[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!

 

[brian_]

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 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).

 

[electro wrks]

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.

 

[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.

 

[brian_]

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.

Yes, but if the centre of aerodynamic pressure is too far behind the centre of mass, it is apparently difficult to control the vehicle - to make it turn if you need to. One of the fully streamlined two-wheeled entrants at Speed Week made a video about that.

One advantage with electric bikes is that the batteries can be easily moved around to adjust the center of mass.

But the battery is also bulky, and tends to fill almost all available space, so it can be hard to move much. There is likely more room to move the relatively dense engine in a conventional vehicle.

 

[electro wrks]

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.

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

 

[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.

 

[electro wrks]

Yes, but if the centre of aerodynamic pressure is too far behind the centre of mass, it is apparently difficult to control the vehicle - to make it turn if you need to. One of the fully streamlined two-wheeled entrants at Speed Week made a video about that.

Yes brian, you do not want to overcorrect a problem and then create another problem. The main task at Bonneville, AIR, is to point your vehicle in a straight line and try to keep it that way for the whole speed run. Unless, coleastering, you were on some kind of slalom course.

But the battery is also bulky, and tends to fill almost all available space, so it can be hard to move much. There is likely more room to move the relatively dense engine in a conventional vehicle.

Do you mean an ICE vehicle as a "conventional vehicle"? In my crazy ICE car days, the first thing we usually did to improve the balance of the vehicle, was to move the 12V battery to the trunk. It sure was a lot easier than moving the engine! In a relatively open structure, like coleastering's bike, it would be very easy to move portions of the battery to different locations. Or, even easier to move ballast around, as he apparently did, to improve the straight line performance.

 

[brian_]

Yes brian, you do not want to overcorrect a problem and then create another problem. The main task at Bonneville, AIR, is to point your vehicle in a straight line and try to keep it that way for the whole speed run. Unless, coleastering, you were on some kind of slalom course.

Right... but with any side wind, the apparent wind direction and the direction of travel are not the same, thus the need to fight the vehicle's tendency to "weathervane".

This is the video that I mentioned earlier:
Lark Streamliner | Vehicle Dynamics part 1
I haven't seen the rest of the series, and the aero work here is crude, but he does discuss the centre of pressure vs. centre of mass issue.

Do you mean an ICE vehicle as a "conventional vehicle"? In my crazy ICE car days, the first thing we usually did to improve the balance of the vehicle, was to move the 12V battery to the trunk. It sure was a lot easier than moving the engine! In a relatively open structure, like coleastering's bike, it would be very easy to move portions of the battery to different locations. Or, even easier to move ballast around, as he apparently did, to improve the straight line performance.

Yes, I moved the battery in my first competition-prepared vehicle, too. It was, after all, a convenient box of lead; it wasn't an enormous thing comprising a large fraction of the vehicle mass and volume, as an EV battery is. Also, the car was production-based so moving the engine would be difficult, in contrast to these land speed competition streamliners which are custom-designed, allowing the designer to determine engine placement.

In most production EVs the battery would be even more difficult to shift in position for competition use than the engine would be in an ICE-powered vehicle... but of course we're not talking about a production bike here.

This bike is nice in this aspect because the rider straddles a backbone with battery and other components hung under it, so those components can be shuffled for ballast. The general layout is fixed in the only really practical configuration: two wheels, a tailcone behind the rear wheel, and everything else between the wheels. If you look at a typical enclosed streamliner (with two wheels or four) any significant shift of major components such as battery would mean relocating the driver's compartment - it's a substantial design change, not a tweak of mounting points.

Of course small lumps of ballast are the easiest things to move, but a well-designed vehicle has minimal ballast (when complete, unlike the unfaired version of this bike) because just about anything else - battery, motor, structure, etc - is a better use of mass (which has to be supported and accelerated) than just ballast. Ballast is for tuning (as Cole is using it), not to fix fundamental design problems.

 

[electro wrks]

In most production EVs the battery would be even more difficult to shift in position for competition use than the engine would be in an ICE-powered vehicle...

I think the veracity of that statement is too dependent on the engine and battery placement in a given vehicle. How am I going to shift the engine/transaxle around in a front wheel drive vehicle? Move it to the rear? Yeah, that's going to be easy to do. I could open a sub floor battery box, leaving some battery modules in the box, and pull out some to place them in a better location for a particular vehicle. brian, you are just thinking in too narrow of a range of possibilities.

... but of course we're not talking about a production bike here.

No, we are not. And, this is primarily a DIY forum, as you have reminded me in the past. It would be a good idea for the DIY builder to, if possible, have some provision(s) for adjusting vehicle balance, if a problem should arise. The batteries being quite heavy, seem to me to be a good candidate for doing this. If you have front and rear battery boxes, maybe have provisions to shift modules between the two to correct a steering issue. Maybe your battery box doesn't take up all of the available space. Maybe it could be shifted back and fore to correct a problem. Again, you need to think outside of the box! Or, between the boxes! Or, in shifted boxes!

 

[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.

 

[brian_]

I think the veracity of that statement is too dependent on the engine and battery placement in a given vehicle. How am I going to shift the engine/transaxle around in a front wheel drive vehicle?

I thought we were talking about land speed streamliners - you can put the motor where ever you want, and don't need to drive any specific axle. Even production front-wheel-drive cars have been built with the engine ahead of, over, and behind the front axle line.

It would be a good idea for the DIY builder to, if possible, have some provision(s) for adjusting vehicle balance, if a problem should arise. The batteries being quite heavy, seem to me to be a good candidate for doing this.

Absolutely! It's just easier to move a relatively small engine than a relatively larger battery, and most of these streamliners don't have a bunch of extra space to have half-filled boxes of battery modules so they can be shifted around like ballast in a submarine's tanks.