a 9-5. Unfortunately, I did not face a very "cooperative environment" and struggled immensely to find a place for the sofa. At a desparate moment, I was locking the sofa to a tree on the sidewalk, receiving a threat by the council the same day. I was very close to giving up the project and saw no way, when I tried my last idea (just to have tried) and more or less broke down at the local Indian takeaway which I had befriended the week prior. "Now you relax first and have a Chai", followed by 5 minutes of intense phone calls, and the cook had actually found a place for my sofa at his colleague's house. Phew!!

Wiring everything up was throughout this project a tremendous task in my head, and it turned out that I required multiple attempts. When I had started earlier in the year, my connectors were by far not robust enough, and my strategy was far too ill-defined for the complexity of the task. Back then, I had come up with a sequential tree-like approach where components are connected via branches to nodes. For example, the battery was the top-level node, which had the ignition switch as a leaf, the alternator as a leaf etc. Then, the ignition switch would be another node that distributes power to the indicator switch etc. This approach was simple on a high level, but deriving the low-level physical wiring layout from this proved very complex. Inspired by the concept of a "line replacable unit" from work, I now derived a new architecture driven by functional requirements. With the objective of maximising maintainability and reducing debugging efforts, I concluded that most faults would occur on components instead of wires. Hence, I opted for a bus architecture, essentially providing connector interfaces to a wire harness so that components could plug into a harness system that connects everything. If a component fails, it can simply be unplugged from the harness and replaced. Wire colours were introduced which were assigned sequentially by "nets". For example, everything in the "post ignition switch" stage is orange, the left indicator power circuit is green and so on. That way, fault levels can be specified: If only one indicator fails in the front, then the fault level is low and one only has to consider the wire colour leading directly to this indicator lamp. If all four indicators fail, the fault level is most likely higher up around the indicator switch since it controls all four indicators.

Technically (according to the inspection manual), I could have kept my very simple, unprotected steering rod as is for approval. As my coworker noted however, the steering column had bent under some load and the current situation was not really "nice", albeit viable from an engineering standpoint. Hence, I decided to upgrade and thereby also simplify the steering arrangement by running the steering rod in a fixed outer tube, which would also mount the speedometer and indicator switch. This would lead to a more sturdy steering experience, weight savings in the front (critical for dynamics) and the opportunity to flexibly upgrade the steering rod diameter if more strength is needed later on. I also re-ran some steering torque calculations to get a safety factor on the rod of around 1.8 (decent, with opportunity for future improvement).

The MSVA manual prescribes mirrors which enable the driver to overlook a prescribed region. Luckily, these do not count towards the width of the vehicle, an initial worry of mine! I will probably take a look at some quad mirrors...

Seat belts are the only aspect of the vehicle which the DVSA places some structural rigidity constraints on. And these are significant: A seat belt anchoring point

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A particularly difficult road legality requirement to check is external projections: no object on the front or sides of the vehicle shall have an edge radius smaller than 2.5mm, all edges have to be blunted, and many more specific rules. To fulfill this, I will make use of 3D printing and epoxy resin glue. I dread this work a bit, there is so much to consider...

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