Aug 21, 2015 | By Simon

Although we’ve seen a number of unique 3D printing projects focused on changing the way we get from Point A to Point B, many of these have involved next-generation world-class design for race cars, airplanes and rockets utilizing advanced metal-based processes such as direct laser metal sintering (DMLS).  Yet for one Western Australian man, this involved little more than an old broken petrol-driven bicycle and an UP Mini 3D printer.  

(photo: David Kitson)

After finding the bicycle in a pile of trash over Christmas, David Kitson(46) of Stratton repaired it back into working condition. "Over Christmas, I found an old broken petrol-driven bicycle being thrown out on a rubbish pile." Kitson told us. "I repaired and rebuilt it and this introduced me to powered-cycling, which is fun, but the bikes had a lot of problems and ran off 2-stroke fuel which means you have to carry fuel with them. At some point, I decided the smelly and noisy bike could be improved on, so came up with the idea of a 4-stroke model, then thought about making it a hybrid."

Since he had already spent a good amount of time using 3D printers to create night vision equipment and develop military replacement parts, he knew that he could make the micro-sized generator parts for new hybrid design directly from his 3D printer.  

"So as the idea to build a micro-sized generator progressed, I needed to make a flange to hold an electric motor and a petrol one together to see if making a small generator for a bicycle was possible, as all the ones that could be bought were too heavy," Kitson said.

Through an iterative process that involved modeling test parts and redesigning them based on tests, the resulting parts ended up working much better than expected.

"Now my question from the 3D work with night vision came to mind and I wanted to know just how strong I could make a flange, and they got bigger and more complicated." Kiston added. "Then I started printing internal structural parts. After a while, I said 'Hey, I can actually probably build this entire thing 3D printed, with just components bolted into it' and then it became a challenge on how to print something that large on the PP3DP UP Mini 3D printer." 

“I went back to the drawing board, well, CorelCAD application, and when I finished, I had something that worked, but not well,” Kitson told 3Ders. 

“A few modifications though and it worked extremely well. Then I began working on how to eliminate everything that wasn't 3D printed and also that wasn't COTS ( Commercial off-the-shelf ) and succeeded with everything except the electronics components. It all slots together and I reduced parts count dramatically.”

An early part that failed under testing while investigating how strong the components could be made. ( failed at 1 kW )

By the time he was this far along in the process, Kitson began to realize the true potential of the vehicle - particularly in being able to commute to his day job on the bike for less than ¼ the price of public transportation.  Additionally, any parts that broke could easily be re-printed and replaced for a very low cost.  

“From a 3D perspective, it’s almost a work of crazy art, in that I’ve been wracking my brain at every stage working out how to build huge parts in a UPMini within the small build volume of 120x120x120mm,” said Kitson.

The torque transfer plate is 3D printed, yet gets the power from the engine to the generator. It uses steel bolts under tension to act as "pre-stressed" inserts to keep it operational. Estimated life - 100 hours ( current part still under test ). Costs a couple of dollars to print.

“I decided to try and make everything that wasn’t commercial (off the shelf) 3D printed, which means all that is required to build one is essentially a 3D printer. Congestion on roads is getting worse, and they keep looking for alternatives.”

Ultimately, Kitson calculated that it was cheaper to build and operate the generator over the lifetime of the cycle, including the cost of fuel, than to get batteries that even came close to what the petrol system could put out, both power-wise and range-wise.

The battery compartment without the 120kg nylon straps ( cable ties ) - Uses 12.5mm wide cable ties to hold everything. VERY strong. Green = batteries and electronics. Cyan = 3D printed braces.

With the straps installed - the batteries are now locked in, yet easily removed by taking out three straps. Straps cost about $0.50 each.

Since his epiphany, Kitson has been actively developing and updating his design with over 40 hours of testing and counting in the latest version alone.  "Maintenance is simple and it gets me 25km ( about 16 miles ) into the office just as quickly as public transport or vehicles on heavy traffic days, yet at a fraction of the cost. Most importantly, because I don't have to over-exert myself, I don't sweat," said Kitson.

However - as to be expected - the build didn’t come without its unique set of challenges, too.  Among others that Kitson has had to consider is preventing the ABS material from which is parts are made out of from heating up.  To solve this, he channeled a high volume of airflow through the part to keep the temperatures as cool as possible.  According to Kitson, it was small discoveries and challenges such as this that built upon each other to determine the most optimal design for each of the other parts.  

"From that perspective, I guess I kind of just fell into it stage by stage," Kitson added. "I didn't know where the trip was taking me, I just wanted to play around, and before I knew it, each small discovery built upon the last until I had made it to a functional hybrid system that worked as I had originally envisioned. I found myself wanting to find a way to build a hybrid electric/petrol bicycle that people could order online, print parts at home and then assemble in about a few hours." 

Another early printed design that failed under operation on the test-bench - The printed body couldn't handle the torque at full speed -  This led to design changes in the way forces were allowed to be applied to the printed parts.

In total - aside from the actual internal combustion engine, the electronics and the generator core - every part of Kitson’s design has been 3D printed including everything from lever arms on the throttle control box and air filter plates to electronics cover panels and the generator coverings.     

“Overall, many parts I thought couldn't be used straight out the printer turned out possible - it just took a little thinking about it,” said Kitson.  

“I also designed things in such a way that little support material was needed or had to be removed. That really helped, both saving plastic as well as reducing difficulty of manufacture. The engine mounts are 3D printed too. The motor just slides on and off the rear bicycle rack.”

To print all of the parts, Kitson used “a few hundred grams” of  black ABS 1.75mm filament over the course of many, many hours.  While he hasn’t kept track of the total amount of time it’s taken to print all of the parts, he does recall that the longest print time for a single part was 10 hours while smaller parts typically take 2 or 3 hours on the “fast” setting, since quality isn’t an issue.  He estimates that if one were to print all of the parts from scratch, a full system would take about 3 days in total on the UP Mini 3D printer.   

As for what’s next with the project, Kitson is following in the footsteps of so many other independent hardware developers these days and wants to make the design plans free to download and 3D print for all, however he would eventually like to sell some components - such as electronics - for those who prefer a pre-assembled option and to cover basic operational costs.

All the printed components of the Mk1. ( Protype #7 ) - Parts in Cyan and Red are electronics. White, Purple, Yellow and Blue parts are all 3D printed ABS plastic. The parts assemble and are held in place by just 4 primary bolts. All images credit: David Kitson

“With this project, it will finally be possible for disabled people and people who cannot ride distances without assistance to use bicycles for touring, and to explore places and parts of our country that are not available to those with un-extended electrical systems.”

With a range of 50km on a single tank, Kitson’s design is capable of travelling about five times what the top electric systems can at full power. "It would be suitable to around 80% of commuters that aren't strong or fit enough to ride a bicycle a long way." Kitson said. "Unlike the European standard bicycles, the full system I developed will actually add it's power to whatever you put in, so the benefit of pedaling is that you get there quicker and you can take a break whenever you need or want."

And it’s been confirmed by the Western Australian Department of Transport to be street legal. "The system conforms to the EN15194 standard as well ( Clip-on charger exceptions ) so should be legal in most of the world." Kitson added. "It also meets safety and emission standards for small motors, so the applications to which it can be put are far beyond small bicycles."

For his future projects, Kitson wants to develop stuff that can be made on small home 3D printers. "I've been looking into a lot of ways that 3D manufacturing can be taken out of the rapid prototyping era and into practical application, even with smaller printers. Why can't we build stronger parts? Why is anything more than a small printer needed? This project really challenged me to think outside the box to create large strong parts from smaller components. I can't print a large battery box, but I could print several heavy-duty brackets and use 120kg cable ties to make a battery compartment. Maybe ABS plastic isn't that hard, but if you can design stuff right, it can take a lot of load."

Kitson, who also wrote Turing Evolved, a science-fiction novel that was ranked as the #1 best techno-thriller on Amazon in 2013 for 6 solid months, has long held a fascination with technology and the “the edge of contemporary development,” including the near future of rapid manufacturing.    

“I guess that's the key to knowing where all of this is headed,” he says.  

“I looked at the past two hundred years and extrapolated forward to create a world not all that different to the one we're already living in.”



Posted in 3D Printing Applications



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Ion-Christopher wrote at 2/10/2016 12:47:38 AM:

I agree that it needs a trailer option that will double as a push cart. Public transportation becomes an issue with oil and gas so you would have to empty it out completely and then refill it for use. Think of that. As for the noise - I have these suggested avenues to consider besides the obvious of a far better muffler: * Gearing the generator to run about 5x faster than the gas motor (sandwiching an orbital unit in-between.) * Choosing a low RPM gas motor to power it (a stroker) * Containment - and active air, or passive water cooling

J wrote at 8/23/2015 3:09:34 PM:

Very Cool!

Kit wrote at 8/23/2015 12:03:47 AM:

Nice engineering project...though as a rideable ebike hybrid, it's going to be ass heavy besides making way too much noise! He would have had a better system by setting up the 4 stroke motor and generator on a "push" bike trailer and use it as a range extending backup to the rear hub electric motor (w/sine wave controller inside or out) and a 18650 cell 20ah range battery pack! This would be a dead silent ride.

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