[EV-4-Me]

For those of you not on the Facebook page, (where I already detailed a bit of the effort) a team of guys including myself built a bike to go to the 2021 Bonneville Motorcycle Speed Trials this past week. We ended up going significantly faster than calculated, with absolutely fantastic salt conditions (best in years). We managed 12 total runs, with only one mechanical failure (broke a chain) and no electrical failures. Our slowest runs were the first two of the week, unfaired, at 140mph. We ended up the week with our fastest run at 167mph average across the mile and 172.7mph peak. We should end up with a certified national record just under 167mph.

The records in our class, AMA sub 150kg A and APS-Electric, were previously 114mph and 113mph. While we didn't register for the FIM equivalent classes, those records were each ~110mph, making our motorcycle, unofficially, the fastest electric motorcycle in the world under 150kg. Pretty cool!

 

[EV-4-Me]

Congratulations!

The bike looks good; even in bare form it's a clean design.

It's good to see that Bonneville went well for at least one EV team this year... the cars and and an enclosed motorcycle didn't fare so well during Speed Week earlier in August.

Bonneville Motorcycle Speed Trials (still showing only 2019 records and results; the 2020 event was cancelled)

As far as I can tell from the rules, "A" is a frame classification of special construction (i.e. not production), and "APS" is the Partial Streamlining variant of that. "W" is the engine classification for electric, and there are specific technical rules of electric vehicles (section 3.22-L-24), with three classes by weight (up to 150 kg being the lightest).

Yep, that's correct! The FIM class is the same, but has a much more stringent rule set for drivetrain design.

If I remember from my basic aerodynamics training, for stability, you always want the center of mass ahead of the aerodynamic center. This applies to aircraft, rockets like the new Spacex Starship, and motorcycles, particularly with dustbin type fairings, like this one. One advantage with electric bikes is that the batteries can be easily moved around to adjust the center of mass. Notice the batteries shifted to the front of the lower battery box. I'd be worried riding this bike if I raised my head up at the wrong time, the aero center might shift in front of the center of mass and cause stability issues! Have you noticed any problems with this?

Great job on a what looks like a fun project.

Good catch! The batteries are actually heavier in the rear of the box, with three of our five strands rear and two front. The extra volume in the front of the box is for the BMS stack, disconnect, connectors, and buttons. Based on what people told us of the friction coefficient, we thought we'd be traction limited to around 145mph with fairings. When we significantly exceeded that, we found the Cp estimation was off. We added more trail and shifted our ballast to the front of the bike to compensate and never had any issues after that.

 

[EV-4-Me]

What did you use for ballast, where is it located, and how much did you use?

In the unfaired runs, we needed more weight overall, so we used qty. 2-2lb diving weights and qty. 2-7lb lead bricks. Those were all located under the driver's crotch. We removed the two 7lb bricks, but kept the diving weights in the same location rear for the first two faired runs where we found out we had an instability. From the 3rd run on, we kept the diving weights about 6" from the head tube, both on the left side, since we have a significant right-side bias (motor hanging out).We also added more fork preload and dropped the tubes in the triples about 1/4" and that fixed it.

 

[EV-4-Me]

I think y'all are both correct, though multiple battery boxes is always a compromise I think should be avoided. Doing it correctly and safely means another set of contactors, busbars, heavy outside conductors that are difficult to manipulate, more mounting tabs, more mounting locations, is tougher to maintain isolation, etc...

We removed as much weight as possible after the major items were placed by grinding tabs, removing superfluous parts, adding speed holes, moving small items, and optimizing wire harness length, specifically to be able to use as much ballast weight as we could. Without advanced software tools for CFD, or wind tunnel time, we considered our Cp estimation to be a pretty rough educated guess, so needed to be able to make some significant weight changes.

There's a lot we'd do different if building from scratch. The frame we used is actually from an attempt in the late 2000's that never went anywhere and was designed for an IC engine, so we made some compromises to avoid changing the frame structure significantly, just for sake of keeping the build timeline in tact. We started this project in earnest in late January, though we first got the frame in November 2020. For example, we have a hella long chain. Had we been able to fit it, we would have put the motor as far back as rules allow (tangent to the front of the rear wheel essentially), then used the then wide-open front space for the battery box. They weigh within a couple pounds of each other, actually, and it would have made internal box packaging far, far easier.