Electric Motocross Project
The new generation batteries that make the BMW project so potent has even more significance here because of the extreme power to weight ratio which is so important in a bike.
This project is intended to demonstrate this potential by conversion of full performance race ready Honda CRF250R's to race ready full performance electric(CRF2eR) with equal or better performance.
Imagine how this quiet machine could change the riding opportunities. Neighbors will no longer even know you are riding. The tracks around the country that have closed because of noise would be able to continue with full electric motocross. When trail riding, you literally see more activity from "sneaking up" on wildlife as well as minimizing your impact. Keep in mind this bike is not silent, especially at speed, but relatively silent.
At walking speed, there is a slight chain noise only.
The rewards from conversion verses ground up design are significant. We are starting with a known package that any CRF rider would immediately feel comfortable with and can withstand the pounding of the most brutal motocross tracks. This is accomplished by matching the weight and weight distribution of the original gas powered design and building the electric drive system with equal or greater tolerance to normal "abuse" by pro riders on the track.
Updates are appended to the bottom of this page
Click on images to view full size
October 2007
The CRF250R to CRF2eR conversion is being developed simultaneously with the BMW project because they share the same battery management design as well as being the initial test platform. This off road application demands peak currents that are twice that of the BMW peak current (because of the 10x voltage difference).
The general design is scaleable to any cell size and cell count to accommodate different motors/controllers, current and storage capacity.
Two fresh CRF250R bikes...
The motor is out in no time
The rolling chassis ready for electrifying
December 2007 update
Drive system is complete. Battery packaging and mounting is nearing completion.
Road testing was planned for January 08, but is looking more like February.
Working the Alu billet on the lathe:
Prototype battery boxes being constructed
January 2008 update
There was some extra work needed to get the new battery cell welder running...
Three phase power is needed which means creating it from single phase power.
Here is the unit I wired up to convert Single phase 240VAC to 3 Phase 240VAC.
It is a rotary converter that uses 240VAC to spin this idle motor while having 3 phase taps.
February 2008 update
A milestone reached Saturday February 2nd: First welded packs take form:
Cell welding begins
The last plate of the first pack is ready to place and weld:
Here is the first pack with full current path welded. These packs can deliver nearly 1000 Amps as specified from the cell manufacturer. This will never limit the power delivery since the motor drive system can only draw 600 Amps peak!
This portion of the power package goes into the location of the original air intake box. It's battery management circuit will be placed in the space above the cells along with a large fuse and 600 Amp cable headers before being covered.
We did no welding or drilling to the original Alu chassis; here we are welding the frame mounts to our new down tubes. All pieces simply bolt on with captive nuts everywhere.
The complete set of components fabricated for this prototype ready for final assembly along with the motor and control system... The results of two months of design and fab:
A dyno test is planned for a side by side comparison between the original gas powered CRF250R machine and this new electric CRF2eR. The performance curves will be overlaid .....Stay tuned...
We will first need to work out the controller settings for best power delivery as well as the charging system details.
February 16 2008 update
Today a milestone was reached in the project; the real world testing has begun!
But first, here are some shots of the final assembly from the previous days...
The chassis with some of our new components bolted in place.
Here is where the 3rd of three packs go. All packs are designed to fit inside various original spaces to allow all outside surfaces to remain unchanged.
The upper battery box drops right in. We are adding 4 pounds of copper wire to deliver the 600 Amp peak currents.
The bike is just about ready to roll....
Hyper throttle..there was some adjustment needed
The finished package, minus side panels
View from the rear
side by side
February 24 2008 update
The first dry dirt testing and what an awesome result..
March 08 2008 update:
The new look, complete with side panels
Also, Electric MX and related topics discussed in detail
May 2008 update:
We are very focused on two near term goals:
1. The BMS turn on and installation. There is a bit of software work remaining.
2. Replication of the machine with CNC mfg means. We are working on a 2nd build to fully evaluate the complete package.
August 2008 update:
Parts are arriving for the 2nd version/build of our CRF2eR from 3rd party vendors that replicated our design with CNC machining.
We have dropped the weight and improved the drive system with custom spline'd shafts that are much lighter but very capable of handling the full power/torque transferred to the rear wheel, just as the stock sprockets do.
Here is the CAD view of our new drive system mounting plates:
A couple sets of the mounting hardware
September 08 update:
This new custom splined shaft allows the use of off-the-shelf sprockets that are light and inexpensive. Assembly just got a lot easier too.
Here is the chassis before installation of the motor controllers, cells and wiring
This bike currently has street tires for hitting the dyno at the next opportunity and some asphalt testing...
The BMS electronics and software are nearing completion that will be added to this chassis for full range testing.
Also in progress: a custom 2kW charger that will obtain a full charge in 40 minutes.
Update March 2009
Contactor added for safety disconnect and lower off state leakage.
The BMS interface wiring is now fully installed and ready for control SW work.
The new dashboard with range gauge at left and temperature readout at right.
Fully enclosed (underside included) ALU package guards wiring and keeps the dirt out.
Update Aug 2009
OK, now that the BMS (battery management sys) is installed and working, I can finally go full throttle with a sense of confidence in the cell control. I learned early how quickly cells can be destroyed with such high currents involved. These cells are very robust when properly monitored/controlled, however.
So, let the serious fun begin:
Heads up about the noise level in the first video. Because of the auto gain mic input on the camera, it cranks up the gain from the lack of noise when nearby to the volume level that would match a four stroke, for example, in your audio playback.
Here are a couple pics from the dyno session
I will post the curve data when I get the gas bike dyno data to overlay directly.
Dyno session with CRF250X and CRF250R is planned for Thursday Aug 6.
I was able to monitor the cell voltages with precision while full on the throttle
sorry for the blurry display..
The charging is automatic now, just plug the cable into the... what else...the filler neck.
When the charge is done, the LED (next to the plug) turns from red to green.
With the relatively weak charger I have now, it takes more than 45 minutes to charge after playing hard for about 15 minutes. I will be cranking up the current to the point the charge will take 20 minutes for a full capacity (2kW/4kW charger 120V/ 240V).
These cells have the ability to charge in under 10 minutes, you just need a charger that can deliver it.
Although charging is automatic, here I am monitoring the charging details (gray, flat comm cable) just to be sure all is OK.
Here are the three battery boxes which have their own BMS boards attached.
The center box has them installed internally with only their communication pins protruding.
These BMS boards were designed for the BMW but also work fine here as a development platform. So far, so good: After approx 16 charge/ride cycles, no faults or communication errors, even under full power.
Here is the waveform of the current drawn from the pack during a couple throttle blips:
The scale in this case is 1mV/Amp showing a peak of 570 Amps. I limit the current to 300 Amps per motor so this got very close to the 600 Amp total from a blip while on the bike stand, where I applied some rear brake for load, thus the flat segments in the waveform. The brake disc gets very hot very fast doing this.
Sneak peek at another bike conversion that has been going on in the background:
This AC motor drive conversion has a unique twist to it...
Update Aug 12
Here is the power and speed curve data of the electric CRF2eR:
This is true SAE rear wheel power displayed.
I have the CRF250X and CRF250R data now and will overlay soon. It needs to have the transmission ratios factored in for the entire speed range.
Here is the quick comparison of rear wheel peak horsepower values:
CRF2eR = 25 HP
CRF250X = 26 HP
CRF250R = 33 HP
The torque is significantly higher in the electric that makes it much better at off-the-line acceleration, so it looks like the gas bikes are first doomed on the supercross tracks...
I finally performed the weigh in:
CRF250X = 253 lbs
CRF2eR = 279 lbs
-----
26 lbs over
Well, with these outdated motors, it is more like the weight of the CRF450X ...
Despite this weight, you can clearly see the true acceleration from the dyno data. Considering the peak power from 25 to 30 MPH, this will truly be competitive on a tight track.
I made a discovery after posting this dyno data and after our day on the track (see below): I later found all the fat copper lugs were getting so hot, it burned off the insulation around them. The thing that caught my eye was some dark color on one battery box cover that turned out to be charred FR4 material inside that was from a terminal bolt that was glowing red hot while full throttle. This is what happens if there is resistance in the current path and large currents flowing; power is dissipated (and wasted). No cells were hurt in the incident, FYI.
So, because of that, the dyno data shows lower on the plot (above) than it actually is. Now that the resistive losses have been resolved, it will deliver more HP and now may exceed the 250X peak power, we will have to re-dyno to find out. Despite this wasted power, it performed very well on the track. Now it will perform even better and with more range than I reported below.
Update Jan 23 2010
The time has come to give up some detail about what has been going on with the worlds fastest and most capable electric motocross bike:
State of gen1 CRF2eR electric:
First off, I haven't yet mentioned that we had an official track test day in late August at the Albany Motocross park. We rode the electric CRF2eR 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...
2. Got 6 laps under full power. Not bad for this small, but potent pack. On the last two laps, I trippled 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 I 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...
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.
<BMW Project work pages Rav4ev>
