[WIP] Smart Roadster (with BMW i3 motor and inverter)

[janosch]

I am in beautiful Cornwall this week, my friend Chris is embarking on converting his '04 roadster!

He has stripped the car of the ICE components already and will have a new subframe made once we spin the motor on a bench successfully.

Battery system and BMS are undecided, might be the first application of the flying ADC BMS?! Let's see how it matures over the summer.

[janosch]

Mocked with rear crossframe for suspension in.

[Pete9008]

Nice

Will be following with interest as I think you will be finished before me!

Do you need to flip or reverse the I3 motor?

Been wondering about doing a new subframe too. Are you confident that the DVLA won't treat it as part of the monocoque (I know they shouldn't but they seem a law unto themselves on these things!)?

[CJW]

Planning for the motor to be installed in same orientation as in the i3.

It's quite a tight fit front to back, looks like some of the motor castings for the air conditioning motor/compressor on the i3 will need to be trimmed back. The back end of the gearbox is also very close to the central bolt nuts on the rear x-frame. With careful positioning, reversing the rear x-frame bolts, and possibly a modification to the x-frame it should be doable.

The rear subframe and suspension will all be original. Having it zinc thermal sprayed, painted, and will build an adaptor frame that links the i3 motor to the original motor mount positions. Will share CAD file for that when it's done.

Hoping to use the original motor mounts, reinforced with Powerflex inserts. Will keep an eye on them and have custom ones made if necessary as the torque from the i3 I think is around three times as much as the original motor .

[Pete9008]

Sounds good!

Bear in mind that the motor mounts see driveshaft torque reaction not motor/engine torque. The higher ratio of the Roadster box 1st gear balances things up a bit and the mounts will have been designed to handle that. The i3 is likely still higher but probably not by enough to worry the uprated bushes.

[janosch]

Ok,

I set up a precharge circuit, connected 24V and wanted to spin the motor with manualid, but not getting a PWM noise.

udcsw, udcmin I set to 0V.
I gave it manualid 1A and 4A in firmware 5.24 and 4.97 (sine and foc).

Old firmware shows 200V no matter if DC is connected or not, makes sense, the i3 sensor scaling wasn't in that firmware yet. Same for temperature which reads too high.

New firmware shows 0V and 24V when its there.

I can get into manualRun but it won't do PWM.

Any thoughts on how to give this a test spin?

[johu]

Set snshs to i3 in 5.24 software, that will give you correct readings for temphs and udc

Edit: you did... That's odd
Still not home, will check back later

[janosch]

Yes, get good readings on 5.24, but not on 4.97.

We are populating the AmpSeal and trying normal `run` mode for today to get some noise or a rotation out of it.

If we need to do syncofs with this motor we would need `manualRun` in the future - I think I volunteer to fix that bug to make `manualRun` work in later revisions so firmware doesn't need to be flashed back and forth, but thats for another day.

EDIT: Ok, udc now reads 0V in 5.24 even though I can measure 24V at the inverter pins, wonder if I damaged the sensor, but can't see how or when.
It comes in through GPIOC3, just checking if I can measure something there on the mini mainboard.

[Pete9008]

Might be worth having a look here viewtopic.php?t=3097. Not tested on real hardware yet, so only use if you are comfortable with that, but it does reintroduce manual mode (but in a slightly different way!).

[janosch]

Measuring 0.92V on UDC pin on mini mainboard, no matter if 24V on DC bus or not, that can't be right.

Trying to trace this now where it's coming from.Is it coming through SPI for the i3? looking at the code.

Edit: Yes, it is coming through SPI of course.

But snshs is set to i3, why does it still not read the voltage?
There is some noise on idc and il1, il2, but not on udc.

Has my flashing backwards and forwards overwritten something?
The behaviour reminds me of the overwritten can map for the Tesla charger.

Params attached.

[CJW]

After a hiatus over the summer I have resumed work on the conversion.

-traced the resolver and motor temperature connections
-ordered some PCB's to simplify their connection to the openinverter drop-in board
-info posted on page 9 of the main i3 hacking thread: viewtopic.php?p=63507#p63507

-i3 motor and transmission weighed 69.6kg, I believe without the inverter or engine mounts. Will confirm and update as well.
-weighed various ICE components upon removal to keep track of net vehicle weight and help with battery design, posted below. Weights of anything over a few kg measured with digital household scales so should be considered approximate. Will confirm and update this post.

image.png (11.29 KiB) Viewed 1803 times

[CJW]

Current thinking for the battery:

-build 96s1p pack from LG Chem E78 pouch cells or similar
-27.5kWh total so around 25 kWh usable
-104kg for the cells, plus additional weight of cooling and packaging
-located above rear subframe where fuel tank was positioned, pending outcome of F/R weight distribution calcs. The height isn't ideal but the i3 motor's mass will be lower than the ICE engine, and a full fuel tank (ie tank and fuel) weighed around 36kg, so the net increase to CoG will hopefully not be too great.
-upgrade capacity in the future as more energy dense cells become available

Specs from LG Chem below.

[Scott166]

Good work! I'll be following with interest to see how you get he motor spinning

[CJW]

Finally got the motor spinning successfully with the drop-in board so next step is to figure out how to fit it in the sub-frame and get a set of mounts made. It's quite a tight fit, hoping to be able to get everything in without having to modify the cross-frame to create more space. Aware that the motor is going to need some space to move in the mounts, and also that some of the suspension components may flex under load.

View from above:

The back of the gearbox is close to the rear cross-frame bolts at the moment. Need to finalise the height of the motor relative to the main subframe box section as this affects the clearance. Should also be able to move the motor further forward once the air conditioning compressor mounts are gone:

Location of the air conditioning compressor mounts - the one on the lower right is actually touching the de Dion tube, preventing the motor from sitting closer to the tube, and further forward:

Close up of the air conditioning compressor mounts:

[CJW]

Air conditioning compressor mounts removed...

[CJW]

With the motor back in the subframe and the aircon mounts out the way, it now appears there's (just) sufficient space for it so will be getting on with designing/fabricating the mounting frames.

[CJW]

Reviewed motor position in the subframe again today. Current thinking for the motor mounts is:

-Run a box section across the two rear mounts
-Run another box section from the rear box section to the forward engine mount, with a laser cut plate picking up the various mounting holes on the side of the motor via bolts through spacer tubes
-Single tube connected to a piece of angle should be able to pick up the three mounting holes on the left hand side

Very rough sketch below.