23
Jan

What’s been going on

Written by admin. Posted in Build Diary

The time has come to give up some detail about what has been going on with what we think and have been told is the “worlds fastest and most capable electric motocross bike”: 

State of gen1 CRF2eR electric:

First off, we haven’t yet mentioned that we had an official track test day in late August at the Albany Motocross park. We rode the electric e-MotoCRF250R full on, wheel to wheel with the gas powered CRF250R equivalent. We also traded bikes to each try the complement.  The results: 

1. Whichever of us was on the electric bike was faster, mainly because of how tight this track is. With only one speed on the electric, on a long straight stretch, the gas bike would eventually blow past. It was always the fastest off the line and up to ~30MPH! In the tight woods section, the electric was king roost! Keep in mind that this is simply the first prototype… Gen2 will be much better…. stay tuned…

2. Got 6 laps under full power. Not bad for this small, but potent pack. On the last two laps, Bob tripled the jump heading into the woods with ease, nervous at first, but it felt “normal” on this 60+ foot jump.

The current machine started life as a development/practice design, quite literally, with it’s heavy cast iron motors consuming the space that should hold the batteries. This is what was available at the time, but it certainly has proven without a doubt that the batteries are indeed ready, and thus has generated new incentive for us to design the ultimate motocross bike. 

Just to give you a sense of the capability of the cells that are inside our CRF2eR, check out this plot we received from Radu, the team leader of MIT’s Electric Vehicle Team that recently demonstrated a charge time of under 10 minutes on an electric street bike.

In the background, they set up a stress test on a single cell that was charged in 12 minutes and discharged in 10 minutes, continuously.  They plotted the capacity change over time as seen below. After 1400 cycles, the capacity only drops a few percent under this continuous stress. 

1,400+ cycles, ~30 days (equivalent to 300,000 car miles). Note that at this high charge rate, you can’t get 100% capacity into them, that is why you see ~90%.

At “normal” current demand levels, the charge/discharge cycle count extends much further. 

Now, imagine a bike with a custom brushless motor that doubles the output power of this current 2 motor design! (4x the power density!) Water cooling, 2x the range, 97% motor efficiency, full variable regen braking, and mud riding OK with a fully sealed package (normal pressure washer cleanup), for just some of the highlights….the others you will see posted later.

Because of the significant potential of this machine with good batteries, the design of the ultimate drive system is the focus for performance with the potential to beat 450’s and on a bike that weighs less than the 250R.  It all comes down to power/weight ratio.  Forget about saving gas or reducing emissions (although it does), performance will speak for itself on the track. 

As this generation 2 machine comes together, we are nearing the holy grail of charge capacity with batteries that will meet or exceed the range of a gas bike. This is why the focus on the ultimate drive system. These cells WILL happen, it is just a matter of time now and we will be ready… (for our street e-motos, our smaller REX range extender, will soothe any range anxiety fears)

Today @ Colorado State University – Inexpensive, longer-lasting batteries could revolutionize the military, automobiles, and health care

And yet another new announcement on a breakthrough that will significantly increase the current delivery and cycle life of the standard Lithium Ion Iron Phosphate cells, the same chemistry as is used in our CRF2eR: 

Lithium Ion Batteries Recharged in Seconds

The important detail with both these breakthroughs is the significant reduction of the cells internal resistance.  This allows for very high currents without creating heat, which is a big part of the mechanical stress that limits the charge rate in all batteries.  To decrease the resistance this far adds greatly to the cells cycle life as well as not needing to actively cool the batteries when fast charging. 

For those technically minded, you may wonder where you may get the enormous power for fast charging, especially when away from outlets? Think storage pack sitting in the rig that got you there. With excess capacity there (relative to bike size charge), VERY fast charge can happen without any generation or transportation losses. Even the new plug-in hybrids have enough energy stored in their battery packs that will handle multiple motos worth of charge put into the bikes. There are ways to prevent having generators run in the pits. 

This, by the way, is the principle that will allow 5-10 minute charging with large electric vehicle packs that would otherwise require having a fat grid-tied connection to dump that much current in that short of time. 

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