Can’t belive you made this whole build from scratch in like a month and half^^"
now I’m ashamed, I’ve more than one to finish
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Second ride today - unbelieveable warm air moving through town made it really pleasant.
I dialed the brake down to -20A, but that’s not strong enough. I did a couple of in-situ adjustments and landed on -26A which is still just a bit weak but good for flatlanding and mild hills. I do have a (really steep) test descent on the Chief Sealth trail that is the acid test - make sure I can steady-speed down the hill, but I didn’t make time to get down there today.
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I like those connectors cos they can be split apart and used as singles as well. Wonder what kind of current they are rated for 
The are rated 55A, well above the 4A that my charger puts out 
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I know I’m a little late to the game, but i will admit that having an onboard BMS for charging is pretty nice. Previously for my 10S5P I had to break it up into 2 banks to charge it because my offboard charger maxed out at 6S. So I had to charge one bank, then the other and the charger maxed out at 6A, but for whatever reason only actively charged at 2.6A.
So while this arrangement with the LLT is probably not safer it is a whole lot more convenient.
As such I’ve ordered 2 more smaller BMS’s and will be retrofitting FS1 and the mountain board.
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How’s the turning radius on the board?
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Pretty wide, I’d say about 5’ having not actually measured it.
Minor update, swapped out the big dumb charge port for this slick smaller Anderson.
This way I can make a cover plate of some sort that might also serve as a flip-up headlight housing. Still noodling on that.
I also started looking at code to get this TFT display on the board to show bat V and current speed.
But of course I don’t have the right 8-pin JST in stock so another Digi-Key.
This particular display board was the original that I designed when I made my first board - it had a Zigbee and served as both the display and the receiver to drive the VESC 4.10
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I got the display board to talk to the Stormcore and am able to extract RPM and BatV from it, so I can display current voltage and current mph. Was able to use stock VESCUart to get it.
Voltage displays as green until it gets down to 44.25, yellow between that and 40.8 at which point it turns red.
QUESTION: on a 12S pack what voltage do you generally consider yourself to be at exactly the halfway point between full and Battery Cutoff Start (for me 40.8)? I’m pretty sure it’s not linear.
The problem is the place I want to install it is much smaller than the PCB it’s mounted on - I need a PCB that’s exactly the same size as the display. OshPark to the rescue.
But there is an interesting opportunity to integrate the charge port with the display board housing.
Also look at that beautiful font! No rough edges.
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Just 2 3D printed parts shy of having the display installed on the board. Here is the new carrier board back from OshPark - exactly the same size as the display. (for you nerds that’s a Teensy 3.2)
Test fit of the housing (of course the display didn’t fit correctly into this housing so I had to print a whole 'nother one)
Last ops test of display in housing
Note above that I didn’t have enough space for MPH, so M is MPH, not miles traveled. If the display were bigger that would be the next thing I’d add. But then it’s on the app on the phone, plus Strava, so not as important.
Install the housing.
The two parts I’m printing are the same as the old end plates for the 3D printed enclosure walls, except with a new opening for the wire. So no big drama, but I didn’t bother to go to the trouble to run them through Bud fittings the way I should have. So slightly less waterproof than it was before which, honestly, isn’t much better than IP65 to begin with.
Anyway, once those two parts print I’ll have some notion of how much battery I have left as I travel down life’s trails. Specifically, these trails
Of course these particular trails cause a conundrum. I’ve easily got enough battery to get 20 miles, but not enough for 40+ miles round trip. Not yet anyway
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3.6 volts per cell is the “nominal” for most cells, so that seems like a reasonable place to start. To get more precise you’d want to look at a data sheet for your particular cell. Here’s a chart for Molicel P42A:
It’s not exactly linear, but it’s not far off, at least not until you get close to the end.
The really tricky thing is how the voltage sags under load.
Watching my Davega’s battery meter move around while I’m riding makes me wish that it took current draw into account. It seems to me that rather than just monitoring voltage, it would be better to interpolate from a table, where one axis is voltage and the other is current, and the table cells are battery-remaining percentages.
Something like this…
The numbers in the table are just guesstimates, don’t take them too seriously. I filled in the 100% cells based on a quick look at the datasheet, with 0% across the board at 2.5, and had Excel fill in the rest.
But on second thought it might be better to have it read 0% at 2.75 or even 3.0 volts, partly to have a little extra reserve just in case, and partly to provide some buffer against pulling the voltage down past 2.5, since that seems to be where there’s a risk of damaging the cells.
This is good info, thanks @NateW . It feels like the midpoint I’ve chosen, being about a volt above nominal, is about right to be ultra-conservative about not running out of battery. I’ll be interested in seeing how far I can get on the top half of the pack vs. the bottom half.
There’s a chip called a coulomb counter that is designed specifically for this kind of application. It measures the exact amount of energy put into the pack, and the energy drawn back out so it doesn’t rely on current or voltage and it is always accurate regardless of the power draw rate.
The only tricky part is it requires an inline current sense resistor and in our case that resistor would have to be able to handle ~100A. Too bad they don’t have a less invasive way to measure.
The person who develops a coulomb counter daughterboard and integrates it with DaveGa would do very well.
Looking good! Gonna set up some LED lights in the T slots with a Bluetooth controller? 
That’s a little too much bling for me, but I’ll probably put a taillight on it since it’s the last space that looks unfinished.
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I’ve been riding this new machine for a couple of months now and today I went back to the older version and I suddenly realized why I prefer the new one so much more. Even though the old machine is objectively a better carver, this one is much smoother and I think that’s because of the “speed grade” tires that are on it.
Which is to say that the cheapie 6" tires that are on the old machine aren’t round, so the ride is just naturally rougher. I never realized they weren’t round until I rode this machine.
So now I have another upgrade opportunity on my hands. I might try shaving them first, see if that makes a difference.
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Daddy’s got a new set of shoes!
There are the speed rated BKB’s - I thought I’d try them before I spent a bunch of money on the Hoyt speed rated 5"ers.
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How long is your standing platform?
Got any pictures with your feet on?
The deck itself is 25.5". The deck stance exactly matches my snowboard stance.
Here’s a piccie with some shoes (size 11) for reference. It looked too dorky for me to shoot a picture of me on it.
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It would be interesting to feel what that set up is like with the trucks so far from your feet. I really think it looks neat.