[DRIVING] VX220 with Tesla SDU

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Pete9008
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Re: VX220 with Tesla SDU

Post by Pete9008 »

That's something to be proud of!

8-)
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Peter
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Re: VX220 with Tesla SDU

Post by Peter »

Hi Charlie. Excellent, nearly sorted, soon be showing mega money cars your rear end at the traffic light grand prix :-) List your parameters please, I will check against mine to see what could be limiting.
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Re: VX220 with Tesla SDU

Post by catphish »

Params attached. My suspicion at the moment is that the combination of high fslipmax (6) and low voltage (boost=2200, fweak=220) at 300V input is causing it to stall at full throttle.
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vx220-first-drive.json
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Peter
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Re: VX220 with Tesla SDU

Post by Peter »

Hi Charlie. Suggest you keep Boost as it is until you get your bespoke driveshafts, raising that will get you more torque on starting so may bust those welds :-( Fweak is ok, that will give good low down torque at that setting. Throtramp is as it says, 20 is fine for a gentle start. I am sure its down to current limiting, will do a few tests and come back to you in 15 mins or so using your idcmax and ocurlim settings as against mine.
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Re: VX220 with Tesla SDU

Post by catphish »

Peter wrote: Fri Jul 15, 2022 8:59 pm Hi Charlie. Suggest you keep Boost as it is until you get your bespoke driveshafts, raising that will get you more torque on starting so may bust those welds :-( Fweak is ok, that will give good low down torque at that setting. Throtramp is as it says, 20 is fine for a gentle start. I am sure its down to current limiting, will do a few tests and come back to you in 15 mins or so using your idcmax and ocurlim settings as against mine.
Can you remind me of your settings and battery voltage? Then I can compare. The more I think about it, the more I think it's probably stalling due to running too much slip at not enough voltage (ie not hitting a derating limit but just stalling from too much slip).
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Peter
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Re: VX220 with Tesla SDU

Post by Peter »

Hi Charlie. Did some tests, cant repeat your issue though sorry to say. iacmax is the current limiter, that does what it says but does not shut down the drive just limits current. Your setting of 800 is not causing me any problems at full throttle from start.
Your settings for acceleration in my opinion are quite gentle(ish) compared with what can be had.
My settings..
Battery fully charged 330v
Fslipmin 2
Fslipmax 6
Boost 4000
iacmax 1000
idcmax 500
Throtramp 2.1
Slipstart 55
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Re: VX220 with Tesla SDU

Post by catphish »

Peter wrote: Fri Jul 15, 2022 9:37 pm Hi Charlie. Did some tests, cant repeat your issue though sorry to say. iacmax is the current limiter, that does what it says but does not shut down the drive just limits current. Your setting of 800 is not causing me any problems at full throttle from start.
Your settings for acceleration in my opinion are quite gentle(ish) compared with what can be had.
My settings..
Battery fully charged 330v
Fslipmin 2
Fslipmax 6
Boost 4000
iacmax 1000
idcmax 500
Throtramp 2.1
Slipstart 55
Thanks, your boost is super high compared to mine, which somewhat confirms my suspicion that my voltage is running too low. What are your values for fweak and udcnom? Those are the other main settings that control voltage.

PS. How did you reach that boost value of 4000? That's nearly double the stock value! My own testing seemed to show the stock value was a bit low, but I was scared to crank it up.
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Peter
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Re: VX220 with Tesla SDU

Post by Peter »

Fweak 250
Udcnom 0
Boost gets you off the line quicker, I have tested at 6500 in the past, equivalent to warp factor 9 Scottie :-) It sets the voltage at which the motor starts off at.
I suggest you use the graphing functions, I was wondering if its voltage sag or due to throttle calibration at the top end ??
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Re: VX220 with Tesla SDU

Post by catphish »

I reduced by max slip from 6 to 4 and the car is now smooth up to full throttle. It's currently pretty weak, but plenty fast enough to be fun in the carpark. Looking forward to finishing the last few items and MOT now so I can get out on the road :)
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Peter
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Re: VX220 with Tesla SDU

Post by Peter »

Hi Charlie. Thats good. What do you mean by 'weak' ?
Increase slipstart to 60 and put slipmax back to 6, try that
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Re: VX220 with Tesla SDU

Post by catphish »

Peter wrote: Mon Jul 18, 2022 8:53 pm Hi Charlie. Thats good. What do you mean by 'weak' ?
Increase slipstart to 60 and put slipmax back to 6, try that
When I say weak, I just mean it doesn't have that much torque.

This is expected because I'm running it at quite a low voltage. The voltage just isn't high enough for a slip of 6.

As a comparison:
* We are running similar battery voltage (you said fully charged 330V, I'm running 80S which is about 330V fully charged.
* You have boost=4000 (that's about 10% or 33V at 0RPM full throttle.
* I have boost=2200, that's about 5.5% or 18V at 0 RPM full throttle.

This mans I would expect only (approximately) 55% of the current and 55% torque that you get. Slip (fslipmax) should also generally be increased with voltage (too little and you waste power doing nothing, too much and you stall like I did previously), so it makes sense for mine to be lower than yours accordingly.

If I want more torque, all I have to do is increase boost and decrease fweak, but for now I'm preferring to keep it less aggressive. :)
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Re: VX220 with Tesla SDU

Post by Peter »

I just had a playtime with Fweak, dropped it down to 100 (from my original 250) and tested in steps of +25.
Very interesting to say the least, low down torque goes up dramatically but watch out for overcurrent shut down, and potential broken driveshafts !
Just to see what happens I tried Fweak at 100, way too easy to loose traction from standstill, would be lethal in the rain.
At Fweak 150 and Boost 4000 I can smoke my tyres easily !!
Settled at Fweak 200 with Boost lowered to 3300. Still easy to spin the tyres but better for every day driving.
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Re: VX220 with Tesla SDU

Post by Peter »

With respect to battery voltage we are using the same modules and pack voltage, however you have 15 modules where I am using 10 so you will have less voltage sag, therefore better performance I would say.
Whats you tyre size?
Based on SDU diff ratio of 9.34 that gives 107.07 wheel revs per minute at 1000 rpm.
At 10K rpm I will see 72 mph approx.
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Re: VX220 with Tesla SDU

Post by catphish »

I think really the only question is how high I dare to set boost with welded driveshafts! What did you do about your driveshafts?
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Re: VX220 with Tesla SDU

Post by EV_Builder »

Aren't you saying also that those parameters should be adjusted as battery voltage drops?
SoC dependant? (with a offset)
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see http://www.wdrautomatisering.nl for bespoke BMS modules.
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Re: VX220 with Tesla SDU

Post by Peter »

As the Smart driveshafts use a hollow tube I turned only about 0.5mm off the Tesla shafts to make them a slide in fit ( glad I did too as the aftermarket Tesla shafts were not true to the cv joints !!).
I drilled holes in the Smart tube 180 degrees apart near the end of the slide in and near the end where the Tesla shaft exits then plu welded the holes making sure the weld melted the Tesla shaft first. Once done I then ran a weld around where the Tesla shaft exits the Smart tube. So far its held up ok. Just a bit p****d off the aftermarket Tesla cv joints are not top quality. I will do a drawing if my fit and weld explanation doesnt make sense :-)
Taking into consideration the spline size on the early Smart hubs I am surprised they have not let go as I have given them many an opportunity to say 'No more please' :-)
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Peter
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Re: VX220 with Tesla SDU

Post by Peter »

Hi EV_Builder. If my memory serves me thats what udcnom can do if set.
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Re: VX220 with Tesla SDU

Post by catphish »

EV_Builder wrote: Mon Jul 18, 2022 9:40 pm Aren't you saying also that those parameters should be adjusted as battery voltage drops?
SoC dependant? (with a offset)
If you set udcnom to your nominal voltage it will make these adjustments automatically :)
For some reason I don't feel comfortable with it and prefer my torque to fall off with state of charge. Maybe I'll change my mind on this later.
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Re: VX220 with Tesla SDU

Post by catphish »

So today I did a few of the final things on the car:
* Re-greased and re-booted the CV joints
* Replaced bleed nipped and bled brakes
* Secured all cables and pipes

The knocking noise i previously mentioned came back. I spend 3 hours completely disassembling and re-assembling the drive axles and CV joints to check everything. The shafts are definitely not too long or too short, there's a weirdly large amount of lateral play where the tripod joints fit into the drive unit on both sides (maybe 7mm) but they won't come out, so they're definitely locked in securely. After putting everything back together the noise is gone, so it remains a mystery.

Got the car up to 30MPH on a test drive, still a little scared :D

The final remaining TODO list (hopefully less than one day's work, and not requiring a lift):
* Drain water from coolant loop and fill with proper coolant.
* Install rear clamshell and wheel arch liners
* Install parcel shelf and speakers
* Install passenger seat and seatbelts
* Install dashboard
* Reduce handbrake tension, there's a small amount of brake rubbing since I attached the handbrake cable (I will hopefully get the MOT mechanic to do this, as I don't have any energy left to figure this out!)

MOT is booked for Friday, fingers crossed!
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Peter
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Re: VX220 with Tesla SDU

Post by Peter »

You should be scared :-) A monster is lying in wait for the powerful parameters !!
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Re: VX220 with Tesla SDU

Post by Peter »

I predict 0-60 times of 4 (ish) seconds and 100 mile range, but not both at the same time :-)
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Re: VX220 with Tesla SDU

Post by catphish »

Car has now passed its MOT and has been on the road, yay!
Unfortunately I have one new problem, one of my cell voltages is way off from the others. I don't know if it's a bad cell or a bad BMS module, but in order to investigate I'm going to have to remove the rear clamshell from the car again :cry:
cellvolts.png
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Re: VX220 with Tesla SDU

Post by johu »

Nice, congratulations :D

Cell taps are a constant source of trouble in DIY. I also have 100mV delta that doesn't actually exist between two adjacent cells. Sometimes it jumps to the correct value where you can see they are balanced and then it jumps to the large delta again.
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Re: VX220 with Tesla SDU

Post by catphish »

Thanks! I'm confident I can fix this, it's just going to be a big hassle (at least a day's work), because of how tightly everything is packed in this car.

In order to investigate, I need to remove the seats, parcel shelf, rear wheel arch liners, rear clamshell, and finally battery box lid. I can then swap the slave BMS board on the bad module. Fingers crossed this solves the problem.

If it doesn't, I'll have to remove the bad battery module from the battery box. Luckily I have a spare, but getting the modules out of the box isn't a fun process, particularly with the box in the car!

On the subject of driving, the car is now very smooth off the line and extremely nice and consistent to drive up to approx 55-60 mph. At this point, torque feels a little jittery.

By my calculations, fweak is at 52mph (probably approx 55mph on my speedo), so something is causing hesitation at around fweak. I could be hitting a derate (as it's at peak power at this point). I'll get some logging on it next week once I've dealt with the battery issue.
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Re: VX220 with Tesla SDU

Post by Peter »

Congrats on passing the MOT. Dont forget to give your friendly neighborhood petrol station a wave as you pass by :-)
If you remember I also had a bad cell and no matter if I swapped the BMS module or tested the cell connections neither solved it so hope you dont have the same issue. My weird cell reported 3.1v even though it was at 3.8v !!
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