Honda CRF250R Conversion "The CRE?"

Hello reader,

This will be my thread documenting the conversion of a 2006 Honda CRF250R. I hope to provide as much detail as I can to possibly help anyone who is also interested in doing something similar.

Goals:
The bike will hopefully be used for casual off-roading/enduro type riding rather than race/motocross.
I hope to achieve a range of atleast 3 hours though I'm well aware that depends on the riding style etc.
Such a use case wouldn't require a lot of power but I'll be honest, I am aiming for around 60hp for a nice round value for bragging rights That would be about 46-47kW before factoring in various losses.
Hopefully it ends up looking like this, minus the exhausts and ICE ofcourse.



Choices made so far:
So to meet the power requirement I decided to go for a combination of a Zero 75-7 motor and a Sevcon Gen 4 Size 6.
Regarding the battery I've done a lot of research, measuring and designing to come to the conclusion of making a 28s20p pack of VTC5As. Such a pack should be able to do about 50kW peaks with ease, I will explain later on how I came to this conclusion.

Motor:
Zero Z-Force 75-7 SPM, I paid for and was trying to buy a 75-7R IPM motor but the seller turned out to be mis-informed on what exactly he had and it turned out to be a 75-7 SPM. No worries, it should still be able to do the job of 47kW peaks and we are in the discussion of a partial refund as of this post, hopefully this happens and I don't end up having to file a dispute for a complete refund and returning the motor...

Controller:
Sevcon Gen 4 Size 6, essentially the same controller that Zero uses with their own bikes though I sourced this new from a friend who works for a company that converts vehicles for customers. They do not supply either the IXXAT cable or the Sevcon DVT software so I got those from Voltsport.co.uk

Battery:
28s20p configuration of VTC5A's, I would need to pull about 500A (25A/cell) to achieve the 47kW because looking at pulse discharge curves/graphs I shouldn't face a voltage drop lower than nominal at full stage of charge (ie fully charged battery shouldn't drop beyond 3.7V/cell under a 10 second pulse discharge of 25A/cell). Even at a continuous discharge rate of 25A/cell the pack would average a voltage of around 3.3V/cell from full to empty. I ordered 600 to have 40 spare on hand.

Components bought/sourced so far:
Zero Z-Force 75-7 SPM Motor
Sevcon Gen 4 Size 6
Sevcon IXXAT Cable & DVT Software
600* VTC5A cells
Ampseal 35Pin Connector Kit (for the Sevcon)
Domino Twist Grip Throttle IP67 0-5K Ohm
Tyco 5 Pin Connector Kit (for the Domino Throttle to Sevcon)
DB9 Female DIY Connector (for the IXXAT cable to Sevcon)
Delphi 8 Pin Male Connector Kit (for the 75-7 to Sevcon)
Tyco LEV200A4NAF Contactor (compatible with the Sevcon and 116V friendly)
Schneider XB4BG21 Key Switch (will take pack voltage)

other:
kWeld Complete Kit
Turnigy Graphene Panther 6600mAh 3s 75C Battery
Turnigy P403 Battery Charger
Turnigy Fire Retardant Battery Bag

Will update the list as I need more components.

So tonight I placed the motor into the bike with a piece of foam under to make it sit straight. I will design the mount tomorrow.



I am aware that the rear sprocket and front sprocket should be in line to one another, but if I'm correct that should be when the bike is under load. For example when I'm actually sitting on it so in that case the motor should maybe sit a centimetre or two lower than how I've placed it but that would mean having to cut a bit of the fins off the motor which I want to avoid. Does anybody with some experience think I can get away with it as is?

I think in cases like this things just have to fit where they fit.

The position of the motor sprocket related to the swing arm pivot point and the rear sprocket all effect the amount of anti-squat you will get during acceleration. The diameters of the sprockets you will need on this project will probably be far outside the range you would ever find on a gas bike. Having a huge rear sprocket and tiny front sprocket will change this suspension behavior some.

So you are likely going to compromise on some things. Its not worth hacking parts off of your motor unless you have a really good understanding of suspension geometry and are sure you are moving the motor to the ideal spot.

I guess I will try it with the motor as is and if it doesn't work then I can cut off a bit of the fins and make a new mount.

I believe this motor should spin up to 5500rpm so I've made the calculation that I need a reduction of about 10:53 front:rear to get a top speed of about 130kph/80mph. A lower top speed would require a custom made rear sprocket which I would like to avoid.

I also have the question of mounting points, I would have the two original mounts but think I would need a third. I've seen builds doing something around the swing arm but never understood it. Otherwise I could use where the frame and subframe bolt together for the third and rear mounting point.

With the larger rear sprocket you may be able to get away with a higher front sprocket since you should have a fair amount of anti-squat.

it would be very interested how you get so many cells in this small frame . I have a 75/7 and a sevcon size 6 in my shelf, also a old 2007 crf 250 Frame. if it works i will do the same

It's possible depending on the shape of the battery you decide to go for. If you want it to be easy to swap out and a basic box like shape then the maximum I could design for was around 420 cells for 28s15p but I would rather have a larger range/potential power and just find a faster charging solution instead.

I will admit that I haven't reached the 560 threshold yet. I am at 520 so far (26s20p) but to be fair this is because I am aiming for a fairly basic double cell stack. I have more than enough space to have 40 cells on a third level but feel it would look weird as a battery pack as a whole. I keep redesigning the pack and thinking of ideas to try fit all 560 on two levels otherwise I will have to go for the small third level.

The below design is 327.6mm at the widest point, length of 320.2mm, the rear is the thinnest point at 145.6mm and a height of 14mm, I have 15mm before I reach the frame from above (these dimensions do not take into account the metal enclosure itself). Then the third level will essentially be where the gas tank is. The gas tank will also have enough space for a small on-board charger though I do plan to only have an off-bike charger capable of around 5kW for an hour charge.



Also the reason why each cell "level" will be its own module is purely because I made a larger complete module out of cardboard and it wasn't possible to install but when I made the above as two separate modules for each level it became possible.

I've seen batteries mounted in the space where the radiators were. More of a modular setup though.

the dimension looks a little bit like my old conversion

How many cells were you able to fit in that? I've made a new design I'll post later tonight that can fit all 560 in just 2 layers.