I have a pre-build thread for my e-CRX conversion here on AEVA but I don't have a build thread for my new electric race bike. It's been a long and expensive journey to this point so I thought its time to share my experience. I do have a full build thread on Endless-Sphere, which you are most welcome to read, but for this forum I want to share not just what I did, but the reasoning and planning behind each design feature. So let's make a start, shall we?
Introduction
It all began back in 2011 when I'd built Voltron the electric Suzuki RG. It had a pair of Agni brushed DC motors fused at the shaft, they were wired in parallel from a 1200 A Kelly controller and 6 kWh of A123 lithium powered the 160 kg bike up to 180 km/h. Together with Dan and Jason/Jon, we made a bit of Aussie electric racing history. And it was a piece of sh*t. #89 was 'unique'. My building skills leave a lot to be desired, but the point is, I built it, I raced it, I had some wins and I had some DNFs. But boy, did I learn a lot from the experience. The bike handled like crap around corners, the motors were prone to overheat and throw molten solder, and the while bike was a safety risk should it ever get wet. I knew I had to do better. If I was to build another electric bike, it needed to be faster, have a higher thermal budget and be more 'modular' - that is, I needed to be able to pull each part off and put it back on again in minutes, not days.
What the new bike needed to be
1. It needed to be build from a proper racing chassis. Not some agricultural experiment from 1985. I had contemplated using a modern day sports bike as a basis - either a CBR or a GSXR. It would need to be based on a 1000 cc equivalent as these had the room and the strength.
2. It needed a single, very powerful motor. Not a pair of DC Indian smoke machines. AC was most attractive as brushes are a real weak point at high motor speeds. I needed it to be competitive with at least a 600 cc petrol bike - meaning I need at least 90 kW at the rear wheel.
3. It needed to be modular. I need to be able to hoist the battery out in one go. I need to be able to drop the motor out in minutes, or pull the controller out if I had to work on the suspension linkages. Essentially, I want to be able to do a full stripdown of the key parts, do a service and put it all together between races, not between seasons.
4. It needed to be rugged. IP67 type rugged. This bike is for racing, so it will be crashed and thrown up the road at 100 km/h. I'd like to be able to wheel it back to the pits and replace the broken bits and get back on track. Motorcycles can survive some fast crashes if they do it right, but not if the important components are held in place by compression straps and gaffa tape. I also wanted it to be raced in the rain without fear of shocks.
Donor chassis?
I'd not long had some success at Winton raceway when I started to make plans for the new bike. Where to start? Chassis, or components? Chassis selection was going to be tough as it limits your choice of components. I sought out donor chassis which had already been race-prepped. Eventually I settled on the GSXR1000. The 2004 GSXR had a huge main frame with enough room to fit stacks of cells and components. I even measured up a 2007 GSXR and it was even better - vastly improved handling with a big frame. I found a 2005 GSXR1000 for sale in Melbourne, and after much diligent saving, I bought it and had it shipped over.
And f**k me the frame was too small

It was looking increasingly like I need a fully custom racing frame - one without exhaust header bolts and countershaft mounts...
Motor selection
Around about this time I was trying to decide which motor I should use. I wanted it to be powerful. Stupidly powerful. More power than I would ever use in a race. Why? Because I needed my racing skills to be well clear of the thermal limits of the motor. My DC motors would have put out a mere 45 kW on a good day, yet they were always on the brink of incineration. Having more and using proportionally less of it eaves me with enough headroom to push my limits before the motors limits were pushed.
I learned that there was a certain power envelope which was absent in the electric motor world. This happened to be about the 60-90 kW region. It has since gotten better, but at the time I was a bit stuck for options. I could choose between the UQM Powerphase 125 motor, the Carbon motor, an Emrax motor, Remy, Yasa or Evo. One thing was obvious - power to weight was going to be the main driver here. And continuous power, not peak. When you are racing, you are hard on the throttle 90% of the time, so 'peak' just isn't good enough. Based on continuous power output, I needed something in the order of 2 kW/kg.
I'd narrowed it down to UQM, Evo or Yasa. Yasa was simply too expensive. It was a $14,000 motor, although on paper it's power to weight of 3.8 kW/kg might be worth every penny. UQM was also expensive - $22,000 but that included the inverter. It's power to weight was a bit low for my liking, and the size of the motor was hard to accommodate. Evo made two sizes - the AFM130 and the AFM 140. The 130 was 300 mm in diameter, while the 140 was 400 mm across. Remarkably, they were barely 115 mm wide. Axial flux is where the magic happened. Seems you can get much better power to weight by intersecting magnetic fields axially rather than radially. And torque! This motor has it in tiptrucks.
Lots of things lead to my decision to get the Evo motor. The $11,000 landed price tag was a bit hard to swallow, but it's certainly cheaper than the alternatives. But it had the high continuous power I wanted. The 130 or the 140? I settled on the 140 despite it's large diameter. On paper it claims 75 kW all day long, but the guys at Evo have tested it at 100 kW for several hours. They doubted the 130's ability to do this, but were confident the 140 could deliver. I committed to it

It needs high volts. There were several winding configurations to choose from, and I chose the AFM140-4. I will get to the rationale behind this in my next post.