Model based Design (or How the Sausage is made...)
Read below for the second part of Ely's take on everything Lightfighter...
Regarding how the Lightfighter came to be, the process went something like this: First we chose our ideal parts based on Brian's and my past experience with electric race bikes; primarily the electric motor, the drive inverter and the battery cell module but including the more generic bits like wheels, forks, tires etc. A number of factors were examined here although we generally defaulted to cost, familiarity and availability. It helped if sponsorship was in play or if a partner was willing to support the cause with parts. Next, I made 3D models of all these existing parts, with as much detail as possible. In some cases, the manufacturer provided these models but generally I would physically measure and make my own 3D solid models to digitize all the parts using Solidworks modeling software.
We always assumed that this bike would be competitive against 600 to 1,000 cc sportbikes, based on the known power specifications of our proposed drive system. With that target in mind, we chose a 2015+ Yamaha R1 as a baseline for the critical geometries; wheelbase, rake, trail, chain line and drive sprocket positions, shock linkage pivots and so on. Note this could have been any one of a number of modern track day sport bikes as they are all similar in design, but Yamaha established the benchmark. I then made a background sketch of the R1's various coordinates as a flat 2-dimensional side view template to construct our 3D bike over, with a firm rule that any deviation from the Yamaha geometries could make the bike not handle like the iconic Yamaha. Yamaha chassis dimensions are widely known and published online, which helped a lot. I also made a template in CAD that delineated the minimum safe lean angle (50 degrees) as dictated by AMA Racing Tech Inspection. An obvious concern early on was the width of the Parker motor; a potential game-changer.
A motorcycle chassis is a complex bracket that integrates several disassociated parts into a unique high performing entity. As such, it establishes the motorcycle's identity. Other crucial parts like wheels, brakes and suspension are fairly generic; you can interchange them from OEM to aftermarket due to their commonality, but the chassis defines the essence of the bike. We designed our Lightfighter to feel as awesome as the Yamaha R1. Full stop.
After a few months spent modeling all the existing parts, it was time to start putting them into an assembly and creating our own proprietary chassis design. For me, this is like playing with Lego toys. I have all these dimensionally accurate and complex 3D motorcycle components in a virtual world where I can easily flip, mirror, rotate, copy and position them. The various parts all get mated to one another in a 3D workspace. I control their positions relative to the background Yamaha sketch to the nearest millimeter then mate them up so the model has both integrity and structure, as if I were actually bolting metal together. If holes don't line up right, it means the models are wrong and I stop and fix it. I treat the model like the real thing because it has all the agency and dimensional seriousness of the real thing. I will soon use my modeled parts to create and drive CNC toolpaths so it needs to be a perfect representation of my design intent with all the sniggly details fully featured in the model. If a virtual dimension is off one thousandth of an inch, the actual machined part will include this error six months from now when I make it!
Once I had everything positioned in the model, I started connecting the dots with virtual steel tubes. Much of frame building involves cutting, bending and fitting and welding chrome moly aircraft tubing; that's the fabricator's art. But shape-wise, a frame designs itself to some extent, based on the positions of, say, a threaded motor mounting boss. Or the angle of the steering shaft of my fork model or the position of the swingarm pivot. I proposed a frame initially to Brian for his feedback and sent him a completed side view of the proposed bike with the frame, wheels, tires, motor, battery, etc in position and scale. He quickly rendered over it with ink and we did that back and forth for several iterations, taking into account Brian's concern for track worthiness and my concerns for manufacturability. After all, I had to make it and he needed to race it, so it was a productive feedback loop with a great race bike as our common goal. It really helps to trust each other at this stage!
We finally came up with a frame design we liked so I started to design the frame weld and assembly fixture. This involved creating a new solid model assembly file that starts with our derived frame model fixed in virtual space. On the actual frame, all the frame tubes and the attachment bosses and brackets need to be positioned and held rigidly for real world welding, so I construct an armature structure that accurately locates all the parts that bolt to the frame. In this case, I chose 1” x 2” aluminum flat bar as my fixture medium. This is what the entire fixture will be made from. It's crazy strong and fairly cheap so I buy a full length of it so I have plenty on hand to hold whatever needs holding. The fixture parts (in purple) are located and pinned in position with 2 steel dowel pins and a single bolt (not shown in this picture). This way, as the frame gets tack welded together, I can remove the fixture parts once they're no longer needed and get better access for final welding. If I do everything right, the welded frame can be put back in or out of the fixture easily, which confirms that no twisting or warping occurred during the welding processes.
One awesome feature of Solidworks that saves tons of work is called parametric association. This means that if we decide later on that the wheelbase, for instance, needs to be shortened a half inch, I can simply go in to my original 2 dimensional Yamaha background sketch (remember that?) and move the coordinate that established wheelbase. Since the frame model is associated and derived from that sketch, Solidworks will modify my frame model accordingly. It will also update the weld and assembly fixture parts to reflect the change. It's similar to how your word processor re-positions text if you delete a sentence or paragraph, but much more complex. It has to do a lot of math! And it does the changes across all the files associated with the main assembly. Usually, I delete or suppress the parametric references once I have 'frozen' a part's design, to avoid unintended changes. It's important to keep the 3D assembly files stable because it's the only tangible deliverable asset from several months work, at this stage.
The Motor/ Gearbox Unit
Early on, it was clear that the Parker-Hannifin motor in its standard commercial package was too wide to fit in our preferred position; low and near the ideal center of gravity. It was also quite heavy as it was designed for heavy 4 wheeled vehicles. So, I decided to compact their design, figuring I could squeeze away an inch from each side provided I shortened the rotor as well as the main stator case extrusion. And since we needed a reducing gearbox to optimize the performance profile of this motor, it meant new end cases were in order so 'just do everything it needs' was my mantra. In the end, I had to completely repackage their motor. A few simple mods would not have worked.
Most motorcycle engine integrations, gas and electric, require two stages of gear reduction to the rear wheel. Doing the math, we found that roughly a 2 to 1 reduction in the first, primary stage gearbox and 2.5 to 1 for the secondary, final chain to rear wheel would put us in the 150 MPH ballpark. I chose helical gears instead of straight cut 'racing' gears for our primary drive because electric motors are so quiet, the whine and ringing of straight cut gears would surely be annoying. Helical gears' efficiency penalty is nearly negligible and the quieter running should reduce rider fatigue. I chose to use a third, intermediate gear, which allowed better control of the position of the countershaft sprocket, without changing the MGU (motor gearbox unit) overall output ratio.
Machining away 1 inch from both sides of the main extrusion of the Parker was pretty straightforward as there was a lot of dead space in their design. But in doing this, all 16 of the end case attachment bolt threaded holes needed to be rethreaded an inch into the original extrusion.I also added 6 blind tapped holes in their extrusion to attach the shock linkage pivot which is usually part of a typical (Yamaha R1) extruded aluminum spar frame. This let me position the shock bellcrank anchor where I wanted it, referenced from the 2D background template.
I redesigned their rotor by first removing the crazy powerful magnet stacks so I could machine the rotor without it sticking to the CNC machine table. These big honkers will cause big damage to life and limb if you aren't careful. They are very attractive (groan). The rotor was shortened and I threaded and added a drive keyway for the new rotor pinion gear. The original rotor used a long splined output shaft but there was enough 'meat' to allow my reworking it an inch shorter. I also hollowed out the core to lighten it by about 25%. Then I pressed the magnets back on and had it balanced.
I used a jackshaft to put a stock Yamaha style countershaft sprocket on the opposite side of the MGU from the primary gearcase. By having the secondary and primary reduction sets on opposite sides, it allows you to keep both gearsets narrow and keep the motor mass centered. Otherwise, the motor would need to be offset, increasing the MGU width beyond the AMA legal width for lean angle clearance. Not too suprisingly, almost every gas bike is also packaged this way for the same reason; it's more compact.
The new endcases I redesigned have removeable main bearing bosses so the motor can be disassembled without presses or special pullers. I added frame and swingarm attach bosses on both sides and redesigned the Parker coolant manifold to a narrower design that increased our lean angle clearance and made tidier coolant hose routing.
...And that's where Ely stopped. I'll press him for a follow-up, so please leave other areas of the bike or topics you'd like to hear from him about in the comments.
If you enjoyed all the details in this post, check out this one from awhile back as well: Building Lightfighter v2.0 (lightfighter-racing.com) - Brian.