Catching Feelings: Scooter Build, Pt. 2
Aside from the legal considerations, it’s now time to make a whole bunch of decisions about how this thing is going to work and what it will look like.
So the designerly bits:
I’m weighing the merits of building a reverse trike (two wheels in the front with a driven wheel in the back mounted on a spring arm or something similar) versus building the standard two wheeled variant that everyone is used to seeing everywhere all the time. I very much like the idea of a reverse trike as it provides a substantial increase in stability and potentially also utility (cargo box) plus it’s just different however it also increases complexity a great deal. I would be remiss if I neglected to also mention the Aprilia Magnet concept:
The Magnet is the brainchild of a then-student named Heikki Naulapaa who used this as thesis justification for graduation from the Royal College of Art in London in 2004. Clearly this concept firmly lodged itself in my brain pan because I saw it for the first time 12 years ago and I haven’t stopped thinking about it since. I also love Formula 1 racing with my every fiber and the semi-recent release of the BAC Mono has only rekindled my love for the form.
On the flip side, a two wheeled vehicle is unquestionably far more mechanically simple as it lacks a steering rack. An OEM replacement rack can be bought very cheaply, especially if buying a used part, but the supporting structures are fabrication intensive. A two-wheeled scooter would also allow for a higher degree of maneuverability and would also be far lighter than a reverse trike. This weight concern, given the extremely low maximum power specification for scooters, is a heavy (no pun intended) one. A scooter that accelerates slowly on the road is certainly less safe than one that quickly gets up to speed. Obviously this problem can be overcome with proper gearing- and most OEM replacement scooter engines come with a built in continuously variable transmission- but it’s still something that I’m going to contend with throughout the build regardless of whether it’s two or three wheels.
I’m also using this as an excuse to flesh out some skills in Fusion 360 that have not directly transferred over from my prior in-depth knowledge of Solidworks. Specifically, the surfacing in Fusion is still a little bit of an unknown and feels a lot more like shaping clay than dragging vector lines about to define form. I’m looking forward to modeling the whole assembly as completely as possible so that I can perform some serious finite element analysis on the geometry. At this point, there’s no question that a trike will perform better under load and be more protective of the rider (me!) than a two wheeled design; I strongly suspect that the FEA will confirm this and more.
The last big mechanical design question is whether to make this vehicle gas or electric powered. For me, the clear winner in a perfect world is electric any day of the week. The motor is far smaller meaning that it can be shoehorned into tighter places on the vehicle which in turn would help limit overall size and therefore frame weight, replacement electric motors are way cheaper than replacement engines, and there’s ostensibly less maintenance required to keep the motor spinning. The batteries are definitely a limiting factor here in that they are extremely heavy; the plus side is that, unlike a gas tank, the batteries can be distributed as low as possible on the frame and spread evenly across the assembly so as to improve balance. Finally, electric motors benefit from instant torque which is a HUGE advantage over gasoline engines especially in a lower speed application such as this one. The biggest downside to the electric motor versus gasoline engine debate is one of cost. While the motor itself is cheaper than a gasoline engine, the battery pack and associated control system drives up the cost a lot. A quick back of the Field Notes calculation guesstimates that an electric power system (motor, batteries, speed controller, and incidentals) would run about $825. That build out assumes the use of eight of those batteries to hit the correct voltage. As the motor would be de-rated to comply with the law, I think it’s reasonable to assume that it would draw an average of 40ish amps during use. Assuming that 40 amp draw, the batteries would last for about three quarters of an hour which- at a constant top speed of 30 miles per hour- means that the range is about 21.5 miles. Realistically, I would never want to drain the batteries to completely empty as this can severely damage the battery pack so a good guesstimate for effective range is probably closer to 15 miles. As I won’t be taking this thing for any long journeys throughout the great state of Rhode Island and will exclusively use this for bopping around town and the quiet places west of the city, the range is acceptable.
A gasoline engine on the other hand runs $250 when new. I can probably pick one up for much cheaper used from a salvage yard or a recently crashed vehicle. The range on such a powertrain is practically unlimited as gas stations are ubiquitous. Additionally, the mileage on these engines is borderline insane- 80 mpg is a very conservative target.
Ultimately, I think it’s going to come down to cost as like all things in life sooo… gasoline? It still may be possible to get a cheaper battery system. If I find one, I will install it.
In the meantime, if you or someone you know has recently crashed your/their scooter and the engine still works but the rest of the bike is totally effed, shoot me an email. I’m interested.
Marco Cross is a traveling potted plant salesman and industrial designer/design strategist for hire. His website is www.marcocross.com.