RIPPERTON
1 kW
Should just copy my battery design (Rippy Scoot)
Dont compress the cells, give them 1mm gap.
Dont compress the cells, give them 1mm gap.
CRF #2 - 250R - LGX P41A 20s1p - EM200
- Thread starter bananu7
- Start date
I appreciate your response.
All the elements of my design stem from tackling practical problems.
Compressing the cells has been shown to reduce their chance of swelling and improve the lifetime performance. There's a link to a paper analyzing that higher in the thread.
Not having a carrier but just bolting everything together means it's much harder to prevent chaffing and movevent inside of the battery. Mine isn't going into a scooter that will roll on smooth pavement, it's going into a dirtbike where it will experience constant harsh vibrations and large g-forces. I want to take all of that away from the cells themselves, and suspending them in a carrier means i can do just that. I can all by eliminate flexion of the electrodes, rubbing of the cells against each other and the enclosure etc.
This also seems to be a common practice in industrial designs which those cells have been designed for in the first place. In there, each cell is glued to a plastic carrier with appropriate spacing and then the entire stack is compressed together. The electrodes are often welded, of course, but there's still no movement of them because they rest on the edges of the plastic carrier plates. I tried to strike a balance between a fully professional design and something that I can fabricate myself. I do not consider the protection elements optional.
P.S. I would probably try to wing it more if the bike wasn't going for sale. I definitely wouldn't want to hand over an unsafe battery, so I'd rather overkill it a bit.
P.S.2. I've just realised the positive busbar line is a perfect spot to put an internal 500A fuse which I didn't have space for in the battery for #1.
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Nice build! How thick are these plates? I'm in the same situation and do NOT want to use the wobbely LK mounts.
If one would mill the hub down 1mm, so the sprocket sits inwards and also would mill the motor mounting tabs 1mm aswell, do you believe, that placing the mount on the outside coule be possible?
I found a source locally. AFAIK they're still available, but require pickup in person. It's a very much "while supplies last, don't ask too many questions" kind of situation
I'd offer to get them for you but i need to actually build the battery and verify they're up to spec, which will hopefully happen in the coming winter months.
6mm. Forgot which alloy specifically. They're way stiffer than 3mm stainless sheet at least by feel. 5mm would likely be okay as well.
I'd personally avoid modifying the hub like that, as that means, for example, that the chain slider would be offset. I think it should be possible to get the plate on the outside and somehow make it all fit. Might require grinding of a bit of bottom frame welds, maybe a bit of the swingarm and optimizing the shape.
That being said, my #1 bike has been running the entire season with the inside mount with 0 problems whatsoever. I was initially cautious as well, but this part of the build has literally been the least problematic once put in place. I didn't have to check/tighten anything not even once, everything seems solid, so in my opinion modifying the motor is the easiest way to solve this particular problem and stay within the limits of this particular frame.
P.S. I also just realized that i have contradicted myself a bit, considering that the #2 does have a different hub, with the Kawasaki wheel and all... So maybe that's not such a bad idea if all you need is like 1mm. The OEM hub isn't very thick in that area though and they do crack around sprocket mounting bolts, so I'd be very careful. I'd probably try cutting a custom offset sprocket before attempting to modify the hub, actually. If you have a hobby CNC, that's a totally doable process, and perhaps even easier in a way than milling the hub evenly.
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RideAlongMechanic
10 µW
- Joined
- Apr 27, 2022
- Messages
- 5
Nice Choice on the build. I also Just picked up a crf 250 to build. I was evaluating pouch style cells, but struggling to fit them in the frame via 3dmodel. Do you have an estimate on the overall dimensions yet?
Also there are couple 3d scans out there of the CRF frame, it has been helpful for my research/layout. A cr500 conversion scan exists on grabcad. Front motor mount and y are modified from the crf250 to fit the 500. and another on the electric motorcycle builds facebook page for a battery cage design.
Also there are couple 3d scans out there of the CRF frame, it has been helpful for my research/layout. A cr500 conversion scan exists on grabcad. Front motor mount and y are modified from the crf250 to fit the 500. and another on the electric motorcycle builds facebook page for a battery cage design.
Yeah; the dimension of the pack including the BMS on the side suggest it will all barely fit. I'm currently working on other parts so the battery is paused, but will get back to it next.
I have been a horrible builder lately, with no updates. The main reason was that I did way less than I planned to over the winter. I wanted to have the #2 bike ready for the season, and it's still far from that.
I am fighting my analysis paralysis by trying to make steady progress on one part right now - the airbox/electronics holder. I went through many design iterations, especially in the digital realm:
I tried Blender, Solid Edge and new to me Plasticity. I worked from 3D scans, surfaces, solids, triangles... I ended up with a model i liked and tried preparing it for a printer, which was very disappointing (would use too much plastic, wouldn't fit/would need complex splitting that took me a lot of time, would take forever to print).
I suppose maybe posting about failures isn't that bad either? It's not always the first thing that works.
Anyway, I went back to physical sculpting. I dug out my old model with half of the old airbox embedded in the foam. I started using a different filler (much softer), I started using scraping, planing, shaving and rasping instead of sanding (which means foam and filler flakes instead of dust, much better). And it's actually going kinda okay? It was a lot of a psychological barrier where I felt it was going nowhere, so i had no motivation to keep working on it. Now that I kinda realize all models look like shit in the middle stages and stopped caring, I can actually make meaningful progress. And it turns out I'm way better at shaping by hand/by eye than on the computer screen.
Because i made it narrower on top, I'll actually need a split mould. I'm not very happy about it as it's going to be my first time using ez-mould, and adding a split makes it all more difficult, but i feel i have all the theory i need for this. I might need to buy some glass microballoon filler and some gelcoat pigment though.
This part is very important for the bike because it'd allow me to prepare almost all of the wiring (except two final wires going to the battery) and make it functionally complete, sans battery. At the same time, I plan to make at least two copies and put the second one in bike #1, but that might get a bit more complicated - go to thread #1 for more details.
I am fighting my analysis paralysis by trying to make steady progress on one part right now - the airbox/electronics holder. I went through many design iterations, especially in the digital realm:
I tried Blender, Solid Edge and new to me Plasticity. I worked from 3D scans, surfaces, solids, triangles... I ended up with a model i liked and tried preparing it for a printer, which was very disappointing (would use too much plastic, wouldn't fit/would need complex splitting that took me a lot of time, would take forever to print).
I suppose maybe posting about failures isn't that bad either? It's not always the first thing that works.
Anyway, I went back to physical sculpting. I dug out my old model with half of the old airbox embedded in the foam. I started using a different filler (much softer), I started using scraping, planing, shaving and rasping instead of sanding (which means foam and filler flakes instead of dust, much better). And it's actually going kinda okay? It was a lot of a psychological barrier where I felt it was going nowhere, so i had no motivation to keep working on it. Now that I kinda realize all models look like shit in the middle stages and stopped caring, I can actually make meaningful progress. And it turns out I'm way better at shaping by hand/by eye than on the computer screen.
Because i made it narrower on top, I'll actually need a split mould. I'm not very happy about it as it's going to be my first time using ez-mould, and adding a split makes it all more difficult, but i feel i have all the theory i need for this. I might need to buy some glass microballoon filler and some gelcoat pigment though.
This part is very important for the bike because it'd allow me to prepare almost all of the wiring (except two final wires going to the battery) and make it functionally complete, sans battery. At the same time, I plan to make at least two copies and put the second one in bike #1, but that might get a bit more complicated - go to thread #1 for more details.
I have finished sanding the pattern for the airbox. I have a photo somewhere but it's nothing spectacular, the same but smoother. I ran into a huge bummer though. When getting ready to put the pattern coat on, I realized my entire, new, 5KG can of PCP (Pattern Coat Primer, not the drug) has gone bad through the winter freezes... Super annoying.
I already have a new can on its way to me, along with a fresh batch of MEKP. I'm determined to get this to the finish line. Meanwhile, bike #1 is getting a bit more complicated, so check that thread too.
I already have a new can on its way to me, along with a fresh batch of MEKP. I'm determined to get this to the finish line. Meanwhile, bike #1 is getting a bit more complicated, so check that thread too.
The pattern has been coated with first layer, sanded and the 2nd layer is curing as I'm writing this. The oven is working splendidly, keeping 21+/-2 degrees C inside. Photos are straight after curing of the first layer, before sanding. I've added a lot of thixotropic silica powder to make it denser and allow me to put it thicker in places where it could be helpful. It wasn't a very good idea because i just made it all uneven again but it sanded off very easily. The primer, when fresh, it's a really good product. If all goes well, i should be able to start with the first half of the mold tomorrow.
Small update: I got two more layers of PCP on it (4 total), each subsequent one thinner than the previous. First used about 170g, second about 150, third 100 and fourth just about 60g. If i had the shape right the first time i could've used way less, but i kept sanding through it. I think a cheap spray paint would be really helpful for flattening key surfaces.
Either way, 4 layers and some extra filler is really as far as i want to take this. It's currently cured and waiting for last sand and polish, and I should be ready to prep it for taking the first half of the mold. I'll put it on a base plate, seal bottom with wax, and put a plastic fence across it that will form the side profile of the mold. Wanted to do that over the weekend, but life got in the way again...
Either way, 4 layers and some extra filler is really as far as i want to take this. It's currently cured and waiting for last sand and polish, and I should be ready to prep it for taking the first half of the mold. I'll put it on a base plate, seal bottom with wax, and put a plastic fence across it that will form the side profile of the mold. Wanted to do that over the weekend, but life got in the way again...
I sanded the pattern down, but didn't do a very good job at it. Still had a lot of scratches from lower grits, but I decided I've put way too much effort into it already.
When fitting everything, I realized the shape is so complex that it will require a 3-piece mold, as it won't release from just two halves. That doesn't mean much more material used, but it's yet another molding cycle to do. It's two layers of gelcoat (4-8h after each), then a coupling coat (4-8h) then the reinforcement, and that multiplies by the number of parts of the mold. So it's easy to see that even such a small thing can take days even when everything goes according to plan. At that point i don't have much choice so I'm just going with it, but will certainly take it into account in my next projects.
At least all the hours of youtube videos watched meant i felt right at home when doing the seal. I figured it would be even easier if I had a CNC mill, as i could just scan the part and generate a perfectly matching cross-section shape.
In the end, first layer of gelcoat went on, and the second will follow right after:
The oven is really helping here as at least I have a decent sealed place to put it in where I'm not afraid it wil get knocked over and don't have to worry about temperature swings (it still gets down to single digits in the night).
When fitting everything, I realized the shape is so complex that it will require a 3-piece mold, as it won't release from just two halves. That doesn't mean much more material used, but it's yet another molding cycle to do. It's two layers of gelcoat (4-8h after each), then a coupling coat (4-8h) then the reinforcement, and that multiplies by the number of parts of the mold. So it's easy to see that even such a small thing can take days even when everything goes according to plan. At that point i don't have much choice so I'm just going with it, but will certainly take it into account in my next projects.
At least all the hours of youtube videos watched meant i felt right at home when doing the seal. I figured it would be even easier if I had a CNC mill, as i could just scan the part and generate a perfectly matching cross-section shape.
In the end, first layer of gelcoat went on, and the second will follow right after:
The oven is really helping here as at least I have a decent sealed place to put it in where I'm not afraid it wil get knocked over and don't have to worry about temperature swings (it still gets down to single digits in the night).
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